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Science and Art: A Future for Stone
Hughes, John; Howind, Torsten
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Hughes, J., & Howind, T. (Eds.) (2016). Science and Art: A Future for Stone: Proceedings of the 13th
International Congress on the Deterioration and Conservation of Stone, Volume 2. Paisley: University of the
West of Scotland.
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Download date: 15 Sep 2016
SCIENCE AND ART: A FUTURE FOR STONE
PROCEEDINGS OF THE 13TH INTERNATIONAL CONGRESS ON THE
DETERIORATION AND CONSERVATION OF STONE
6th to 10th September 2016, Paisley, Scotland
VOLUME II
Edited by
John J. Hughes and Torsten Howind
© University of the West of Scotland, Paisley, 2016
13th International Congress on the Deterioration and Conservation of Stone
Licenced under a Creative Commons Attribution 4.0 International License.
ISBN: 978-1-903978-58-0
ISBN: 978-1-903978-55-9 (eBook)
ISBN: 978-1-903978-59-7 (Set: Volume 1&2)
ISBN: 978-1-903978-56-6 (eBook-Set: Volume 1&2)
Hughes J.J. and Howind T. (Editors), “Science and Art: A Future for Stone. Proceedings of
the 13th International Congress on the Deterioration and Conservation of Stone”,
University of the West of Scotland, Paisley, September 6 th to 10th, 2016.
Cover image: The front door of the Paisley Technical College building, now University of
the West of Scotland. T.G. Abercrombie, architect 1898. Photograph and cover design by
T. Howind.
II
13th International Congress on the Deterioration and Conservation of Stone
PREFACE
Standing under the portico of the Paisley Town Hall, completed in 1882, and looking south
east towards the West Façade of Paisley Abbey, built in the 13 th to 15th Century, it is
possible to compare two historical periods in Scottish building where the use of stone was
unavoidable. Walking further into the historic centre of Paisley, or any other town or city in
Scotland, reveals the ubiquitous use of uncovered natural stone in our architecture, and also
the problems that it faces. The challenge in maintaining the essential integral character of
our towns for the future, and to recognise and enhance their values is a complex one, but
not our challenge alone. Much hard work is still needed to characterise, assess and propose
conservation approaches that are compatible with the existing fabric and prevailing
philosophies, in Scotland and around the world.
We sought to bring the 13th Congress to a damp Scotland of decaying stone structures, to
share our stone-built heritage with the conservation community and also to focus on the
needs of stone conservation for our built heritage in Scotland. We hope that by bringing
some global attention to the issue, in the country were, arguably, modern geology began,
we demonstrate the sharing of our common heritage and our values in seeking its
understanding and protection.
In these volumes you will find the proceeds of the work of many people, the conservators,
practitioners and even academics and researchers whose concern is the protection of our
stone-made cultural heritage. The Permanent Scientific Committee (PSC) of the Stone
Congresses worked to review each contribution followed by revision by the authors. The
editing effort by ourselves involved direct improvements to text, in many cases, and by one
of us in particular to the formatting. However, beyond the title pages and abstracts, after
review by the PSC and revision by the authors, proof correction was limited. The contents
and accuracy of the papers are therefore the responsibility of the authors.
John J. Hughes and Torsten Howind
Paisley, Scotland, August 2016
III
13th International Congress on the Deterioration and Conservation of Stone
Permanent scientific committee
Christine Bläuer
Conservation Science Consulting Sàrl, Fribourg, Switzerland
Ann Bourgès
Ministère de la culture et de la communication, Paris, France
Susanna Bracci
Italian National Research Council, Rome, Italy
Philippe Bromblet (Vice-President)
Centre Interdisciplinaire de Conservation et Restauration du Patrimoine (CICRP), Marseille, France
Hilde De Clercq (President)
Royal Institute for Cultural Heritage, Brussels, Belgium
Eric Doehne
Scripps College, Claremont, CA, United States of America
Miloš Drdácký
Academy of Sciences of the Czech Republic, Prague, Czech Republic
Christoph Franzen
Institut für Diagnostik und Konservierung an Denkmalen in Sachsen und Sachsen Anhalt e.V.,
Dresden, Germany
Jadwiga Łukaszewicz
Department for Conservation of Architectonic Elements and Details, Faculty of Fine Arts,
Nicolaus Copernicus University, Toruń, Poland
Antonia Moropoulou
School of Chemical Engineering, National Technical University of Athens, Greece
Stefan Simon
Institute for the Preservation of Cultural Heritage (IPCH), Yale University, West Haven, CT,
United States of America
Ákos Török
Department of Construction Materials and Engineering Geology,
Budapest University of Technology and Economics, Budapest, Hungary
Johannes Weber
Institute of Art and Technology, Conservation Science, University of Applied Arts Vienna, Austria
George W. Scherer
Civil and Environmental Engineering Department, Princeton University, United States of America
David A. Young
Heritage Consultant, Melbourne, Australia
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13th International Congress on the Deterioration and Conservation of Stone
ACKNOWLEDGEMENTS
Historic Environment Scotland, for their assistance and support in the hosting of the
Congress Dinner at the Kelvingrove Art Gallery and Museum, Glasgow. Ewan Hyslop,
Maureen Young and Christa Gerdwilker are thanked for their voluntary input to the
organisation of technical visits to Largs and Glasgow.
The British Geological Survey.
Our commercial sponsors: SINT Technologies, Surface Measurement Systems,
GC Laser Systems, Fokus GmbH Leipzig and Remmers.
Renfrewshire Council and the staff of the Town Hall.
The community at Paisley Abbey.
Alexander Collins, excursion guide.
Drew Wilson, Richard Potts and Stuart Johnson of UWS’s Corporate Marketing for design
and layout of the Congress Logo, programmes and other printed matter.
Finally, thanks must go to Alison Wright (formerly of Glasgow University), who bravely
bore our application to host the Congress to New York in 2012, without complaint. On this
occasion we must also thank the team at the University of the West of Scotland; Georgia
Adam, Irene Edmiston, Gaia Frola, Matt Gilmour and Emma Paterson, without whose
efforts the Congress could not have been held.
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This page has been left intentionally blank.
VI
13th International Congress on the Deterioration and Conservation of Stone
CONTENTS
Volume I
Damage ................................................................................................................................. 1
Traffic-induced Emissions on Stone Buildings.................................................................. 3
M. Auras, P. Bundschuh, J. Eichhorn, D. Kirchner, M. Mach, B. Seewald,
D. Scheuvens and R. Snethlage
Weathering Patterns of the Carved Stone and Conservation Challenges - World
Heritage Site of Qutb Complex, New Delhi .................................................................... 13
S.S. Bais and S.C. Pandey
Effect of Microorganism Activities in a Polluted Area on the Alteration of
Limestone used in Historical Buildings ........................................................................... 25
C. Balland-Bolou-Bi, M. Saheb, N. Bousserrhine, S. Abbad-Andaloussi,
V. Alphonse, S. Nowak, A. Chabas, K. Desboeufs and A. Verney-Carron
Granite and Marine Salt Weathering Anomalies from Submerged and Inter-tidal
and Coastal Archaeological Monuments in Ireland ......................................................... 33
J. Bolton
Decay of Mesozoic Saltrio and Viggiù Limestones: Relationship between Microstructural, Compositional and Environmental Characteristics ......................................... 41
G. Cavallo, R. Bugini, D. Biondelli and S. Franscella
Role of Hydro-mechanical Coupling in the Damage Process of Limestones Used
in Historical Buildings ..................................................................................................... 49
F. Cherblanc, J. Berthonneau and P. Bromblet
The Contribution of Traditional Techniques to New Technology to Evaluate the
Potential Risk of Stone Deterioration by Microorganisms .............................................. 57
E. Sirt-Ciplak, A. Cetin-Gozen and E.N. Caner-Saltık
Porosimetric Changes and Consequences for Damage Phenomena Induced by
Organic and Inorganic Consolidation Treatments on Highly Porous Limestone ............. 67
P. Croveri, L. Dei, J. Cassar and O. Chiantore
Alteration of Marble Stones by Red Discoloration Phenomena ...................................... 75
O.A. Cuzman, S. Vettori, F. Fratini, E. Cantisani, S. Ciattini, L. Chelazzi,
M. Ricci and C.A. Garzonio
Quantifying Salt Crystallization Dynamics in Sandstone Using 4D Laboratory Xray Micro-CT ................................................................................................................... 83
H. Derluyn, M.A. Boone, J. Desarnaud, L. Grementieri, L. Molari,
S. de Miranda, N. Shahidzadeh and V. Cnudde
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Investigation of Salt Solution Behaviour in Building Stones Using Paper Pulp
Poultices Under Laboratory Conditions ........................................................................... 91
I. Egartner and O. Sass
Experimental Study of the Ageing of Building Stones Exposed to Sulfurous and
Nitric Acid Atmospheres ................................................................................................. 99
S. Gibeaux, C. Thomachot-Schneider, A. Schneider, V. Cnudde, T. De Kock,
V. Barbin and P. Vazquez
Geological Studies on Volcanic Tuffs Used as Natural Building Stones in the
historical Center of San Luis Potosi, Mexico ................................................................ 107
R.A. López Doncel, W. Wedekind, N. Cardona-Velázquez, P.S. GonzálezSámano, R. Dohrmann, S. Siegesmund and C. Pötzl.
Weathering and Deterioration of Building Stones in Templo Mayor, Mexico City ...... 117
G. Mora Navarro, R.A. López Doncel, M. Espinosa Pesqueira and
W. Wedekind
Decay Products of the Kersantite Building Stone in the Monument of the Small
Staircase at the Kalemegdan Park (Belgrade, Serbia) .................................................... 125
N. Novaković, M. Franković, V. Matović, K. Šarić and S. Erić
Relationship between the Durability and Fabric of Pasargadae Carbonate Stones
(Archaelogical Site from Achaemenid Period, South of Iran) ....................................... 133
A. Shekofteh, H. Ahmadi and M. Yazdi
Biodeterioration of Limestone Built Heritage: A Multidisciplinary Challenge ............. 139
P.J.A. Skipper, H. Schulze, D.R. Williams and R.A. Dixon
Characterisation of a Pink Discoloration on Stone in the Pnom Krom Temple
(Angkor, Cambodia) ...................................................................................................... 147
M. Tescari, F. Bartoli, A. Casanova Municchia, T. Boun Suy and G. Caneva
Influence of the Villarlod Molasse Anisotropy on Cracking Advances in the
Comprehension of the Desquamation Mechanisms ....................................................... 155
M. Tiennot, A. Bourgès and J.-D. Mertz
Decay phenomena of marbles in the archaeological site of Hierapolis of Phrygiae
(Denizli, Turkey) ........................................................................................................... 165
S. Vettori S. Bracci, P. Caggia, E. Cantisani, O.A. Cuzman, T. Ismaelli, C.
Riminesi, B. Sacchi, G. Scardozzi and F. D’Andria
Freezing-thawing Phenomena in Limestones and Consequences for their Physical
and Mechanical Properties ............................................................................................. 173
C. Walbert, J. Eslami, A.-L. Beaucour, A. Bourgès and A. Noumowe
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13th International Congress on the Deterioration and Conservation of Stone
Rapid Degradation of Stylolitic Limestones Used in Building Cladding Panels ........... 181
T. Wangler, A. Aguilar Sanchez and T. Peri
Swelling Clay and its Inhibition in the Villarlod Molasse ............................................. 189
T. Wangler
First Investigations of the Weathering and Deterioration of Rock Cut Monuments
in Myra, Lycia (Turkey) ................................................................................................ 197
W. Wedekind, R.A. López Doncel, B. Marié and O. Salvadori
Contour Scaling at the Angkor Temples: Causes, Consquences and Conservation ....... 205
W. Wedekind, C. Gross, A. van den Kerkhof and S. Siegesmund
Georgia Marble at the Minnesota State Capitol: Examining the Correlations
between Marble Composition, Local Climate, Climate and Durability ......................... 215
P.G. Whitenack and M.J. Scheffler
Investigation Methods ..................................................................................................... 223
The Effect of Salt Crystallisation on the Mechanical Properties of Limestone:
Statistical Correlation between Non-Destructive and Destructive Techniques ............. 225
N. Aly, A. Hamed, M. Gomez-Heras, D. Benavente and M. Alvarez de Buergo
Computational simulation: Four Important Structural Elements to Protect the
Buildings in Ancient Persian Engineering ..................................................................... 233
A. AmirShahkarami, M. Mehdiabadi and H. Ashooriha
Material Analysis of Tarsus’ (Mersîn, Turkey) Traditional Buildings for the
Development of Conservation Strategies ....................................................................... 243
M.C. Atikoğlu, A. Tavukçuoğlu, B.A. Güney, E.N. Caner-Saltık, O. Doğan,
M.K. Ardoğa and M. Mayhar
Artifical Ageing Techniques on Various Lithotypes for Testing of Stone
Consolidants .................................................................................................................. 253
M. Ban, A.J. Baragona, E. Ghaffari, J. Weber and A. Rohatsch
Applications of Image Analysis to Marble Samples ...................................................... 261
R. Bellopede, E. Castelletto, N. Marcone and P. Marini
The Effects of Commercial Ethyl Silicate Based Consolidation Products on
Limestone ...................................................................................................................... 271
T. Berto, S. Godts and H. De Clercq
Field Exposure Tests to Evaluate the Efficiency of Nano-Structured Consolidants
on Carrara Marble .......................................................................................................... 281
A. Bonazza, G. Vidorni, I. Natali, C. Giosuè, F. Tittarelli and C. Sabbioni
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13th International Congress on the Deterioration and Conservation of Stone
Electrophoresis as a Tool to Remove Salts from Stone Building Materials –
Results from Lab Experiments and an On-site Application ........................................... 289
H. De Clercq, S. Godts, L. Debailleux, Y. Vanhellemont, N. Vanwynsberghe,
L. Derammelaere and V. De Swaef
Salt Weathering of Sandstone During Drying: Effect of Primary and Secondary
Crystallisation ................................................................................................................ 299
J. Desarnaud, H. Derluyn, L. Grementieri, L. Molari, S. de Miranda,
V. Cnudde and N. Shahidzadeh
Handheld X-Ray Flourescence Analysis (HH-XRF): A Non-Destructive Tool for
Distinguishing Sandstones in Historic Structures .......................................................... 309
P.A. Everett and M.R. Gillespie
Intrinsic Parameters Conditioning the Formation of Mn-rich Patinas on Luneville
Sandstones ..................................................................................................................... 317
L. Gatuingt, S. Rossano, J.-D. Mertz, B. Lanson and O. Rozenbaum
Smart Hydrophobic TiO2-nanocomposites for the Protection of Stone Cultural
Heritage ......................................................................................................................... 325
F. Gherardi, A. Colombo, S. Goidanich and L. Toniolo
Salt Extraction by Poulticing Unravelled? ..................................................................... 333
S. Godts, H. De Clercq and L. Debailleux
Quantifying the Damage and Decay for Conservation Projects: Identification,
Classification and Analysis of the Decay and Deterioration in Stone ........................... 343
P.T. Janbade N. Thakur and B.N. Tandon
The Potential of Laser Scanning to Describe Stone degradation ................................... 353
R. Janvier, X. Brunetaud, K. Beck, S. Janvier-Badosa and M. Al-Mukhtar
Application of Colorimetry for the Post-Fire Diagnosis of Historical Monuments ....... 361
S. Janvier-Badosa, K. Beck, X. Brunetaud, Á. Török and M. Al-Mukhtar
Developing Application Technology of Infrared Thermography for
Documentation of Blistering Zone ................................................................................ 369
Y.H. Jo and C.H. Lee
Stability Evaluation and Behaviour Monitoring of Songsanri Royal Tomb
Complex in Gongju, Korea ............................................................................................ 375
S.H. Kim, C.H. Lee, Y.H. Jo and S.H. Yun
Simulated Weathering and Other Testing of Dimension Stone ..................................... 381
D. Kneezel
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13th International Congress on the Deterioration and Conservation of Stone
IR Thermography Imaging of Water Capillary imbibtion into Pourous Stones of a
Gallo-Roman Site .......................................................................................................... 391
J. Liu, J. Wassermann, C.-D. Nguyen, J.-D. Mertz, D. Giovannacci, R. Hébert,
B. Ledesert, V. Barriere, D. Vermeersch and Y. Mélinge
Investigation of Urban Rock Varnish on the Sandstone of the Smithonian Castle ........ 399
R.A. Livingston, C.A. Grissom, E.P. Vicenzi, Z.A. Weldon-Yochim, N.C. Little,
J.G. Douglas, A.J. Fowler, C.M. Santelli, D.S. Macholdt, D.L. Ortiz-Montalvo
and S.S. Watson
Petrophysical Characterization of Both Original and Replacment Stone Used in
Archtectural Herritage of Morelio (Mexico) ................................................................. 407
J. Martinez-Martinez, A. Pola Villaseñor, L. García-Sánchez, G. ReyesAgustín, L.S. Osorio Ocampo, J.L. Macías Vazquez and J. Robles-Camacho
Assesment of a Non-Destructive and Portable Mini Permeameter Based on a
Pulse Decay Flow Applied to Historical Surfaces of Porous Materials ......................... 415
J.-D. Mertz, E. Colas, A. Ben Yahmed and R. Lenormand
Monitoring of Salts Content in Monuments of Toruń Old Town Complex ................... 423
W. Oberta and J.W. Łukaszewicz
Comparability of Non-Destructive Moisture Measurement Techniques on
Masonry During Simulated Wetting .............................................................................. 431
S.A. Orr, H.A. Viles, A.B. Leslie and D. Stelfox
Water Absorption and Pore-Size Ditribution of Silica Acid Ester Consolidated
Porous Limestone .......................................................................................................... 439
Z. Pápay and Á. Török
Conservation Status and Behaviour Monitoring System of Gongsanseong Fortress
Wall in Gongju, Korea .................................................................................................. 445
J.H. Park, K.K. Yang, C.U. Park, Y.H. Jo and C.H. Lee
Ground Penetrating Radar and the Detection of Structural Anomalies of High
Historical Value: A Case Study of a Burgher House in Toruń, Poland ......................... 451
M. Pilarska, J. Rogóż, A. Cupa, K. Krynicka-Szroeder and P. Szroeder
Strategies for the Conservation of Built Heritage Based on the Analysis of Rare
Events ............................................................................................................................ 459
Y. Praticò, F. Girardet and R.J. Flatt
Direct Measurement of Salt Crystallisation Pressure at the Pore Scale ......................... 467
N. Shahidzadeh, J. Desarnaud and D. Bonn
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13th International Congress on the Deterioration and Conservation of Stone
Drilling Resistance Measurement in Masonry Buildings: A Statistical Approach to
Characterise Non-homogeneous Materials .................................................................... 475
E. Valentini and A. Benincasa
In situ Assessment of the Stone Conservation State by its Water Absorbing
Behaviour: A Hands-On Methodology .......................................................................... 483
D. Vandevoorde, T. De Kock and V. Cnudde
Surface hardness Testing for the Evaluation of Consolidation OF POROUS STONES ...... 491
W. Wedekind, C. Pötzl, R.A. López Doncel, T.V. Platz and S. Siegesmund
Other Materials................................................................................................................ 501
Long-term Monitoring of Decay Evolution in Bricks and Lime Mortar Affected
by Salt Crystallisation .................................................................................................... 503
C. Colla, E. Gabrielli and F. Grüner
Assessment of the Physical Behaviour of Historic Bricks and their Mechanical
Characteristics via Absorption and Ultrasound Tests .................................................... 511
C. Colla and E. Gabrielli
Acrylic-based Mortar for Stone Repair: A Viscoelastic Analysis of the Thermal
Stresses .......................................................................................................................... 521
T. Demoulin , G.W. Scherer, F. Girardet and R.J. Flatt
Characterization and Test Treatments of Cast-Stone Medallions at the
Smithsonian ................................................................................................................... 529
C.A. Grissom, E. Aloiz, E.P. Vicenzi, N.C. Little and A.E. Charola
Composition of Stone Plasters and Pigmented Plasters Applied in the 1920s and
1930s in Berlin, Germany .............................................................................................. 537
S. Laue
Recovering the Architectural Heritage of the Nueva Tabarca Island (Spain) by
Studying the Durability of Original and Repair Mortars ............................................... 545
J. Martinez-Martinez and A. Arizzi
Stone-mortar Interaction of Similar Weathered Stone Repair Mortars Used in
Historic Buildings .......................................................................................................... 553
B. Menendez, P. Lopez-Arce, J.-D. Mertz, M. Tagnit-Hamou, S. Aggoun,
A. Kaci, M. Guiavarch and A. Cousture
Restoration of Weathered Load Bearing Masonry with Optimised Gypsum based
mortars ........................................................................................................................... 561
B. Middendorf and U. Huster
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13th International Congress on the Deterioration and Conservation of Stone
Acquisition and Analysis of Petrophysical Properties of the Rock of the Masonry
of the Cathedral of Aguascalientes, Mexico .................................................................. 569
R. Padilla Ceniceros, J. Pacheco Martínez and R.A. López Doncel
The Assessment and Treatment of Two Cast Stone Fountains from the 1920’s in
Palm Beach, Florida, USA: Technical and Theoretical Issues in the Preservation
of Aged Cast Stone ........................................................................................................ 575
M. Rabinowitz, J. Sembrat and P. Miller
Dating the Pre-Romanesque Church of San Miguel de Lillo, Spain: New Methods
for Historic Buildings .................................................................................................... 583
A. Rojo, L.L.Cabo, C.M. Grossi and F.J. Alonso
Swelling Inhibition of Clay-Bearing Building Materials used in Architectural
Monuments .................................................................................................................... 591
A. Stefanis and P. Theoulakis
Long-term Mechanical Changes of Repair Mortar Used in Restoration of Porous
Limestone Heritage ........................................................................................................ 599
B. Szemerey-Kiss and Á. Török
Proprietary Mortars for Masonry Repair: Developing a Predictive Framework for
Assessing Compatibility ................................................................................................ 607
C. Torney
Study of Efficiency and Compatibility on Successive Applications of Treatments
for Islamic Gypsum and Plaster from the Alhambra ..................................................... 613
R. Villegas Sanchez, F. Arroyo Torralvo, R. Rubio Domene and
E. Correa Gomez
Comparative Studies on Masonry Bricks and Bedding Mortars of the Fortress
Masonry of The Teutonic Order State in Prussia: Malbork, Toruń, and Radzyń
Chełmiński Castles ........................................................................................................ 621
K. Witkowska and J.W. Łukaszewicz
Organic Additives in Mortars: An Historical Tradition through a Critical Analysis
of Recent Literature ....................................................................................................... 631
K. Zhang, L. Rampazzi, A. Sansonetti and A. Grimoldi
Abstracts ........................................................................................................................... 639
Impact of Heat Exposure (Fire Damage) on the Properties of Sandstone ...................... 641
T. Howind, W. Zhu and J.J. Hughes
Sandstone Weathering: New Approaches to Assess Building Stone Decay .................. 642
J. Dassow, M. Lee, P. Harkness, S. Hild and A.B. Leslie
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13th International Congress on the Deterioration and Conservation of Stone
Pore-scale Freeze-Thaw Experiments with Environmental Micro-CT .......................... 643
T. De Kock, H. Derluyn, T. De Schryver, M.A. Boone and V. Cnudde
Conservation Study of Stone Masonries Using IRT: Discover Hidden Information
by Thermal Properties .................................................................................................... 644
C. Franzen and J.-M. Vallet
Active IRT and Theoretical Simulation Inputs for the Voids Determination in
Building Material ........................................................................................................... 645
K. Mouhoubi, C. Franzen, J.-M. Vallet, V. Detalle, O. Guillon and L. Bodnar
Evaluation of Harmfulness of Traditional Cleaning Techniques of Stone with 3D
Optical Microscopy Profilometry .................................................................................. 646
C. Tedeschi , M.P. Riccardi , S. Perego and M. Taccia
Multifunctional Polymers for the Restoration of the Deteriorated Mineral Gypsum
(Selenite) of the Minoan Palatial Monuments of Knossos ............................................. 647
I.E. Grammatikakis, K.D. Demadis and K. Papathanasiou
Consolidant Efficiency of Newly Developed Consolidant Based on the Soluble
Calcium Compounds...................................................................................................... 649
A. Pondelak, L. Škrlep, T. Howind, J.J. Hughes and A. Sever Škapin
List of Authors ................................................................................................................ XXI
List of Keywords ........................................................................................................... XXV
Volume II
Conservation .................................................................................................................... 651
Analysis, Testing and Development of Safe Cleaning Methods of Rusted Stone
Material .......................................................................................................................... 653
J. Aguiar, S. Bracci, B. Sacchi and B. Salvadori
Preliminary Studies in Using Lime with Additives as a Substitute for Resins as
Adhesives in Stone Conservation .................................................................................. 663
J. Alonso and M. Franković
Freeze Thaw and Salt Crystallisation Testing of Nanolime Treated Weathered
Bath Stone ...................................................................................................................... 671
R.J. Ball and G.L. Pesce, M. Nuño, D. Odgers and A. Henry
Thermosetting Methyl Methacrylate Adhesive for Stone: Charcterisation,
Application Techniques and Long-term Performance Elevation ................................... 679
Z. Barov
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Consolidation Effects on Sandstone Toughness ............................................................ 687
M. Drdácký, M. Šperl and I. Jandejsek
Is the Shelter at Hagar Qim in Malta Effective at Protecting the Limestone
Remains? ....................................................................................................................... 695
C. Cabello-Briones and H.A. Viles
Assessment of the Cleaning Efficiency of a Self-cleaning Coating on Two Stones
Under Natural Ageing .................................................................................................... 703
P.M. Carmona-Quiroga, S. Kang and H.A. Viles
Exploitation of the Natural Water Repellency of Limestones for the Protection of
Building Façades ........................................................................................................... 711
C. Charalambous and I. Ioannou
The Use of New Laser Technology to Precisely Control the Level of Stone
Cleaning ......................................................................................................................... 719
B. Dajnowski and A. Dajnowski
Cleaning Stone – The Possibilities for an Objective Evaluation.................................... 729
J. Ďoubal
The Natural Weathering of an Artificially Induced Calcium Oxalate Patina on
Soft Limestone ............................................................................................................... 737
T. Dreyfuss and J. Cassar
A Comparison of Three Methods of Consolidation for Clacerous Mixed Stones ......... 745
J. Espinosa-Gaitán and A. Martín-Chicano
Seasonal Stone Sheltering: Winter Covers .................................................................... 753
C. Franzen and K. Kraus
Performance and Permanence of TiO2-based Surface Treatments for Architectural
Heritage: Some Experimental Findings from On-site and Laboratory Testing ............ 761
E. Franzoni, R. Gabrielli, E. Sassoni, A. Fregni, G. Graziani, N. Roveri and
E. D’Amen
The Impact of Science on Conservation Practice: Sandstone Consolidation in
Scottish Built Heritage ................................................................................................... 769
C. Gerdwilker, A. Forster, C. Torney and E. Hyslop
Use of Local Stone in the Midwestern United States: Successes, Failures and
Considerations ............................................................................................................... 777
E. Gerns and R. Will
Laser Yellowing of Hematite-Gypsum Mixtures: A Multi Scale Characterisation ....... 785
M. Godet, V. Vergès-Belmin, C. Andraud, M. Saheb, J. Monnier, E. Leroy and
J. Bourgon
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13th International Congress on the Deterioration and Conservation of Stone
The Use of Hydroxyapatite for Consolidation of Calcareous Stones: Light
Limestone Pińczów and Gotland Sandstone (Part I) .................................................... 793
A. Górniak, J.W. Łukaszewicz, B. Wiśniewska
Marble Protection by Hydroxyapatite Coatings ............................................................. 803
G. Graziani, E. Sassoni, E. Franzoni and G.W. Scherer
Use of Consolidants and Pre-Consolidants in Sandstone with Swelling Clay at the
Muncipal Theatre of São Paulo...................................................................................... 811
D. Grossi, E.A. Del Lama and G.W. Scherer
Assessing the Impact of Natural Stone Burial upon Performance for Potential
Conservation Purposes ................................................................................................... 817
B.J. Hunt and C.M. Grossi
Study of Protective Measures of Stone Monuments in Cold Regions ........................... 825
T. Ishizaki
Study of Consolidation of Porous and Dense Limestones by Bacillus Cereus
Biomineralization .......................................................................................................... 831
J.M. Jakutajć, J.W. Łukaszewicz and J. Karbowska-Berent
Assessment of Dolomite Conservation by Treatment with Nano-Dispersive
Calcium Hydroxide Solution ......................................................................................... 839
F. Karahan Dağ, Ç.T. Mısır, S. Çömez, M. Erdil, A. Tavukçuoğlu, E.N. CanerSaltık, B.A. Güney and E. Caner
European Project “NANO-CATHEDRAL: Nanomaterials for conservation of
European architectural heritage developed by research on characteristic
lithotypes” ...................................................................................................................... 847
A. Lazzeri, M.-B. Coltelli, V. Castelvetro, S. Bianchi, O. Chiantore,
M. Lezzerini, L. Niccolai, J. Weber, A. Rohatsch, F. Gherardi and
L. Toniolo
New Polymer Architectures for Architectural Stone Preservation ................................ 855
A. Lazzeri, S. Bianchi, V. Castelvetro, O. Chiantore, M.-B. Coltelli,
F. Gherardi, M. Lezzerini, T. Poli, F. Signori, D. Smacchia and L. Toniolo
Trials of Biocide Cleaning Agents on Argillaceous Sandstone in a Temperate
Region ............................................................................................................................ 863
E. S. Long and D.A. Young
Development of a methodology for the Restoration of Stone Sculptures using
Magnets ......................................................................................................................... 871
X. Mas-Barberà, M.A. Rodríguez, L. Pérez and S. Ruiz
XVI
13th International Congress on the Deterioration and Conservation of Stone
The Rock Reliefs “Steinerne Album” of Großjena, Germany – Problems of
Deterioration and Approaches for a Lasting Preservation ............................................. 879
J. Meinhardt, T. Arnold and K. Böhm
Ethyl-silicate Consolidation for Porous Limestone Coated with Oil Paint – A
Comparison of Application Methods ............................................................................. 889
M. Milchin, J. Weber, G. Krist, E. Ghaffari and S. Karacsonyi
Electro-desalination of Sulfate Contaminated Carbonaceous Sandstone – Risk for
Salt Induced Decay During the Process ......................................................................... 897
L.M. Ottosen
Permeable POSS-based Hybrids: New Protective Materials for Historical
Sandstone ....................................................................................................................... 905
A. Pan, S. Yang and L. He
Differential Effects of Treatments on the Dynamics of Biological Recolonisation
of Travertine: Case Study of the Tiber’s Embankments (Rome, Italy) .......................... 915
S. Pascucci, F. Bartoli, A. Casanova Municchia and G. Caneva
Statistical Analysis at the Service of Conservation Practice: DOE for the
Optimisation of Stone Consolidation Procedures .......................................................... 923
Y. Praticò, F. Caruso, T. Wangler and R.J. Flatt
Vacuum-Circling Process: A Innovative Stone Conservation Method .......................... 931
E. Pummer
Sustainable Conservation in a Monumental Cemetery .................................................. 939
S. Salvini
Consolidation of Sugaring Marble by Hydroxyapatite: Some Recent
Developments in Producing and Treating Decayed Samples ........................................ 947
E. Sassoni, G. Graziani, E. Franzoni and G.W. Scherer
Application of Ethyl Silicate Based Consolidants on Sandstone with PArtial
Vacuum: A Laboratory Study ....................................................................................... 955
H. Siedel, J. Wichert and T. Frühwirt
Mould Attacks! A Practical and Effective Method
of Treating Mould
Contaminated Stonework ............................................................................................... 963
B. Stanley, N. Luxford and S. Downes
Injection Grouts based on Lithium Slicate Binder: A Rview of Injectability and
Cohesive Integrity .......................................................................................................... 971
A. Thorn
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13th International Congress on the Deterioration and Conservation of Stone
Innovative Treatments and Materials for the Conservation of the Strongly Saltcontaminated Michaelis Church in Zeitz, Germany ...................................................... 981
W. Wedekind, R.A. López-Doncel, J. Rüdrich and Y. Rieffel
Field Trials of Desalination by Captive-head Washing ................................................ 991
D. Young
Digitisation ....................................................................................................................... 997
Digital Mapping as a Tool for Assessing the Conservation State of the
Romanesque Portals of the Cathedral of our Lady in Tournai, Belgium ....................... 999
J. De Roy, S. Huysmans, L. Hoornaert, L. Fontaine and N. Verhulst
Digital Field Documentation: The Central Park Obelisk ............................................. 1009
C. Gembinski
Computational Imaging Techniques for Documentation and Conservation of
Gravestones at Jewish Cemeteries in Germany ........................................................... 1017
C.A. Graham and S. Simon
A Metadata-supported Database Schema for Stone Conservation Projects ................. 1025
E. Kardara and T. Pomonis
3D Photo Monitoring as a Long-term Monument Mapping Method for Stone
Sculptures .................................................................................................................... 1031
B. Kozub and P. Kozub
Emerging Digitisation Trends in Stonemasonry Practice ............................................ 1041
S. McGibbon and M. Abdel-Wahab
Digitalisation and Documentation of Stone Deterioration, Using Close-Range
Digital Photogrammetry .............................................................................................. 1051
M.Á. Soto-Zamora, R.A. López-Doncel, G. Araiza-Garaygordobil and
I.E. Vizcaino-Hernández
Recording, Monitoring and Managing the Conservation of Historic Sites: A New
Application for BGS SIGMA ...................................................................................... 1059
E.A. Tracey, N. Smith and K. Lawrie
Case Studies.................................................................................................................... 1067
Condition Survey of Aquia Creek Sandstone Columns From the U.S. Capitol ReErected at the U.S. National Arboretum ..................................................................... 1069
E. Aloiz, C. Grissom, R.A. Livingston and A.E. Charola
The Black Surfaces of the Porta Nigra in Trier (Germany) and the Question of
Cleaning ....................................................................................................................... 1077
M. Auras, H. Ettl, W. Hartleitner and T. Meier
XVIII
13th International Congress on the Deterioration and Conservation of Stone
The Conservation of Giovanni Labus’s Sculpture of Bonaventura Bavallieri
(1844) and Antonio Galli’s Sculpture of Carlo Ottavio Castiglione (1855) ................ 1089
I. Ruiz Bazán, V. Bresciani, A. Balloi, A. Quarto, I. Marelli, M. Colella,
C. Sotgia and F. Arosio
Restoration Off-set by the Public Exhibition of Decorated Stone Elements
Rescued from the demolished Vacaresti Monastery, Romania .................................... 1097
C. Bîrzu
Rosslyn Chapel - A Review of the Conservation & Access Project ............................ 1103
N. Boyes
Laboratory and in situ evaluation of restoration treatments in two important
monuments in Padua: “Loggia Cornaro” and “Stele of Minerva” ............................... 1111
V. Fassina, S. Benchiarin and G. Molin
Investigations Guiding the Stone Restoration of the “Schöner Erker” in Torgau,
Germany ...................................................................................................................... 1119
C. Franzen, H. Siedel, S. Pfefferkorn, A. Kiesewetter and S. Weise
Ananlysis and Treatment of the Fire-Damaged Marble Plaque from Thomas
Jefferson’s Grave Marker ............................................................................................ 1129
C. Grissom, E. Vicenzi, J. Giaccai, N.C. Little, C. France, A.E. Charola and
R.A. Livingston
The Diagnostic and Monitoring Approach for the Preventive Conservation of the
Façade of the Milan Cathedral ..................................................................................... 1137
D. Gulotta, P. Fermo, A. Bonazza and L. Toniolo
Enviromental Monitoring and Surface Treatment Tests for Conservation of the
Rock-Hewn Church of Üzümlü, Cappadocia .............................................................. 1145
C. Iba, Y. Taniguchi, K. Koizumi, K. Watanabe, K. Sano C. Piao and
M. Yoshioka
Time Tested Repairs: A Review of 11 Years of Cementery Stone Repair .................. 1153
M. Jablonski
The Current State and Factors of Salt Deterioration of the Buddha Statue Carved
onto a Cliff at Motomachi in Oita Prefecture of Japan ................................................ 1163
K. Kiriyama, S. Wakiya, N. Takatori, D. Ogura, M. Abuku and Y. Kohdzuma
The Durbar Square and the Royal Palace of Patan, Nepal – Stone Conservation
Before and after the Great Earthquake of April 2015 .................................................. 1171
G. Krist, M. Milchin and M. Haselberger
XIX
13th International Congress on the Deterioration and Conservation of Stone
Restoring the Past Experience of Stone Masonry in Burkina Faso for Fostering the
use of Local Materials.................................................................................................. 1181
A. Lawane, A. Pantet, R. Vinai and J.H. Thomassin
Protection of Medieval Tombstones (Stećci) with Ammonium Oxalate Treatment .... 1189
V. Marinković and D. Mudronja
Influence of Water Evaporation on the Degradation of Wall Paintings in Hagia
Sophia, Istanbul ........................................................................................................... 1201
E. Mizutani, D. Ogura, T. Ishizaki, M. Abuku and J. Sasaki
Conservation of Magai-Wareishi-jizo, A Buddha Statue Carved into a Granite
Rockface on the Seashore ............................................................................................ 1211
M. Morii, N. Kuchitsu, T. Kawaguchi, H. Matsuda and S. Tokimoto
Evaluation of the Preservation State of the Holy Aedicule in the Holy Sepulchre
Complex in Jerusalem .................................................................................................. 1219
A. Moropoulou, K. Labropoulos, E. Alexakis, E.T. Delegou, P. Moundoulas,
M. Apostolopoulou and A. Bakolas
Conservation of Machu Picchu Archaeological Site: Investigation and
Experimental Restoration Works of the “Temple of the Sun” ..................................... 1227
T. Nishiura, I. Ono, A. Ito, H. Fujita, M. Morii, F. Astete and C. Cano
Las Casas Tapadas de Plazuelas – Structural Damage, Weathering Characteristics
and Technical Properties of Volcanic Rocks in Guanajuato, Mexico .......................... 1237
C. Pötzl, R.A. López-Doncel, W. Wedekind and S. Siegesmund
Desalinating the Asyut Dog in the MUSÉE DU LOUVRE ......................................... 1247
O. Rolland, V. Vergès-Belmin, M. Etienne, H. Guichard, S. Duberson and
P. Bromblet
Investigation of Salt Crystallisation in a Stone Buddha Carved into a Cliff with a
Shelter by Numerical Analysis of Heat and Moisture Behaviour in the Cliff.............. 1255
N. Takatori, D. Ogura, S. Wakiya, M. Abuku, K. Kiriyama and Y. Kohdzuma
Scientific Examination of a Painted Thracian Tomb Discovered Near
Alexandrovo Village, Bulgaria .................................................................................... 1263
V. Todorov, K. Frangova and T. Marinov
Case Study of the Episcopal Group of Frejus (France): Diagnosis and Treatment
of Clay Containing Sandstones in Marine Environment .............................................. 1271
M. Trubert, B. Brunet-Imbault, P. Bromblet and C. Guinamard
The Polychromed Bethlehem Portal of Huy, Belgium: Evaluation and
Maintenance of a 25 Year Old Treatment .................................................................... 1279
J. Vereecke, L. Rossen, K. Raymakers and M. Stillhammerova
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13th International Congress on the Deterioration and Conservation of Stone
Exploring the Performance of Pompignan Limestone as Exterior Cladding and
Pavers in the Mid-Atlantic Region of the United States .............................................. 1287
R. Wentzel and M. Coggin
Abstracts ......................................................................................................................... 1295
Mechanisms of Carbonate-oxalate Transformation: Effectiveness of Protective
Treatments for Marble based on Oxalate Surface Layers ............................................ 1297
A. Burgos-Cara, C. Rodríguez-Navarro and E. Ruiz-Agudo
Preservation of Built Cultural Heritage Using Nanotechnology Based Coatings:
Responding to Conservation Values? .......................................................................... 1299
J.J. Hughes, L.P. Singh, P.C. Thapliyal, T. Howind and W. Zhu
Innovative Developments in the Field of Stone Conservation by the Acrylic Resin
Total Impregnation Process of Natural Stones by the JBACH Company .................... 1300
G. Scholz, R.J.G. Sobott, H.W. Ibach
MONUMENTUM: Digital 3D Modelling and Data Management for the
Conservation of Decorated Stone Buildings ................................................................ 1301
L. De Luca, J.-M. Vallet, P. Bromblet, M. Pierrot-Desseilligny, X. Brunetaud,
F. Dubois, M. Bagneris, M. Al Mukhtar, F. Cherblanc, O. Guillon and
J. Tugas
Investigation of Building Stones Used in the Al-Azhar mosque (Historic Cairo,
Egypt) .......................................................................................................................... 1303
N. Aly, A. Hamed, Á. Török, M. Gomez-Heras and M. Alvarez de Buergo
The Effect of Reburial on Stone Deterioration: Experimental Case Study, Oxford,
England ........................................................................................................................ 1304
N. Zaman and H. Viles
List of Authors ............................................................................................................. XXIII
List of Keywords ........................................................................................................ XXVII
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13th International Congress on the Deterioration and Conservation of Stone
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13th International Congress on the Deterioration and Conservation of Stone
CONSERVATION
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
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652
ANALYSIS, TESTING AND DEVELOPMENT OF SAFE CLEANING
METHODS OF RUSTED STONE MATERIAL
J. Aguiar1, S. Bracci2, B. Sacchi2 and B. Salvadori2*
Abstract
Rust stains are a widespread problem for natural stones of both civil buildings and cultural
heritage, particularly for white marbles. For this reason, the aim of this work was to
develop new methods of treatment/application, in order to identify a safe protocol for
cleaning rusted marbles. Three different treatments were applied on several specimens of
both dolomitic and calcitic marble, properly stained with rust to mimic real situations (the
stone specimens were exposed to the natural environment for about six months in contact
with rusted iron). Marble specimens were characterized before and after treatment and
monitored during the cleaning tests. The specimens were characterized by SEM-EDS
(Scanning Electron Microscopy coupled with Energy Dispersive System), XRD (X-Ray
Diffraction), XRF (X-Ray Fluorescence), FTIR (Fourier Transform Infrared Spectroscopy)
and color measurements. In addition, microscopic and macroscopic analyses of the stone
surface along with tests of short and long term capillary absorption were carried out.
A series of test trials were conducted in order to identify the best conditions in terms of
concentrations and contact time, starting from the data reported in literature. New methods
of treatment application were verified, substituting the usual Cellulose Poultice with Agar.
The latter is a gel already used in many other contexts, being something new in this field,
which possesses great applicability in the field of conservation of stone materials. After the
application of the cleaning method, the specimens were characterised again in order to
understand which treatment was more effective and less harmful. The study indicates that
for a very intense and deep penetration into the stone, a solution of 3.5% (w/v) of Sodium
Dithionite buffered with Ammonium Carbonate to pH 7 applied with Agar support would
be appropriate.
Keywords: stone, rust removal, sodium dithionite, ammonium citrate,
sodium hexametaphosphate
1
J. Aguiar
Department of Conservation and Restoration, Nova University, Lisbon, Portugal,
2
S. Bracci , B. Sacchi and B. Salvadori*
CNR-ICVBC Institute for the Conservation and Valorization of Cultural Heritage, Sesto Fiorentino
(Florence), Italy
b.salvadori@icvbc.cnr.it
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
1. Introduction
Rust stains in stone are mostly caused by iron corrosion of architectonic elements such as
grades, nails and supports (Matero and Tagle 1995). The cleaning methodology should
improve the visual appearance of the stone, promoting its stability (Selwyn and Tse 2009),
while preventing physical and/or chemical changes such as abrasion of the surface and
introduction of soluble salts (Aires-Barros 2001) (Amoroso and Fassina 1983). While many
researchers tested different chemical compounds, there is no definitive comparative
assessment identifying an efficient and safe method. This paper reports the preliminary
results of an investigation carried out to setup a proper methodology for rust removal from
both calcitic and dolomitic marbles, largely used in the construction of built heritage. Some
promising chemical products reported in the literature were used, exploring different
application procedures. Studies about this topic are not recent and a clear definition of a
good treatment is not still defined. It comes out from the literature that for appropriate
treatment of marble the pH has to be adjusted to pH 7-8, being this the fundamental point to
avoid the dissolution of the calcite (Cushman and Wolbers 2007). Another crucial factor to
be controlled is the contact time between the sample and the poultice (Amoroso and Fassina
1983). Because of its insolubility in water, rust is difficult to remove (Matero and Tagle
1995; Irwin 2011). The removal may be performed by dissolution in acids, complexation or
chemical reduction with or without complexing agents (Burgess 1991). The choice of
appropriate chelating agents should enable the removal of the metal ion, avoiding the
dissolution of calcite (Selwyn and Tse 2009; Burgess 1991). For instance, EDTA is far too
strong a chelator to use for this application, as calcium will be taken up and brought into
solution (Tab. 1); on the other hand, Citrate should be safer for the marble surface, but
neither of these materials, EDTA included, is able to efficiently bind the iron species
(Cushman and Wolbers 2007).
Tab. 1: Solubility product (pKsp) of prevalent calcium and iron species in the marble matrix
and in the iron staining and constants of chelate formation (pK f) of Ca(II), Fe(II) and
Fe(III) (CRC Handbook 2003)
Ca(II)
Fe(II)
Fe(III)
a
pKsp
pKf (Citrate)
pKf (EDTA)
8.3a
16.3b
38.6c
4.7
3.1
12.5
11.0
14.3
24.2
CaCO3; b Fe(OH)2; c Fe(OH)3
Sodium Hexametaphosphate is a deflocculant/chelating agent used in the field of
conservation for the cleaning of stone materials, due to its neutral pH which makes it safe
for marble. It is a weaker chelating agent than EDTA and for this reason it is indicated for
calcareous stones. Good results in rust removal after several applications have been
reported (CTS newsletter 2006).
Reducing agents can be used as well, to convert the orange-red Fe(III) form to the much
more water soluble Fe(II) form. (Selwyn and Tse 2009; Irwin 2011) (Vanýsek 1991). To
this aim, the use of the reducing agent Sodium Dithionite, Na2S2O4, to remove iron stains
was first suggested in 1968 (Stambolov 1968) and it is currently applied to clean a variety
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
of inorganic materials (Selwyn and Tse 2009) (Irwin 2011). Its reaction with goethite yields
the more soluble Fe(OH)2 which can be removed with water:
2FeOOH + S2O42-+4H+ 2Fe2+ + 2HSO3- + 2H2O
Also Ammonium Citrate has been reported as an effective chelating agent in removing iron
stains (Matero and Tagle 1995). However, the literature points out that the Citrate is able to
attack the calcareous stone (Gervais et al., 2010).
2. Materials and methods
2.1. Stone specimens
Two types of marble, with different resistance against acids, were used: one calcitic
(CaCO3), which quickly reacts with acids, and one dolomitic (CaMg(CO3)2), less reactive.
XRD analyses confirmed the composition of the selected specimens (data not reported).
Eighteen specimens of each lithotype (size 5×5×2 cm) were exposed outdoors for about six
months in contact with rusted iron. The specimens were washed with water before
performing the tests.
2.2. Investigation techniques
The specimens were characterized before and after cleaning treatments to monitor changes
in terms of color, iron and/or salt residues. Color measurements (Hunt 1991) were
performed according to the procedure described in (EN 15886:2010) using the CIELAB
1976 method, with the standard illuminant D65 and observer 10°. The color coordinates
L*, a* and b* were recorded for each selected area (Ø ~ 8 mm), using a Minolta cm-700d
spectrophotometer. For each specimen, four spots of interest were selected corresponding to
rust stains and five measurements were taken on each area. A mask properly prepared for
each specimen enabled the repositioning of the instrument on the same areas during the
monitoring steps. The colorimeter was calibrated against a SPECTRALON® prior to each
measurement. Surface changes were monitored through photographic documentation, with
a digital reflex camera Canon 7D equipped with Canon EFS 60 mm macro lens, and a
Stemi 2000 (Zeiss) stereomicroscope with ACT 1 software. Elemental characterization of
the surfaces was performed with a portable X-Ray fluorescence spectrometer Tracer III-SD
(Bruker) using the following conditions: Rh source, Pd slit, Ti and Al filter, 40 KV, 30 μA,
60 seconds. Chemical analyses were performed with a portable Bruker Optics ALPHA FTIR spectrometer equipped with SiC Globar source and DTGS detector. For non-invasive
chemical characterization of the surface compounds, the instrument was equipped with a
front-reflection module and a video camera. The spectra were acquired in total reflection
mode collecting 256 scans, with 4 cm−1 resolution in the 4000–400 cm−1 range and a
measuring spot of 6 mm in diameter. Powders taken from the surface of the specimens were
analyzed through an attenuated total reflection module (ATR) with diamond crystal. The
collected IR spectra were processed using OPUS 7.2 software. On the same powdered
samples, XRD analyses were performed using a X-ray diffractometer X'Pert PRO
PANalytical with anticathode Cu (λ = 1.54 Å, investigated 2θ 3–70°, step size 0.017°, time
per step 50 s), equipped with a multidetector X'Celerator. Data processing was performed
using HighScore software and ICDD database.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
2.3. Reagents
All chemicals were used as supplied. Sodium Dithionite Na2S2O4 (technical grade, 85%,
SDT) and Ammonium Hydroxide NH4OH (20.0-30.0%, AM) were purchased from SigmaAldrich; Ammonium Citrate dibasic HOC(CO2H)(CH2CO2NH4)2 (≥99.0%, AC),
Ammonium Carbonate (NH4)2CO3 (>99.7%, AmmC) and Sodium Hydrogencarbonate
NaHCO3 (≥99.7%, SodHC) were purchased from Fluka Analytical; Sodium
Hexametaphosphate NaPO3 (technical grade, HMP) was supplied by CTS srl (Florence,
Italy).
2.4. Cleaning tests
Each cleaning agent was used in different concentrations and contact times (Tab. 2)
selected after a series of preliminary tests. The solutions were buffered at pH ≈ 7 to avoid
the dissolution of calcite which is favoured at pH < 7.6 (Thorn 2005). Ammonia was used
for Sodium Hexamethaphosphate and Ammonium Citrate solutions. As suggested by some
authors (Mehra and Jackson 1960) (Lem and Wayman 1970), Sodium Hydrogencarbonate
was used for the SDT solutions, slowing down the decomposition of the Sodium Dithionite
which is faster at acidic pH. To reduce the amount of sodium in solution and contamination
of the surfaces, the use of Ammonium Carbonate instead of Sodium Hydrogencarbonate
was also tested. Besides the traditional Cellulose poultice, Agar gel was used as well
(Campani et al., 2006, Gulotta et al., 2014). With Sodium Hexametaphosphate, the Agar
film did not form: since this cleaning agent acts as a deflocculant, it does not allow the
folding of the Agar fibers.
Tab. 2: Cleaning treatments applied on stained marble samples.
Cleaning agent
Concentration
% (w/v)
a
pH
6
Sodium
Dithionite
(SDT)
3.5
7
Sodium
Hexametaphosphate
(HMP)
10
Ammonium Citrate
(AC)
Contact
time
(hours)
SodHC
or
AmmC
Ce, Ag
2
7
AM
Ce
24
8
AM
Ce, Ag
3
5
Poulticea
6/7
5
2
Buffer
agent
Ce: Cellulose; Ag: Agar
3. Results and discussion
The comparison of the two lithotypes showed a different appearance of rust stains, also
visible in cross section (not reported). Rust formed large spots on dolomite, while a sort of
finely distributed, light staining was found on calcite. This could be due to the slightly
different porosity of the two lithotypes and different crystals size (larger in dolomite than
calcite). However, the penetration depth was quite similar, ranging from 10 to 25 μm.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3.1. Sodium Dithionite
Fig. 1 shows the effects of the SDT cleaning intervention. Less concentrated solution
applied for longer contact time (3.5% solution, 6 hours) removed the rust stains more
efficiently than the more concentrated solution applied for shorter contact time
(7% solution, 3 hours), especially in the case of dolomite. FT-IR analyses of the marble
surface did not reveal any residual cleaning product, while XRF analyses showed minimal
amount of iron on dolomite, not visible to the naked eye (Fig. 2).
Fig. 1: Comparison between treatments on calcitic (C) and dolomitic (D) samples with
SDT.
This confirms the importance of an appropriate washing of the stone substrate after
applying the treatment, to completely remove iron(II) ions, avoiding eventual re-staining
(colourless, remaining iron(II) ions may be oxidized back to rust-coloured
iron(III)oxyhydroxides). After treatment, colour measurements ascertained the regression
of the chromatic coordinates to those registered on unstained surfaces (Tab. 3 and Tab. 4).
This was particularly evident on calcitic samples treated for 6 hours with SDT 3.5%, in
Cellulose poultice. However, some yellowing (increase of b*) was also detected after most
of the treatments.
Good results were also achieved through the use of Agar gel to support the cleaning
solution. Indeed, the Agar allowed faster removal of stains with respect to Cellulose
poultice, also permitting the monitoring in real time due to the transparency of the gel
(Fig. 3).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 2: XRF spectra of the dolomite specimen treated with SDT 3.5%-6hours before (---)
and after cleaning (---).
Before
30 min
90 min
180 min (3h))
Fig. 3: Timeline SDT 3.5% with Agar poultice.
Tab. 3: Color measurements of the stained (t0), cleaned (t1) and reference unstained (Ref.)
calcitic specimens.
L*
Cleaning
product
% (w/v)
contact
time (h)
Poultice
buffer
SDT
3.5
5
A
SDT
3.5
5
SDT
7
SDT
Ref.
a*
b*
t0
t1
t0
t1
t0
t1
AmmC
79.6
83.9
2.5
-0.6
20.4
1.0
C
AmmC
66.1
84.2
11.8
-1.0
28.3
2.9
3
C
SodHC
75.7
81.1
3.2
-1.0
23.1
1.6
3.5
6
C
SodHC
78.6
84.6
2.5
-0.9
16.5
-0.7
-
-
-
-
-
83.4
-
-0.7
-
-1.0
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 4: Color measurements of the stained (t0), cleaned (t1) and reference unstained (Ref.)
dolomitic specimens.
L*
Cleaning
product
% (w/v)
contact
time (h)
Poultice
buffer
SDT
3.5
5
A
SDT
3.5
5
SDT
7
SDT
Ref.
♣
a*
b*
t0
t1
t0
t1
t0
t1
AmmC
70.5
86.4
11.3
-0.1
32.9
4.6
C
AmmC
65.1
85.7
14.1
0.4
34.3
4.6
3
C
SodHC
70.5
83.2
10.0
1.2
28.3
10.1
3.5
6
C
SodHC
71.5
86.5
11.3
-0.5
27.1
4.2
-
-
-
-
-
83.4
-
-0.7
-
-1.6
♣
N.B.: Rust stain after cleaning
3.2. Sodium Hexametaphosphate and Ammonium Citrate
Fig. 4 shows the results of cleaning with HMP and AC. Although the highest concentration
and longest contact time reported in the literature were used for both of the products, the
methods appeared less effective than SDT. The use of Agar instead of Cellulose did not
improve the results. It can be noticed that only the most superficial rust stains were
removed, particularly for AC, which resulted safe for the marble surfaces.
Fig. 4: Calcitic (C) and dolomitic (D) samples before/after application of Sodium
Hexametaphosfate 10% (left) and Ammonium Citrate 5% (right).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
4. Conclusions
The use of Sodium Dithionite proved to be the most effective product for rusted stone
cleaning, compared to Sodium Hexametaphosphate and Ammonium Citrate. Contact time
and concentration were the key factor in the removal process. Sodium Dithionite acts as a
reducing agent, making possible to wash away the reduced Fe(II) iron from the stone. The
combination with a proper buffer, such as Ammonium Carbonate, allowed to prolong the
cleaning agent’s life (which decomposes rapidly in the presence of oxygen), raise the pH to
a safe value for stone and minimize the amount of sodium salts on the cleaned surface. Rust
stains were removed from the surfaces, leaving no or minimal iron residues. The use of
Sodium Hexametaphosphate was not effective, while Ammonium Citrate showed some
results on light or superficial stains. The use of Agar gel instead of Cellulose poultice
enabled the monitoring of the treatment without touching the poultice, which is really
advantageous on sensitive substrates. In conclusion, based on the present results, for rust
removal from marble the 6-hour application of Sodium Dithionite 3.5%, buffered with
Ammonium Carbonate, in Agar, followed by accurate washing of the stone surface is
advisable. However, further studies will allow for checking the depth of rust cleaning and
the complete absence of harmful effects on the surfaces.
References
Aires-Barros, L., (2001), "As Rochas dos Monumentos Portugueses, Lisboa: Instituto
Português do Património Arquitetónico, Coleção Cadernos", Vol. I e II. ISBN
9728087810.
Amoroso, G.G. and Fassina, V., (1983), "Stone Decay and Conservation: Atmospheric
Pollution, Cleaning, Consolidation and Protecting", Materials Science
Monographs, 11. Elsevier Science Publishing Company Inc., New York, ISBN
9780444421463, 453pp.
Burgess, H., 1991, The use of chelating agents in conservation treatments, The Paper
Conservator 15, 36-44.
Campani, E., Casoli, A., Cremonesi, P., Saccani, I., Signorini, E. (2006), "Use of Agarose
and Agar for preparing “Rigid gels”". CESMAR 7, Quaderno 4, Il Prato, Padova,
Italy, ISBN 8889566655, 52pp.
Cremonesi, P., 2006, Applicazione di metodologie di intervento più recenti per la pulitura
del materiale cartaceo. Atti delle giornate di studio Problemi di Restauro –
Giornate di Studio per storici d’arte, ispettori di Sopritendenza, conservatori e
operatori museali. 39-46.
CTS
Srl., 2006, Una vecchia ruggine [http://www.ctseurope.com/site/dettaglionews.php?id=45 Accessed 23rd August 2015].
Cushman, M. and Wolbers, R., 2007, A new approach to cleaning iron-stained marble
surfaces, WAAC Newsletter, 29 (2), 23-8.
Doehne, E. and Price, C. A., (2010), "Stone Conservation, An Overview of Current
Research", 2nd edition, Getty Publications, Los Angeles, CA, ISBN
9781606060469, 160pp.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
EN 15886:2010, Conservation of Cultural Property. Test Methods. Color Measurement of
Surfaces, 2010.
Erhard, M. W., (1994), "Stone in Architecture: Properties, Durability in Man’s
Environment", 3rd ed., Springer Verlag, Berlin, ISBN 978366210072, 309pp.
Gervais, C., 2010, Cleaning marble with ammonium citrate, Studies in Conservation, 55,
164-176.
Gulotta, D., Salviello, D., Gherardi, F., Toniolo, L., Anzani, M., Rabbolini, A. and
Goidanich, S., 2014, Setup of a sustainable indoor cleaning methodology for the
sculpted stone surfaces of the Duomo of Milan, Heritage Science, 2:6, 1-13.
Hunt, R.W.G. (1991), "Measuring Colour", 2nd edition, Ellis Horwood, Chichester, ISBN
013567686X, 313pp.
Irwin, S., 2011, A comparison of the use of sodium metabisulfite and sodium dithionite for
removing rust stains from paper, American Institute for Conservation, The Book
and Paper Group Annual, 30, 37-46.
Lem, W.J. and Wayman, M., 1970, Decomposition of aqueous dithionite. Part II. A
reaction mechanism for the decomposition of aqueous sodium dithionite, Canadian
Journal of Chemistry, 48, 782-7.
Lide, D. R., (2002), "CRC Handbook of Chemistry and Physics", 83rd Edition, CRC Press,
Boca Raton, FL, ISBN 0849304830, 2664pp.
Matero, F.G. and Tagle, A. A, 1995, Cleaning, iron stain removal and surface repair of
architectural marble and crystalline limestone: The Metropolitan Club, Journal of
the American Institute of Conservation, 34, 49-68.
Mehra, O.P. and Jackson, M.L., 1960, Iron oxide removal from soils and clays by a
dithionite-citrate system buffered with sodium bicarbonate. Proceedings of the
Seventh National Conference on Clays and Clay Minerals, Swineford, A. (ed.),
Washington D.C., Pergamon Press, 317-327.
Selwyn, L. and Tse S., 2009, The chemistry of sodium dithionite and its use in
conservation, Studies in Conservation, 54 (Supplement 1), 61-73.
Stambolov, T., 1968, Notes on the Removal of Iron from Calcareous Stone, Studies in
Conservation, 13 (1), 45-7.
Thorn, A., 2005, Treatment of heavily iron-stained limestone and marble sculpture,
Proceedings of the ICOM Committee for Conservation 14th Triennial Meeting,
Verger, I. (ed.), the Hague, Netherlands, James & James, London, 888-894.
Zaini, N. 2009, Calcite-Dolomite mapping to assess dolomitization patterns using
laboratory spectra and hyperspectral remote sensing: a case study of Bédarieux
Mining Area, SE France, Master of Science Thesis, International Institute for GeoInformation Science and Earth Observation Enschede, The Netherlands.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
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662
PRELIMINARY STUDIES IN USING LIME WITH ADDITIVES AS
A SUBSTITUTE FOR RESINS AS ADHESIVES IN STONE
CONSERVATION
J. Alonso1* and M. Franković2
Abstract
The use of synthetic resins as adhesives is very common in stone conservation based on its
good performance and gluing speed, even though it is known for irreversibility and
different characteristics compared to natural stone. The main goal of this paper is to explore
the possibilities of using lime with different organic additives as adhesives in stone
conservation, considering that the bond should be slightly weaker than the stone. Six
different adhesive mixes were designed for preliminary evaluation using the following
ingredients: lime putty, NHL3.5, casein, acrylic colloidal dispersion, butadien-styrol latex,
fumed silica, distilled water. Properties of adhesive mixes that were evaluated were
shrinkage, wrapping, rigidity, brittleness, water absorption and weathering performance.
Samples of limestone and marble were glued and tested with cantilever to evaluate its
performance. Based on those preliminary results, three adhesive mixes were selected for
further testing. To evaluate the structural performance of adhesives, limestone semi-circular
specimens were bonded and tested under the Brazilian nut test. This test measures indirect
tensile and shear of the interfacial material and allows the inspection and interpretation of
the fracture patterns. Preliminary tests and assessment of adhesive mixtures performance
gave promising results, since the mechanical resistance and weathering properties of
adhesives match the requirements searched, even though further investigation and
discussion should be developed.
Keywords: cultural heritage, stone, conservation, additives, adhesives, lime
1. Introduction
Many different natural products are described in conservation literature as glues for
bonding different materials since ancient times. Use of natural resins or animal glues is well
known throughout history. Since 17thcentury, adhesion systems using different mixes,
based on casein, rosin or “mistura” (Mix of colophony resin and beeswax) were in wide use
as stone adhesives. However, when at the beginning of the 20 th century, synthetic resins
were invented, they quickly substituted these traditional methods.
1
J. Alonso*
PROSKENE SLP. Madrid, Spain
estudio@proskene.com
2
M. Franković
Central Institute for Conservation in Belgrade, Serbia
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Use of epoxy resins as adhesives is very common in stone conservation, even though its
known irreversibility and different characteristics compared to natural stone. Good
performance and gluing speed make it an easy and useful product. Comparing properties of
epoxy resins to limestone and hydraulic lime mortar properties show that mechanical
properties (i.e. compressive, tensile and flexural strength) of epoxy resin is up to 10 times
higher than those of limestone or hydraulic lime mortars. On the other hand, their porosity,
permeability and water absorption are approximately zero (Sikadur product data sheet.
SikaCorporation). As an intermediate solution to irreversibility, some authors have studied
an interface of acrylic resin (Paraloid B72) to achieve reversibility of the bond
(Podany et al. 2001). We believe, and so is confirmed by other authors in recent papers
(Podany et al. 2009), that as a general stone bonding criteria, mechanical results obtained
by gluing two pieces of stone should be equivalent or slightly lower than the original.
Creating “weak” bonds from a mechanical point of view ensures that, if the stone breaks
again, it would be in the same place, thus avoiding creating new damages. To this “weak”
adhesions some pins could be added if necessary, improving the final resistance of the joint
(Devreux and Spada 2015). We consider these criteria more reasonable from a stone
conservator point of view than gluing with high performance adhesives. Starting from the
idea that adhesive properties should match stone properties, this preliminary study is
exploring possibilities of using lime with different organic additives as adhesives in stone
conservation. Study was aimed at gluing limestone with the lime based adhesives, in order
to best match the properties of the stone. It relied on traditional recipe for lime-casein
mixture, which was then modified by changing or replacing main ingredients to better suit
practical requests of quality control and availability of materials. Performance of the
mixtures was compared to the performance of traditional lime-casein mixture and to
mechanical performance of the limestone. The objective of this study was to assess the
potential of using lime based mixtures as adhesives for stone in order to create a base on
which more in depth research could be founded. Apart from the mechanical performance of
adhesives, which was the main criteria for their evaluation, mixtures were evaluated by
other properties that can be of interest from the conservation point of view, such as their
workability, ease of application, appearance, water absorption and resistance to weathering.
2. Methodology
This study consisted of several stages, which had the objective to assess properties of
adhesive mixtures, their weathering behaviour and to evaluate their structural performance.
2.1. Adhesive mixtures
In the first stage, six adhesive mixtures were designed and their properties observed.
Traditional recipe for lime putty-casein mix was a starting point in designing adhesive
mixtures. Recipe was then modified by replacing lime putty with natural hydraulic lime
(Lafarge NHL 3.5 Z®) and by replacing casein with two different synthetic additives butadien-styrollatex (Policem®) and acrylic colloidal dispersion (Primal 60A®). Diluting
or thickening agents were added in order to achieve good working properties of adhesive
mixtures. Distilled water was used to dilute mixtures and fumed silica (Aerosil®) as a
thickener. Composition of adhesive mixtures is given in Tab. 1.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1:Composition of adhesive mixtures and observation of fresh mixtures properties.
Adhesive
mixture No.
Composition
Proportion (Vol.)
1
Lime putty+casein
1:1
2
NHL 3.5+casein+distilledwater
1: 1:0.5
3
NHL 3.5+butadien-styrol latex
2:1
4
NHL 3.5+butadien-styrol latex fumedsilica
1:1:0.5
5
NHL 3.5+ acrylic colloidal dispersion + fumedsilica 1:1:0.5
6
NHL 3.5+ acrylic colloidal dispersion
1:1
2.2. Observation of adhesive mixtures properties
Samples of adhesive mixtures were poured into PE circular moulds, 2 mm thick and 50 mm
in diameter and left to cure at room temperature for 7 days. Their appearance, curing
behaviour and properties after curing were then assessed in order to collect additional
information about the mixtures. Shrinkage was assessed by comparing changes in sample
dimensions before and after drying. For water absorption, water drop test was performed.
Wrapping and brittleness of dried samples, as well as consistency of fresh mixtures were
assessed by macroscopic visual examination.
2.3. Structural performance
Gluing limestone samples with adhesive mixtures and performing tensile tests assessed
structural performance of the adhesive mixtures. Testing was done in two steps. In order to
select the most promising adhesive samples to be tested in laboratory, preliminary
cantilever test was performed. Three adhesive mixtures were then selected for further
testing.
2.3.1. The cantilever test
The cantilever beam test is a method used to measure the flexural strength of a material. A
cantilever beam is clamped at one end and the other remains free. A load is applied
progressively to the free end until failure. The beam breaks at the fixed side, where
maximum effort is happening. Top of the beam is in tensile effort and bottom in
compression.
M = P×L
where M is the bending moment, P is the applied load and L is the
distance to the support.
M/W
where is the stress, M is the bending moment and W the resistant
moment.
Specimens of 340×32×22 mm, made of limestone with stylolites (commercial name
Sunny), were cut in half using mosaic's hammer and anvil. Adhesive mixtures were applied
to both sides; samples were joined and left to cure in vertical position for 7 days and then
tested (Fig. 1, Tab. 2).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 2: Cantilever load test data at 7 days.
Sample No.
P, N
M, Nmm
W, mm3
, N/mm2
1
-
-
-
-
2
137.34
16480.80
2581.33
6.385
3
78.48
9417.60
2581.33
3.648
4
78.48
9417.60
2581.33
3.648
5
78.48
9417.60
2581.33
3.648
6
107.91
6474.60
2581.33
2.508
Fig. 1: Preparing samples and cantilever test: a – limestone samples; b – applying the
adhesive mixture 1; c – setting of samples; d and e – cantilever test.
2.3.2. The Brazilian nut test
Based on results of preliminary cantilever test, three adhesive mixtures (samples 1, 2, and
6) were selected to be tested in laboratory under the Brazilian nut test. Brazilian Test is a
geotechnical laboratory test for indirect measurement of tensile strength of rocks. Due to its
simplicity and efficiency, it is amongst the most commonly used laboratory testing methods
in geotechnical investigation (Amadei 2015). In the Brazilian test, two opposing normal
strip loads at the disc periphery load a disc shape specimen of the rock. The standard used
is ASTM D3967-95, used by Jorjani to assess the potential adhesive for marble repair
(Jorjani et al. 2008). The load is continuously increased at a constant rate until failure of the
sample occurs. The loading rate depends on the material and may vary from 10 to 50
kN/min. At the failure, the tensile strength of the rock is calculated as follows.
_t=2P/(DL)
where _t is the tensile stress, P is the load, D is the
diameter of the sample and L is the thickness.
The above equation uses the theory of elasticity for isotropic continuous media and gives
the tensile stress perpendicular to the loaded diameter at the centre of the disc at the time of
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
failure. For every adhesive three samples were prepared. The stone samples were made of
oolitic limestone (commercial name Capri). Cylinders with a diameter of mean value 83.8
mm and a height of 21 mm were cut in halves with electrical saw. The surface was smooth,
clean and semi polished. After preparing the surfaces, the adhesive mixtures were applied
to both sides of the wetted samples with a spatula, two pieces were then pressed together
and excess adhesive was brushed away. Samples were clamped and left to cure at room
temperature for 28 days. After specimen preparation was complete, tensile tests were
conducted by the authors using a "Controls" – Advantest 9, frame range 0-100 kN, with the
adapter for tensile testing for concrete and concrete blocks at The Highway Institute in
Belgrade, Serbia. The applied load P was increased at a rate of 0.03 MPa/s (Fig. 2)
Fig. 2 Preparing samples and Brazilian nut test: applying adhesive mixture (a and b);
setting of samples (c); Brazilian nut test (d and e).
2.4. Weathering behaviour
Resistance of adhesive mixtures to weathering was assessed by leaving the samples
exposed to elements for one year and monitoring their decay. Adhesive mixtures 2 and 6
were tested on site. They were used to reattach broken fragments on limestone gravestones
at the medieval necropolis Crkvine in Priboj, Serbia. Necropolis is located in the southwest
part of Serbia, in the valley of the river Lim, at the 400-500 m altitude. The climate is
continental, with an average annual temperature of 9.3°C, a mean precipitation value
752 mm and 15% of snowfall. Fragments of limestone were reattached in October 2014. On
one gravestone adhesive mixture 2 was used, on another mixture 6. After reattachment of
fragments, wider cracks were pointed with hydraulic lime mortar. They were assessed after
one year's exposure to the elements.
3. Results and discussion
3.1. Observation of adhesive mixtures properties
Observations of adhesive mixtures properties are given in Tab. 3. Properties of fresh and
cured mixtures were assessed. In fresh mixtures, viscosity changed significantly in samples
where thickening agent was added, but difference in viscosity between the sample with
butadiene-styrol latex (sample 3) and the one with acrylic colloidal dispersion (sample 6)
was noticeable as well.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 3: Observation of adhesive mixtures properties
Adhesive
mixture No.
Fresh
mixture
Cured mixture
Shrinkage Wrapping
1
viscous
7%
noticable
2
viscous
5%
noticable
2%
no, cracked
2%
no
3
4
thick
paste
thick
paste
5
paste
7%
slight
6
viscous
5%
slight,
cracked
Flexibility
Water drop
absorption
rigid, brittle,
some absorption
break easily
rigid, brittle,
some absorption
break easily
flexible,
total absorption
resiststobraking
flexible,
medium
resiststobraking
absorption
rigid,
no absorption
veryhardtobrake
flexible,
no absorption
hardtobrake
All the samples shrank upon curing, but to the different degree. Shrinking manifested as
wrapping and cracking. From the observations of cured samples, it could be concluded that
properties of the mixtures can be related to the additive - butadiene-styrol latex samples
being the most flexible and casein samples being the most brittle. Presence of fumed silica
in the mixtures did not seem to have the effect on preventing shrinking or cracking.
Presence of cracks might have affected shrinkage, i.e. it can be suspected that sample
number 6 would have shrunk more if it did not crack. Water drop absorption test showed
that samples with acrylic colloid dispersion (5 and 6) did not absorb water at all, ones with
casein (1 and 2) showed some absorption, while ones with butadiene-styrol latex (3 and 4)
completely absorbed water drop within 1 minute.
3.2. Observation of the structural failure by indirect tensile (Brazilian Test)
Compressive strength applied on both sides of the circular specimens creates tensile efforts
that cause diametric vertical cracks coincident with the load axis (isotropic rocks).
Specimens numbered one (limestone glued with adhesive mixture 1 - lime putty and casein)
broke on the adhesive layer, clean and fragile break and adhesive remains on both sides.
The range of the results is very wide, can´t be considered consistent, possibly lime putty
setting problems happened. Specimens numbered two (limestone glued with adhesive
mixture 2 - NHL 3.5 and casein) broke on the adhesive layer, clean and fragile break and
adhesive remains on both sides. Specimens numbered six (limestone glued with adhesive
mixture 6 - NHL 3.5 and acrylic dispersion) broke on the adhesive layer. The adhesive
remained on both sides but the elasticity of the bond deformed till definitive fracture (no
fragile fracture). Using lime putty and casein as an adhesive presents very diverse tensile
results. One result is very close to the ones reached with NHL, but the other two are
significantly lower. This could be due to setting problems. Adhesives composed of Natural
Hydraulic Lime and casein or acrylic dispersion perform mostly equal. They perform
almost 70% of the natural stone tensile resistance.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 4: Brazilian nut test data at 28 days.
Sample No.
Adhesive mixture no.
P, N
s, N/mm2
1-1
1
5.071
1.796
1-2
1
2.425
0.859
1-3
1
14.624
5.181
2-1
2
18.035
6.389
2-2
2
13.004
4.607
2-3
2
15.572
5.516
3-1
6
15.107
5.352
3-2
6
17.535
6.212
3-3
6
15.514
5.496
Average
2.612
5.504
5.687
3.3. Weathering behaviour
Adhesive mixture samples were left exposed to elements in the beginning of December
2013. After two months sample 1 broke in half. After 4 months upon exposure, sample 1
disaggregated completely while sample 2 started cracking and flaking. The other samples
were unchanged. After 6 months sample 2 also disaggregated, while the other samples
started to be colonized by microorganisms. Samples did not show any visible decay effects.
When handled while wet, they all showed certain degree of flexibility, but stiffened again
upon drying. Fifteen months upon exposure, samples 3, 4, 5 and 6 still did not show any
significant decay effects; on their surface only a thin reddish bio-film could be noticed
(Fig. 3).
Fig. 3: Properties of adhesive mixtures: samples after curing (a and b); monitoring
weathering of samples (c 1/2014, d 3/2014, e 5/2014, f 11/2014).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
After a year's exposure to elements on site, fragments reattached with both adhesive
mixtures (2 and 6) are in good condition. There are no noticeable signs of decay. It can be
argued that, if used for bonding and not directly exposed to the elements, both adhesive
mixtures perform well after one year. Monitoring should be continued in a longer period of
time in order to attain more data on the behaviour of adhesive mixtures applied on site.
4. Conclusions
Study in using lime with additives as a substitute for resins as adhesives in stone
conservation gave promising preliminary results. Resistance of the bond is always lower
than the natural stone, but strong enough to be considered. Samples brake on the joint line,
therefore no additional damage to stone is made. Adhesives composed of NHL with either
casein or acrylic dispersion, perform almost 70% of the natural stone tensile resistance.
Adding pins to the bond could make the bond even more resistant. Tested adhesives do not
require using solvents; they are health and eco friendly. They are compatible with natural
stone and can be used on wet surfaces. Although setting time is longer than epoxy resin,
they are relatively easy to work with. Last, they could be removed, thus allowing for the
reversibility of the treatment. Further research should be developed, in order to better
understand long-term behaviour and resistance of the mixes to weathering and
biodeterioration.
References
Amadei, B., 2015, Principles and procedures of the Brazilian test, University of Colorado,
CVEN 5768, Lectures notes 8.
Devreux, G. and Spada, S., 2015, Experiences in anchoring systems in the restoration of
stone artefacts, IIC, News in Conservation, Issue 50, pp. 11-14.
Jorjani, M. et al., 2008, An evaluation of adhesives for marble repair, The American
Institute for Conservation of Historic& Artistic Work, Objects Specialty Group
Postprints, Volume Fifteen, pp.95-07.
Podany, J., et al., 2001,Paraloid B-72 as a Structural Adhesive and as a Barrier within
Structural Adhesive Bonds:Evaluations of Strength and Reversibility, Journal of
the American Institute for Conservation, Vol. 40, No. 1, pp.15-33.
Podany, J., Risser, E. and Sanchez E., 2009,Never forever: assembly of sculpture guided by
the demands of disassembly, Holding it All Together: Ancient and Modern
Approaches to Joining, Repair and Consolidation, Ambers, J. et al. (eds.),
Archetype Publications, ISBN: 9781904982470, pp. 134-142.
Wang, R.,Lackner, R and Wang, P.-M., 2011,Effect of Styrene–Butadiene Rubber Latex on
Mechanical Properties of Cementitious Materials Highlighted by Means of
Nanoindentation, Strain 47, doi: 10.1111/j.1475-1305.2008.00549, pp 117-126.
670
FREEZE THAW AND SALT CRYSTALLISATION TESTING OF
NANOLIME TREATED WEATHERED BATH STONE
R.J. Ball1* and G.L. Pesce1, M. Nuño1, D. Odgers2 and A. Henry3
Abstract
This paper describes the effects of freeze thaw and salt crystallisation on weathered Bath
stones treated with nanolime. Specimens were characterised using drilling resistance
measurements to evaluate the variation in surface and subsurface integrity following
application of nanolime and subsequent testing. A number of different regimes used to
apply the nanolime are reported. The tests did not suggest any negative impacts due to the
presence of nanolime on the freeze-thaw tested specimens, however evidence of subsurface damage was observed on some specimens subjected to salt crystallisation.
Keywords: weathered stone degradation, freeze thaw, nanolime, salt crystallisation,
drilling resistance
1. Introduction
Many historic and new buildings are built using natural limestone due to its availability
workability and aesthetic appearance. However, since the industrial revolution the level of
atmospheric pollutants has increased substantially and this had resulted in an acceleration
of degradation of stone surfaces. Common pollutants such as sulphur dioxide and oxides of
nitrogen form acids that etch the surface reducing mechanical strength and also, for certain
stone types, result in the formation of a crust, commonly gypsum (Nuno et al., 2015). Such
crusts are often much less permeable compared to the underlying stone and lead to the
undesirable trapping of moisture and salts in the subsurface layer. In addition to the effect
of pollutants, erosion from weathering plays an important part in stone decay.
To consolidate surfaces of decayed stone, treatments are commonly applied aiming to
restore or maintain a desirable level of strength and integrity. There is a wide variety of
treatments available based on a range of different chemical systems including organosilicon
compounds, ethyl silicate or ethyl-methacrylate. (Ferreira Pinto and Delgado Rodrigues
2012; Karatasios et al., 2009; Esbert et al., 1991). However it is generally accepted that
when identifying a suitable consolidant, materials which have some chemical compatibility
with the stone to be consolidated have a reduced risk of undesirable effects. All, chemical,
1
R.J. Ball*, G.L.A. Pesce and M. Nuño
BRE Centre for Innovative Construction Materials, Department of Architecture and Civil
Engineering, Bath, United Kingdom
r.j.ball@bath.ac.uk
2
D. Odgers
The Old Stable, Peacock Hill House, Barton St. David, Somerton, United Kingdom
3
A. Henry
Historic England, Engine House, Fire Fly Ave, Swindon, United Kingdom
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
physical and mechanical properties are important, and in the case of limestone, lime
(calcium hydroxide) based materials may offer such compatibility. For many years lime
water and milk of lime, have been applied as a consolidant. The former is a clear solution of
lime in water whereas the latter consists of micro-sized particles of calcium hydroxide as a
suspension in a saturated aqueous solution of calcium hydroxide. When either product is
applied to stone, evaporation of the liquid carrier results in the deposition of calcium
hydroxide which subsequently carbonates depositing calcium carbonate on the surface and
within the pores of the stone providing an increase in strength. However this particular
approach has several drawbacks including: (i) the micro sized calcium hydroxide particles
of milk of lime may be larger than the stone pores reducing the amount of lime deposited
within the stone; (ii) although lime dissolved in the lime water may enter the stone the
actual amount deposited upon evaporation is only about 1.8g per litre of water; (iii) in order
to deposit a sufficient quantity of calcium hydroxide to give a reasonable level of
consolidation the process of applying the lime water must be repeated numerous times, in
some cases up to forty. Aside from the labour intensive nature of such a treatment
repeatedly wetting and drying the stone with water (the most important natural solvent) can
mobilise soluble salts contained within the stone. In some instances this can lead to further
damage, negating any increase in strength arising from the use of the consolidant.
In the late 1990’s researchers at the University of Florence including Baglioni, Dei and
Salvadori synthesised nanometre sized calcium hydroxide to be used in the field of cultural
heritage. This was added to an organic carrier, often an alcohol, forming what is now
commonly called nanolime which generally has a particle size <150nm. Properties such as
rapid evaporation of the solvent, small particle size and a liquid carrier that does not
dissolve salts within the stone, have generated much interest from the conservation
industry. Originally formulated for the restoration of deteriorating fresco paintings, in the
last few years this material has been used as a stone consolidant in a number of countries
including the UK.
Due to its relatively recent introduction and the lack of research there still remain many
unanswered questions regarding its medium to long term effects. Recent studies focussed
on weathered stones (Pesce et al., 2013) and findings from the International Workshop on
the Application of Nanolime for Consolidation of Weathered Stone, held at the University
of Bath in September 2015, have highlighted the importance of factors such as application
technique, environmental conditions and stone type on the effects of treatments. Depths of
penetration and formation of surface crusts are extremely hard to predict on site, yet can
have a significant influence on the post-treatment behaviour of the stone. Previous studies
often highlight the adverse effects of treatments that result in accelerating the onset of
damage (Dei and Salvadori, 2006). Salt crystallisation and freeze-thaw cycling are two
mechanisms to which many of the stones treated with nanolime in the UK will be
subjected. In this paper we report on the likely effect of nanolime on stones subject to
freeze/thaw cycling and salt crystallisation.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
2. Experimental methods
2.1. Preparation of specimens
Cube shaped specimens approximately 100 mm in each direction were cut from carefully
selected pieces of weathered Bath stone. The weathered surface of each stone was treated
with commercial nanolime CaLoSiL® E25, containing 25g/l calcium hydroxide in ethanol.
A detailed analysis of porosity in the Bath stone used is given in Pesce (2013). A reduction
in porosity of around 6% was reported when comparing weathered to un-weathered stone.
A number of different treatment regimens including: different numbers of applications,
period between applications, post treatment spraying with water during curing and
variations in relative humidity during curing was chosen to represent methodologies and
conditions expected in the UK. In total 15 individual treatments were applied, labelled A to
O, and given in Tab. 1. The surface and sub-surface characteristics of each specimen before
treatment with nanolime, after treatment with nanolime and following freeze-thaw and salt
crystallisation testing was evaluated. A SINT Technology s.r.l. Drilling Resistance
Measurement System (DRMS) was used to characterise mechanical properties of each
stone to a depth of 30 mm (and therefore to evaluate the penetration depth of the
consolidant). Due to the natural heterogeneity of stone in order to obtain a representative
measure of the surface and sub-surface properties, each stone was drilled three times using
a 5 mm diameter flat ended diamond drill bit and results were averaged to produce a single
drilling resistance profile. All tests were undertaken using a 600-rpm rotational speed and
penetration rate of 10 mm/min.
Tab. 1: Relative humidity during curing, number and timing of applications and details of
water spraying during curing of test specimens.
Relative humidity
Post application
water spraying
1
Number of
applications
of nanolime
6 within
2 hours
6 in a
day
90
90
90
60
30
3 sprays/
day
(1 day)
3 sprays/
day
(4 days)
-
-
-
B
C
A
J
M
E
F
D
K
N
H
I
G
L
O
Letters A – O indicate the specimen identification and treatment conditions
Two of each specimen type were produced providing one for freeze-thaw and the other for
salt crystallisation testing. Specimens were subjected to 15 individual freeze-thaw cycles
where each cycle consisted of firstly saturating the stone surface with water followed by
placing it in a freezer at -22°C for 48 hours. In order to promote unidirectional freezing
from the nanolime treated surface into the bulk of the specimen (simulating the natural
process of freezing that occurs in stone on a building), the remaining 5 untreated faces of
the cubes were covered in a 60 mm layer of rigid phenolic foam insulation, Fig. 1a.
Following freezing, the specimens were removed from the freezer and thawed at 19°C and
76% relative humidity.
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An epoxy coating was applied to four faces of the salt crystallisation specimens leaving top
and bottom faces uncoated Fig. 1b. Salt crystallisation within the surface of the specimens
was initiated by firstly allowing a saturated solution of sodium sulphate to diffuse into the
nanolime treated surface. This was achieved by immersion in a tray of the liquid to a
height of 35 mm with the nanolime treated face in the vertical orientation, specimen turned
onto side as shown in Fig. 1c, therefore leaving the remaining 65 mm of treated surface out
of the solution. The 48 hour immersion period was sufficient to allow saturation of the
stone surface above the liquid level by capillary action. Each specimen was then removed
and allowed to dry for 48 hours at 19°C and 76% relative humidity. The epoxy resin
coating ensured that the evaporation of moisture and flow of salts were towards, and out of,
the nanolime treated surface. Three cycles were sufficient to cause a range of different
severities of damage over the different of specimens, and therefore to allow comparison
between the treatment regimes.
Fig. 1: Stone specimens: (a) freeze thaw, (b & c) salt crystallisation.
3. Results
3.1. Freeze thaw cycling
Visual examination of the specimen surfaces subjected to freeze thaw cycling revealed a
variation in the severity of damage observed on different areas. This was attributed to
natural variations of the stone surface. To evaluate this effect on drilling resistance,
measurements were taken in both areas of severe and areas of low damage. Each stone
behaved slightly differently and comparisons of the drilling resistance measurements taken
at different stages of the specimen’s treatment are given in Tab. 2. All specimens except
those subject to a single application in low RH (30% and 60%) showed an increase in the
stone integrity after application of nanolime. An (*) is shown where an increase in the stone
integrity after application of nanolime was not detected. This was defined as when the
drilling resistance of the nanolime treated stone increased compared to the untreated stone.
In almost all cases a sharp increase in the drilling resistance of the treated stone signified
that a nanolime crust had been formed. The exceptions were those specimens indicated by
the symbol (§) in the table. Where the drilling resistance of the stone subjected to freeze
thaw cycling was greater than that of the original stone, but generally less than the treated
stone this was classed as an improvement, and denoted by the symbol †. In this case the
application of nanolime had mitigated against the effects of freeze thaw cycling. Fig. 2
shows the drilling resistance profiles for stone H. It is clear that the application of nanolime
has increased the hardness of the surface crust and a modest increase in the resistance of the
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
sub surface layer to a depth of approximately 9 mm. Following the freeze thaw cycling the
drilling resistance is seen to drop. However for the area classed as ‘less damaged’ the
resistance is still greater than that of the untreated stone. In the ‘more damaged’ area the
drilling resistance has dropped below that of the untreated stone.
Tab. 2: Summary of DRMS profiles from specimens subjected to freeze thaw cycling
Relative humidity
90
90
90
60
30
Post application water
spraying
3 sprays/
day
(1 day)
3 sprays/
day
(4 days)
-
-
-
†
†
*§
*§
†
†
†
§
No. of
applications of
nanolime
1
6 within 2 hours
6 in a day
†
†
* = No detectable increase in integrity of stone after application of nanolime, § = No crust
formed on stone, † = Improvement in the stone resistance to freeze thaw cycling attributed
to the application of nanolime.
Fig. 2: Drilling resistance profiles of stone H subjected to freeze thaw cycling.
3.2. Salt crystallisation
A summary of the drilling resistance measurements from the salt crystallisation tests are
given in Tab. 3. An (*) is given where the application of nanolime led to an increase in the
drilling resistance before immersion in the salt solution. A number of the specimens
showed an increase in the drilling resistance following salt crystallisation cycles. Visual
examination attributed this to the precipitation of salts in the surface pores resulting in the
increased drilling resistance, as indicated by the Greek letter ϕ in Tab. 3. A further effect
that was observed on a number of the stones was a decrease in the drilling resistance within
the subsurface at a depth between 5 and 10 mm. This is denoted in the table by symbol (‡).
Fig. 3 shows the drilling resistance profiles for stone G subjected to salt crystallisation,
which can be considered as a successful treatment. The application of nanolime has resulted
in an increase in the drilling resistance to a depth of 6 mm. Following salt crystallisation
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
cycling the drilling resistance was reduced, however it is still greater than that of the
untreated stone, and therefore the presence of nanolime has been beneficial. In comparison
the drilling resistance profiles from stone D subjected to salt crystallisation are shown in
Fig. 4. The application of nanolime has increased the drilling resistance to a depth of
approximately 8 mm, however it has also produced a surface crust, indicated by the peak at
a depth <1mm. Following salt crystallisation cycles the strength of this crust has increased,
however a weakening of the stone is observed in the subsurface layer.
Tab. 3: Summary of DRMS profiles from specimens subjected to salt crystallisation
Relative humidity
90
90
90
60
30
Post application water
spraying
3 sprays/
day
(1 day)
3 sprays/
day
(4 days)
-
-
-
*§
* §
No. of
applications of
nanolime
1
§ϕ‡
*
‡
‡
6 within 2 hours
§ϕ‡
*§
‡
ϕ ‡
6 in a day
*§ϕ
* ϕ
ϕ
§
* = No detectable increase in integrity of stone after application of nanolime, § = No
nanolime crust formed on stone, ϕ = evidence of a salt crust, ‡ = subsurface weakening
Fig. 3: Drilling resistance profiles of stone G subjected to salt crystallisation cycling.
4. Discussion
Examination of the drilling resistance profiles for the stones before and after treatment with
nanolime revealed that an increase in drilling resistance, between 5 and 10 mm, was
observed on the majority of stones. Stones J and M, which received 1 application of
nanolime and were cured in an atmosphere of relative humidity 60% and 30%, respectively,
did not show an improvement. This result highlights the importance of the presence of
water in promoting the carbonation of nanolime through the formation of carbonic acid.
Stones C, F, H and I that were used in the salt crystallisation tests also did not show an
increase in drilling resistance following treatment with the nanolime. Further work is
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required to determine the cause of this observation especially considering that the
equivalent stones which were used for freeze thaw tests did show an increase in drilling
resistance.
Fig. 4: Drilling resistance profiles of stone D subjected to salt crystallisation cycling.
The majority of specimens used to evaluate the effect of freeze thaw cycling had evidence
of crust formation on the surface. From the specimens where the nanolime treatment
appeared to have been beneficial following freeze thaw cycling the most consistent effect
was observed in the specimens that, after application of nanolime, were sprayed with water
3 times a day for 4 days. Such treatment, which would be expected to maintain a high
humidity in and around the stone, could again be enhancing the effect of carbonic acid
formation and thus carbonation.
From the specimens treated with nanolime and subjected to salt crystallisation, a much
larger proportion did not show evidence of an improvement as a result of the application of
nanolime, prior to the salt tests. As there was little correlation with the equivalent
specimens prepared for the freeze thaw tests this difference must be attributed to natural
variations in the weathered stone. This is perhaps not unexpected and a common problem
associated with tests using natural materials. However as a result some caution must be
exercised when drawing more specific conclusions.
Perhaps the most noticeable difference between the freeze thaw and salt crystallisation tests
was an increase in drilling resistance of the surface crust following salt crystallisation. This
increase would be consistent with the precipitation of sodium sulphate within a pre-existing
naturally formed gypsum or consolidant induced (nanolime) crust. Consideration of all the
specimens shows a definite pattern in which salt crystallisation to nanolime treated surfaces
results in a weakened subsurface region. This may be due to the crust on the surface being
less permeable but further tests would be required to establish the exact mechanism.
Changes in the surface permeability attributed to the nanolime treatment may restrict the
flow of salt solution out of the surface during the drying cycle. This could therefore
promote an enhanced precipitation, and therefore accelerated deterioration of the stone.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
5. Conclusions
This paper provides a summary of results obtained from a study to evaluate the effects of
freeze thaw and salt crystallisation on nanolime treated stone. A total of 30 different
specimens were conditioned and 315 holes were drilled. Despite the extensive data obtained
natural variations in the stone means caution must be exercised when drawing conclusions.
The key findings are summarised below:
High relative humidity of 90% enhanced the consolidating effect of nanolime
compared to equivalent specimens exposed to a lower humidity of 60 and 30%.
Spraying nanolime treated surfaces with water immediately after application can, in
some circumstances, improve the consolidation effect by providing a humid
environment where carbonation is promoted.
All stones treated with nanolime, and subjected to freeze thaw cycling, either
showed an improvement in drilling resistance as a result of the presence of
nanolime or no improvement. Within this study there was no evidence which
suggested a negative effect on drilling resistance due to the presence of nanolime
being applied to the surface.
In a number of the tests performed to investigate the effect of salt crystallisation,
drilling resistance measurements indicated that a weakened sub surface layer was
formed. This suggests that damage from salt crystallisation may be exacerbated by
changes in surface properties of stone which can be attributed to treatment with
nanolime.
References
Dei, L. and Salvadori, B., 2006, Nanotechnology in cultural heritage conservation:
nanometric slaked lime saves architectonic and artistic surface from decay.
Journal of Cultural Heritage 7(2): 110–115.
Esbert, R. M., Montoto, M., and Ordaz, J., 1991, Rock as a construction material:
durability, deterioration and conservation. Materiales De Construcción 41(221):
61–73.
Ferreira Pinto A. and Delgado Rodrigues J., 2012, Consolidation of carbonate stone:
influence of treatment procedures on the strengthening action of consolidants.
Journal of Cultural Heritage 13(2): 154–166.
Karatasios, I., Theoulakis, P., Kalagri, A., Sapalidis, A., and Kilikoglou, V., 2009,
Evaluation of consolidation treatments of marly limestones used in archaeological
monuments. Construction and Building Materials 23(8): 2803– 2812.
Nuño, M., Pesce, G. L., Bowen, C. R., Xenophontos, P. and Ball, R. J., 2015,
Environmental performance of nano-structured Ca(OH)2/TiO2 photocatalytic
coatings for buildings. Building and Environment 92: 734-742.
Pesce, G. L., Morgan, D., Odgers, D., Henry, A., Allen, M., and Ball, R. J., 2013,
Consolidation of weathered limestone using nanolime. Proceedings of the ICE Construction Materials 166(4): 213–228.
678
THERMOSETTING METHYL METHACRYLATE ADHESIVE FOR
STONE: CHARCTERISATION, APPLICATION TECHNIQUES
AND LONG-TERM PERFORMANCE ELEVATION
Z. Barov1*
Abstract
A two-component thermosetting adhesive for fractured stone and ceramic objects is
composed of polymethyl methacrylate copolymer (powder) containing hardener, and a
liquid monomer. When the two components are mixed the powder rapidly dissolves in the
monomer and the mixture begins to cure. The powder/liquid ratio can vary considerably
allowing the formation of an adhesive with various viscosities. The resulting syrup or paste
can be used as adhesive, gap-filler and reconstruction material for marble restoration. After
polymerization it produces a resin with Tg of 74 - 85C, depending on the presence of inert
filler. This, together with its photochemical stability, makes it quite appropriate for outdoor
applications. The complete polymerization occurs in 24 hours. but after 40-50 minutes the
connection is sufficiently strong to allow handling. The polymer produces sufficiently
strong join that is also resistant to air pollutants. It remains totally reversible in a variety of
solvents even after long time. This allows dissembling of complex pinned joints, usually
quite difficult to achieve with other adhesives. A special technique has been developed for
reassembling complex joints. It consists of fixing the fragment to a sled mounted on tracks,
allowing moving it back and forth without loosing the alignment. This permits application
of the adhesive, placing of pins and then fast and precise reassembling. When pressure is
applied the excess adhesive is squeezed out of the joint. Because the shrinkage upon curing
is minimal all the gaps that may be present stay filled. When mixed with some pigments it
can be used as an external gap filler and reconstruction material for restoration of missing
marble elements. It produces matt surface that can be additionally carved and patinated.
The system has been applied on several artifacts and has withstood outdoor exposure for
decades.
Keywords: reversible stone adhesive, thermosetting polymethyl methacrylate,
technical investigations, application techniques, fill material
1
Z. Barov*
ETHOS, conservation of ancient art, United States of America
barov.ethos.art@mac.com
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
1. Introduction
When in the early 1970’s there was a need to remove the lid of a newly discovered
medieval sarcophagus without employing tools that could damage the stone, it was decided
to adhere hooks to it with the use of a reversible adhesive. Veseslin Vekov and Alexandar
Savov of the National Institute for the Monuments of Culture in Sofia, Bulgaria were
responsible for the choice of the adhesive. Two-component, solvent reversible polymethyl
methacrylate system (PMMA), Colacryl, made by ICI, was selected by them, tested and
successfully employed on the project. The same type of adhesive but made by different
manufacturer was tested for long-term application and used by the author routinely, in
various projects, for stone and ceramic reassembly (Barov, 1985). After more than 30 years
of outdoor exposure it proved to be excellent glue, resisting high temperature fluctuations
and direct sunlight. Its high glass transition temperature (Tg) held the joins firmly even
when the surface temperatures of a black diorite sculpture reassembled with it reached, in
many occasions, the levels of 60-63C. Subsequently, it became clear that because of its
photochemical stability it could be used as a fill material for surface gaps and for rebuilding
missing areas on marble objects. Being a thermosetting resin it exhibits very low shrinkage
upon curing, which is a useful property for gluing fragments with worn interfaces, where
missing sections must be filled to insure continuous surface contact of the adhesive film
with the substrate. The fast curing time allows layering when thick fills must be applied.
That helps avoiding excessive temperature increase during the curing of large masses. It is
also very useful for achieving colour matches when building restored parts because the
resin is semi translucent and allows achieving subtle colour nuances with the addition of
small amount of pigments in each layer. Finally, its prompt reversibility in many solvents,
even after decades of outdoor exposure, insures the separation of joins reinforced with one
or several pins, even when they are deeply embedded into the substrate.
2. Use of PMMA as an adhesive
The first attempts of reassembling stone artifacts with PMMA were made only on the bases
of manufacturers information about the characteristics of the product. The resin was
developed mainly for use in dentistry. It is supplied as a two-component system: The
polymer, polymethyl methacrylate is in powder form. It is usually based not only on a pure
methyl methacrylate but is copolymerized with other acrylates (2-ethyl hexyl acrylate) to
decrease the Tg of the polymer and to improve some of its physical properties (W.H.A
Plastics, 2002). The brand we usually employ, Teets Cold Cure Denture Material,
manufactured by Co-Oral-Ite Dental Manufacturing Company in the USA, has a Tg of
74C (our measurements). The polymer contains small amount of plasticizer, dialkyl
phthalate and a hardener, organic peroxide. The second ingredient of the two-part system is
a liquid methyl methacrylate monomer (manufacturers’ data). When mixed with the
powder it forms a syrup or paste that is used as an adhesive or fill material. It is stabilized
with a small amount of inhibitor, hydroquinone, to prevent spontaneous polymerization.
Upon combining, the powder dissolves in the monomer quite fast – after one to two
minutes of mixing. At the same time the monomer reacts with the hardener, present in the
powder, initiating the curing process. The ratio between the two components can vary
considerably allowing the production of mixtures with different viscosity. The ratio
suggested by the manufacturer is 2 parts of powder to 1 of liquid but the mixture is too
thick for normal gluing purposes and is usually reduced to 1:1 or even with less amount of
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
polymer. When applied over the interfaces the substrate absorbs part of the monomer. To
avoid the initial loss of liquid, especially in highly porous materials, is a good practice to
brush the surfaces with small amount of pure monomer, before the application of the glue.
Some monomer evaporates during the preparation and application processes that also
increase the viscosity of the mixture.
The curing is exothermic and initiates 15-20 min. after the mixing of the components. The
temperature increases rapidly, but most of it is absorbed by the substrate. The reaction takes
10-15 minutes after which the heat generation stops and the adhesive film becomes hard.
Theoretically the complete curing occurs after 24 hrs. but the join becomes sufficiently
strong after 30-40 min. to allow manipulation of the glued fragments, if necessary. It is
better, however, to allow complete curing before applying substantial stress on the joint.
Although the adhesive is sufficiently strong and at the same time resistant to high
environmental temperatures it should not be presumed unconditionally reliable for very
long outdoor exposure where the temperature fluctuations generate continuous stress on the
joins. Its longevity could be affected mainly by the differences of the coefficients of
thermal expansion of the film and the substrate. The stress could be aggravated by the
position of the attached fragment that can protrude horizontally and add the negative effect
of vibrations, especially those caused by earthquakes that can increase significantly the
vulnerability of the joints. Although the author has not noticed separations after 30 years of
outdoor exposure, this does not mean that the perfect adhesion will continue indefinitely.
For these reasons the connections are reinforced with the addition of rigid pins that have
several positive effects: To increase the gluing surface and the general strength of the joint;
To increase its rigidity and especially to prevent the fragment(s) from falling off if the
adhesive fails completely. Disassembly of pined joints in the future could be a difficult task
because if the pins are selected and placed properly (an issue not covered in detail here)
makes a future separation very difficult to accomplish if other adhesive has been used.
The system is composed of two parts (powder and liquid) to speed up the preparation of the
mixture, to decrease the evaporation of the monomer and especially to decrease the curing
time. Using only monomer and curing agent as an adhesive is much more difficult even if
thickened with fumed silica and after several unsuccessful attempts it was decided to
exclude it from our tests and practical work.
In normal temperature (20-25°C) the working time of the Teets Cold Cure adhesive is
around 15 min. including mixing the two components together, applying the mixture on the
interfaces, filling the pin holes, coating the pins and aligning correctly the fragments. For
large and complex joins this time could be not sufficiently long and there is a chance that
imperfect connections could result from the hurried manipulation. Initially it was attempted
to slow down the curing process by adding the inhibitor hydroquinone. It however changed
the colour of the PMMA, from transparent to pink and was dimmed inappropriate. Two
other inhibitors were also tested, the antioxidants Butylated hydroxyanisole (BHA) and 2,6D tert-butyl d-methylphenol but the results were again unsatisfactory.
2.1. Alignment technique
To compensate for the relatively short working life of the system some mechanical
improvements of the gluing process were developed and implemented in several projects.
One of the most time consuming operation is to align correctly a large and heavy broken
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
detail to an immovable object (statue) especially if the joint must be reinforced with one or
several pins. The operation includes application of the adhesive its injection into the holes
where the pins will be inserted and then the fragment must be aligned correctly and pressed
strongly until the complete curing of the resin takes place. The fragment could be
positioned above the immovable object (the best case), or protruding sideways, beneath the
object vertically or in an angle.
In order to shorten the reassembling process, the fragment is installed onto a sled that is
mounted on a track with two or four members. Both the sled and the track are made of
wood. The track is parallel to the axis of the fragment and to the pin, if such is present, and
is firmly connected to a supporting structure. It allows the sled to move back and forth
along the axis of the fragment but restricts movements in any other direction. The track and
the sled are aligned so that the fragment and the object fit correctly together before any glue
is applied. Subsequently the sled/detail assembly is moved away from the object far enough
to expose the two interfaces. The adhesive is applied with brush on both sides then the
assembly is moved back to the object and pressed firmly until the adhesive sets. In some
cases we have used ratchet straps to accomplish the movement and the pressure and other
times – a bottle jack. Usually some excess adhesive is pressed out of the joint and must be
wiped off with acetone-soaked rag from the visible areas. In some cases the sled should
have some polyethylene sheet lining to prevent gluing the stone to it.
Fig. 1: The detail to be bonded is mounted on a wooden sled and pressed with bottle jack.
The small elements of the wooden support are attached to themselves and to the sled with
cyanoacrylate gel.
If a pin is required, the hole must be drilled first in the object, before installing the tracks.
Subsequently the tracks are built and the fragment, attached to the sled, is dry-fitted to the
object. To mark the place where the hole should be drilled into the fragment, a ball of
cotton is inserted in the hole of the object, prior to the dry fitting, so that some of it
protrudes slightly above the surface of the interface. The visible side is painted with
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
gouache or acrylic colour and when the fragment is pressed to the object the whet colour
leaves a paint mark on the other interface, indicating the drilling spot. The same technique
could be applied if there is more than one pin. After drilling the second hole, the pin is
glued to the fragment and while the adhesive is still in the stage of hardening the fragment,
fixed to the sled, is fitted to the object so that the pin is correctly positioned for the final
assembly. After the curing, the fragment is pulled back and adhesive is injected into the
hole of the object as well as applied over the pin. To prevent the adhesive to run out it could
be thickened and made jell-like with the addition of fumed silica. The rest of the gluing
proceeds as described above.
2.2. Reversibility
Being soluble in many solvents the PMMA can be removed not only from the joins but also
from the holes where the pins are embedded. In simple cases wrapping solvent containing
compresses, covered with polyethylene foil around the joins could dissolve the adhesive.
For more complicated joints building a temporary container around the glue line allows to
keep large amount of solvent in contact with the glue and the surrounding substrate for a
long time. Such container can be build out of aluminum-lined cardboard, shaped around the
fragment and adhered to it with substance insoluble to the solvent to be used. If acetone is
employed a thickened with fumed silica polyvinyl alcohol (PVOH) or hide glue can be
used. These two adhesives are easily removable afterward with water or steam. The
container is made out of several pieces of cardboard joined together with staples,
cyanoacrylate gel, etc. Before use, the joints are sealed with thickened PVOH or animal
glue. The aluminum-lined side faces the object and prevents excessive absorption of the
solvent by the cardboard. If aluminum faced cardboard is unavailable the internal surface
can be coated with a layer of 15% PVOH. For large and complicated joins the author
applies the adhesive on stripes over the interfaces in order to leave narrow unglued
channels that facilitate the penetration of the solvent used for eventual disassembling in the
future.
2.3. Characteristics of the adhesive
From aesthetic point of view there are two positive qualities unique to this system. First, it
does not darken the surface of the stone, unlike dissolved acrylics, epoxies and polyesters
that form slightly darker margins or intensified colour of the non-white stones or terracotta
at the glue boundaries. Second, it produces totally mat surface that blends quite well with
the surrounding original material and requires very little additional work to finish when
used as fill or as reconstruction material.
From technical point of view, the adhesive power of the cured film to the substrate appears
to be inferior to the cohesion forces of most stones used in the architecture and in the arts.
This is an important issue, especially for outdoor objects (or architectural details), which
joins are going to fail, sooner or later, as discussed above. Indoor objects are not totally
immune either to joint failures caused by vibrations, earthquakes, etc. In both cases
adhesives stronger than the substrate will cause detachment of a thin layer of original off
the surface of the interfaces. In our tests most of the epoxies as well as Paraloid B72
develop very strong adhesion to stone and ceramics causing breakage of the substrate. In
most cases the PMMA separates cleanly from the inorganic surfaces.
From purely practical point of view the system provides very fast final results that is quite
convenient when reassembling objects with multiple breaks. Because of the fast initial
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
curing, the connection becomes sufficiently strong after 40-50 min. and one can proceed to
the next join or to any kind of other manipulation. For very large objects, of course, is
advisable to wait 24 hrs. before proceeding.
Some of the most important properties of the cured adhesive were tested to determine the
numeric values of its performance and become aware of the resin’s limits. It was important
to determine, in a first place, the adhesive power of the system to stone and ceramic
substrates. Two different tests were performed: lap shear adhesive strength (ASTM D 90549) and tensile strength of the stone/adhesive joint. The results show that the PMMA
system is weaker than the cohesion of the substrate. At the same time it is sufficiently
strong to hold large and heavy fragments together: the result of the lap shear test is 2.45
MPa (25 kg/cm2) (Barov, 1986).
The resin was also tested to determine several other properties that were important for the
design of the different applications. The tensile strength is 55 MPa (561 kg/cm 2) quite
strong and at the level of the epoxy resins. The elongation is 7%, again close to some
popular epoxies and Young’s modulus is 1280 MPa (13052 kg/cm 2). The Tg was
determined with Differential scanning calorimetry (DSC) and the result is 74°C. The
addition of glass microspheres increases the Tg of the cured resin to 85 for 10% w/w of
added filler. These results were obtained during series of tests performed for the selection
of the materials for the restoration of the Nine Muses Sarcophagus in the Hearst Castle, CA.
The report prepared by Ethos, conservation of ancient art partnership and the Chemistry
department of Cal Poly, San Luis Obispo is not published. Some technical data, not
mentioned here were covered by the author in the material “The Restoration And
Subsequent Earthquake-Safe Mounting Of Four Sculpted Columns Broken During An
Earthquake At The Hearst Castle” in the 12th International Congress on the Deterioration
and Conservation of Stone, New York 2012.
2.4. Long-time behavior
The first time the adhesive was used for the reassembling of an outdoor fractured stone
object was on one of the heads of the Sekmet fountain and the ceramic Persian tile panel in
the Hearst Castle in California, more than 30 years ago (Barov, 1986). The head sculpted in
dark gray, almost black diorite is displayed on the southern side of the main terrace under
daily exposure of sunlight. The air temperature reaches the maximum of 44 C during the
summer and drops occasionally under the freezing point during the winter months with
daily fluctuations averaging 8C with an average of the sunny days of 186/year in this
region, according to the local records. The surface temperature of the dark gray stone,
however, have reached 63C on the side directly exposed to the sun while the temperature
of the north side was 23.5C, according to our measurements. The numerous joins of the
two objects have held perfectly since 1985, for a period of more than 30 years resisting the
temperature and humidity fluctuations and the dynamic stress produced by frequent
earthquakes, including the 6.6 tremor of 2003. All joins were made with Teets Cold Cure.
3. PMMA as a gap filler and reconstruction material
In addition to the use of the system as an adhesive its qualities of colour stability and ease
of application make it an appropriate material for gap filling and reconstruction of missing
details, especially on marble. If no inert fillers are added the cured resin is almost
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
completely transparent. With the addition of inert powders, such as glass microspheres, it
becomes translucent light grey, almost white. For achieving of a close colour matching to
the surrounding original material it is often necessary to add small amounts of colour stable
pigments that are already pre-mixed in small amount of monomer.
3.1. Application technique and esthetic issues
As stated before, the curing process is exothermic. The temperature increase is quite small
when the resin is employed as an adhesive because the film is usually quite thin. When used
as a fill or reconstruction material however, the mass of resin is much larger and that could
lead to fast and substantial increase of the temperature to the point that the resin could start
boiling. Large missing areas must be filed gradually, on several layers, because the
temperature increase is proportional to the mass of resin employed. Diminishing the
thickness of single application insures faster dissipation of the heat and avoidance of
deformations caused by boiling. The fast curing allows building large reconstructions quite
fast. New layer, 1-2 cm thick, can be placed about one hour after the application of the
previous.
The colouring of the fills or reconstructions is also facilitated by the fast curing process.
Fine colour nuances are achieved by adding thin layers with slight colour differences
between them. Because the resin is translucent, the under-layers transpire through the
surface layer, creating colour nuances that can approximate quite well the complex
patinated surface of the surrounding original. Obtaining white colour values requires adding
large amounts of glass microspheres, which decreases the strength of the cured fill.
Fig. 2: Reconstructed detail (tip of the nose) before and after. The head is approximately
25% over life-size.
This can be quite positive for indoor applications, but such fills are not strong enough to
resist the outdoor deterioration agents. Fortunately there are PMMA systems available on
the market today that are premixed with titanium dioxide that makes obtaining of a base
light colour much easier. One such product is Bosworth Duz-All All-Purpose Self-Cure
Acrylic Repair Material, Keystone industries, USA. The amount of pigment in the mixture
is very small and its presence virtually does not diminish the strength of the fill.
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Not staining the stone is another very important quality of the PMMA fills. They do not
produce a darker shade on the stone at the boundary of the fills or reconstructions, which
elimination is always a problem when using other organic materials.
In our practice we usually adjust the translucency of the fills to that of the original,
especially when working on marble. In our measurements a one cm thick slab of Thasos
marble blocks approximately 97.4% of the light. Five cm thick slab does not transmit
visibly any light in normal environment but some thin sections and small details look much
more convincingly integrated with the original if they match the translucency of the
original. Toot Col Cure resin mixed with 10% of glass microspheres w/w has a
translucency virtually identical to that of this particular marble. Duz-All system, premixed
with titanium dioxide, has lower translucency, blocking 99.4% of the light. It can be
adjusted by mixing the white with translucent Duz-All, also produced by Keystone.
4. Conclusion
In a 30 years outdoor exposure the PMMA two-component system has performed quite
well as a stone adhesive. It has some of the epoxy characteristics mainly low shrinkage
after curing and excellent gap-filling properties but at the same time is reversible, nonyellowing and has a higher Tg. It produces weaker bonds, which in most cases is a positive
quality and sets fast that could be restrictive in some complicated applications. A gluing
technique, in which the smaller fragment is mounted on a sled, accelerates the process of
reassembly and produces precise joins. Its reversibility allows disassembling pined joins
even after long periods of time. There are many manufactures worldwide that produce this
type of system and the author has not explored most of them in search of a product with
longer working time. Nevertheless the PMMA systems described here are applicable in
large variety of cases and could be a preferred alternative where reversibility, nonyellowing and high Tg are important.
Acknowledgements
The author would like to acknowledge the contribution of Veseslin Vekov, structural
engineer and the late Alexandar Savov, scientist, National Institute for the Monuments of
Culture, Sofia, Bulgaria who first applied the PMMA system in the early 1970’s. Tanks are
also due to Eddy de Witte, IRPA and Dane Jones, Cal Poly, San Luis Obispo for valuable
advice regarding the use of inhibitors.
References
Barov, Z. "The Use of Methyl Methacrylate as an Adhesive in the Conservation of Two
Objects from the W. R. Hearst Collection" in Preprints of the contributions to the
Bologna Congress, Case Studies in the Conservation of Stone and Wall Paintings,
Brommelle, N. and Smith, P. (eds.), IIC, London (1986) 112-115.
W. H. W. Plastics.
Cold
Cure
Denture
material,
MSDS,
www.whwplastics.com/downloads/msds/Cold-Cure%20Combined.pdf.
686
2002
CONSOLIDATION EFFECTS ON SANDSTONE TOUGHNESS
M. Drdácký1*, M. Šperl2 and I. Jandejsek3
Abstract
The paper presents a methodology for investigating fracture phenomena in sandstone
treated for consolidation. It demonstrates the preparation of test specimens with a cyclic
loading generated crack, monitoring of the test specimen preparation and verification by
means of X-ray microCT and DIC techniques. Finally, the influence of various
consolidation agents on the toughness of cracked specimens is demonstrated.
Keywords: cracks in stone, consolidation, toughness
1. Introduction
Cracks in stone monuments are a very common defect. In addition to naturally arising
cracks due to geological and tectonic processes, cracks in many historical structures
indicate the action of external forces accompanied by internal strain gradients. This is
usually a repetitive process, and damage accumulation may occur in porous brittle or quasibrittle materials. The authors (Drdácký, Šperl, Jandejsek 2016) performed a study of
environmental fatigue effects on sandstone from Božanov (one of the typical medieval rock
materials used in Charles Bridge in Prague, the Czech Republic) due to the accumulation of
damage. An investigation was performed with the Young modulus and the Poisson number,
using a verified methodology for testing stone in simple tension and in cycling simple
tension/compression loading. They developed a methodology suitable for testing historical
stone subjected to repeated tension strains. The results show that the first tension loaddisplacement can be approximated very satisfactorily by a power function, and the optical
DIC method demonstrated once again its capacity and suitability for measuring complex
deformation fields on porous surfaces and on naturally well-structured surfaces.
Nevertheless, the methodology used required painstaking specimen preparation and highlyskilled staff and can be recommended only for special small-series tests.
Crack propagation and sandstone toughness has been experimentally investigated by
several researchers in the past using test specimens of various shapes and dimensions
provided with crack initiation notches. In papers by Le, Bažant and Bazant 2011, Le &
Bažant 2011, Kirane and Bažant 2015, and Le, Manning and Labuz 2014, many basic
references are presented. From these papers it follows that size effect plays an important
role in fracture and must be considered in toughness research. In our case, in which
comparative tests on the influence of various consolidants on crack propagation were
carried out, the size effect was supposed not to influence the results substantially. However,
Nara et al. 2012 demonstrated the influence of the moisture content and relative humidity
1
M. Drdácký*, M. Šperl and I. Jandejsek
Academy of Sciences of the Czech Republic, Prague, Czech Republic
drdacky@itam.cas.cz
*corresponding author
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on the fracture toughness of stones and therefore these parameters were carefully controlled
in the present tests.
The aim of this experimental study was to investigate the effects of consolidation on
cracked sandstone behaviour, particularly its toughness (Šperl et al. 2016). Experimental
investigations on specimens with cracks have very rarely been published. One such study
by Feng et al. 2015 was focused on experimental research into strength restoration of
cracked sandstone. Only one consolidation agent was applied – a high polymer adhesive
called MEYCO 364, with a very fast setting and hardening time. The approach was based
on crushing cylindrical sandstone specimens, placing them carefully in a special cylindrical
mould that was then injected with the adhesive polymer. Subsequently, the specimens were
released from the mould and tested again after maturing. Naturally, such an approach was
not suitable for the purposes of the present study.
2. Božanov Sandstone
Božanov Sandstone is one type of medieval stone used in the construction of the 14thcentury Charles Bridge in Prague. Božanov stone is a greyish-beige gross quartz grain
strong arkose sandstone without marked layering (Fig. 1). The material tested was extracted
from the 11th arch of the Charles bridge parapet wall, which had to be replaced during
recent repair because it has a rather deeply located detachment crack parallel to the surface,
probably due to some previous surface treatment which locked moisture inside the stone.
The material can be characterized as a quasi-brittle inelastic silicate composite.
Fig 1: Composition of the Božanov sandstone.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3. Methodology
Test specimens with dimensions of 20×20×100 mm3 were placed on one side in the centre
with an initiation notch 1 mm thick and 2 mm deep. Then the specimens were cyclically
loaded in three-point bending generated by a resonance pulsating Rumul Mikrotron frame
(Fig. 2). The initiation notch was placed on the side in tension and the load pulsated in a
mode with the asymmetry of the cycle being R = 0.0385 – i.e., with a nearly vanishing load
cycle. The resonance loading frame started cycling with an initial force impulse and then
the loaded specimen acted as an elastic member in the system. The cycling at a given force
was controlled by a resonance frequency which was dependent on the stiffness of the test
specimen (Vavřík et al. 2013). Then, a change in stiffness of the specimen was followed up
during the loading, which signalled the crack initiation and propagation, and enabled
control of the crack depth. To this end, a change in loading frequency was measured. In this
way it was possible to prepare a series of test specimens with approximately the same
damage in front of the initiation notch. However, a series of preliminary tests had to be
carried out in order to identify a suitable level for the loading force. They included a static
three-point bending test (3PB) and a series of fatigue tests on various low-force levels to
determine the approximate fatigue behaviour of the test material.
Fig. 2: Cyclic loading of the test specimen in an electromagnetic resonance frame.
Then, in order to ascertain the depth of the initiated cracks X-ray micro-tomography was
applied. A special table-top loading device allowing simultaneous X-ray imaging of the test
specimen during loading was employed. A specimen was loaded in a cylindrical chamber
made of a high-strength composite which had a low attenuation for X-rays and allowed
observation from all directions. Both simple 2D transmission images and CT acquisitions
could be acquired in individual loading steps. The focal spot of the X-ray source was
approximately 50 μm with this setting, which was sufficient with respect to the desired
resolution. A scintillation flat panel detector of 2048×2048 pixels resolution and 200 μm
single pixel size was used. The resulting imaging geometry allowed ×4 magnification,
which entailed the resolution of 50 μm at one pixel. The standard three-point bending test
was performed with the specimen. The load was applied only until the moment when the
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crack was observable by simple transmission radiography. In this position CT data (1200
projections per 360°) was acquired. The acquisition time of one projection was 2s. The
images obtained were corrected with regard to beam hardening effect by a set of aluminium
filters and subsequently a final CT reconstruction was carried out. A 3D visualization of the
reconstruction obtained was performed in a VG studio.
Then, specimens with similar cracks were consolidated and the most typical agents were
applied: elastified Steinfestiger 300 (cca 30% concentration of the active substance),
Paraloid B72 (2% concentration), Funcosil 100 (10% concentration of the active
substance); and after maturing they were tested in static standard three-point bending. The
products were applied by immersing the specimens up to one half of the profile crosssection height in the agent bath for 4 hours, then wrapped in a plastic foil after removal
from the bath, which protected the specimens from drying quickly.
4. Results and Discussion
Cycling the specimens in the high frequency resonance loading frame helped to understand
fatigue behaviour of the Božanov sandstone. At a given force level (3PB arrangement under
point load cycling from -10 N to -260 N) the majority of specimens exhibited fatigue life in
a range between 90 000 and 140 000 cycles. However, there were specimens with one order
lower or higher fatigue life due to the heterogeneity of the sandstone. To prepare the test
specimens, a lower number of loading cycles was applied (between 32 000 and 40 000),
and only specimens exhibiting behaviour similar to those of the above mentioned majority
were accepted for further experiments. A typical record of the change of resonance
frequency is presented in Fig. 3. Visible steps are the results of the regulation loop reaction
which keeps the mean loading value within an interval of +/- 2 N.
Fig. 3: Decrease of loading frequency during cycling of the specimen BO_10 (for 134N).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The character of the damage after cycling was determined by means of X-ray CT. It was
not possible to identify the crack originating in the grannular structure of the sandstone
without applying a slight 3PB loading to the specimen and opening the crack. Thus, the
specimen under investigation (BO_5 after 140,300 cycles) was loaded with 200 N and
under such loading scanned with the X-ray CT. Then the DIC method was used to identify
similar situations within the sections in the specimen depth. DIC proved to be a useful tool
for crack propagation studies, e.g. Lin and Labuz 2013. A comparison of crack
visualisations for loaded and unloaded specimens is shown in Fig. 4.
Fig. 4: X-ray pictures of unloaded (left) and loaded (right) sandstone specimen BO_5
Then, three types of specimens were tested with regard to three point bending - notched
beams, notch beams with cracks generated by cycling and notched beams with cracks after
consolidation. The test results are presented in Tab. 1. The results show the beneficial
influence of consolidation on the cracked sandstone specimens. The reference specimen
with the initiation notch attained an average bending strength of 5.05 MPa, the notched
specimen with cycled crack one of 4.56 MPa and the consolidated speciemens one of about
6 MPa. The broken halves of the test beams were used for comparative tests on full profile
beams after prolongation by the prothesis method (Drdácký 2007). The results were
influenced by cycling; however, it may be seen that consolidation eliminated the influence
of crack degradation effects (Fig. 5).
For all specimens the absorbed energy needed to create the critical macrocrack was
calculated. The specimen without a crack exhibited the maximum energy, as expected. The
specimens with cracks exhibited lower energy, which was almost constant for all
specimens. From these results and the load displacement diagrams it follows that the
consolidated material becomes stronger but more brittle with a lower capacity of
deformation absorbtion.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Results of three point bending tests for Božanov sandstone.
Spec.
No.
Fmax
Height
Width
Span
Number
of cycles
Bending
strength
[N]
[mm]
[mm]
[mm]
[-]
[MPa]
BO_N
433.26 20.82
20.66
60
0
BO_20
363
20.45
20.68
60
0
Average bending strength of the notched specimens
BO_9
393.15 20.74
21.6
60
32,248
Bending strength of the notched beam with crack
BO_10
487.33 20.86
21.02
60
38,044
BO_11
509.78 21.02
20.69
60
35,000
BO_16
562.18 20.82
19.32
60
43,457
BO_19
515.49 20.94
19.18
60
42,236
5.26
4.83
5.05
4.56
4.56
5.70
6.09
6.61
6.10
Treatment
None
None
None
None
KSE 100
KSE 100
KSE 300
Paraloid
Fig. 5: Results of 3PB tests on four types of test specimens.
Load displacement diagrams together with changes in the deformability (apparent modulus
of elasticity) were recorded; one example is presented in Fig. 6. The modulus of elasticity
gradually degraded during the course of loading; however, in the case of the consolidated
sandstone, the decrease started to be very slight rather early and the modulus was almost
constant up to the failure.
The acquired ultimate loads were used to calculate KIC toughness (Gross 1965), which
attained the value of 0.331 for the notched beam, 0.349 for the notched beam with the crack
and from 0.449 to 0.561 for the consolidated cracked beam in MPam0.5. The toughness
values are approximate estimates based on an engineering approach to the crack depth
assessment from the above mentioned X-ray CT scans and the DIC reconstructions.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3PB_Sandstone BO_10
600
25000
Rtf = 5,70 MPa
conventional E
modulus (secant
method)= 11 610
MPa
500
20000
Force
15000
300
10000
E modulus [MPa]
minus (-) Force [N]
400
200
immediate E modulus
5000
100
0
0
0,005
0,01
0,015
0,02
0,025
0,03
0,035
0,04
0
0,045
minus (-) Deflection [mm]
Fig. 6: Summary diagram for 3PB test of the specimen BO_10.
5. Conclusions
The described methodology involving the use of the resonance loading frame to generate
cycled cracks in stone was demonstrated. It enables the successful creation of well-defined
and controlled crack damage in stone.
The computer X-ray microtomography is a useful tool for visualizing and measuring
generated cracks in combination with the digital image correlation technique. The crack is
usually close and to identify its depth the specimen must be loaded slightly in order to open
the crack and make it more visible.
The tests with consolidated specimens proved the positive effects of consolidation with
regard to strength and toughness. All notched and cracked specimens after consolidation
with ethylsilicates KSE 100, KSE 300 and Paraloid B72 attained values above full profile
strength.
The full profile specimen exhibited the greatest energy absorption necessary to create a
critical macrocrack leading to overall loss of stability of the specimen. The notched and
cracked specimens after consolidation with ethylsilicates needed less energy, which in the
case of the increased strength of the consolidated sandstone, shows that the material
becomes stiffer and more brittle with a higher modulus of elasticity and a lower capacity to
absorb deformation energy. Consolidation with Paraloid B72, on the other hand, required
much more energy (3.5 times more than with ethylsilicates).
The toughness of untreated notched and cracked specimens reached almost same values,
which means that with such heterogeneous material we cannot expect stress concentration
factors similar to those of metals. Consolidation with the abovementioned agents increases
the toughness of Božanov quartz sandstone substantially (up to 70%).
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Acknowledgements
Support from the GAČR P105/12/G059 & the SADeCET NPU I project is acknowledged.
References
Drdácký, M., Šperl, M., Jandejsek, I. (2016) Pilot experiments on cumulative tensile
damage to stone monuments. (to be published by Cambridge Scholars Publishing),
8 p.
Feng, X., Zhang, N., Zheng, X., Pan, D. (2015) Strength restoration of cracked sandstone
and coal under a uniaxial compression test and correlated damage source location
based on acoustic emission, PloS ONE 10 (12): e0145757. doi:
10.1371/journal.pone.0145757, 20 p.
Gross - NASA TN D-3092, 1965 Stress-Intensity Factors for 3PB Specimens by Boundary
Collocation.
Kirane, K., Bažant, Z.P. (2015) Size effect in Paris law for quasibrittle materials analyzed
by the microplane constitutive model M7, Mechanic Research Communications,
68, 60–64.
Le, J.-L., Bažant, Z.P., Bazant, M.Z. (2011) Unified nano-mechanics based probabilistic
theory of quasibrittle and brittle structures: I. Strength, static crack growth,
lifetime and scaling, J. of the Mech. and Phys. of Solids, 59, 1291–1321.
Le, J.-L., Bažant, Z.P. (2011) Unified nano-mechanics based probabilistic theory of
quasibrittle and brittle structures: II. Fatigue crack growth, lifetime and scaling, J.
of the Mech. and Phys. of Solids, 59, 1322–1337.
Le, J.-L., Manning, J., Labuz, J.F. (2014) Scaling of fatigue crack growth in rock, Int. J. of
Rock Mechanics & Mining Sci., 72, 71–79.
Lin, Q., Labuz, J.F.: (2013) Fracture of sandstone characteristics by digital image
correlation, Int. J. of Rock Mechanics & Mining Sci., 60, 235–245.
Nara, Y., Morimoto, K., Hiroyoshi, N., Yoneda, T., Kaneko, K., Benson, Ph.M. (2012)
Influence of relative humidity on fracture toughness of rock: Implications for
subcritical crack growth, Int. J. of Solids and Structures, 49, 2471–2481.
Šperl, M., Drdácký, M., Jandejsek, I. (2016) Experimental study of consolidation effects on
sandstone toughness, Proc. of the 17th International Conference on Experimental
Mechanics (ICEM 17) – E.E.Gdoutos (ed.), Rhodos, July 3-7, 2016, 2p.
Vavřík, D., Jandejsek, I., Fíla, T, Veselý, V. (2013) Radiographic observation and semianalytical reconstruction of fracture process zone silicate composite specimen,
Acta Technica CSAV. 2013, Vol. 58, No. 3, pp. 315–326, 2013.
694
IS THE SHELTER AT HAGAR QIM IN MALTA EFFECTIVE AT
PROTECTING THE LIMESTONE REMAINS?
C. Cabello-Briones1* and H.A. Viles1
Abstract
Shelters are structures built over archaeological sites to protect the remains from decay.
They may prevent direct sunlight and rainfall reaching the remains, but they may also
enhance decay by modifying microclimatic conditions. Lightweight, open shelters (without
lateral cladding) are a popular preventive conservation strategy for sites in the
Mediterranean basin but there have been few scientific assessments of the impacts of
shelters on limestone decay. Hagar Qim in Malta is a UNESCO World Heritage Site
containing the remains of a megalithic temple constructed of local limestone. The
effectiveness of the shelter at Hagar Qim, built in 2009 with a fiberglass and PTFE
membrane, was evaluated during a 1 year campaign using two methods: (a) monitoring
microclimatic conditions outside and inside the shelter (centre and periphery) and (b)
monitoring soiling and decay of small limestone blocks located outside and inside the
shelter (centre only). Microclimatic conditions were monitored using i-button® loggers to
record temperature and RH over the whole year, with shorter term monitoring of dust
deposited on horizontal surfaces. Soiling and decay of Globigerina and Coralline limestone
blocks (9×3×3 cm) over the year were quantified by comparing a number of stone
properties before and after exposure. Results are presented here for weight, surface
hardness and surface colour. This research demonstrated that, in general, the shelter at
Hagar Qim is effective at reducing limestone decay and the site would be exposed to more
damaging conditions if it was not sheltered. However, the shelter has also been found to
enhance some decay mechanisms such as dust deposition under the central part of the
shelter and NaCl crystallisation events on the periphery.
Keywords: shelters, archaeological sites, limestone decay, monitoring, Hagar Qim
1. Introduction
The prehistoric site of Hagar Qim consists of megalithic buildings built between 3600 and
3200 BC. It is situated at the top of a hill, less than 1 km away from the sea, on the south
western coast of Malta (location: lat. N 35.8277, long. E 14.4417).The site was inscribed on
the UNESCO World Heritage list in 1992 because of its significance for human history.
The temple was built exclusively with Globigerina limestone, probably quarried near the
site, which is a relatively soft bioclastic limestone still widely used for construction in
Malta. Globigerina limestone is prone to powdering and alveolisation, mainly due to salt
weathering (Cassar, 2007). These patterns are defined respectively as granular
disintegration and formation of cavities on the stone surface (ICOMOS International
1
C. Cabello-Briones* and H.A. Viles
Oxford University Centre for the Environment, University of Oxford, United Kingdom
cristina.cabello-briones@ouce.ox.ac.uk
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Scientific Committee for Stone ISCS, 2008). An open shelter (without lateral cladding)
was installed over the remains in 2008 to reduce environmental risks (Fig. 1).
Fig. 1: Shelter over the megalithic temples at Hagar Qim, Malta.
Before sheltering Hagar Qim, Istituto di Scienze dell'Atmosfera e del Clima (CNR-ISAC)
carried out a study on the microclimate and stones of the site, which determined that the
main decay mechanism at Hagar Qim was salt weathering from marine aerosols
(unpublished report for Heritage Malta, 2006). High solar radiation, wind and RH
fluctuations were thought to enhance salt dissolution and recrystallization. In addition, high
diurnal temperature ranges and solar radiation were hypothesized to produce mechanical
stresses on the ruins. An open shelter made of a fiberglass and PTFE membrane was
thought to be the best conservation solution until further research could be undertaken
(Stroud, 2010). Membrane structures are considered lightweight as they require minimal
supporting elements (Zanelli et al., 2013). Light-weight, open shelters have increasingly
been proposed as medium-term preventive conservation methods due to, for example, their
high flexibility and modularity. However, as yet there has been little specific research on
their effects on archaeological remains (Demas, 2013).
2. Materials and methods
2.1. Monitoring of microclimatic conditions and dust deposition
Shelters should provide protection for the stone remains by reducing the frequency and/or
range of microclimatic fluctuations which cause stone decay. The impact of the open
shelter at Hagar Qim on microclimatic conditions was evaluated by monitoring
temperature, RH and dust deposition inside (centre and periphery) and outside the shelter
from 29th July 2013 to 22nd July 2014. The monitoring of the peripheral location started
later than the others, on the 18th October 2013, for logistical reasons. The most central
location possible under the shelter was selected as a fully protected position and was
compared with a fully exposed (outside) and a partly exposed location (periphery) (Fig. 2).
The chosen peripheral location is located towards the edge of the site (SW), where possible
inadequacies in the coverage of the shelter were detected after a rapid visual assessment.
Low-cost and easy to hide temperature and RH loggers (i-button® hygrochron dataloggers,
accuracy = ±0.5% RH and ±0.5°C) were synchronised to record at all three positions every
60 minutes. From the data collected, the number of times a day RH crossed the 75%
threshold was used as proxy for NaCl crystallisation events. The amount of dust deposited
on horizontal surfaces inside and outside the shelter was studied using self-adhesive,
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
transparent vinyl film patches (10×10 cm) during one week in October 2013 and for three
months between October 2013 and January 2014. The adhesive part of the patch was left
exposed and a small area (10×3.5 cm), which remained covered, was used as a control.
After exposure, they were analysed by imaging processing techniques. Pictures of the
samples were taken with a camera (DFK 51BU02.H, Imaging Sources, sensor Sony CCD,
sensibility 0.15 lx) set with a fixed exposure. An integrating sphere light source, which
provides spatially uniform luminance, was placed on the other side of the film. Mean
opacity values were calculated by studying the amount of light that passed through the
samples (transmittance) in comparison to the control area. Mean values refer to the amount
of pixels in the processed images (1280×960).
Fig. 2: Monitoring positions – 1: centre, 2: periphery and 3: outside of the shelter.
2.2. Monitoring of decay with limestone blocks
The degree and nature of decay and soiling were determined by measuring dry weight,
surface hardness and surface colour in Globigerina and Coralline limestone blocks before
and after exposure for one year. Four replicates (9×3×3 cm) of each stone type were
exposed from 17th July 2013 to 22th July 2014 inside (centre) and outside the shelter.
Because of potential visibility of blocks to tourists it was not possible to place a set of
replicates in the peripheral location. In addition, three blocks per stone type were left in the
laboratory and used as controls. The tests to evaluate change in stone properties were
carried out under the same conditions before and after exposing the blocks. Comparison of
changes in stone properties between locations permitted an assessment of the different rates
of deterioration and soiling outside vs. inside the shelter. The reason for using small blocks
was to obtain representative information about decay within a short exposure period
without invasive sampling of the remains themselves. The stone types used in this study
present different vulnerabilities to decay (Tab. 1). Globigerina is very soft and porous and
a greater degree of weathering was expected. Both are commonly used in Maltese cultural
heritage.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Physical properties of the stone samples used.
Standard test
Property
Globigerina
Coralline
BS EN 3755:2008
Water absorption at
atmospheric pressure (Ab)
14.75%
3.36%
BS EN 1936:2006
Open porosity (Po)
31.18%
BS EN 1936:2006
Apparent density (ρb)
11.01%
3
1789.72 kg/m
2356.52 kg/m3
Weight was quantified using a balance (Sartorius AG Göttingen, ±0.01 g accuracy) and
weight change expressed as a percentage of initial dry weight. This method has been
extensively used to calculate the amount and rate of stone weathering, for example in
relation to salt accumulation and erosion (Moses, 2000). Surface hardness was assessed
using an Equotip 3 (Proceq), an electronic rebound hardness testing device often used to
study stone deterioration (Moses et al., 2014). After a pilot study based on the study of
Viles et al., (2011), 18 single impacts for Globigerina and 36 for Coralline were determined
to be adequate sample sizes. The median of hardness readings from each stone block was
used to summarise the data. Colour changes were measured with a spectrophotometer (CM700d, Konica Minolta) and the results expressed using the International Commission on
Illumination (CIE) L*a*b system. Ten measurements (SCE) per stone block were taken on
different points of the top horizontal surface and the mean used to summarise the data set.
Two-way ANOVA tests were undertaken to determine if there were statistically significant
differences in stone properties between positions and stone type. These analyses were
complemented with post-hoc all multiple comparison tests (Holm-Sidak method).
3. Results
3.1. Monitoring of microclimatic conditions
3.1.1. Temperature
The temperature inside the shelter (centre and periphery) followed the temperature outside
and exhibited similar daily and seasonal fluctuations. However, there were some significant
differences between locations within the site. Non-parametric Mann-Whitney-Wilcoxon
tests on daily mean temperatures showed that in summer, the outside was warmer than the
centre of the shelter (U=561, P= 2.328e-10) and the centre was significantly warmer than the
periphery (U=406, P=3.986e-06). In winter, the central part of the shelter was warmer than
outside (U=454, P=2.398e-10) but the temperatures on the periphery were higher than in the
centre of the shelter (U=455.5, P=6.787e -10). Therefore, the outside had the most extreme
environment with higher temperatures in summer and lower in winter. In spring and
summer, the centre was warmer than the periphery due to higher temperatures at night. In
addition, the periphery was slightly warmer than the centre in winter. This result can be
related to a problem with the shelter covering area, which allows direct solar radiation on
the ruins towards the edge. Differences between maximum and minimum temperatures per
day were calculated to examine temperature fluctuations (Fig. 3). The daily temperature
range was higher outside over the whole year, especially in spring and summer. The daily
temperature range in the periphery of the shelter was higher than in the centre during
autumn and winter and closer to the outside values.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 3: Monthly means of diurnal temperature range outside, in the centre and on the
periphery of the shelter.
A multilevel linear model with day as random effect for the diurnal temperature ranges was
fitted in order to find out if the differences depended upon location. The statistical analysis
indicates significant differences in diurnal temperature ranges between outside and the
periphery of the shelter (t= -25.497, DF=1661, P<0.001) and between the periphery and
centre of the shelter (t= -14.638, DF=1661, P<0.001). As expected, the central part of the
shelter had a more stable microclimate in terms of temperature than outside and on the
periphery. The more variable microclimate in autumn and winter in the peripheral parts of
the shelter illustrates the limitations to the sheltering effect.
3.1.2. NaCl crystallisation events
The daily number of salt crystallisation events was relatively constant in all positions
during the majority of the year, with a slight decrease in winter (when RH is often above
75%). The number of times the NaCl threshold was crossed in a year was fitted as the
response in a Poisson Generalised Linear Model (GLM) with ‘Position’ as explanatory
variable and with ‘Day’ as the second level. The results showed significant differences in
the number of events between outside and the centre (t=2.695, DF=1590, P=0.007) and
between outside and the periphery of the shelter (t=5.305, DF=1590, P<0.001). There were
more NaCl crystallisation events in the central part of the shelter (daily mean=2.10) than
outside (daily mean=1.83), and more at the periphery (daily mean=2.45) than in the centre
(t=2.837, DF=1590, P=0.004). This unexpected finding illustrates the more variable
microclimate (in terms of RH fluctuations crossing the 75% threshold) found in the
peripheral parts of the shelter.
3.1.3. Dust deposition
Malta is characterised by high daily wind speeds. The shelter reduces wind speeds inside
the site but there is turbulence probably due to the effect of the monument itself (Farrugia
and Schembri, 2008). Opacity data collected from the vinyl film patches showed that there
was more dust deposition inside the shelter than outside. The sheltered samples showed less
light transmittance values (i.e. higher opacity) than the ones located outside the shelter for
the same amount of time (Tab. 2). After three months, the sample located inside the shelter
showed 381% less light transmittance than the control area. The amount of dust deposition
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is probably an underestimate as the surface of the film became fully covered before the end
of the experiment and could not collect more.
Tab. 2: Mean opacity (%) values of unsheltered and sheltered samples.
Unsheltered
Sheltered
1 week
3 months
1 week
3 months
-0.80
54.42
10.34
381.68
Δm ,%
3.2. Monitoring of decay with limestone blocks
3.2.1. Dry weight
All Globigerina blocks lost weight, especially those located under the shelter. In
comparison, Coralline samples located outside gained in weight whereas the ones inside
lost weight (Fig. 4). Globigerina samples lost significantly more weight inside than outside
the shelter (t=3.225, P=0.005) and those inside the shelter lost more weight than Coralline
blocks in the same position (t=3.708, P=0.002). The difference between inside and outside
Coralline blocks is also significant (t=5.639, P<0.001).
Fig. 4: Weight change as percentage of initial dry weight of the Globigerina and Coralline
replicates placed outside and inside the shelter after 12 months.
3.2.2. Surface hardness
All the samples increased in hardness, especially Coralline blocks outside the shelter.
However, the blocks did not change significantly in hardness over the one year period. As a
result, there were no significant differences in behaviour between those located inside and
those outside.
3.2.3. Surface colour
Most of the stone blocks showed an overall colour difference over 3.8 dE*ab, which
indicates that the change is distinctively perceptible to the naked eye (Bieske and Vandahl,
2008). Globigerina samples located outside the shelter changed significantly more in colour
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
than the blocks placed inside (t=7.641, P<0.001). In addition, Globigerina blocks outside
changed more in colour than the Coralline ones in the same position (t=9.483, P<0.001).
The difference in colour change in Coralline blocks between inside and outside is not
significant (t=0.125, P=0.903). In addition, CIELAB differences in dL*
(lightness/darkness) and db* (yellow/blue) were examined to determine the characteristics
of the colour changes. Globigerina and Coralline blocks became yellower and darker in
both positions, with the Globigerina blocks outside showing the greatest change (Tab. 3).
Tab. 3: Mean colour difference in Globigerina and Coralline blocks after 12 months.
Globigerina
Coralline
Position
dE*ab (D65)
dL* (D65)
db* (D65)
Outside
12.88
-8.22
8.70
Centre
6.59
-4.55
4.22
Outside
5.08
-4.49
0.40
Centre
5.18
-5.03
0.17
4. Discussion and Conclusions
Temperatures outside the shelter fluctuated more than in the centre and on the periphery
showing higher maximum temperatures in summer and lower in winter. The maximum
differences between inside and outside were registered during the hottest months. The
shelter was able to reduce daily temperature differences and keep the temperatures in the
centre of the shelter lower and stable. The temperature on the periphery varied more than in
the centre, and a fault in the shelter design allowed direct solar radiation to significantly
increase temperatures at this point during winter. As temperature is not as high in this
season than in summer the risk of thermal stress is reduced. However, the probability of
having more NaCl crystallisation events on the periphery than outside the shelter is higher
due to daily RH fluctuations. On the other hand, there was more dust deposition inside than
outside the shelter. Dust from the arid surroundings is likely to access the area under the
shelter driven by wind and accumulate when wind reduces velocity and increases
turbulence under the shelter. However, the risk of salt weathering inside the shelter is lower
than outside because the microclimate is more stable.
Globigerina and Coralline limestone samples inside and outside the shelter turned darker
and yellower after a year of exposure. Although colour change could be due to natural
weathering, the conditions outside the shelter might have enhanced it as the chromatic
alteration was observed mainly on Globigerina blocks located outside.
Samples inside the shelter lost more weight than those outside. The great temperature
ranges outside could have had a low effect on weathering. However, it is more likely to
assume that there was an increase in weight due to, for example, accumulation of salts, and
the combined effect with temperature fluctuations resulting in a final slight change of
weight. In addition, Coralline samples outside the shelter gained in weight and all of the
Coralline samples but mainly those outside the shelter increased in hardness. This suggests
that great temperature ranges outside the shelter in combination with the effect of salts are
the main cause of decay. This study has demonstrated that the shelter reduced temperature
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
fluctuations, minimizing the risk of physical weathering. Therefore, the shelter at Hagar
Qim is effective at reducing limestone decay and the site would be exposed to more
damaging conditions if it was not sheltered. This research has also proven that small stone
samples provide an effective, rapid and non-invasive method to monitor deterioration at
sheltered archaeological sites.
Acknowledgments
We thank Heritage Malta, especially Dr. Katya Stroud and Mario Galea, for their help and
support. We also acknowledge Dr. Daniel Lunn and Dr. Javier Muñóz for sharing their
knowledge. This research was funded by EPSRC and La Caixa Foundation.
References
Bieske, K. and Vandahl, C., 2008, A Study about Colour-Difference Thresholds, in
proceedings of Lux et Color Vespremiensis, Veszprem, Virtual Environments and
Imaging Technology Laboratory of the Faculty of Technical Informatics.
Cassar, J. 2007. Malta: buildings, materials and deterioration, STONE. Newsletter on stone
decay, 2, 3-4.
Demas, M., 2013, Protective Shelters for Archaeological Sites, in Mosaics In Situ. An
Overview of Literature on Conservation of Mosaics In Situ, Roby, T. & Demas,
M.
(eds.),
Los
Angeles:
The
Getty
Conservation
Institute
(http://hdl.handle.net/10020/gci_pubs/lit_review, accessed 24th November 2015).
Farrugia, S. and Schembri, J. A., 2008, Wind funnelling underneath the Hagar Qim
protective shelter. Malta Archaeological Review, 9, 51-59.
ICOMOS International Scientific Committee for Stone, 2008, ICOMOS-ISCS: Illustrated
glossary on stone deterioration patterns = Glossaire illustré sur les formes
d'altération de la pierre, Paris: ICOMOS, ISBN: 978-2-918086-00-0.
Moses, C., 2000, Field rock block exposure trials. Zeitschrift fur Geomorphologie
Supplementband, 120, 33-50.
Moses, C., Robinson, D. and Barlow, J., 2014, Methods for measuring rock surface
weathering and erosion: A critical review. Earth-Science Reviews, 135, 141–161.
Stroud, K., 2010, Hagar Qim & Mnjdra Prehistoric Temples (Qrendi), in Malta Insight
Heritage Guides, Heritage Malta, Midsea Books, ISBN: 978-99932-7-317-2.
Viles, H., Goudie, A., Grab, S. and Lalley, J., 2011, The use of the Schmidt Hammer and
Equotip for rock hardness assessment in geomorphology and heritage science: a
comparative analysis, Earth Surface processes and Landforms, 36, 320–333.
Zanelli, A., Rosina, E., Beccarelli, P., Maffei, R. and Carra, G., 2013, Innovative solutions
for ultra-lightweight textile shelters covering archaeological sites, in Structures
and Architecture: New concepts, applications and challenges, Cruz, P. (ed.), CRC
Press, ISBN: 978-0-415-66195-9.
702
ASSESSMENT OF THE CLEANING EFFICIENCY OF A SELFCLEANING COATING ON TWO STONES UNDER NATURAL
AGEING
P.M. Carmona-Quiroga1*, S. Kang2 and H.A. Viles1
Abstract
Implementation of preventive treatments to protect built heritage from soiling is of
particular value given the high cost of cleaning practices, which sometimes may put in
danger the already weathered materials and the limited financial resources available for
conservation. In different fields, including construction, TiO 2 dispersions have been gaining
ground as a self-cleaning treatment because of their photocatalytic activity. When irradiated
with UV light, crystalline nanoparticles are able to photo-oxidise and decompose bacteria,
organic and inorganic compounds. Moreover, they prevent, due to a superhydrophilic
effect, contact between dirt and the material’s surface. However, in the field of architectural
heritage research on the application of these coatings to stones is still limited. The present
study explores the efficiency and durability of a self-cleaning coating on Portland limestone
(Dorset, England) and Locharbriggs sandstone (Dumfries, Scotland) over time under
natural weathering conditions in the South of England (Wytham Woods, Oxford). One or
two coats of the treatment were applied on the surface of 8.5×6.5×1 cm³ slabs of these two
materials by spraying. Colour, gloss, and self-cleaning efficiency of the surface of the slabs
(photodegradation of methylene blue stain) were analysed before and after the treatment
was applied to assess how compatible the treatment is with the stones. To evaluate how
permanent is the photocatalytic activity under a rainy regime, the photodegradation test was
also performed on coated stones naturally aged for 4 and 6 months in the field site.
Keywords: self-cleaning coating, TiO2, ageing, natural weathering, photocatalytic activity
1. Introduction
Soiling of surfaces through air pollution (SO 2, NOx, O3, HNO3, particulate matter and acid
rainfall) can be very severe for urban cultural heritage objects. The corrosion products not
only accelerate erosion rates of building materials and cause aesthetic damage
(Varotsos et al., 2009; Viles et al., 2002) but also cleaning procedures with either water,
abrasive or chemical methods or combined procedures can themselves alter the roughness
and porosity of already weathered surfaces (Vazquez-Calvo et al., 2012) making them more
susceptible to the penetration of future dirt (Ďoubal 2014). In fact, cleaning of stone is
considered one of the most critical processes in monument restoration (Ďoubal 2014).
1
P.M. Carmona-Quiroga* and H.A. Viles
School of Geography and the Environment, University of Oxford, United Kingdom
paula.carmona-quiroga@ouce.oc.ac.uk
2
S. Kang
Department of Cultural Heritage Conservation Sciences, Kongju National University, South Korea
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The conviction that prevention is an effective option to the soiling problem is gaining
ground. In fact, since the early 1990s, self-cleaning (anti-soiling) coatings have been used
on some building materials such as tiles, paving gloss, cement mortar, glass, PVC fabric,
etc. (Chen and Poon 2009). However, on stones (of historic and contemporary building and
monuments) their uses are quite limited in spite of their potential benefits (Munafò et al.,
2015).
Self-cleaning effect is obtained by two photochemical phenomena of TiO 2 nanoparticles
under UV irradiation: a) the photocatalytic one that promotes the decomposition of air
pollutants and bacteria that darken the surface of building materials via redox reaction and
b) the super-hydrophilic one that flattens water droplets on the surface of titania film
preventing the adhesion of dirt.
Up to date research on the value of these coatings for protection of stone cultural heritage
objects has been principally based on studying their compatibility (physical properties of
the substrates such as colour, permeability, superficial morphology and water absorption),
and evaluating their efficiency in de-polluting, self-cleaning and decomposing bacteria
(Munafò et al., 2015; Licciulli et al., 2011; Pinho and Mosquera 2011; Quagliarini et al.,
2012). However, their durability has been much less explored (Munafò et al., 2015) and
such studies have been carried out under accelerated (lab) weathering conditions, with salt
crystallisation (Bergamonti et al., 2015; Pinho et al., 2013), UV-A light irradiation (La
Russa et al., 2012), or combined procedures (UV-A irradiation and simulated rain,
Munafò et al., 2014). Of all the weathering agents, UV exposure is considered one of the
most important (Munafò et al., 2014), whereas the effect of rain is more uncertain since it
could improve the performance of titania instead of increasing its weathering (washing) due
to regenerative effect of water on TiO2. In any case, the photocatalytic efficiency of the
coatings is related to the type and duration of the weathering conditions and the interaction
between coatings and substrates (Munafò et al., 2014).
The aim of this study is to extend current knowledge of the performance of self-cleaning
coatings on natural stones by exploring the durability of one of these products using a longterm exposure trial under natural weathering conditions. Samples of Portland limestone
(Dorset, England) and Locharbriggs sandstone (Dumfries, Southern Scotland) have been
left outdoors for 4 and 6 months at a test site in the South of England (Wytham Woods,
Oxford) to test the evolution of the photocatalytic efficiency of a TiO 2 coating.
2. Materials and methods
Two stone types widely used in the built heritage of UK were selected to study the
durability of a self-cleaning coating under outdoor conditions. Locharbriggs is a Permian
red sandstone of fine to medium grain-size and distinctive aeolian cross lamination
(Pandey et al., 2014) mainly composed of quartz, with some feldspars and clays and very
few little rock fragments as shown in the polarized microscope images of Fig. 1a taken
with a DP30 digital camera fitted to a Meiji ML9000 microscope. Portland limestone
(Whitbed) is a Jurassic white oolitic limestone, with subspheric and subelongated oolites
from 0.1 to 0.5 mm in diameter, some of them with a quartz nucleus, low proportion of
micritic matrix and big and scattered fossil fragments (Fig. 1b).
The two stone types were characterised with FTIR. KBr pellets were analysed on a Nicolet
6700 infrared spectrophotometer with the following settings: range, 4000-400 cm-1; scans,
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
10; spectral resolution, 4 cm-1. The FTIR spectrum of sandstone only exhibited the bands
characteristic of quartz (1169-467 cm-1) whereas the limestone spectrum contained
vibration bands from the CO32- in calcite (1433, 874 and 714 cm-1), along with very low
intensity bands attributable to the vibrations generated by Si-O bonds (1165-1003 cm-1)
(Fig. 1). In addition, the water-accessible porosity of the samples was measured to
EN 1936:2006 standard. Mean values of open porosity were slightly higher for limestone
(12 vol% vs. 10 vol% of the sandstone).
69
6
a
586
3437
79
8 779
519
1169
1088
467
b
1630
345
4
1003 714
1165
1120
87
4
1433
3600 3000 2400 1800 1200 600
wavenumber (cm-1 )
Fig. 1: Polarising optical microscope images and FTIR spectra of a) Locharbriggs
sandstone and b) Portland limestone - Whitbed (scale bar: 100 μm).
To apply the self-cleaning coating a commercial aqueous dispersion of TiO2 (anatase)
nanoparticles (10-40 nm) was sprayed at room temperature onto one face of stone slabs of
8.5 cm×6.5 cm×1 cm. One or two coats were applied on consecutive days (in triplicate)
and the product uptake (dry weight) was measured.
Before and after applying the self-cleaning product, colour coordinates of the stones were
recorded (5 measurements per slab) with a Minolta cm-700d spectrophotometer using the
L* a* b* colour standard (CIE 1976). L* values measure lightness; a* measures the red
(+)/green(-)hue and b* denotes the yellow (+)/blue (-) hue. The chromatic changes in the
samples after coating were also expressed in terms of total colour variation
ΔE*(ΔE*=(ΔL*2+Δa*2+Δb*2)1/2, CIE 1976).
A TQC glossmeter was used to determine changes in gloss at a reflection angle of 85º
(Garcia and Malaga 2012); 3 measurements per slab. The peak-to-valley height of the
surfaces was measured with a PosiTector SPG surface profile gauge also before and after
coating application (20 measurements per slab).
Coated specimens were naturally exposed in Wytham Woods (5 miles away from central
Oxford in a non-polluted area) on a rack facing south for 4 and 6 months. Climatic
conditions over the period were taken from the nearby Radcliffe Meteorological Station of
the University of Oxford. After the end of each exposure period the cleaning efficiency of
the coating was assessed though the methylene blue test adapted from the literature (UNI
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
11259:2008; Graziani et al., 2014) in which rhodamine B stain (artificial dirt) was replaced
by methylene blue because the former produces no contrast on the red surface of the
sandstone. 24 h after applying the dye on the TiO2-coated and uncoated surfaces (2 ml on
the sandstone slabs and 3 ml on limestone of a 0.1 wt% aqueous solution), the specimens
were irradiated with a 20 W UV-A (λ= 365 nm) black light for up 190 hours. Coating
distribution before and after ageing was examined with a JEOL JSM -5910 scanning
electron microscope (SEM) equipped with a 20-kV Oxford INCA energy-dispersive X-Ray
spectrometer (EDS).
3. Results and discussion
3.1. Physical characterization of the coated stones
The physical properties of the surface of the stones before and after being coated with one
or two layers of the self-cleaning product are given in Tab. 1. The average roughness of the
limestone is lower than the sandstone in spite of having limestone voids on the surface, this
would condition the differences in the (already low) product consumption between the two
stones, with sandstone being the substrate that on an average absorbed more in spite of
being a less porous material (10 vol% vs 12% of the limestone).
25
Mean air temperature (°C)
Rain (mm)
Sun (hrs)
20
15
10
5
0
24 Feb 24 Mar
24 Apr
24 May
10 Aug 10 Sep 2015
Fig. 2: Rack for outdoor exposure of the samples and climatic conditions for the exposure
period.
One coat of the product did not change the surface colour of the specimens, however two
coats on the red sandstone slightly whitened the surface (L* increased) enough to be
perceptible to the naked eye (ΔE* >3, Berns 2000) but acceptable in conservation studies
(ΔE*≤5, Berns 2000). As found in the literature titania modified the colour of darkcoloured stones more than lighter ones (Munafò et al., 2015). The treatment did not modify
the gloss of the specimens, nor their surface roughness.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Physical properties of the stones untreated and treated with the self-cleaning
coating.
limestone
uncoated
2
product uptake (residue, g/m )
roughness (peak to valley height, µm)
L*
a*
colour
b*
ΔE*
gloss units at 85°
product uptake (residue, g/m2)
roughness (peak to valley height, µm)
L*
a*
colour
b*
ΔE*
gloss units at 85°
58 ± 35
77.82 ± 1.22
2.06 ± 0.22
8.95 ± 0.62
1.8 ± 0.7
sandstone
uncoated
103 ± 51
53.23 ± 1.82
13.96 ± 0.89
17.45 ± 1.39
0.4 ± 0.1
1 coat
2 coats
5.24 ±1.90
58 ± 45
77.75 ± 1.27
1.87 ± 0.27
9.75 ± 0.60
0.88
2.1 ± 0.8
7.06 ± 1.58
57 ± 50
77.96 ± 1.22
1.62 ± 0.28
10.73 ± 0.64
1.84
2.1 ± 0.9
1 coat
2 coats
6.60 ± 1.80
8.82 ± 1.79
120 ± 43
55.90 ± 1.75
12.15 ± 1.26
16.03 ± 1.27
4.12
0.4 ± 0.1
111 ± 49
55.18 ± 2.01
13.09 ± 0.68
16.70 ± 1.00
2.17
0.4 ± 0.1
3.2. Durability of the self-cleaning coating
Coated stones were naturally weathered in a non-polluted area (Wytham Woods; Oxford),
under a rainy-regime for 4 and 6 months from February to October 2015 and the climatic
conditions were monitored (Fig. 2). During these two periods of time the samples were
exposed to 750 and 1022 hours of sunshine, 135 and 255 mm of rain, respectively, and a
range of temperatures between 3.8 and 22.1°C (Fig. 2). After each of the exposure times the
photodegradation of methylene blue (staining agent) was determined in the lab under UV-A
radiation at different time intervals (up to 190 h) through measuring the colour variation of
the surfaces (Fig. 3) (the reference colour value was measured after methylene blue was
applied and let dry for 24 hours). The results reveal that on limestone the photodegradation
of the organic stain is more effective than on sandstone. This may be because of the
different amount of dye applied on the surfaces. Even though on the most porous material,
limestone, more stain was applied (3 ml vs 2 ml on sandstone) it was more easily absorbed
and less was retained on the surface (as illustrated in Fig. 3). On both substrates two layer
coatings promoted faster degradation of the stain than one layer, however once the coated
substrates were naturally weathered for 6 months these differences no longer existed, as
Munafo et al. (2014) also found on artificial weathering conditions, and the surfaces ended
up exhibiting a very low (residual) photoactivity.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
a)
14
UT
1c
2c
b)
1c-4m
2c-4m
30
1c-6m
2c-6m
12
25
10
20
8
E*15
E*
UT
1c
2c
1c-4m
2c-4m
1c-6m
2c-6m
a)
0h
48 h
120 h
190 h
b)
6
10
4
5
2
0
0
0
50
100
150
time (hours)
200
0
50
100
150
time (hours)
200
Fig. 3: Colour variation (ΔE*) of a) sandstone and b) limestone during photo degradation
of MB: uncoated (UT), treated (1 and 2 coats) and weathered (for 4 and 6 months). On the
right, photodegadation of MB on unweathered coated stones (2 layers).
a
1
a
2
Si
Si
Ti
Ti
b
2)
b
1
C
a
C
a Ti
Ti
Fig. 4. SEM images and EDS analysis of the coated (2 layers) sandstone (a) and limestone
(b) before (1) and after (2) six months of weathering (traces of the coating marked with a
circle)
Coated samples were examined with SEM (equipped with EDS analyser) before and after
being weathered for 6 months in order to examine the distribution of the self-cleaning
product (Fig. 4). Titania coating is observed semi-continuously across both surfaces before
weathering. On sandstone, it is cracked (Fig. 4a1) whereas on limestone it partially covers
the oolites surfaces as a sort of crust (Fig. 4b1). The EDS spectra of the areas analysed
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
show a higher content of Ti on the surface on sandstone than on limestone, corresponding
to the higher product uptake (Tab. 1). However after the outdoor exposure (6 months) the
content of Ti decreases significantly on both surfaces (Fig. 4a2, b2). Only small traces of
TiO2 still remain but the coating has been mostly removed. This explains the loss of
photocatalytic effectiveness previously determined.
4. Conclusions
An aqueous dispersion of TiO2 nanoparticles did not alter the aesthetic of either
Locharbriggs sandstone or Portland limestone when applied in one layer, however on the
red sandstone the application of 2 coats of the product whitened the surface slightly but to
an admissible level in conservation studies.
Regarding its durability under natural environmental conditions in a rainy regime, the
coating after 6 months of exposure in the South of England is gradually removed from the
surfaces of both stones and the photocatalytic activity is lost regardless of the amount of
product applied (1 or 2 layers).
Acknowledgements
Funding from the Marie Curie Action (FP7-2013) under REA grant agreement PIEF-GA2013-622417 is gratefully acknowledged. Sanha Kang wishes to thank Kongju National
University (Republic of Korea) for funding her research stay.
References
Bergamonti, L., Alfieri, I., Lorenzi, A., Predieri, G., Barone, G., Gemelli, G., Mazzoleni,
P., Raneri, S., Bersani, D. and Lottici, P.P., 2015, Nanocrystalline TiO2 coatings
by sol–gel: photocatalytic activity on Pietra di Noto biocalcarenite, J. Sol-Gel Sci.
Technol. 75, 141-151.
Berns, R.S., 2000, Billmeyer and Saltzman’s Principles of Color Technology, WileyInterscience, New York.
Chen, J. and Poon, C-S., 2009, Photocatalytic construction and building materials: From
fundamentals to applications, Building and Environment 44, 1899-1906.
Commission Internationale de l'Eclairage (CIE), 1976, Colorimetry, Bureau central de la
CIE, Paris.
Ďoubal, J., 2014, Research into methods of cleaning silicate sandstones used for historical
monuments, J. of Architectural Conservation 20, 123-138.
EN 1936:2006, Natural stone test methods - Determination of real density and apparent
density, and of total and open porosity, European committee for standardization.
García, O. and Malaga, K., 2012, Definition of the procedure to determine the suitability
and durability of an anti-graffiti product for application on cultural heritage porous
materials, J. of Cultural Heritage 13, 77-82.
Graziani, L., Quagliarini, E., Bondioli, F. and D’Orazio, M., 20014, Durability of selfcleaning TiO2 coatings on fired clay brick façades: Effects of UV exposure and
wet & dry cycles, Building and Environment 71, 193-203.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
La Russa, M.F., Ruffolo, S.A., Rovella, N., Belfiore, C.M., Palermo, A.M., Guzzia, M.T.
and Crisci, G.M., 2012, Multifunctional TiO2 coatings for Cultural Heritage,
Progress in Organic Coatings 74, 186-191.
Licciulli, A., Calia, A., Lettieri, M., Diso, D., Masieri, M., Franza, S., Amadelli, R. and
Casarano, G., 2011, Photocatalytic TiO2 coatings on limestone, J. Sol-Gel Sci.
Technol. 60, 437-444.
Munafò, P., Goffredo, G.B. and Quagliarini, E., 2015, TiO 2-based nanocoatings for
preserving architectural stone surfaces: an overview, Construction and Building
Materials 84, 201-218.
Munafò, P., Quagliarini, E., Goffredo, G.B., Bondioli, F. and Licciulli, A., 2014, Durability
of nano-engineered TiO2 self-cleaning treatments on limestone, Construction and
Building Materials 65, 218-231.
Pandey, S.C., Pollard, A.M., Viles, H.A. and Tellam, J.H., 2014, Influence of ion exchange
processes on salt transport and distribution in historic sandstone buildings, Applied
Geochemistry 48, 176-183.
Pinho, L. and Mosquera, M.J., 2011, Titania-silica nanocomposite photocatalysts with
application in stone self-cleaning, J. Phys. Chem. C 115, 22851-22862.
Pinho, L., Elhaddad, F., Facio, D.S. and Mosquera, M.J.,2013, A novel TiO2–SiO2
nanocomposite converts a very friable stone into a self-cleaning building material,
Applied Surface Science 275, 389-396.
Quagliarini, E., Bondioli, F., Goffredo, G., Cordoni, C. and Munafò, P., 2012, Self-cleaning
and de-polluting stone surfaces: TiO2 nanoparticles for limestone, Construction
and Building Materials 37, 51-57.
UNI 11259:2008, Determination of the photocatalytic activity of hydraulic binders e
Rodammina test method, Ente nazionale italiano di unificazione.
Varotsos, C., Tzanis, C. and Cracknell, A., 2009, The enhanced deterioration of the cultural
heritage monuments due to air pollution, Environ. Sci. Pollut. Res. 16, 590-592.
Vazquez-Calvo, C., Alvarez de Buergo, M., Fort, R. and Varas-Muriel, M.J., 2012, The
measurement of surface roughness to determine the suitability of different
methods for stone cleaning, J. Geophys. Eng. 9, S108-S117.
Viles, H.A., Taylor, M.P., Yates, T.J.S. and Massey S.W., 2002, Soiling and decay of
N.M.E.P. limestone tablets, The Science of the Total Environment 292, 215–229.
710
EXPLOITATION OF THE NATURAL WATER REPELLENCY OF
LIMESTONES FOR THE PROTECTION OF BUILDING FAÇADES
C. Charalambous1 and I. Ioannou1*
Abstract
Natural stone is one of the oldest building materials used all over the world. However,
almost all existing stone buildings and monuments show clear evidence of decay and
weathering. One of the most common causes contributing towards the weathering of stones
and porous materials in general is the presence of moisture. As such, the process of water
movement within this geomaterial should be fully understood in order to assess potential
damages and subsequently minimize the deterioration of stone buildings and façades. In
previous research work, limestone has been shown to possess an inherent water repellency.
This was attributed to the presence of organic contaminants, such as fatty acids, in the pore
network of the material. In this paper, the natural water repellency of limestones is revisited
and exploited to further reduce the wettability of building and decorative stone from
Cyprus. A laboratory treatment based on the inherent composition of the samples under
investigation is proposed. This succeeds in significantly and permanently reducing the
water capillary absorption, and hence the wettability of limestones, without modifying their
composition or appearance. The results provide strong evidence that the aforementioned
treatment may be potentially used in practice to protect stone façades.
Keywords: limestone, wettability, fatty acid, sorptivity, Cyprus, water repellency
1. Introduction
Natural stone is susceptible to water-mediated decay processes, such as salt crystallization
and frost weathering, induced by alternate cycles of wetting and drying. While some
researchers (e.g. Walker et al., 2012) suggest the use of hydrophobic surface coatings in
order to protect existing stonework in monuments and cultural heritage sites, others (e.g.
Thomas et al., 1993; Taylor et al., 2000; Ioannou et al., 2004) have noted that stones, and
in particular limestones, have a natural resistance to water absorption; the latter is indicated
by an observed anomaly during water capillary absorption experiments, suggesting a low
affinity for water and consequently a reduced water wetting index (β < 1). Taylor et al.
(2000) and Ioannou et al. (2004) agree that there is no indication of microstructural change
or reactivity in the limestone samples they have tested to explain the low water absorption
observed. Instead, capillary absorption tests with aqueous organic solutions (i.e. ethanol, 2propanol, n-heptane) suggested that the low affinity of the limestone samples for water was
a contact angle effect, possibly due to a layer of organic contaminants favouring partial
wettability to water (Ioannou et al., 2004). It is worth noting that, according to the
1
C. Charalambous and I. Ioannou*
Department of Civil and Environmental Engineering, University of Cyprus, Cyprus
ioannis@ucy.ac.cy
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
literature, the most severe modification of calcite surfaces is attributed to the absorption of
carboxylic and especially fatty acids. A number of researchers (e.g. Zullic and Morse, 1988;
Rezaei Gomari et al., 2006) agree that fatty acids are irreversibly adsorbed by a calcite
surface. Traube’s rule states that “adsorption increases strongly and regularly with
increasing homolog chain length” (Zullic and Morse, 1988). As a result, short chain fatty
acids (C4 to C12) are not permanently absorbed on calcite surfaces. In contrast, strongest
affinity for carbonate surfaces is shown by medium-to-long chain fatty acids and
carboxylated polymers (Thomas et al., 1993). The long, straight chains of some fatty acids
and the small size of the carboxyl groups allow them to form a nearly close-packed
hydrocarbon layer above the calcite surface, which excludes water and prevents desorption
and carbonate dissolution (Thomas et al., 1993). The aforementioned layer is formed due to
the alkyl units of the long straight chains of the fatty acids, which are considered to be
hydrophobic (Zullic and Morse, 1988; Thomas et al., 1993; Ioannou et al., 2004). This
hydrophobicity primarily controls the solubility of fatty acids and provides an additional
mechanism for chemical interactions with carbonate surfaces.
In this paper, the natural water repellency of limestones is revisited and exploited to further
reduce the wettability of building and decorative stones from Cyprus. A laboratory
developed hydrophobic treatment, based on the inherent composition of the samples under
investigation, and in particular the presence of naturally occurring organic contaminants,
such as fatty acids, is proposed. This treatment may be potentially used to protect stone
façades in monuments and historic buildings, as well as in contemporary structures.
2. Experimental Work
Four different, freshly quarried calcareous rocks from Cyprus were used in this study
(Tab. 1). These rocks were quarried in the areas of Lympia, Anogyra, Agios Theodoros and
Kivides. Cubic specimens (70×70×70 ± 5 mm) were used in all the tests, to better facilitate
result comparison. Initially, the sorptivity (S) of all specimens was measured at different
temperatures using both water and organic liquids. The results were plotted against (σ/η) ½,
where σ [N m-1] is the surface tension and η [N s m-2] the viscosity of the wetting liquids at
each temperature. From the graphs, the so-called intrinsic sorptivity (SI) and the wetting
index (β) of each specimen were estimated (Taylor et al., 2000):
1/2
𝑆 = 𝑆𝐼 (𝛽 ∗ 𝜎⁄𝜂 )
(Eq. 1)
All the samples were then heated in a furnace at 400 oC for approximately 5 hours, so that
any organic contaminants could be removed. The target temperature of 400°C was
gradually reached during the heating procedure (i.e. by increasing the temperature by
100°C every one hour). In order to minimize the risk of damage, all samples were preheated at 105°C. At the end of the heat treatment, the specimens were allowed to cool down
to room temperature, before repeating the sorptivity measurements using water and organic
liquids. Sodium oleate was then applied to the limestone specimens under pressure.
Cylindrical cores measuring 27 mm in diameter and 70 mm in length were used for the
sodium oleate treatment. These were drilled out of the original heat treated samples. The
cores were dried to constant weight at 105 oC in an air oven and were then vacuum
saturated with de-ionised water. Following vacuum saturation, they were loaded into a
Hassler cell and a containing pressure of 34 bar was established. Sodium oleate was then
injected into the cores by a chromatography pump. Two pore volumes of 0.5% w/w sodium
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
oleate were used. This was based upon the pore volume of an average core and the amount
of sodium salt required to form a monolayer. After the injection of sodium oleate, 8-9 pore
volumes of de-ionised water were also pumped into the cores to remove any residual salt.
The samples were left to dry at room temperature. All the specimens were subjected to
thermal analyses using a TG-DTA instrument, both before and after the heat and sodium
oleate treatments. A dry, clean, non-heat-treated Lympia stone was further treated with
sodium oleate by brushing its top surface. The concentration of sodium oleate used in this
surface treatment was also 0.5% w/w. Following brushing, the treated sample was allowed
to dry at room temperature. Its sorptivity was measured before and after the treatment to
observe the effect of sodium oleate treatment on its water wettability.
Tab. 1: Physical properties and mineralogical composition of the limestones under study.
Specimen
Open
Porosity
(EN 1936)
Water
Sorptivity
(EN 1925)
Mineralogy
(XRD)
%
mmmin½
Lympia
41
1.21
calcite (98%), quartz (2%)
Anogyra
23
0.08
calcite (89%), quartz (5%), illite
(traces), albite (4%), heulandite (2%)
Agios
Theodoros
28
0.30
calcite (56%), quartz (7%),
montmorillonite (traces), pyroxene
(10%), illite (traces), plagioclase
(18%), heulandite (2%), aragonite
(7%), analcime (5%)
Kivides
31
0.13
calcite (82%), quartz (4%),
plagioclase (9%), pyroxene (2%),
montmorillonite (traces), aragonite
(3%), illite (traces)
3. Results and discussion
3.1. Sorptivity measurements
For each specimen and for all liquids, the cumulative absorption per unit surface area i
increased linearly with the square root of time t½. Consequently, the sorptivity S (=i/t½) was
derived from the slopes of the graphs. When sorptivity values were plotted against (σ/η)½,
the data points fell into two groups, which lied on separate straight lines (Fig. 1). Despite
the fact that both the organic liquids and the water sorptivity values increased linearly with
(σ/η) ½, the water data lied on a line with a lesser slope. This confirms previous related work
(Ioannou et al., 2004), and demonstrates a marked water anomaly in the case of limestone
specimens.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 1: S versus (σ/η) ½ for water and organic liquids for all limestones under study: (a)
Lympia, (b) Anogyra, (c) Agios Theodoros and (d) Kivides.
It is worth noting that pure organic liquids have low energy tensions and, thus, exhibit
complete wetting (Fox and Zisman, 1950; Taylor et al., 2000). Partial wetting therefore
seems to exist when water is used as the acting liquid; the slopes of the respective lines are
markedly lower (β < 1). This can be explained by a degree of hydrophobicity of the calcite
surface of limestones, which seems not to have a good affinity for water. The gradients of
both lines in Fig. 1 were used to estimate the so-called intrinsic sorptivity of each specimen
(Taylor et al., 2000). Using the values of intrinsic sorptivity and Eq. 1, the water wetting
index (β) of each stone was calculated. Water wetting indices before and after each
treatment and intrinsic sorptivity values for each sample are shown in Tab. 2. The highest
original water wetting index was observed in the case of Anogyra stone, while the lowest
one was estimated for the Agios Theodoros stone. This can be attributed to the mineralogy
of this stone (Tab. 1) and in particular to the presence of clay minerals, which are known to
contain significant amounts of organic impurities (Sayyouh et al., 1990).
3.2. Heat treatment
Fig. 2 shows that the organic liquid S versus (σ/η) ½ lines after heat treatment do not vary
from the ones before heat treatment in all cases; the water lines, however, have a
significantly higher slope, which in the cases of Agios Theodoros and Kivides limestones
increased with the number of heat treatments (not shown in the graph for clarity reasons).
This confirms that the intrinsic sorptivity of all samples remains unchanged, whereas their
water wetting indices change (Tab. 2). The results strongly indicate that the heat treatment
managed to “remove” a large amount of organic contaminants from the specimens, while
their inorganic mineralogical composition was not affected. According to the literature,
thermal degradation of organic contaminants occurs at temperatures >400°C, while CaCO 3
is stable until 400°C (Gaffey et al., 1991). Therefore, organic contaminants are most likely
charred rather than removed at the target temperature of the heat treatment adopted in this
study (Love and Woronow, 1991). This is confirmed by the black crust layer, probably a
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
carbon residue, which appeared on the top surface of all samples after the 5 hour heat
treatment. It is worth noting that after a single heat treatment at 400°C, Anogyra limestone
appeared almost hydrophilic (β = 0.92). The samples from Lympia, Agios Theodoros and
Kivides, albeit showing a significant increase in their water wetting indices after the 1st heat
treatment, were still very much partially wetted. Nevertheless, after a 2 nd treatment, Kivides
stone was nearly fully wetted by water (β = 0.97). As for the Agios Theodoros stone,
although its water wetting index was also further increased after the 2nd heat treatment, a 3rd
treatment was carried out. At the end of this treatment, the sample was fully wetted by
water since its water wetting index was 1 (Tab. 2); this suggests that whatever organic
contaminants this stone contains, they are strongly bound to its surface and it is therefore
difficult to remove them.
Fig. 2: S versus (σ/η) ½ for organic liquids and water before and after all treatments.
( ) organic liquids line, (o) water before treatments, ( ) water after final heat treatment,
( ) water after treatment with sodium oleate and flushing de-ionised water (see section
3.3). (a) Lympia, (b) Anogyra, (c) Agios Theodoros and (d) Kivides limestone.
3.3. Treatment with Sodium Oleate
The results of the capillary absorption experiments after treatment with sodium oleate and
subsequent flushing with de-ionised water are also shown in Fig. 2. The organic liquids line
remained generally unchanged after treatment with sodium oleate, whereas the water line
had a much lower slope. Hence, there was a significant reduction in the water wetting
indices of the specimens (Tab. 2). These results provide strong evidence that sodium oleate
adsorbs well on calcite surfaces, causing a reduction in their wettability. Better diffusion of
sodium oleate was achieved by flushing de-ionised water through the treated samples. The
largest difference in water wetting index after treatment with sodium oleate was observed
for Anogyra limestone, which had been converted from a nearly fully water-wetted stone
(β = 0.92) to a nearly hydrophobic stone (β = 0.02), before flushing amounts of de-ionised
water through it. The sodium oleate treated stones from Agios Theodoros, Lympia and
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Kivides reached down to almost the same β with Anogyra stone after flushing with deionised water; however, Lympia stone originally had a water wetting index β = 0.42
(after heat treatment).
Tab. 2: Water wetting indices before and after each treatment for all limestones under
study.
Specimen
Intrinsic
Sorptivity
×10-4 mm½
Water Wetting Indices
Original
After final
heat
treatment
After
treatment
with
sodium
oleate
After
flushing
deionised
water
Lympia
8.11
0.21
0.42
0.16
0.03
Anogyra
0.75
0.35
0.92
0.02
0.02
Agios
Theodoros
5.04
0.03
1.00
0.33
0.01
Kivides
1.41
0.07
0.97
0.08
0.05
In order to investigate the practical applicability of the treatment with sodium oleate, the
surface of a freshly quarried specimen of Lympia limestone was repeatedly brushed with
sodium oleate (0.5 % w/w). After a single brushing, the sorptivity of this specimen was
reduced by 10%. Further treatments reduced its sorptivity by nearly 90%, while flushing
with de-ionised water led to a final reduction of 95% (compared to the original sorptivity).
The results strongly indicate that sodium oleate reduces the water absorption of limestone
by modifying its surface wettability. Through brushing with sodium oleate (0.5 % w/w), the
calcite surface of Lympia stone has turned from hydrophilic to almost hydrophobic. Sodium
oleate chemically adsorbed on the CaCO3 surface of Lympia stone, which interacted in
itself with oleate anions, thus giving the surface a Ca-oleate product. Ca-oleate is water
insoluble and remains on the CaCO3 surface. The chemical reaction can be described
according to Eq. 2 and 3. The chemisorption is not reversible and the reaction takes place
only in one direction.
NaOH + C17H33COOH→ C17 H33COONa + H2O
(Eq. 2)
CaCO3 + 2C17H33COONa → (C17H33 COO)2Ca + Na2CO3
(Eq. 3)
The unsaturated bond of sodium oleate affects the close packing of carbon chains at the
surface of the stone (Sayan, 2005; Alinnor and Enenebeaku, 2014).
3.4. Thermal analysis
The differential thermal analyses (DTA) results of the original stone samples showed a
small exothermic peak near 300°C; this peak disappeared after heat treatment and reappeared after the treatment with sodium oleate (see for example Fig. 3).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
oC
uV
0
200
400
600
800
1000
0
-20
-40
-60
-80
-100
After Final Heat Treatment
After Treatment with sodium oleate 0.5% w/w
Before All Treatments
Fig. 3: DTA results for Agios Theodoros limestone.
Weight loss at this temperature, followed by an exothermic peak, is indicative of a double
bond (C=O) cleavage and of the formation of intermediate products, which are rich in
oxygen (Middendorf et al., 2005; Roonasi and Holmgren, 2009). This can be linked to the
presence of organic impurities and sodium oleate in particular. It is worth noting that the
original peak was more prominent in the Agios Theodoros stone; this was the sample that
needed three heat treatments to remove its naturally occurring organic contaminants.
4. Conclusions
The anomalously low water absorption of limestones from Cyprus has been confirmed by
the data illustrated in this paper. When the specimens were subjected to capillary absorption
experiments with water and organic liquids, a significant differentiation in S vs (σ/η) ½
graphs was observed: water data were evidently on a line of lesser slope compared to
organic liquid data. Heat treatment led to a significant increase of the water wetting indices
of the stones under study. This strongly suggests that the stones’ anomalously low original
water absorption may be attributed to the presence of a hydrophobic organic contaminants
adlayer below their surface. The latter was charred (and hence became inactive) at
temperatures around 400°C. The apparent natural water repellency of limestones from
Cyprus was exploited through chemical modification of their surfaces using sodium oleate.
This strongly adhered to the stones’ calcite surfaces, rendering them water repellent. DTA
results provided evidence that sodium oleate (or other similar fatty acid products) may be
responsible for the anomalously low water absorption of untreated limestones. This work
has practical significance, since the durability of stone masonry is largely controlled by
processes mediated by water. Partial wettability of limestones is desirable, in order for their
durability to be boosted. Treatments based on naturally occurring organic contaminants can
therefore be used to induce partial wettability to limestones.
References
Alinnor I.J. and Enenebeaku C.K., 2014, Adsorption Characteristics of Sodium Oleate onto
Calcite, Int. J. of Pure and Applied Chemistry 4, 88-96.
Fox H.W. and Zisman W.A., 1950, The spreading of liquids on low energy surfaces. I.
polytetrafluoroethylene, J. of Colloid Science 5, 514-531.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Gaffey S.J., Kolak J.J. and Bronnimann C.E., 1991, Effects of drying, heating, annealing
and roasting on carbonate skeletal material, with geochemical and diagenetic
implications, Geochimica et Cosmochimica Acta 55, 1627-1640.
Ioannou I., Hoff W.D. and Hall C., 2004, On the role of organic adlayers in the anomalous
water sorptivity of Lepine limestone, J. of Colloid and Interface Science, 279, 228234.
Love K.M. and Woronow A., 1991, Chemical changes induced in aragonite using
treatments for the destruction of organic material, Chemical Geology, 93, 291-301.
Middendorf B., Hughes J.J., Callebeaut K., Baronio G. and Papayianni I., 2005,
Investigation methods for the characterisation of historic mortars. Part 1:
Mineralogical Characterisation, Materials and Structures, 38, 761-769.
Rezaei Gomari K.A., Denoyel R. and Hamouda A.A., 2006, Wettability of calcite and mica
modified by different long-chain fatty acids (C18 acids), J. of Colloid and Interface
Science 297, 470-479.
Roonasi P. and Holmgren A., 2009, A Fourier transform infrared (FTIR) and
thermogravimetric analysis (TGA) study of oleate adsorbed on magnetite nanoparticle surface, Applied Surface Science, 255, 5891-5895.
Sayan P., 2005, Effect of sodium oleate on the agglomeration of calcium carbonate, Crystal
Research and Technology, 40, No. 3, 226- 232.
Sayyouh M.H., Dahab A.S. and Omar A.E., 1990, Effect of clay content on wettability of
sandstone reservoirs, J. of Petroleum Science and Engineering, 4, 119-125.
Taylor S., Hall C., Hoff W.D. and Wilson M., 2000, Partial wetting in capillary absorption
by limestones, J. of Colloid and Interface Science, 224, 351-357.
Thomas M., Clouse J.A. and Longo J.M., 1993, Adsorption of organic compounds on
carbonate minerals: 1. Model compounds and their influence on mineral wettability,
Chemical Geology, 109, 201.
Walker R., Wilson K., Lee A., Woodford J., Grassian V., Baltusaitis J., Rubasinghege G.,
Cibin G. and Dent A., 2012, Preservation of York Minister historic limestone by
hydrophobic surface coatings, Scientific Reports, 2:880, 1-5.
Zullig J.J. and Morse J.W., 1988, Interaction of organic acids with carbonate mineral
surfaces in seawater and related solutions: I. Fatty acid adsorption, Geochimica et
Cosmochimica Acta, 52, 1667-167.
718
THE USE OF NEW LASER TECHNOLOGY TO PRECISELY
CONTROL THE LEVEL OF STONE CLEANING
B. Dajnowski1* and A. Dajnowski1
Abstract
Laser ablation cleaning has significantly evolved over the years and offers unique solutions
to monumental and architectural stone cleaning problems. Laser cleaning, when applicable,
is an attractive technology because it does not involve the use of any chemicals or abrasive
media, which can often be logistically problematic and require significant efforts for
containment and disposal. With a proper understanding of the ablation threshold of the
material and the damage threshold of the stone substrate, it is possible to safely clean a
soiled stone surface without affecting the substrate. It is also possible to precisely control
the level of cleaning and achieve consistent results ranging from fully clean to partially
clean surfaces. This level of control can be particularly useful in situations where a fully
clean surface is not desirable and some level of historic patina needs to be preserved or
matched in the cleaning process. This research will demonstrate different levels of laser
cleaning that can be achieved on a variety of stone surfaces by fine-tuning laser parameters
such as fluence, pulse duration, and pulse frequency. The GC-1 Laser Cleaning System, a
new laser cleaning technology developed specifically for art and architecture conservation
will be introduced. In addition to findings from research performed at the Conservation of
Sculpture & Objects Studio conservation lab, real world treatment examples such as the
laser cleaning of the over 3,500 year-old ancient Egyptian obelisk of Pharaoh Thutmose III
in Central Park, NY will be presented.
Keywords: laser cleaning, ablation, GC-1, conservation, obelisk, stone, granite, limestone
1. Introduction
Many years in the making, the first GC-1 Laser Cleaning System (Fig. 1) was built by
Bartosz Dajnowski in 2014 to meet the conservation needs of the 3,500 year old Egyptian
obelisk in Central Park, NY. This new cutting edge system is the result of over a decade of
hands on laser experience, laser research, professional training, optical engineering, and
frustration with the shortcomings of existing laser systems. The compact and portable
1064 nm GC-1 laser system is air-cooled, has no consumable parts, and plugs into any
standard 110 V or 220 V outlet in the world. This system was built specifically to meet the
needs of art and architecture conservation and is being used on cultural heritage projects
across North America, and has led to the formation of a new company called G.C. Laser
Systems Inc. (www.GCLasers.com) that specializes in evolving laser applications
technology for the world of cultural heritage preservation. This paper will go over some of
1
B. Dajnowski* and A. Dajnowski
Conservation of Sculpture & Objects Studio, Inc, (CSOS), United States of America
BDajnowski@CSOSinc.com
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
the practical applications of this system and illustrate how its unique features make it an
effective tool for cleaning stone.
b)
a)
Fig. 1: a) First GC-1 Laser Cleaning System Prototype; b) New generation of the GC-1
which measures: W=41.3 cm/L=74 cm/H=56 cm. (Multiple patents pending worldwide).
2. Working principle of laser cleaning
The method of laser cleaning relies on taking advantage of the fact that various materials
will absorb different wavelengths of light depending on properties such as their color and
chemical composition. Laser parameters such as wavelength, pulse duration, and energy
density/fluence can be tuned to selectively excite a layer of unwanted material in order to
remove it from an original surface that does not get affected by the same laser parameters.
Examples of unwanted layers of material include corrosion, soiling, graffiti, and coatings
on monuments. The atoms and molecules of the contaminant get so excited by the laser
energy they absorb that molecular bonds are broken, particles are ejected, and the
contaminant is vaporized/ablated. Unlike mechanical or abrasive cleaning methods which
rely on mechanically impacting the surface to get contaminants to break free, this method
relies on exciting the contaminant so that it separates from the surface on its own.
Tuning a laser cleaning system can result in a variety of photomechanical, photothermal,
and photochemical effects that can aid in the removal of an unwanted layer such as
contaminants, corrosion, coatings, or paint. The goal is for the laser to discriminate
between the unwanted layer and the substrate. Ideally the unwanted layer absorbs the laser
pulses while the original substrate reflects them. Once the laser reaches the substrate, it
does not absorb into it and simply reflects off the surface. Laser cleaning relies on
calibrating laser parameters to selectively remove unwanted layers of material or coatings.
Fig. 2 shows the following steps:
1.) The contaminant layer (red) needs to be removed from the original substrate
(green).
2.) Laser parameters are calibrated to ablate away the contaminant without damaging
the substrate.
3.) The substrate is uncovered to reveal a clean and undamaged surface.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 2: Laser cleaning of a contaminant off of a substrate.
3. Precision of Laser cleaning
The efficacy and precision of a properly tuned laser to discriminate between a contaminant
and a substrate is illustrated in Fig. 3, where blue tape is used to mask of a test area on
discolored architectural limestone for laser cleaning tests. This orange colored limestone is
from the historic façade of the Oklahoma State Capitol Building. The building had a
silicon-based coating applied in the 1980s, which has since discolored orange and proved
difficult to remove with other methods. CSOS conducted laser-cleaning tests on the façade
under the supervision of Treanor Architects in 2015. The image shows that something as
simple as paper or blue painters tape can be used to mask off an area while laser cleaning
tests were performed (Fig. 3).
Fig. 3: Using blue tape to mask off areas for laser of a discolored coating from
architectural limestone (left), and detail of cleaning results (right).
The laser settings used here did not damage or penetrate through the blue tape, and they did
not damage or alter the surface texture of the limestone while removing the discolored
orange film. The laser does not affect the area covered by the tape, resulting in a much
defined border during cleaning. Tape or other optical barriers can be used to strategically
mask off parts of a stone structure from being exposed to the laser. For example, window
seals can be easily masked off during laser cleaning. By comparison, chemical cleaning of
architectural stone could compromise window seals while air abrasive methods could etch
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glass, not to mention potentially erode the stone surface. The GC-1 laser system has a red
aiming beam feature that can be activated to show exactly where the laser will fire (Fig. 4).
When the trigger is pulled, the red aiming beam is replaced with the 1064 nm laser beam
that does the ablation.
Fig. 4: The red aiming beam of the GC-1 is used to target an area of architectural marble
before firing the laser to remove dark gypsum crust.
4. Precise control over laser parameters
The lasers typically used for such treatments have very short pulses in the nanosecond
range. It is common practice and very important that laser cleaning case studies to report
the fluence of the laser pulses being used. Fluence, also known as energy density, is simply
the ratio of energy per pulse over the surface area of the pulse, and is typically measured in
Joules/cm². The concentration of laser energy should be set to give satisfactory cleaning
results while remaining below the damage threshold of the substrate. However, there are
many other parameters to take into consideration such as pulse duration. In general, shorter
pulses result in more of a photomechanical effect and longer pulses result in less
photomechanical effect, more plasma formation and the potential for more photothermal
effect. For example, a 10ns pulse generates more photomechanical shock on a surface than
a 100 ns pulse because the laser energy is delivered over a much shorter period of time.
Longer pulses result in longer reactions and more plasma formation. Depending on the
nature of the soiling/contaminant being removed and the characteristics of the substrate, a
shorter or longer pulse duration may be optimal for effective cleaning. A 1064 nm laser
emitting 10 ns pulses can give completely different cleaning results than a laser system
emitting 100 ns pulses. Longer pulses in the nanosecond region are more gentle on fragile
surfaces than shorter pulses. Unlike other laser systems that have a set pulse duration, the
GC-1 laser cleaning system is unique because it allows the conservator to select a wide
range of pulse durations ranging from 10ns – 250 ns [additional pulse duration options and
laser systems are in development by G.C. Laser Systems Inc.], and those pulse durations
are independent of pulse frequency. Pulse frequency is finely tunable from 1 kHz – 1 MHz.
For example, the operator could chose to have the laser emit any desired exact number of
pulses, such as 202,542 or 202,543 pulses per second. Laser energy, fluence, and scan
speed are also precisely controlled and tunable via a touch screen user interface. Spot size
can be changed simply by changing focal lenses in the scanner, allowing for an extended
range of fluence options.
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b)
a)
Fig. 5: a) Different levels of consistent cleaning of fire damaged granite;
b) Historic limestone with dark biological growth by tuning laser parameters.
The granite sample in Fig. 5 was exposed to fire and soot and then washed to remove
superficial loose soot from the stone. This process was repeated 8 times until a dark and
well-adhered soot layer remained on the surface. Precise tuning of critical laser parameters
can allow a conservator to control the level of cleaning of stone to achieve very uniform
and consistent results. Fig. 5 illustrates the wide range of levels of “clean” that can be
achieved on fire-damaged granite. The Indiana limestone sample on the right is covered
with dark biological growth from being exposed to the elements for many years. Both
biological growth and atmospheric pollution can be removed from stone with laser ablation,
and the laser system will not clean beyond a certain level that it has been tuned to. Partial
cleaning can be useful when the treatment goal is not to make a surface look like new, but
to leave behind some level of patina. For example, if a large historic stone building has an
overall level of historic patina, but suddenly experiences a fire in one area. It could be
undesirable to over clean the fire-damaged area, which would then look too new relative to
the rest of the façade. With a well-tuned laser it is possible to precisely control the level of
cleaning to better match the tonality of the rest of the building.
5. Unique scanning system
Conservators use either low pulse frequency lasers or high pulse frequency lasers for
treatments. Low frequency lasers typically generate a maximum of less than 50 pulses per
second (50 Hz) and are commonly used on small-scale projects or objects. High frequency
lasers generate thousands or hundreds of thousands of pulses per second, delivered via a
scanning system, and are more efficient for use on larger conservation projects. A common
scan system uses for high frequency lasers is a line scan system. The line scan is typically
created by an oscillating galvanometer mirror that directs the laser beam back and forth
along one axis, resulting in a line. Such line scanners can be effective tools for
conservation; however they can have inherent difficulties. When the beam reaches the
endpoint, the mirror has to physically stop and change direction. Although this process of
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changing direction is extremely fast, lasting only a small fraction of a second, it is still long
enough for more laser energy to be delivered to the endpoints of the scan line, resulting in
“hot spots” as are shown in Fig. 6. Hot spots in a cleaning system can produce uneven
results. By comparison, the unique circular scan pattern of the GC-1 laser system delivers a
continuous even distribution of laser energy over the path of the scan. There is no stopping
or changing direction of the beam and therefore no end point hot spots. Fig. 6 and Fig. 7
illustrate how a circular scan pattern is a geometrically more efficient solution. A line scan
pattern, as shown in Fig. 6a, will expose every point on a surface once as it moves past an
area. In contrast, as a circular scan moves over a surface, the leading edge of the circle
passes over an area first (1) and then the trailing edge passes over the same area again (2).
There are two separate exposures of the laser beam to any given point with each movement
of the laser across the surface. This can make cleaning twice as fast, particularly in cases
where multiple passes of the laser are often needed. The probability of thorough cleaning is
significantly increased because anything that might be missed or under cleaned by the
leading edge (1) will be exposed to the laser parameters again as the trailing edge (2)
reaches it. In short, this process results in two passes of the laser with any given physical
movement where a line scan only offers one pass of the laser per physical movement.
a)
b)
Fig. 6: a) Comparison of a typical line scanner to the GC-1 circular scan pattern;
b) Multiple angles of exposure as the laser moves across a surface.
The laser beam comes out of the scanner as an expanding cone (Fig. 6b). As the circle/oval
moves over a surface, the leading edge (1) of the cone hits the surface from one angle, and
then as the laser keeps moving the trailing edge (2) of the cone hits the same area from the
exact opposite angle. Textured surfaces are efficiently cleaned by this process because the
laser is able to reach multiple facets of a complex surface with just one pass. The angle of
the cone can be custom modified as well. By comparison, a line scanning system
essentially emits a flat plane of laser light that offers only one angle of incidence per pass.
During actual cleaning trials on various surfaces we have found the rate of cleaning of the
GC-1 to range from five to sixty square feet per hour, depending on the nature of the
material being removed and the substrate being cleaned. For example, carbon deposits are
very quickly removed from a variety of stone surfaces.
6. Limitations
A laser system is simply an additional tool in the toolbox of the conservator. It is by no
means a magic wand and the parameters of the laser need to be thoroughly understood. The
same laser systems can provide excellent results as well as cause irreversible damage to a
surface depending on how it is used, how it is tuned, and the skill of the operator. Not
understanding laser the properties of a laser and the physics behind laser cleaning can lead
to undesirable results or misinterpretations of what is happening during the process.
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Fig. 7 addresses the issue of yellowing of stone that many have observed after laser
cleaning stone, and one reason why this may appear to happen.
Fig. 7: Removing fire damage soiling from a marble surface that was completely black with
soot before laser cleaning (left). The word WAX remains as an actual film of wax on the
surface after cleaning (right).
When the soiling is removed from the white marble with laser, a dark yellow word WAX is
uncovered. Wax was in fact used to spell out the word WAX which was applied prior to
soiling the sample. In this case the laser was tuned to remove the soiling, but the
parameters were not sufficient to remove wax from the surface. An inexperienced operator
may think they have turned the stone yellow, when in fact they have simply failed to
remove a layer of wax residue from the surface that was beneath the soiling. This wax
residue can be removed with different laser parameters or with poulticing and/or chemical
methods. It is not uncommon for stone objects to have been waxed, to have accumulated
oily organic pollutants, or to have been oiled during their history to make them look more
polished. Laser cleaning should not necessarily be considered as a stand-alone technique.
There are many situations in which laser cleaning is most effective when it is part of a
process that involves other conservation methods and treatment steps. It should also be
understood that laser cleaning is a surface cleaning technique and that it is not always
applicable. If the damage threshold of the substrate is exceeding by the available laser
parameters, then it is not safe to laser clean. This is why testing on samples is always
recommended. It is critical to understand that laser cleaning will not extract stains from a
stone and attempting to remove, for example, iron or copper stains from a stone with a laser
can cause permanent damage and discoloration to the stone. Stains should be removed with
traditional poulticing methods, and occasionally a laser may be used to remove the final
thin layer of stain residue from a stone surface after a poulticing campaign. A common
hurdle to incorporating laser cleaning into a project is that the equipment can initially be
relatively expensive when compared to other methods such as pressurized media blasting.
However, with this new technology the increased rate of cleaning, the precise control over
the level of cleaning, and the lack of chemical and abrasive media waste disposal costs
makes it a competitive option to consider.
7. The obelisk of Pharaoh Thutmose III
The ancient Egyptian Obelisk that stands in New Yorks’ Central Park behind the
Metropolitan Museum of Art is made of one piece of solid Aswan granite, weighs
approximately 220 tons, and is over 21 meters tall. This amazing object has a rich history
that involves Thutmose III, Ramses II, Cleopatra, Julius Caesar, the Egyptian government,
the Vanderbilts, masons, and an epic transatlantic voyage to the USA in 1880. This obelisk
is one of a pair of two obelisks, and the second one stands in London. The Central Park
Conservancy (CPC) cares for and maintains the obelisk. After extensive research and
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
testing of chemical cleaning, micro-abrasive cleaning, and laser cleaning methods and
options, the Central Park Conservancy concluded that laser cleaning provided the safest,
most environmentally friendly, and most uniform level of cleaning for the fragile stone
surface. For example, chemical cleaning was uneven and runoffs were difficult to control.
Scanning electron microscopy showed that micro abrasive cleaning abraded the stone
surface while laser cleaning resulted in more thorough cleaning with no impact on the
granular structure of the stone. CSOS was selected to perform the laser cleaning of the
entire obelisk surface, the granite plinth on which it stands, and the four replica bronze
crabs wedged in its corners. CSOS was asked to first conduct tests on loose samples that
had fallen off over time, which were examined by the CPC and by Dr. George Wheeler at
the Metropolitan Museum of Art to ensure that there was no damage being done to the
stone. It was critical not to damage the black biotite inclusions in the granite or to cause
micro shattering of the quartz while removing the dark soiling from the granite. The tests
confirmed that it was possible to safely clean the granite without causing any damage.
More tests were conducted onsite on the obelisk and then the project moved forward under
the supervision of the CPC. To ensure that the project went smoothly, CSOS had one
100 W and three 120 W line scanning laser systems onsite. These systems were custom
modified by CSOS to eliminate hot spots that could potentially damage the stone. This
project was catalyst for the creation of the GC-1, as the first prototype was made to meet
the needs of this project. The GC-1 was the only scanning laser system that could be
carried by one or two people to the top of the scaffold due to its light weight and compact
size. The 70W GC-1 outperformed the other more powerful 100-120 W laser systems on
the project and was proven to clean twice as fast as the line scanning systems. Due to its
efficiency and speed, the GC-1 was used to clean over 60% of the granite surface, despite
the fact that there were typically two line-scanning systems in operation at all times.
Overall, depending on the level of soiling, 100-200 ns pulses were used at a fluence of
1-3 J/cm2. The entire laser cleaning process was done wet by misting the surface with
distilled water just prior to firing the laser, which gives a micro-steam cleaning effect as the
laser vaporizes water that enters the pores of the stone. The wet ablation allows for deeper
cleaning of the surface and also helps protect the surface from potential phase changes by
minimizing plasma exposure to oxygen as the reaction happens under a film of water. The
laser cleaning treatment was a success and Fig. 8 shows that legibility of the hieroglyphs
significantly improved after cleaning as the natural shadows of the carvings are no longer
masked by dark soiling.
The granite surface was examined with a portable USB microscope during treatment to
ensure that no damage was being done to the surface. Photomicrographs were taken to
document the cleaning results. Fig. 9 shows a one area before and after laser cleaning in
regular light and infrared light. IR light helps show carbon on a surface. The images show
that the soiling was successfully removed and that the black biotite inclusions, pink quartz,
white quartz, and other minerals were not damaged during the cleaning process. In fact, the
green arrows point to two small grains of quartz on the surface which are not disrupted at
all by the cleaning process and remain intact.
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Fig. 8: Overall and detailed results of laser cleaning the obelisk.
Fig. 9: Photomicrographs (magnification: ×40) of the surface before and after laser
cleaning. The green arrows point at delicate small grain features that were preserved
during laser cleaning.
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8. Conclusion
Laser cleaning is becoming more popular because it is environmentally friendly and very
precise. The uniqe GC-1 laser cleaning system is a verastile new tool for cleaning stone.
The GC stands for “Game Changer,” because of its’ compact size, tunability, and
reliability. It offers unmatched paramaters and control over cleaning which, in the right
hands, means consistent results on both large and small projects.
Acknowledgements
We would like to thank the conservation staff at CSOS for their work and dedication to
these projects and to the many projects that led up to this point. A special thanks is owed to
Robert Zarycki, Christopher Ciaston, Tadeusz Mlynarczik, and Rosanna Ioppolo. We
would like to thank Tri-State Stone and Brick Co for supplying us with a variety of historic
and new stones for our research. We are grateful to architectural firms such as Wiss, Jenny,
Elstner Associates Inc., Treanor Architects, Kiewit Building Group, Grunley Construction
Company, Atwill-Morin Inc. and the government agencies and cultural institutions such as
the Architect of the Capitol and the Smithsonian that give us the opportunity to test and use
this technology on a variety of unique cultural heritage projects. We are particularly
grateful to the Central Park Conservancy for trusting us to treat the obelisk in Central Park,
especially since this project motivated us to bring the GC-1 laser cleaning system into
existence. Bartosz Dajnowski would like to express his sincere gratitude to the team at the
Laser Applications Lab at the Military University of Technology Institute of
Optoelectronics, Laser Applications Lab in Warsaw for the education and training they
provided him, and in particular the mentorship and friendship of the late Prof. Dr. Hab. Inz.
Jan Marczak.
References
Castillejo, M., 2007, Lasers in the Conservation of Artworks. The Netherlands: CRC
Press.
Nimmrichter, J. 2005. Lasers in the Conservation of Artworks, LACONA VI
Proceedings, Vienna, Austria, Sept. 21‐25, 2005. Germany: Springer.
Koss, A. and Marczak, J., 2005, Application of Lasers in Conservation of Monuments and
Works of Art. Warsaw, Poland: Oficyna Drukarska.
Radvan, R., 2009, Lasers in the Conservation of Artworks VIII, Proceedings of the
International
Conference on Lasers in the Conservation of Artworks VII
(LACONA VIII), 21‐25 September 2009, Sibiu, Romania. The Netherlands:
CRC Press.
728
CLEANING STONE – THE POSSIBILITIES FOR AN OBJECTIVE
EVALUATION
J. Ďoubal1
Abstract
The cleaning of monuments is one of the most common and at the same time most risky
procedures when conserving or renovating monuments. Cleaning monuments can be carried
out only if based on solid knowledge of the actual monument issues, its origin and character
of soiling (using X-rays, FTIR and Raman spectrometry or optical microscopy) as well as
of the substrate material (using for instance SEM, SEM-EDS and petrological analyses of
the cut using polarizing microscopy). The aim of this paper is to present some of the recent
options of objective cleaning results assessment. The paper focuses both on the description
and assessment of instrumental measurement of changes in physical properties (water
uptake, water-vapour permeability, cohesion after testing using a peeling test) and on
optical methods facilitating assessment of cleaning effectivity and the restoration
intervention impact on the substrate (SEM, optical microscopy). The overview of objective
possibilities of evaluating cleaning methods is based on many years of experience of
assessing the results of cleaning on real objects, as well as in laboratory testing.
Keywords: stone, cleaning, evaluation, conservation, compatible treatment
1. Introduction: Cleaning stone monuments
The cleaning of monuments is one of the fundamental and most important aspects of
monument conservation. It is a crucial step both from the point of view of the philosophy
of conservation and from the perspective of the technology and techniques of conservation.
The cleaning of monuments can only be carried out based on in-depth knowledge of the
aspects of the monument in question, of the origin and nature of the soiling and of the state
of the underlying material. The evaluation of the necessity and level of cleaning is
essentially based on assessment from two basic aspects:
In what manner the soiling of the surface influences the state of the underlying
material. When assessing this aspect, it must be considered, based on the survey, whether
the surface soiling could pose a risk to the future life of the monument. It is inspected
whether the change of the physical properties of the surface (such as water uptake, watervapour permeability, changes in thermal and moisture expansion, etc.) is not the source of
damage, and if it is, the severity of the risk is examined. Another important criterion for
evaluating the necessity of cleaning is the question to what extent soiling is a source of
substances harmful to the stone, e.g. water-soluble salts, etc.
1
J. Ďoubal*
Faculty of Conservation – University of Pardubice, Czech Republic
Jakub.doubal@upce.cz
*corresponding author
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In what manner the soiling of the surface compromises the artistic and aesthetic value
of the monument. The impurities may cover the surface as a thick layer which obscures
the surface relief and often alters the sculpting. Soiling is practically always accompanied
by a significant change in colouring. Depending on the type of pollutant, the source of
soiling and the substrate material, impurities also sediment unequally and the resulting
effect may be very far from the original intent of the sculptor. On the other hand, a certain
level of alteration of the original appearance of the monument is generally accepted when
assessing aesthetic positions. This alternation gives rise to the historical value of the
monument and is connected in its life in time - this type of changes in the surface layer is
called a patina. The definition of patina and the necessity of preserving it have been subject
to discussions ever since modern monument care has existed.
It follows from the nature of both aspects that, while with the first one a relatively objective
assessment can be carried out at today’s level of understanding, the other one will always
entail a subjective assessment depending on the time period, aesthetic feelings and point of
view of the assessor. The fact is, however, that both these basic aspects are equally relevant
when it comes to works of art.
There is a broad range of techniques ranging from highly effective ones that are used on
large façades, to sensitive and precise ones that are used on the smallest details of a
sculptor’s work (Fassina 1994, Andrew et al. 1994, Normandin et al. 2005, Ďoubal 2014).
The individual techniques and technologies have their own respective and irrefutable
advantages, but they are also connected with certain risks, when it comes to their
application. When choosing a suitable technology of cleaning, all aspects of the use of the
given method should be taken into account, including its effectiveness, the effect it has on
the substrate and how demanding it is economically.
2. Assessing the results of cleaning
In practice, the results of cleaning are mostly assessed subjectively based on visual
inspection. Objective possibilities of assessment have been described by a large number of
authors (Andrew et al. 1994, Kapsalas et al. 2007, Hauff 2008, Werner 1991, VergesBelmin 1996, Ďoubal 2014).
When assessing the change in appearance (i.e. of the effect of cleaning), it is impossible to
avoid individual assessment since it is aesthetic qualities, which are by their very nature
impossible to measure, that are assessed.
While there are not many instrumental tools for the assessment of appearance, there are a
number of possibilities for assessing possible changes in the characteristics of the surface
after cleaning and of measuring the level of material loss (Ashurst 1994). The principles for
assessing the effect of cleaning (Tab. 1) are based on requirements that have already been
drawn up in the past. In 1997, WTA - The Scientific-Technical Society for the
Rehabilitation of Buildings and for Monument Care drew up a technical regulation called
“The Assessment of Cleaned Stone Surfaces (Goreczky, L. and Hoffmann 1997), which
evaluates measures aimed at cleaning the surfaces of buildings and stones. The system of
assessing interventions introduced by the WTA regulation is based on the evaluation of
selected physical-mechanical parameters, but also on the evaluation of changes in the
chemical composition of material and of alterations in its structure and surface.
Table. 1: Decisive material characteristics for the assessment of cleaning
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Characteristic
Name of
quantity
measured/unit
Methods, norms and
recommendations for trials
In labo
In situ
Optical microscopy
Micro
in polarized and chemical tests
non-polarized
lights, (SEMEDS), X-ray
diffraction (XRD)
Criteria for
positive
assessment
No changes
(material)
Chemical and
mineralogical
characteristic (of the
material as well as of
the soiling)
-
Surface water uptake
Capillary water
uptake
coefficient C
(kg∙m-2·min-1/2)
EN 101518:2009
EN
16302:2013
Ci>C0
Microstructural
properties: thickness
of the layer of
deposits, surface
changes after cleaning
-
Optical
microscopy, SEM,
X-ray tomography
-
Reducing the
thickness of the
layer of deposits,
without disruptions
and changes in
surface
Colour of the soiled
surface and the
referential colour of
the material
(determined by
agreement)
L*, a*, b*, ΔE,
ΔC*
EN 15886:2010
-
Criteria must be
defined
individually for the
respective case
Surface cohesion
(weight of torn-off
material)
Weight of tornoff material
-
Peeling test
No changes
(material)
Surface roughness
Roughness
depth, R
DIN 4768, 4772, EDIN 4760
Optical
microscopy, SEM
-
No changes
(material)
The quality of the cleaning carried out is in practice mostly assessed based on the change in
water uptake, which should increase after the cleaning. However, its level cannot be
quantified with more precision, as the level of cleaning depends on other qualities of the
surface (e.g. it carries shape; underneath the layer of soiling, the stone is completely
decayed and the layer of impurities hardens it, etc.). In practice, the capillary water uptake
is usually determined in situ using Karsten tube test (or its more recent modifications), or
on samples in a laboratory. From the point of view of the mechanism, it is obvious that
absorption power increases when the layer of soiling is made thinner, or when it is
completely removed. Even in that case, the rate of removal is individual and it is necessary
to consider its rate in relation to other characteristics of the surface (especially cohesion and
grain size).
With regard to an aesthetic evaluation of the artwork after cleaning, the assessment of the
colouring of the surface of the material is an important macro-characteristic. These changes
in colouring and other aspects are in practice mostly evaluated visually by comparing the
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cleaned surface to a referential surface of material (surrounding surface, architecture, other
elements within the set, polychromy, etc.). In the case of a need for a more objective
assessment (again with some limitations given by the quality and morphology of the
surface), it is possible to assess the overall change in colouring by means of a portable
spectrometer. Deviations acceptable within the intervention are listed in literature in
absolute values as the changes in colouring. However, for cleaning the exact limits for a
positive evaluation of the intervention have not been published - for understandable
reasons.
2.1. Characteristic of the substrate and deposition of soiling
In order to obtain a basic characteristic of the soiling, the thin section of a representative
sample collected, including soiled surface, will be used. A thin section collected in this
manner allows for a petrological analysis of the stone which will determine the basic
characteristic properties of the rock and help determine the manner of deposition of the
impurities, or the depth of seepage into the substrate, which is an essential property for the
selection of the appropriate rate and method of cleaning. Examination in a polarizing
microscope allows the petrologist to carry out a detailed analysis of the examined stone,
including its mineralogical composition and porous structure. The chemical as well as
mineralogical characteristic of both the substrate and the layer of soiling itself, i.e. the
chemical or phase composition and their microscopic characteristics (e.g. thickness, binding
to substrate, cracks, porosity, etc.) will be provided by a wide range of optical examination
methods supplemented with analytical methods that focus on the elemental and substance
composition. Visual assessment, examination under a stereo magnifying glass or under a
USB microscope is used to assess changes in macro-scope - these examinations are
ordinarily carried out in situ. More exact information, in particular with regard to assessing
changes in the substrate in micro-scope will be provided by microscopic methods on
collected micro samples, processed into cross sections or thin sections (Fig. 1). Microscopic
methods include optical microscopy in polarized light (PLM) and in non-polarized light,
scanning electron microscopy used independently for the study of changes in surface
(change of the thickness of the layer of impurities, changes in the distribution of impurities,
creation of cracks, etc.), but also for the determination of substance composition, in which
case microscopy is used in connection with energy-dispersing X-ray analysis (SEM-EDS).
This method is designed particularly for characterizing the compositions of the layer of
deposits, the effect of cleaning, chemical changes on the surface after the use of the
respective cleaning method (e.g. in the case of chemical cleaning, or the removal of crusts
or of coats of paint etc.). The methods that can be used in these cases include also X-ray
diffraction, or spectroscopic ones such as mid-FTIR and Raman spectroscopies also
coupled to microscopy (Martínez-Arkarazo 2008, Potgieter-Vermaak 2005).
Additional analyses which can contribute to the knowledge of the state of the substrate
underneath the soiling include the measurement of drilling resistance and ultrasound
transmission. These methods can discover for instance a possible decrease of the firmness
of the substrate underneath the crust, or in the layer near the surface, which can influence
the planning of a conservation intervention (e.g. pre-consolidation before cleaning, etc.).
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Fig. 1: Optical microscopy - thin section, deposition of soiling on different sandstones. On
the thin section we can see how deep into the substrate the impurities had penetrated, or if
they close the porous structure of the substrate.
2.2. Selected methods of evaluating cleaning trials
Each cleaning must be preceded by trials on a small surface of historical material. The
results of these trials can be evaluated in the following manner:
Visual inspection: Visual inspection is the essential and indispensable tool for inspecting
the results of cleaning. It provides a relatively clear idea of the resulting aesthetic effect of
the cleaned surface, and based on trials, the most suitable intensity can be chosen from the
perspective of the resulting aesthetic impression. Although visual inspection, possibly
accompanied by the use of simple magnifying tools, such as magnifying glass, photography
and macrophotography, can discover more significant damage to the substrate caused
during cleaning, it is still often insufficient for the evaluation of all possible risk to the
substrate.
Optical surface microscopy: Optical surface microscopy is a highly suitable and widely
available tool for examining the effects of cleaning on the surface of the substrate. It can be
carried out either in non-destructive manner using an USB microscope that allows
sufficient magnification and that can store images, or in situ using a modified field
microscope. Another possibility is to collect samples and examine them using an optical
microscope. Stationary devices provide better-quality images and allow for greater
magnification, or for examination in various types of lighting conditions. Ideal information
is provided by means of comparison photography from before and after cleaning from the
same location, or images of partial cleaning.
Optical Microscopy of a Cross Section: Another tool used to examine the effect of
cleaning on the substrate is optical microscopy of a cross section. This method requires the
collection of a representative sample of the surface, and it provides a reasonably good idea
of the success of cleaning, and with larger magnification, it is possible to discover also
possible negative effects on the substrate, which could become source of problems in the
future. The success rate of this method depends to a large extent on the quality of the
collected sample and of the executed cross section. It is rather a supplementary method of
assessment.
Optical Microscopy of a Thin Section: Very valuable information about the sensitivity of
cleaning and about the interaction with the substrate can be provided by microscopy of a
thin section. Thanks to very good readability, which is significantly higher than in the case
of a cross section, relatively clear conclusions can be drawn from the examination. The thin
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section can also be subjected to polarizing microscopy, which broadens the range of
information acquired. The disadvantage of this method is the difficulty of preparing the
sample, which needs to be prepared at a specialized workspace and is costly.
Fig. 2: Stereoscopic microscope. Thin section - Yellow sandstone - left half of both figures
after cleaning by laser - even after cleaning, there are remains of the patina
on the surface.
Surface electron microscopy – SEM: Surface electron microscopy provides a detailed look
at the changes in the surface morphology. With smaller magnification, the changes can be
examined in the overall appearance of the surface, and with greater magnification it is
possible to get to the level of the individual grains. It is one of the best tools for evaluating
the effect of cleaning on the substrate event though it is still necessary to compare the
results with other methods of examination.
Fig. 3: SEM; magnified 200x. left: uncleaned; middle: micro-sandblasting; right: laser
cleaning. This examination allows for the monitoring of changes in surface morphology.
These changes have a fundamental effect on the behaviours of the surface in the future.
Elemental Analysis SEM –EDS: Some electron microscopes are equipped with a tool that
allows for elemental analysis through energy-dispersive by an X-ray detector. The tool can
be used for the analysis of the individual points, as well as on the entire monitored surface.
Thanks to elemental analysis, it is possible to monitor the elemental composition of the
deposits, or changes in elemental composition before and after cleaning, and to use this tool
as a supplementary analysis for the evaluation of the sensitivity of the cleaning process and
for characterizing the deposits.
2.3. Examining physical properties after cleaning
Measuring the water uptake of cleaned surfaces: It is common practice to assess the effect
of cleaning on the basis of determining the physical-mechanical characteristics of the
surface and their changes after cleaning. It concerns in particular the determination of the
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
capillary activity of the surface, i.e. of the capillary water uptake, which is essential for the
restoration of natural properties that concern the transport of water and water vapour
through the material. Their improvements further influence the successful implementation
of further restoration interventions (e.g. consolidation, filling, retouches, etc.). It is carried
out by determining the coefficient of capillary water uptake on laboratory samples of
regular shape (e.g. drilling cores), or more often in situ using the Karsten tube by
comparing the capillary flow or coefficient of capillary water uptake before and after
cleaning on the given location (or by comparing to other cleaning methods and water
uptakes on the fracture surface). Another significant characteristic is the assessment of
water-vapour permeability and its changes after cleaning. However, this method cannot be
implemented without the collection of a sufficiently large quantity of samples, for which
reason it is not used in practice.
Peeling test: The so-called peeling test can be carried out in order to determine surface
cohesion after cleaning. This test measures the cohesion of material in its lower layers,
which is expressed as the quantity of material that remains stuck to adhesive tape The test
entails the application of both sided adhesive tape onto the substrate and in measuring the
differences in weight before and after the application. This test is also a comparison test and
it may provide information about a possible change in surface cohesion after cleaning
(Drdácký 2012).
3. Conclusion
The presented methods do not, by far, include all the possibilities of assessing a cleaned
surface. The methods had been selected with regard to their contribution to the assessment
of the results of cleaning, and they are also limited by the author’s experience with
assessing cleaning trials. As far as optical methods are concerned, electron microscopy of a
cross section or a thin section was omitted, even though it can surely provide important
information. As regards other methods, certain information could be provided by measuring
the morphology of the surface by means of a needle profilometer, or directly by a machine
for the measurement of surface topography by means of a holographic microscope, the
possibilities of which are currently being tested. Interesting comparison information could
possibly be provided by a sensitive 3D scanner, which would scan the surface before and
after cleaning. The limit of all these methods is that, as opposed to optical methods, the
information about changes in, or loss of material is not closely linked to the possibility of
examining to what extent this loss is limited to impurities, and to what extent it affects the
original substrate. It is obvious that the examination and comparison of various
instrumental methods which could provide relevant information about the effect of cleaning
on the substrate is not concluded yet, nor can it be with regard to the development of new
analytical methods.
Acknowledgements
This contribution is based on the findings and experience gained on the basis of a grant of
the Ministry of Culture of the Czech Republic “Conditions and Requirements of
Compatible Care for Porous Inorganic Materials” DF12P01OVV018.
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References
Andrew, C.A., Young, M.E. and Tonge, K.H., 1994, Stone Cleaning: A Guide for
Practitioners, Historic Scotland and The Robert Gordon University.
ISBN 0 7480 0874 8, 122pp.
Ashurst, N., (1994), Cleaning historic buildings, Donehead, ISBN 18-733-9412-8, 258pp
Drdácký, M., Lesák, J., Rescic, S., Slížková, Z., Tiano, P., and Valach, J., 2012,
Standardization of peeling tests for assessing the cohesion and consolidation
characteristics of historic stone surfaces, Materials and Structures, 45 (4), 505-520.
Ďoubal, J., 2014, Research into the methods of Cleaning the Silicate Sandstones Used for
Historical Monuments, Journal of Architectural Conservation, 20 (2), 123-138.
Fassina, V., 1994, General criteria for the cleaning of stone: Theoretical aspects and
methodology of application. In Stone Material in Monuments: Diagnosis and
Conservation, Mario Adda (ed.), Heraklion, Crete, Scuola universitaria C.U.M.
conservazione dei monumenti, 131–138.
Goreczky, L. and Hoffmann, M. 1997, WTA 3-9-95-D: Bewertung von gereinigten
Werksein – Oberflächen=Assessment of cleaned stone surfaces. Baierbrunn: WTA
publications.
Hauff, G., Kozub, P. and D’Ham, G., 2008, Which cleaning method is the most appropriate
one? A systematic approach to the assessment of cleaning test panels in 11th
International Congress on Deterioration and Conservation of Stone, Niemcewicz
P. (red.), Torun, Poland, Uniwersytetu Mikołaja Kopernika, 381–388 .
Kapsalas, P., Maravelaki-Kalaitzaki, P., Zervakis, M., Delegou, E. T. and Moropoulou, A.,
2007, Optical inspection for quantification of decay on stone surfaces. NDT & E
International, 40, 2–11.
Martínez-Arkarazo, I., Sarmiento, A., Usobiaga, A., Angulo, M., Etxebarria, N., and
Madariaga, J.M., 2007, Thermodynamic and Raman spectroscopic speciation to
define the operating conditions of an innovative cleaning treatment for carbonated
stones based on the use of ion exchangers, Talanta, 75(2), 511-516.
Normandin, K.C., Weiss, N.R. and Slatonm, D., (2005), Cleaning techniques in
conservation practice, Donhead, ISBN 978-187-3394-748, 146pp.
Potgieter-Vermaak, S.S., Godoi, R. H. M., Van Grieken, R., Potgieter, J.H. , Oujja, M.,
and Castillejo, M., 2005, Micro-structural characterization of black crust and laser
cleaning of building stones by micro-Raman and SEM techniques, Spectrochimica
Acta Part A: Molecular and Biomolecular Spectroscopy, 61(11-12), 2460-2467.
Verges-Belmin, V., 1996, Towards a definition of common evaluation criteria for the
cleaning of porous building materials, Science and Technology for Cultural
Heritage, 5, 69-83.
Werner, M., 1991, Research on cleaning methods applied to historical stone monuments in
Science, technology, and European cultural heritage: proceedings of the European
symposium. Boston: Published for the Commission of the European Communities
by Butterworth-Heinemann Publishers, 688–691.
736
THE NATURAL WEATHERING OF AN ARTIFICIALLY INDUCED
CALCIUM OXALATE PATINA ON SOFT LIMESTONE
T. Dreyfuss1* and J. Cassar1
Abstract
This paper focuses on the effects of natural weathering on Globigerina Limestone (Malta)
which was treated with ammonium oxalate to produce a calcium oxalate surface layer. This
study includes the first two phases of a larger research programme. Laboratory samples
were considered first. These were treated and tested in a controlled environment (Phase 1).
Identical samples sets were prepared for Phase 2. These were treated in situ and exposed to
site conditions for the period of one year. In an attempt to simulate site conditions, for both
Phase 1 and Phase 2 samples, the limestone was contaminated with soluble salts before
treatment took place. These included three separate types; sodium chloride, sodium sulfate
and sodium nitrate. Desalinated samples were also included in the study. Scanning Electron
Microscopy (SEM) was carried out on the Phase 1 samples while Drilling Resistance
Measurement System (DRMS) was carried out on the samples of both phases. This paper
focuses on the results from the SEM and correlates these with those results from the DRMS
in light of the influence of natural weathering on an artificial calcium oxalate layer, induced
in the presence of soluble salts.
Keywords: oxalates, consolidation, protection, limestone, treatment durability
1. Introduction
The Maltese Islands, a small island archipelago measuring 316 square kilometres and
located 93km south of Sicily and 288km north of Africa have a large collection of historic
limestone buildings and monuments that span the millennia. These are built in Maltese
Globigerina Limestone - a highly porous calcareous stone which naturally deteriorates in an
environment that is exposed to both water and soluble salts. These buildings and
monuments inevitably require conservation action at certain points in their lifetime which
may include consolidation and/or protective treatments. Many of the historic stone edifices
(pre-1850s) in Malta and Gozo were built without the insertion of a damp proof course,
thus allowing water entry in the form of rising damp together with any soluble salts present.
Additionally, wall construction generally utilised soil infill, usually salt laden, between two
masonry wall leaves. The island environment further enhances salt contamination through
wind driven and aerosol borne salts. The context is therefore a porous limestone which has
a continual supply of water and soluble salts.
1
T. Dreyfuss* and J. Cassar
Department of Conservation and Built Heritage, Faculty for the Built Environment,
University of Malta, Malta
tdrey01@um.edu.mt
* corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Consolidation of exposed Globigerina Limestone which has lost cohesion, manifested as
powdering/ granular disintegration, must therefore take this context into account. The aim
must be to bridge the loose powder/ grains together and to the sound stone beneath with a
compatible material that retains both the water and salt transport properties of the stone that
is being consolidated. Ammonium oxalate treatment on calcareous stone has been studied
as a surface treatment providing protection from acid attack together with possible
consolidating properties (Matteini et al., 1994; Matteini 2007), even on Globigerina
Limestone (Croveri 2004; Mifsud et al., 2006; Dreyfuss et al., 2012 and 2013), which to
date has revealed promising results suggesting its potential use in this respect. The actual
study of ammonium oxalate treatment on Globigerina Limestone in situ and its relationship
with soluble salts present in the stone was the next step. This was to take this research to a
point where the actions and mechanisms of ammonium oxalate treatment are understood in
terms of the parameters presented by a historical building. The two parameters identified
here are the presence of salts and site exposure whilst stone pathology is considered in other
parts of the larger research project (Phase 3). To this end, the parameters included here
were desalinated versus salt contaminated conditions and controlled versus uncontrolled
environments.
2. Methodology
2.1. Globigerina Limestone
The material considered, Globigerina Limestone, of the franka type (Cassar 2004), is a
fine-grained limestone, sedimentary in origin with few to abundant fossils including
planktonic and benthonic foraminifera especially globigerinae which is from where it gets
its name. It is primarily composed of calcium carbonate in the form of calcite crystals
cemented together by non-crystalline calcium carbonate. Besides calcite, Globigerina
Limestone also contains clay minerals, quartz, feldspars, apatite and glauconite. A large
part of the clay minerals consists of kaolinite with smectite, illite-smectite, illite and
vermiculite also being present (Cassar 2002). The porosity is high and varies between 24%
(Cassar 2004) and 41% (Cassar et al., 2001) whilst the majority of pores ≤ 4 μm
(Vannucci et al., 1994).
2.2. Sample preparation
The samples were prepared as 50×50×10 mm³ (for the SEM samples) and 50×50×50 mm³
(for the DRMS samples) cut from stone blocks (approximately w=410 mm × D=230 mm ×
H=267 mm) obtained from the quarry area known as Ta’ l-Iklin in Qrendi (coordinates
51,500; 66,500) at a depth of 12 m below ground level. The horizontal (downward facing
direction) bedding plane was noted in all cases and retained as the treatment and testing
surface for all samples.
The samples consisted of quarry samples with different salt contents, namely desalinated
samples, samples contaminated respectively with saturated solutions of sodium chloride,
sodium sulfate and sodium nitrate. Desalination was carried out by immersion of the
samples in distilled water, repeatedly changing the water until its conductivity revealed that
soluble salts were no longer present (≤3 μS/cm). All of the samples were thus desalinated
and then oven dried for 24 hours at a temperature of 105°C then cooled in the laboratory to
constant mass at 20°C room temperature. One fourth of the samples were then retained to
represent the desalinated type samples, while the remaining samples were divided into three
sets and each set was salinated with a saturated solution of sodium chloride, sodium sulfate
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
and sodium nitrate respectively by immersion for 2 hours. Following immersion, the
samples were air dried.
2.3. Ammonium oxalate treatment
Treatment was carried out to all sides of the samples using a 5% ammonium oxalate
monohydrate solution applied in a cellulose pulp poultice for 24 hours at 20°C; conditions
were 74% RH in the case of the laboratory samples and at 26°C, 70% RH on site.
Following treatment the poultice was manually removed and the samples left to air dry. The
excess pulp was brushed off with a soft nylon brush. Untreated samples were prepared for
all treated sample types.
2.4. Site exposure
The one-year site exposure of the Phase 2 samples included temperatures ranging from
5.6°C to 37.5°C, a total rainfall of 350.7 mm, 3059.4 hours of sunshine, an average Relative
Humidity of 72.4%, 35 days with thunderstorms, 12 days with hail, 4 days with fog and 4
days with “dust haze”. The samples were retrieved after one year for DRMS testing which
was carried out in a laboratory.
3. Testing
The Scanning Electron Microscopy (SEM) samples measured 10×10×10 mm³ and were cut
out of the larger 50×50×10 mm³ samples using a surgical blade. The treated and untreated
samples were examined under identical magnifications for each sample type, for direct
comparison at ×100 and ×2000. The surface morphology, surface topography, surface
features, surface texture, and crystal arrangement were analysed.
Drilling Resistance Measurement System (DRMS) was carried out on the 50×50×50 mm³
cube samples. The depth of the calcium oxalate layer was evaluated through the Drilling
Resistance Measurement System (DRMS). Desalination was carried out before DRMS
testing for all samples that were treated with ammonium oxalate in the presence of a soluble
salt. In the case of untreated samples however, salt free and salinated types were tested.
4. Results & discussion
The DRMS results for the Phase 1 samples revealed a treatment depth of up to 1.60 mm for
samples treated in a salt free environment and 0.70 mm - 1.00 mm in the case of samples
treated in the presence of the soluble salts considered. The depths for the Phase 2 samples
were 0.80 mm in the first instance and 0.70 mm - 0.90 mm in the second (Dreyfuss et al., in
preparation). Therefore, while salt-free conditions induced deeper formations with
treatment (1.60 mm) when compared to salinated conditions (0.70 mm-1.00 mm), this
depth was reduced (from 1.60 mm to 0.80 mm) over the year of site exposure which
indicates that the calcium oxalate formed in this sample type was being weathered away.
Conversely, the depths achieved with treatment in salt-contaminated conditions (0.70mm1.00 mm) were still maintained one year after exposure (0.70 mm-0.90 mm), possibly
suggesting improved durability.
The maximum drilling resistances at the corresponding depths of treatment were also
recorded. The results showed that the increased depths of 1.60 mm in the samples treated in
a salt-free environment were coupled with reduced values of drilling resistance (13.52 N)
when compared to those samples treated in the presence of soluble salts which had
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
shallower treatment depths (0.70 mm-1.0 mm) but a greater drilling resistance (14.79 N21.62 N), (Dreyfuss et al., in preparation).This implies that the newly formed calcium
oxalate in the salt contaminated samples has improved strength characteristics when
compared to the calcium oxalate formed in salt-free environments. These DRMS results
were further analysed and correlated to SEM observations as discussed below.
For SEM anlysis a Merlin FESEM with Carl Zeiss optics and Gemini II column (s/n: 4216)
was used. In the SEM images of the desalinated untreated samples at ×100, individual
calcite crystals/granules were observed together with globigerinae and other fossils. In the
treated samples, the microfossils were still visible and the previously individual
crystals/granules were seen to be more compact. These findings suggest that treatment
results in an improved and more compact surface texture without blocking the
globigerinae/fossils. At higher magnifications (×2000) the desalinated untreated samples
showed that individual crystals/granules (A) were clearly distinguishable, (Fig. 1). In the
treated samples (Fig. 2), the newly formed calcium oxalate was observed to take to form of
flat crystals/plates which were arranged in a layered arrangement/stacked parallel to the
sample surface (B). This arrangement is schematically illustrated in Fig. 4.
Fig. 1: SEM image (x 2000) for desalinated untreated laboratory sample.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 2: SEM image (x 2000) for desalinated treated laboratory sample.
In the untreated salt contaminated samples, salt crystals were seen to completely cover the
sample surface in the sodium chloride and sodium nitrate contaminated samples
respectively. Sodium sulfate was also seen to substantially cover the sample surface
although to a lesser extent since globigerinae were still visible after salt contamination.
These findings confirm that salt contamination has a “pore blocking/coating” effect which
probably inhibits the ammonium oxalate from penetrating deeper resulting in shallower
calcium oxalate formations as observed in the DRMS results above.
After treatment, the amount of surface salt was seen to be greatly reduced in the sodium
chloride and sodium sulfate contaminated sample types. The reduction in surface salt in the
sodium nitrate contaminated samples was seen to occur to a lesser extent (C in Fig. 3)
confirming the blocking/coating behaviour of this salt, also seen in the results from the
DRMS where surface salt concentrations were still present after one year of site exposure
(Dreyfuss et al., in preparation). These conclusions indicate a reduction in salt content
during treatment probably through the water-based poultice.
The morphology observed in the treated, salt contaminated samples showed calcium
oxalate to be formed in a different configuration to that developed in the desalinated
samples. The calcium oxalate was observed as individual crystals (not layered) which were
organised in a vertical arrangement (not horizontal), predominantly perpendicular (not
parallel) to the sample surface (D in Fig. 3). This configuration, which is schematically
illustrated in Figure 5 may be understood to withstand erosion and natural weathering better
than the arrangement of calcium oxalate formed in salt-free conditions (Figure 4), where
the configuration may be more susceptible to erosion. The difference between the newly
formed calcium oxalate crystal orientation in relation to the salt conditions during treatment
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
is currently being investigated further. This physical difference in calcium oxalate crystal
orientation may account for the reduced depths, the increased drilling resistance and the
improved durability achieved in salt laden samples.
Fig. 3: SEM image (x 2000) for sodium nitrate contaminated treated laboratory sample.
Figure 4: Schematic illustration of the whewellite formed in salt free environments.
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Figure 5: Schematic illustration of the whewellite formed in the presence of soluble salts.
5. Conclusions
When compared to treated desalinated samples of the same type, the treated salt
contaminated samples recorded shallower calcium oxalate depths and higher values for the
drilling resistance. This resulted in an increased durability during the one year of site
exposure, after which the depth of induced “hardness” decreased from a range of 0.70 mm
to 1.0 mm to a range of 0.70 mm to 0.90 mm. In the desalinated samples this decreased
from 1.60 mm to 0.80 mm. This difference was explained through the SEM images where
calcium oxalate was seen to form in horizontally stacked layers, parallel to the sample
profile, in the desalinated samples, the physical configuration of which is probably
differently susceptible to erosion. The calcium oxalate formed in the presence of soluble
salts was arranged in a vertical manner, perpendicular to the sample profile, creating an
interlocked network of whewellite crystals. Further research into the reasons for this
varying orientation, as well as treatment and testing of exposed historic limestone is
currently ongoing.
Acknowledgement
The authors widely appreciate the fact that this research work is being funded by the
REACH HIGH Scholars Programme – Post-Doctoral Grants. The grant is part-financed by
the European Union, Operational Programme II — Cohesion Policy 2014- 2020 Investing
in human capital to create more opportunities and promote the wellbeing of society European Social Fund. Furthermore, the authors would like to express the gratitude
torwards the Department of Metallurgy and Materials Engineering, Faculty of Engineering,
University of Malta for carrying out the SEM analysis under the direction of Ing.
J. Camilleri funded under ERDF (Malta) through the project: ‘‘Developing an
Interdisciplinary Material Testing and Rapid Prototyping R&D Facility (Ref. no. 012)’’.
Further thanks also to Dr Silvia Rescic at the CNR-ICVBC (Consiglio Nazionale delle
Richerche Istituto per la Conservazione e Valorizzazione dei Beni Culturali) in Florence,
Italy for assistancing us with the Drilling Resistance Measurements was carried out under
the direction of.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
References
Matteini, M., Moles, A., Giovannoni, S., (1994). Calcium oxalate as a protective mineral
system for wall paintings: methodology and analyses. In: 3rd International
Symposium on the Conservation of Monuments in the Mediterranean Basin,
Venice, Italy, pgs 155-162.
Matteini, M., (2007). Conservation of stone monuments and artefacts: new possibilities
offered by the ammonium oxalate based treatment. http://www.euartech.org/files/CUBA/MATTEINI.pdf
Croveri, P., (2004). Metodologie di consolidamento di materiali lapidei nell’area
Mediterraneo: La Globigerina Limestone maltese – degrado e consolidamento.
Dottorato di Ricerca in Scienza per la Conservazione dei Beni Culturali XVII
cicolo, Universita degli Studi di Firenze, unpublished.
Mifsud, T., Cassar, J., (2006). The treatment of weathered Globigerina Limestone: the
surface conversion of calcium carbonate to calcium oxalate. Proceedings of
Heritage, Weathering and Conservation, Madrid, pgs 727-734.
Dreyfuss, T., Cassar, J., (2012). The performance of an induced calcium oxalate surface on
Globigerina Limestone. In: 12th International Congress on the Deterioration and
Conservation of Stone, New York.
Dreyfuss, T., Cassar., J., (2013). Ammonium oxalate treatment application in the presence
of soluble salts: laboratory results on soft limestone. Built Heritage 2013
Monitoring Conservation Management, Milan, pgs 403-412.
Cassar, J., 2002. Deterioration of the Globigerina Limestone of the Maltese Islands. In:
Siegesmund, S., Weiss, T., and Vollbrecht, A. (eds). Natural Stone, Weathering
Phenomena, Conservation Strategies and Case Studies, Geological Society
London, London, 205, pgs 33-49.
Cassar, J., (2004). Composition and property data of Malta’s building stone for the
construction of a database. Architectural and Sculptural Stone in Cultural
Landscape, R. Prikril, Siegl, P. (Eds), The Karolinium Press, pgs 11-28.
Cassar, J., Vannucci, S., 2001. Petrographical and chemical research on the stone of the
megalithic temples. In: Malta Archaeological Review, 5, pgs 40-45.
Vannucci, S., Alessandrini, G., Cassar, J., Tampone, G., Vannucci, M.L., 1994. Templi
megalitici Preistorici delle isole Maltesi: cause e processi di degradazione del
Globigerina Limestone. In: Fassina, V,. Zezza, F., (Eds), 3rd International
Symposium, “La Conservazione dei Monumenti nel Bacino del Mediterraneo,
Venezia, Italia, pgs 555-565.
Dreyfuss, T., Cassar, J., (in preparation). Consolidation of a soft and porous limestone:
from the laboratory to the field.
744
A COMPARISON OF THREE METHODS OF CONSOLIDATION
FOR CLACEROUS MIXED STONES
J. Espinosa-Gaitán1* and A. Martín-Chicano2
Abstract
In this paper, three stone conservation treatments (alcoxisilanes (TEOS), a combination of
nanolime and TEOS, and microbial carbonate precipitation) have been studied on Puerto
stone, a biocalcarenite with a high presence of coarse quartz grains, high porosity and low
cementation. Several tests were undertaken in order to evaluate and compare the
effectiveness of these treatments, according to EU standards where possible, and following
the most commonly used procedures found in the literature. Changes in colour and
appearance, porosity and hydric properties (water absorption, water desorption, water
vapour permeability) of the stone caused by treatments were measured, in order to
determine their compatibility with the stone. The performance of the products was
evaluated using various tests, such as microdrilling (DRMS), measurement of ultrasound
pulse velocity (UPV), and peeling test. In addition to that, samples were analysed using
scanning electron microscopy (SEM/EDS), providing graphic information of how
consolidants were deposited on the stone surface. This first set of results show that the
combination of nanolime and TEOS offers the best performance as stone consolidant.
Keywords: stone consolidation, TEOS, nanolime, biomineralization, Puerto stone
1. Introduction
There is no doubt that consolidation is one of the most important actions to be taken when
approaching the conservation of built heritage. Building materials are exposed to a broad
variety of elements which may alter their nature, making them weaker and more susceptible
to decay, endangering the structure (Young et al. 1999, Wheeler 2005, Doehne &Price.
2010). Many solutions have been offered from ancient times, using different substances
with the goal of restoring materials their original properties. Stones have been treated with
beeswax, plants extracts or limewash, and a great variety of synthetic substances, resulting
in different degrees of success. Consolidation aims at restoring cohesion, compactness and
mechanic properties to aged stone, without significantly altering other properties such as
colour and hydric properties.
This work aims to determine what consolidant is more suitable for a calcareous mixed stone
(Puerto stone) that was used as building material in several monuments in SW Spain. There
are several stone consolidants commercially available, although not all of them are used
1
J. Espinosa-Gaitán*
Andalusian Institute of Cultural Heritage (IAPH), Seville, Spain
jesus.espinosa@juntadeandalucia.es
2
A. Martín-Chicano
University of Granada, Spain
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
with the same frequency for different reasons. It was important for the study to test
consolidation products that were easy to apply, available, affordable, and with low or null
toxicity. After carrying out a characterisation of the stone, three consolidation treatments
were considered to be tested: alcoxisilanes, nanolime, and biomineralization. Alcoxisilane
based consolidants are the most popular ones. These products are applied diluted in a
volatile solvent, and once the solvent evaporates a sol-gel reaction occurs, leading to
polymerisation inside the pores of the stone, consolidating the damaged material (Wheeler
2005). These products are easy to use, affordable and fairly efficient, in spite of presenting
some problems such as cracking of the silica layer, or incompatibilities when there is
presence of clay or carbonates in the stone. Lime is a natural choice for carbonate stones,
although its low penetration rate is an issue, a problem that was solved with the use of
nanolime. Due to their size, nanolime particles are able to penetrate more deeply into the
stone matrix. Its use is based on the reaction of calcium hydroxide with atmospheric carbon
dioxide in presence of water, resulting in precipitation of calcium carbonate inside the
damaged stone. A combination of alcoxisilanes and nanolime has been proposed as a
consolidation method with better results than the two methods separately (Ziegenbalg and
Piaszczynski 2012). The third tested method consists of inducing the deposition of a
calcium carbonate layer on the surface of the stone, generated by some microorganisms
under the right conditions. Two approaches to this method have been proposed, one takes
advantage of the existing microbiota in the stone (Jiménez-López et al 2007), applying only
a nutrient solution to the damaged stone, whereas a nutrient solution containing bacteria is
sprayed onto the surface of the stone in the other method. The three consolidation methods
were tested in the laboratory.
2. Experimental: Material and Methods
2.1. Stone
The material subject of the present study is Puerto stone, a biocalcarenite with a high
presence of coarse quartz grains (30-40%), high porosity (>30%) and low cementation. It is
a very soft and crumbly rock. This stone is extracted from the San Cristobal quarries, in
Cádiz, SW Spain (Jiménez-Pintor et al. 2002), and has been extensively used in the
construction of several monuments in the area, such as the Cathedral of Seville, Cathedral
and Cartuja of Jerez, etc. It is an Upper Miocene ivory colour biosparite (Folk 1965), with a
large proportion of clastic particles (30-40%), basically formed of coarse quartz grains and
microfossils (bryozoans, algae and foraminifera). The cement of the rock is sparry calcite,
representing 50-60% in the most compact varieties. This is a highly porous stone with an
open porosity of about 35%, predominantly macropores.
Samples for this study were obtained from two fragments of decontextualized ashlars found
in the Cartuja de Jerez, belonging to a demolished part of the building. This fact is very
important for the study, because samples present the same characteristics and degree of
alteration than the actual stone in the building, making results even more relevant than if
samples had been obtained from freshly extracted stone from the quarry.
Two types of test specimens were obtained from the ashlars, planar samples of 4×4×2 cm,
and cubic samples of 4 cm edge according to the recommendations of European standards
for testing materials of Architectural Heritage (CEN/TC-346 Conservation of Cultural
Property: Test methods). The stone in this monument is deteriorating mainly on its surface
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
by granular disaggregation, sanding, scaling, loss of cement, biological attack,
efflorescence, and cracks (ICOMOS-ICMS, 2008), so a consolidation process is needed.
2.2. Treatments and application procedure
The method of application of treatments replicate the way these products are applied in situ,
so results could relate as much as possible to a work situation rather than to a laboratory
environment (Young et al. 1999, Theoulakis et al. 2008). Application with flat brush was
chosen, being one of the most widespread in the field of conservation and restoration.
Cubic samples were treated on all sides, while planar samples were treated only on one of
the squared sides, depending of the type of test to be performed.
The treatments and mode of application are:
W (SILRES® BS OH 100 (Wacker)): Ethyl silicate as supplied by the manufacturer. Three
applications with a flat brush with a 15 min interval between each application under
laboratory conditions (T=23±2°C and RH=50%±5%).
NR+W (NANORESTORE® (C.T.S) + SILRES® BS OH 100 (Wacker)): Nanorestore is
supplied as a dispersion of nanolime particles in isopropyl alcohol. Application procedure
as follows: an ethanol:water solution (1:1 v/v) solution was applied to samples in order to
facilitate the absorption of the consolidant. Nanorestore was applied afterwards with a flat
brush, three times with a 15 min. interval. 24 hours later SILRES OH was applied in the
same way.
KBYO I and KBYO II (KBYO Biological): Nutrient aqueous solution. I and II refers to
the same product obtained under two different fabrication methods. Samples were treated at
the manufacturer’s facilities, according to the method developed and optimised there.
2.3. Laboratory tests
The methodology for assessing the efficiency of the treatment was based on the study of
issues related to compatibility and effectiveness of treatment (The Charter of Krakow,
2000). Samples were cleaned and left to dry in the oven for 24 hours at 60°C. Treatments
were applied according to the method previously described, and samples were left on a rack
at laboratory conditions for three months. UNE-CEN standard tests for conservation of
cultural heritage were performed when possible, following procedures for natural stone
when unavailable. Otherwise, proposed tests in literature were carried out.
2.3.1. Compatibility
Measurement of colour was done according to UNE-EN 15886 procedure, with a Minolta
CR-200 colorimeter (diffused lighting, 0° viewing angle, specular component included, and
D65 standard illuminant). Results are expressed according to the CIE L*a*b* colour space
(CIELAB 1976), that measures three aspects of the object chromaticity. The parameter ∆E*
(∆E* = √(∆L*)2+(∆a*)2+(∆b*)2) provides an idea of global colour change by the difference
in values before and after treatment. When its value exceeds 5 it is assumed that change is
perceptible by the human eye (Delgado-Rodrigues and Grossi 2007, Pérez-Ema et al.
2013).
The change in Open porosity values was obtained following the procedure described in
UNE-EN 1936: 2006, measuring water content under pressure. Determination of drying
properties test was performed according to EN 16322:2013-1 standard. The test is
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
performed on cubic specimens placed on a grid, so that evaporation affects all sides
equally. Water absorption by capillarity was performed following standard UNE-EN
15801: 2010, also on cubic specimens. Water vapour permeability changes (WVP) were
evaluated following standard UNE-EN 15803:2010. Planar samples were used for this test.
Samples were fitted to the lid of a plastic container of similar dimensions, half filled with
silica gel for dry test mode, or a saturated KNO3 solution for wet test mode. Water vapour
may only go through the stone samples, so the lid is sealed with Permagum, a waterproof
sealant.
2.3.2. Effectiveness
The ultrasound pulse velocity test was carried out following the UNE-EN14579: 2005
standard. This technique has been successfully used in determining the effectiveness of
stone consolidation treatments (Sebastián et al. 1999, Pérez-Ema et al. 2013). The
equipment was a Ultrasonic Steinkamp BP-7 tester, with a wave frequency of 40 MHz.
Measurements were determined in the three perpendicular directions of the specimens, in
order to avoid any anisotropy. Values from 15 samples in total were obtained, and the
media of each group of specimens was calculated.
The Peeling tape test was performed in order to establish the granular cohesion degree of
the stone surface and the treatments effects. This test is a method for evaluating the
adhesion of a coating to a substrate. A pressure-sensitive tape is applied to an area of the
surface. In this case recommendations suggested by Drdáckŷ et al. (2012) were followed,
due to the absence of published standards. This process was carried out on two sides of
each sample, three strips per side, and the average was calculated for each type-group of
specimens.
Finally, the DRMS test (Drilling Resistance Measurement System) was performed, in order
to measure the resistance of the stone to be perforated with a drill, keeping a constant
rotation speed and degree of penetration of the drill throughout the test duration. The
equipment was a DRMS Cordless Version 4 device, manufactured by SINT Technology,
with a 5 mm diameter drill. Test conditions were established at 300 rpm rotational speed,
20mm/min of penetration rate, and 20 mm penetration depth. The test was performed on
one specimen of each group, making three perforations on two opposite sides of each
specimen.
In addition, surface-coating characteristics, distribution of the treatments, and microtexture
of stone before and after being treated with consolidants were identified with a Scanning
Electronic Microscopy (SEM) using a JEOL JSM-5600LV microscope with a wolfram
filament and an X ray energy dispersion microanalysis system (EDS) Inca x-sight from
Oxford Instrument.
3. Results and discussion
3.1. Compatibility
Hydric properties results indicate that Puerto stone has a water accessible porosity of 33%,
presenting a high water absorption rate (4cm high samples reach saturation in 2.5 minutes).
Drying rate is also high, about 90% of water content evaporates in one day. This might be
caused by its open porosity which makes absorption and evaporation of water fairly easy.
Tab. 1 presents changes in water content under pressure and open porosity for treated and
untreated samples.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Water content (Wmax) and open porosity values.
Property
Untreated NR+W
W
KBYO I KBYO II
Wmax under vacuum (weight-%)
18.37
14.26
16.21
18.05
17.25
Open porosity (volume-%)
33.41
26.95
29.71
32.47
31.42
There is a general decrease in open porosity values and water content, higher for the NR+W
treated sample, which may be caused by the closure of smaller pores by the action of
consolidants. These samples show the same behaviour in the capillary absorption test,
reaching saturation at an earlier stage than the other treatments. The drying rate is not
altered, and samples lost about 90% of water in a day. The water vapour permeability test
showed little change in the values of the permeability coefficient before and after treatment,
very similar in all cases.
Variation in Colour is presented in Tab. 2. A value greater than 5 for ∆E* means that the
change in colour is visible for the human eye. Results show that none of the treatments alter
this property significantly.
Tab. 2: Change in colour parameters.
Treatment
∆L*
∆a*
∆b*
∆E*
W
-1.76
0.43
1.55
2.38
NR+W
-0.66
0.50
1.84
2.02
KBYO I
-0.22
0.26
1.28
1.32
KBYO II
-1.64
0.41
1.82
2.48
3.2. Effectiveness
Results obtained by the Ultrasound Pulse Velocity show higher UPV values for all treated
samples compared to untreated specimens. A higher velocity means more compactness, and
it is related to a decrease in open porosity. This is very clear for W and NR+W treatments,
but not so for KBYO, where open porosity values were similar to those for untreated stone.
The Drilling resistance measurement (DRMS) test usually offers consistent results for
homogeneous rocks, but not for polymineral, heterogeneous ones, like Puerto stone. The
resistance to perforation varied greatly for the same sample as the test was being carried
out, with a great value dispersion as a result of the variety of minerals and compactness
within the rock, which made very difficult to quantify this property. In spite of this
limitation, an index of global resistance “F” (Newton) for each group of samples was
determined and its standard deviation (σ) was established, considering the average values of
all the measurements from 1 mm to 20 mm of depth. The results obtained were: Untreated:
F (3.49), σ (1.18); NR+W: F (6.50), σ (1,58); W: F (5.48), σ (1,68); KBYO I: F (4.21), σ
(1.00) and KBYO II: F (4.80), σ (1.29). It could be observed that NR+W offered greater
resistance to perforation than the rest of them.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The Peeling test gives best results for NR+W, as shown in Fig. 1. All these treatments
improved the cohesiveness of the damaged stone, giving away less matter on the adhesive
tape.
Fig. 1: Mass of adhered matter on adhesive tape for each treatment.
3.3. Microscopic observation
SEM images allow the observation of how the products are deposited on the stone surface.
Fig. 1 shows the NR+W (a and b) and W (c and d) samples. A layer of product can be
observed, presenting a similar aspect, even with the appearance of some cracks in the layer.
a)
b
)
Fig. 1: SEM-EDX images of treated stone (a for NR+W and b for W).
Images for KBYO treated samples show a similar aspect to untreated samples, as can be
seen in Fig. 2, which could explain the apparently little effect these treatments have on this
stone. Some spheroid granules could be observed (b image), maybe caused by the
treatment, although this was not tested.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
a)
b)
Fig. 2: SEM-EDX images of KBYO I (a) and KBYO II (b) treated samples.
4. Conclusions
In this work, the effectiveness of three consolidation treatments has been tested on Puerto
stone, by looking at changes in hydric properties of the stone, its colour and appearance,
cohesion, compactness, and resistance to perforation, before and after the application of the
treatments. Results obtained from the tests show that the most effective treatment is NR+W,
that is, the combination of Nanorestore and Wacker OH, since it did not alter hydric
properties and colour significantly, and improved compactness, cohesion and resistance to
perforation. It is easy to apply, safe and does not require specific instruments or
installations strange to any standard intervention. The presence of microfractures in the
silica gel layer three months after the application of the product is, however, a fact worth
studying so it can be avoided.
Results obtained for the biomineralization treatments (KBYO) do not match those published
for a different type of carbonatic stones (Jiménez-López et al. 2008, Jroundi et al. 2010),
being in this case most unexpected. This suggests that either this treatment does not suit this
stone or the application method must be tailor made to the stone characteristics, which
could indicate the need to optimize the method according to the characteristics of each type
of stone.
Finally, it is necessary to stress the importance of carrying out preliminary tests before
performing an intervention on any heritage object. An evaluation study of the candidate
treatments in order to assess the best possible one allows more accuracy in interventions.
References
Delgado-Rodrigues,J. and Grossi. A. (2007): Indicators and ratings for the compatibility
assessment of conservation actions. Journal of Cultural Heritage, 8(2007), 32-43
Doehne, E. and C.A. Price. 2010. Stone Conservation: An overview of current research.
Second edition. The Getty Conservation Institute. Los Angeles.
Drdáckŷ M., J. Lesák, S. Rescic, Z. Slížková, P. Tiano and J. Valach. 2012. Standardization
of peeling tests for assessing the cohesion and consolidation characteristics of
historic stone surfaces. Materials and structures, 45:505-520.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Folk, R.L.; 1965, Petrology of Sedimentary Rocks, Hemphill ICOMOS-ICMS, 2008.
Illustrated glossary on stone deterioration patterns.
Jiménez-López C., C. Rodríguez-Navarro, G. Piñar, F.J. Carrillo-Rosúa, M. RodríguezGallego and M.T. González-Muñoz. 2007. Consolidation of degraded ornamental
porous limestone stone by calcium carbonate precipitation induced by the
microbiota inhabiting the stone. Chemosphere, 68 (10), pp. 1929-1936.
Jiménez-López C., F. Jroundi, M. Rodríguez-Gallego, J.M. Arias and M.T. GonzálezMuñoz. 2007. Biomineralization induced by Myxobacteria. Communicating
current research and educational topics and trends in applied microbiology. A.
Méndez-Vilas (Ed.), FORMATEX.
Jiménez-López C., F. Jroundi, C. Pascolini, C. Rodríguez-Navarro, G. Piñar-Larrubia, M.
Rodríguez-Gallego and M.T. González-Muñoz. 2008. Consolidation of quarry
calcarenite by calcium carbonate precipitation induced by bacteria activated
among the microbiota inhabiting the stone. International Biodeterioration &
Biodegradation 62, 352-363.
Jroundi F., E.J. Bedmar, C. Rodríguez-Navarro and M.T. González-Muñoz. 2010.
Consolidation of ornamental stone by microbial carbonatogenesis. Global Stone
Congress 2010.
Pérez-Ema N., M. Álvarez de Buergo, R. Bustamante. 2013. Integrated studies for the
evaluation of conservation treatments of building materials from archaeological
sites. Application to the case of Merida (Spain). International Journal of
Conservation Science. Vol. 4, Special Issue, 693-700.
Sebastián E. M., M. J. de la Torre, O. Cazalla, G. Cultrone, C. Rodriguez-Navarro. 1999.
Evaluation of treatments on biocalcarenites with ultrasound. The e-Journal of NonDestructive Testing, 4, 12.
The Charter of Krakow, 2000: Principles for Conservation and Restoration of Built
Heritage
Theoulakis P., I. Karatasios, N. Stefanis. 2008. Performance criteria and evaluation
parameters for the consolidation of stone. In: Proceedings of the international
symposium: Stone consolidation in cultural heritage. Lisbon, 6-7 May, 2008.
Wheeler, G. 2005. Alkoxysilanes and the Consolidation of Stone. The Getty Conservation
Institute. Los Angeles.
Young, M.E., M. Murray and P. Cordiner. 1999. Sandstone consolidants and water
repellents. Stone consolidants and chemical treatments in Scotland. Report to
Historic Scotland. - http://www2.rgu.ac.uk/schools/mcrg/miconsol.htm
Ziegenbalg G. and E. Piaszczynski. 2012. The combined application of calcium hydroxide
and silicic acid esters – A promising way to consolidate stone and mortar. In: 12th
International Congress on the Deterioration and Conservation of Stone. New
York.
752
SEASONAL STONE SHELTERING: WINTER COVERS
C. Franzen1* and K. Kraus2
Abstract
Protective winter sheltering is a tradition for high grade stone decorations of some
cathedrals and castles in Central Europe. During winter, the often delicate sculptures or
reliefs exposed outdoors in parks and gardens are sheltered by wooden cladding applied
since the 1980s. Different systems of protective sheltering by winter covers can be
distinguished. These include wrapping techniques and several types of box used to cover
the surfaces or objects requiring protection. The distributions of different winter cover types
in Europe seem to reflect local traditions. Recently, systems made from new materials have
come to market. We evaluate different seasonal shelter types and give some general
recommendations for making decisions for the application of protective winter covers. New
environment data measurements, inspection of different materials in use, considerations
about the work load and summer storage are presented.
Keywords: preventive conservation, weathering, protection, winter cover, risk assessment
1. Introduction
It is said the application of protective sheltering systems has a long standing tradition in
European parks and gardens. Objects of art, often of natural stone, are encased during the
cold winter period. In areas north of the Alps valuable marble sculptures were sheltered
with protective winter covers while the citrus fruits of baroque gardens hibernated in
orangeries. Also for sculptures made from sandstone this technique of preventive
conservation came into use. Despite this widespread practice, there is an open question
about the precise time that this form of preventive action started in general, and even for
some specific first class parks and gardens. For example, the documentation of the seasonal
winter sheltering in the park of Versailles, near Paris, winter sheltering can be dated
initially to the beginning of the 1980s. Scientific examination of that preventive
conservation action was started by Berry (2005) with climate measurements in several
British parks and complemented by Rüdrich et al. (2011). Rüdrich (op cit.) addressed a new
development of protective winter covers for the monumental marble statuaries on the
Schlossbrücke in Berlin. Looking at the different kinds of protective sheltering systems a
wide variety can be found. Materials used are metal, fabric and synthetic materials, quite
often in material combinations that mean that a differentiation of winter shelter systems
based on material criterion is not helpful. The main distinction that can be made between
1
C. Franzen*
Institut für Diagnostik und Konservierung an Denkmalen in Sachsen und Sachsen-Anhalt e.V.
(IDK), Schloßplatz 1, D-01067 Dresden, Germany
franzen@idk-denkmal.de
2
K. Kraus
Institut für Steinkonservierung e.V., Große Langgasse 29, D-55116 Mainz, Germany
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
protective winter covers is the bearing mode. Most box type shelters compensate their own
weight with posts in the ground, whereas in most wrapping techniques the cover is carried
by the sculpture. The distribution of several winter protection types in Europe is dominated
by local traditions. Some new types of shelter, fabricated from modern materials are now
coming to the market. In this paper we evaluate different shelter types and give some
general recommendations for decisions making about the application of protective winter
covers. Data from new environment measurements, the inspection of different materials in
use, considerations about the work load and summer storage is discussed.
2. Protective winter covers
The study presented here focusses on seasonal sheltering free standing pieces in parks,
gardens and in castle areas e.g. on balustrades. We will not consider fountains, permanent
shelters, protection shelters for events or building construction bound winter covers. All the
protective winter covering systems are handled twice a year: with some local differences
the system is applied in November and dismantled in March. As a simple consequence of
this, the protective system is employed in-situ for approximately a third of the year and has
to be stored for the remaining time. Summer storage arrangements must be taken into
account. Moreover in terms of workload the installation team is occupied for twice. There
are winter protection systems which have standard dimensions and use standardised
exchangeable structural elements. Others are constructed bespoke for single art objects,
using components that cannot be interchanged easily. In such cases a durable labelling
system is advisable to ensure a consistency and appropriateness of the relation between the
object and its cover. This is even more important if the shelter system consists of several
parts. This may seem rather to be too simple to mention but has serious implications in the
total handling of work planning and the labelling should not get lost during winter
conditions or summer storage. The winter cover is erected by trained garden personal or
specialist subcontractor companies. In several cases stone restorers are involved in planning
or advising the works. Thus, in financial terms there are costs for system planning and
buying, for summer storage and transportation, working time for set up and dismantling
multiplied by the number of workers, repair and time of use.
Fig. 1: Dresden (D), Blüherpark,
wooden boxes.
Fig. 2: Dresden, Großer Garten,
wooden boxes.
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Fig. 3: Wooden box, City of Leipzig(D).
Fig. 4: Wood and tarboard box,
Großharthau.
2.1. The general idea
The idea of winter sheltering is an extra protection of the stone material against
deterioration action in winter. The commonly and vaguely defined aim is to avoid
weathering action from specific winter related damage factors. The sometimes rather airily
enumerated principles and processes are worth considering in some more detail. With
respect to protection from rain, which is ensured in all cases, it is also certain, that in some
parts of Europe, where winter covers are applied, there is more rainfall summer than in
winter. Nevertheless, water coming down in snow does not rest direct on the material.
Looking at temperature one has to acknowledge that as long as the shelter is not heated the
ambient temperature will equilibrate in the shelter and to the stone. Also, frost action is not
eliminated. Obviously the interaction of the object with solare radiation is prevented, but
here the question can be raised about the relevance of the solar insolation in general
weathering action. A similar approach can be taken to the deposition of aerosols on the
surface, especially with respect to the effects of deposition in wind shaded areas. Biological
action is most often mentioned as a risk, and can be increased with the winter cover.
However, if winter shelters do not protect effectively from all the weathering actions that
we assume take place, they do prevent frost action in the wet stone state, if certain factors
are fulfilled. As nearly all published climate measurements demonstrate, in, in the sheltered
volume environmental changes of temperature and humidity adjust in a damped manner (e.
g. Berry 2005, Rieffel 2009).
Fig. 5: Barockschloss Rammenau (D).
Fig. 6: Rheinsberg (D).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 7: Stockholm, Stadthuset,
wooden box.
Fig. 8: Weikersheim (D), tents.
2.2. All Solutions?
In our study we counted that seasonal protective winter sheltering is these days regularly
applied at more than one thousand free exposed stone art objects in central Europe. There is
no standard for the technique and oral or written recommendations (e.g. Wölbert 2005) are
quite vaguely formulated. For protective winter covers applies what of Agnew (2002) states
for shelters in archaeological sites: it is “not a simple matter, although if may appear so to
some stakeholders.”. Thus we can find countless solutions, depending on the local options.
This is true for innumerable kinds of box constructions, e.g. from wood (Fig. 1 to Fig. 7),
boxes with metal planes (Fig. 9, Fig. 10) or other framework constructions like tents
(Fig. 8). The varieties continue with coating and wrapping in fabric (Fig. 11, Fig. 12), with
or without an underconstruction (Fig. 15). Also, to a certain extent, shells of polyurethane
are to be found (Fig. 13). Most often in one park one type of cover is applied to all items,
and that method is unique to that park.At the beginning of our survey of the topic and, not
yet aware of the total variability in the solutions applied in practice, it was decided to focus
attention on three different types: wooden construction, wrapping in fabric with an
underconstruction and polyester shell.
Fig. 9: Biebrich Castle (D), metalcover.
Fig. 10: Berlin (D), metal house.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 11: Versailles (F),
cotton wrapping.
Fig. 12: Moritzburg (D.)
Fig. 13: Weimar, Ilmpark
(D) Ciccum.
3. Field tests
Three types of winter covers were constructed for and applied over trial stone sculpted
columns installed at a site of a research station of the IÖZ Freiberg, Erzgebirge, to obtain
measurement results from different covering options. The trial objects are reused original
columns from the Zwinger in Dresden, set on aged pedestrals (Fig. 14). The columns are
comprised of Cotta type Elbe sandstone. Each column was equipped with climate loggers.
Winter covers were applied in November and dismantled in March. One column named
“Frühling” was wrapped in a procedure as developed in Moritzburg 1999 (Franzen 2011),
the second “Sommer” encased in the Ciccum®, a polyurethane hard foam shell, the third
gets a wooden shelter original from Barockgarten Großedlitz “Herbst” and the fourth
“Winter” is not protected at all.
Fig. 14: Four test columns at the research station: anticlockwise starting right in front:
Frühling (fabric), Sommer (light-weight), Herbst (wood) and Winter (without covering).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 15:
Underconstruction
Fig. 16:
Wrapping in fabric
Fig. 17:
Polyestershell
Fig. 18:
Wooden box
4. Results
The experience from the practical handling of the different systems were documented and
evaluated. Compared to the other methods, the wooden sheltering requires the most
substantial effort, while wrapping demands the discreet application of the underconstruction
directly on the surface of the stone object. In terms of reparability wood allows for the
remediation of small defects on site, while all of the other systems need to be brought to a
workshop for maintenance. In terms of the durability of the solutions our experience, for
most methods indicate that the real life cycle is shorter than the period that is aspired to.
This also has an impact on the cost calculations, a key element in decisions about winter
sheltering. Costs consist of the equipment acquisition, adequate storage of that equipment
the, work in application, repair and maintenance.
Fig. 1: Cutout of climate measurements in the field test ensemble.
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However, from the environmental parameter data logging some more important conclusions
can be drawn. Fig. 1 presents a revealing sub-set of the climate measurements made on the
four experimental stone columns. Winter covers were applied on the 14th of November.
Until that date the data for all the specimens are very hard to separate. In detail it can be
seen that the surface temperatures, given in dotted lines, fluctuate closely to the
environmental temperature data. With the installation of the winter covers a microclimate
arises under the cover. The outer climate is damped to different extents. The temperature
changes beneath the wooden box are reduced, and under the wrapping even more. The
strongest damping can be observed under the polyester shell. These effects are probably
influenced by the material used, but the main regulating parameter is the ventilation. To
assess this, the ventilation number, the complete air exchange per hour, was approximated
by fitting model data. The wooden cover stands on posts giving an unhampered air
exchange, a ventilation number of more than 30 h-1, whilst Ciccum allows the lowest
ventilation about 4 h-1, wrapping in fabric is in between with a ventilation number of about
8 h-1. Those huge differences in air exchange have major control on humidity and moisture
exchange. Stone sculptures that have a low water uptake (low permeability and sorptivity)
do not need to have a drying environment when sheltered. But stone that absorbs relatively
a lot water in the pore system needs an interaction with the air, allowing the stone to dry
out. Theoretically therefore there the recommendation to shelter the material solely in dry
conditions arises, which is in practice not always possible. Thus wet state sheltering is a
possible risk, the shelter system has to cope with. Therefore, ventilation has to be adapted
to those possible risks. Ventilation is to be regarded as the key parameter to distinguish
different shelter systems, as it is a key factor for possible material drying. As this is a
material property the factor has to be related to the material, an important approach which
remains to be researched.
All protective winter shelter systems prevent precipitation falling on the protected
sculptures during winter. Also, the damped microclimate flattens the gradients of
temperature changes; this is to be considered also with respect to direct wind action, which
accelerates the material temperature transformation significantly. With respect to
temperature changes the vulnerability is also material related.
Comparing all different winter shelter systems consisting of various materials, major
distinctive features are not due to those materials but to the grade of ventilation the
construction enables. Both deterioration related parameters of temperature changes and dehumidification are significantly controlled by the ventilation in opposite direction: high
ventilation enables drying but invokes intense temperature fluctuations, while prevented
ventilation stabilises the temperature and impedes any drying. The dimension or degree of
ventilation has to be referred to the material properties of the sculpture to be sheltered.
Acknowledgements
The project was funded by Deutsche Bundesstiftung Umwelt (DBU) grant: Az 30415.
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References
Agnew, N. (2002) Methodology, conservation criteria and performance evaluation for
archaeological site shelters, Conservation and Management of Archaeological
Sites 5(1-2):7-18, DOI: 10.1179/cma.2002.5.1-2.7
Berry J. (2005) Assessing the performance of protective winter covers for outdoor marble
statuary—pilot investigation. In: Verger I, Coccia Paterakis A, Chahine C, Kardes
K, Eshoj B, Hackney S, de Tagle A, Cassar M, Thickett D, Villiers C, Wouters J
(eds) 14th Triennial Meeting The Hague, 12–16 September 2005, Preprints.
Earthscan/James & James, London, pp 879–887.
Franzen, C. (2011) Winter shelter systems for garden sculptures, in: Marcel Stéfanaggi &
Véronique Vergès-Belmin (eds): Jardins de Pierres, Conservation of stone in
Parks, Gardens and Cemeteries, SFIIC Paris ISBN: 2-905430-17-6, p. 132 - 141.
Rieffel, Y. et al. (2009) Entwicklung und Überprüfung von Einhausungssystemen zur
Reduzierung
umweltbedingter
Schädigungen
von
außenexponierten
Marmorobjekten mit dem Ziel des langfristigen Erhalts in situ an einem national
bedeutenden Objektkomplex, den Schlossbrückenfiguren Unter den Linden,
Berlin, Abschlussbericht zum DBU Projekt 24000-45.
Rüdrich, J., Rieffel, Y., Pirskawetz, S., Alpermann, H., Joksch, U., Gengnagel, C., Weise,
F., Plagge, R., Zhao, J., Siegesmund, S. (2011) Development and assessment of
protective winter covers for marble statuaries of the Schlossbrücke, Berlin
(Germany), Environ Earth Sci, Vol. 63/ 7, pp 1823-1848 DOI 10.1007/s12665010-0765-2, online 19. Okt. 2010.
Wölbert, O. (2005) Winterschutzverkleidungen für witterungsgefährdete Objekte. in:
Matthias Exner, Dörthe Jakobs (Hrgs.) Klimastabilisierung und bauphysikalische
Konzepte, Tagung ICOMOS, Reichenau Nov. 2004, S.185 - 190.
760
PERFORMANCE AND PERMANENCE OF TIO2-BASED SURFACE
TREATMENTS FOR ARCHITECTURAL HERITAGE:
SOME EXPERIMENTAL FINDINGS FROM ON-SITE AND
LABORATORY TESTING
E. Franzoni1*, R. Gabrielli2, E. Sassoni1, A. Fregni1,
G. Graziani1, N. Roveri3 and E. D’Amen3
Abstract
The possibility of providing historic façades with self-cleaning ability in urban polluted
environments by means of treatments based on photocatalytic nano-TiO2 dispersions, has
recently received growing attention. The potential impact of these treatments for the
protection of heritage buildings is evidenced by the high number of papers where the
performance of TiO2-based nanocoatings on stone (mainly marble, travertine and
limestone), mortar and brick were investigated by laboratory tests. The results seem
encouraging, even if the nature of the treatments, the kind of substrate and the methods
used for assessing the coatings’ performance differ greatly from one study to the other, thus
making the results difficult to compare or even contradictory. Several aqueous titania
nanodispersions are already available in the market and some applications of these
treatments as trial testing in real heritage buildings are known, but information about their
performance (colour change, self-cleaning ability, etc.) on real substrates and in real
outdoor environments are still very scarce. In particular, the long-term permanence of TiO2
nanoparticles on outdoor exposed surfaces, also in relation with strategies for promoting the
adhesion between nanoparticles and substrate, has also not been fully elucidated yet. In the
present paper, some experimental findings collected during last years from on-site and
laboratory testing campaigns are reported, as a contribution towards a better assessment of
the behaviour of TiO2 treatments when exposed to real and accelerated environmental
conditions.
Keywords: self-cleaning, historic building materials, protection, rain, leaching
1
E. Franzoni*, E. Sassoni, A. Fregni and G. Graziani
Dept. of Civil, Chemical, Environmental and Materials Engineering (DICAM),
University of Bologna, Italy
elisa.franzoni@unibo.it
2
R. Gabrielli
Leonardo S.r.l., Casalecchio di Reno, Italy
3
N. Roveri and E. D’Amen
Chemical Center S.r.l., Castello d’Argile, Italy
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
1. Introduction
While current strategies for surface protection of historic monuments involve the use of
sacrificial layers (as in the past) or water repellents, an ‘active’ kind of protection has been
recently proposed, based on the use of photocatalytic materials (Licciulli et al. 2011, La
Russa et al. 2012). TiO2 nano-particles, in particular, have been investigated for application
on façade materials, as they are expected to catalyse deterioration of several pollutants that
threat building materials and to provide self-cleaning action (Pinho et al. 2013, Quagliarini
et al. 2013, Munafò et al. 2014, Franzoni et al. 2014). Different kinds of substrate,
representative of the historic ones, were treated with different nano-titania dispersions and
tested in laboratory, with positive results (as shown in the review paper Munafò et al.
2015). Porosity, roughness and composition of the substrate were found to be important for
the treatments performance, as well as the composition and particle size of the dispersions.
Nevertheless, the test methods employed in the laboratory studies necessarily involve
simplified conditions with respect to the complex conditions experienced by historic
materials on site. For instance, the self-cleaning ability is determined as the capacity of a
treated surface to discolour a standard organic stain under a standard UV light exposure, but
the on-site exposure is obviously very different, due to the occurrence of complex urban
atmospheres (gases, particulate matter, etc.) and environmental conditions (temperature,
humidity, sun, rain, wind, etc.). Hence, the collection of data from real historic buildings
treated with TiO2is crucial to assess the actual performance of these finishings, and their
compatibility with the original substrates (colour change, microstructural variations, etc.).
Moreover, it is very important to assess the durability of these treatments. In particular, the
permanence of the TiO2 nanoparticles on the surfaces is a key parameter to investigate, as
most of the current treatments are constituted by aqueous nano-dispersions, only
occasionally preceded by primer application, hence the nanoparticles are expected to adhere
to the substrate only mechanically and by weak physical bonding and could be removed by
environmental agents (Franzoni et al. 2014, Graziani et al. 2014).The issue of TiO2 removal
by rain is important also from an environmental point of view (Kaegi et al. 2008).
This paper aims at presenting the results of some studies performed in laboratory and onsite, as a contribution to a better understanding of the aspects highlighted above. Firstly, the
permanence of nano-TiO2 on render and marble samples was investigated in laboratory, by
subjecting the samples to an artificial rain system, in order to understand whether the
nanoparticles and their photocatalytic activity are lost after exposure to rain. Then, aqueous
nanodispersions of TiO2 were applied to three heritage buildings in Bologna (an Istrian
stone decoration of a XX Cent. building, a repair render of a XVIII Cent. portico and some
sandstone ashlars of a XIII Cent. building: Fig.1) and the effects and permanence of the
treatments were investigated.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 1: The places selected in Bologna for testing the nano-TiO2 application. From left to
right: the limestone sculpture in the Mathematics Dept.; the new renders of the former Del
Corso Hotel; sandstone ashlars in ‘Palazzo del Podestà’ during the treatment application.
2. Laboratory testing
2.1. Materials and methods
Dispersions of nano-TiO2 were applied on two kinds of substrates, characterised by
different composition, porosity and surface roughness: a painted render (similar to those
used in historic buildings) and Carrara marble. The render was manufactured mixing
natural hydraulic lime (NHL2, EN 459-1:2010), quartz sand <2 mm, ground brick powder
<1 mm and water, according to the volume proportions: 1-1-1-0.5. Render slabs 1.8 cm
thick were manufactured and cured for 4 weeks at T=20°C and RH=50%, then they were
painted by two brush strokes with an inorganic paint (slaked lime, 5 wt% inorganic
pigments and 5 wt% acrylic polymer). Immediately after paint application, a commercial
aqueous dispersion of TiO2 nanoparticles (anatase, mean size 20-50 nm), with
concentration 3.4 wt% and containing 0.1 wt% of NaOH, was applied by two brush strokes:
a better adhesion of the nanoparticles is expected thanks to the carbonation process of the
paint. Some samples were left untreated (REF). Tests were performed after 2 weeks curing.
Freshly quarried Carrara marble slabs with thickness 2 cm were used for the tests. A 2 wt%
hydro-alcoholic dispersion (20 wt% isopropyl alcohol) of TiO 2 nanoparticles (anatase,
mean size 10-20 nm) was applied by brushing. One stroke was considered enough due to
the low porosity of marble. Some samples were left untreated (REF), for comparison.
Half of the samples was subjected to the methylene blue discolouration test, consisting in
dripping 100 mg of a solution of methylene blue in ethanol (50 mg/l) on the treated and
REF samples and comparing the discolouration after exposure to UV light. Marble samples
were exposed to UV light for 2 hours, while render samples were exposed for 5 hours due
to the difficulty in observing the blue discolouration in such porous samples, where the blue
drop was mainly absorbed by the substrate. The other half of the samples was exposed to an
artificial dripping system aimed at simulating the action of rain on the treated surfaces.
Given the nature of the treatments under testing, that are aqueous dispersions of TiO2
nanoparticles (with no primer), the resistance to rain impact and flow was considered a key
deterioration process to investigate. The samples, having a surface of about 33 cm2, are
positioned under the artificial rain system with a slope of 45° from the horizontal plane.
Two drips of distilled water fall on each sample from a height of about 4 cm, flowing along
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
the surface. The rate of artificial rain on each sample is about 350 ml/hour. The artificial
rainfall was performed for a total of 20 hours (10 cycles of 2 hours rain followed by 22
hours drying) on marble samples and for 4.5 hours of continuous dripping on the render
samples. A continuous dripping instead of rain cycles was preferred for render, for keeping
the substrate in a saturated condition and hence for maximising the water flowing on the
treated surface. Moreover, a shorter exposure was preferred for render, in order not to cause
an excessive leaching of the mortar substrate (not fully carbonated yet). Considering the
average rainfall in the Italian city of Bologna (80 cm/year), the artificial rain performed
corresponds to an exposure of about 2 years for render and 6 years for marble.
After the exposure to artificial rain and subsequent drying, the samples were observed by
SEM and the amount of Ti still present on the surface was analysed by EDS (SEMLEO
EVO 40XVP-MZeiss; EDS analysis system INCA Energy 250, Oxford Analytical
Instruments). Moreover, the methylene blue discolouration test was carried out on the
samples subjected to artificial rain, following the same procedure described above.
2.2. Results and discussion
The results of the methylene blue discolouration test on the render and marble samples are
reported in Fig. 2. After the application of the TiO2-based treatment, both substrates exhibit
some discolouration of the methylene blue under UV exposure (Fig. 2: b and e), differently
from the untreated samples (a and d), thus confirming the photocatalytic action of the
treatment. After exposure to artificial rain, the photocatalytic behaviour of the treatment
seems almost unaltered in the render samples (Fig. 2: c), although the EDS analysis reveals
that the amount of TiO2 on the surface has decreased (two representative EDS spectra
before and after artificial rain are reported in Fig. 3 left and centre). Notably, the amount of
titania deposited by the treatment on the surface is high (Fig. 3 left), probably due to the
higher amount of nanodispersion absorbed by the samples in the two brushing applications.
The TiO2 persistence on the surface can be ascribed to the render roughness, the
enhancement of the nanoparticles adhesion due to paint carbonation and the adsorption
capacity of silicatic fractions in the paint towards nano-TiO2 (although this is a complex
phenomenon depending on the nanoparticles size and concentration (Dietrich et al. 2012)).
In marble samples, the photocatalytic effect seems more limited than in render, according to
visual observations (Fig. 2), although a direct comparison cannot be made between the two
substrates, given the different UV exposure times (2 hrs for marble and 5 for render). In the
case of marble, the TiO2 amount is however quite limited (Fig. 3 right), probably due to the
limited retention capacity of marble in the single brush stroke. After artificial rain, the
photocatalytic action is further reduced (Fig. 2: f) and the Ti presence is barely detectable
by EDS, which points out that possible nano-TiO2 removal is an important issue in marble.
3. On-site testing
3.1. Istrian stone sculpture in the Department of Mathematics in Bologna (XX Cent.)
The carved limestone slab under testing (Fig. 1 left, sculptor Alfonso Leoni) was placed at
the extremity of the portico of the Dept. of Mathematics of the University of Bologna in
1971. The slab is made of Istrian stone, a compact limestone whose aspect and properties
are very similar to marble. In the 2009 conservation works, a commercial nanodispersion of
TiO2 was applied to the sculpture, after cleaning, to investigate its self-cleaning action in a
heavily trafficked area. A primer was applied to promote nanoparticles adhesion (aqueous
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
dispersion of silica gel, surfactants, acrylic polymers and NaOH), by single spraying
(pressure 0.3-0.4 bar; distance nozzle/surface 20-25 cm; expected amount of product
deposited 70 g/m2). Then, a 3.4 wt% aqueous dispersion of anatase nanoparticles (particle
size not reported in the technical datasheet; 0.1 wt% of NaOH; expected amount of product
deposited 50 g/m2) was applied by double spray application (same tool used for the primer).
Fig. 2: The samples subjected to the methylene blue discolouration test.
Fig. 3: EDS of the treated surface of: the render before (left) and after (centre) exposure to
artificial rain; marble before exposure to artificial rain (right) (area analysed 300 m2)
Three years after the treatment, the treated face of the slab (the external one, exposed to
direct rain) appeared substantially unaltered, while the untreated one (the internal one,
under the portico and hence sheltered) exhibited some visible darkening, as shown in Fig. 4
(comparison between 1 and 2 and between 5 and 6). As the treated face was substantially
clean also in the cavities of the sculpture, a combined action of rain wash and self-cleaning
ability can be envisaged. Small samples were taken by chisel from the sculpture, in both
internal and external surfaces, and they were observed by polarised light microscope (PLM)
and ESEM/EDS. A thin layer (1-8 m) very rich in Ti was found on the treated external
face, hence TiO2was still present on the surface after 3 years since application (Fig. 4: 3-4).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
On the untreated internal surface a layer of deposited particulate matter was detected
(Fig. 4: 7-8).
3
4
1
7
2
8
5
6
Fig. 4: External surface of the slab: 1) state at 2009; 2) state at 2012; 3) cross section
observed by PLM and 4) by ESEM (marker 50 m). Internal surface of the slab: 5) state at
2009; 6) state at 2012; 7) cross section observed by PLM and 8) by ESEM (marker 50 m).
3.2. Renovation render of a XVIII Cent. building in Bologna
The 18th Century building selected for the tests was the former Del Corso Hotel in Bologna
(Fig. 1-centre), a neoclassical building affected by a severe degradation of the existing
façade renders, facing a street characterised by intense car and bus traffic. In 2012, the
renders were replaced, using new renders and paint of the same kind of the existing ones
(same materials used in laboratory tests on render samples: § 2.1). Finally, a photocatalytic
self-cleaning finishing (the same used for renders in § 2.1) was applied by a single spray
application to some pillars of the portico, after complete hardening of the paint. In 2015,
some samples of the treated repair renders were collected (Fig.5), in order to evaluate the
amount of TiO2 still present on the surface after 3 years of exposure to the weathering
agents.
The samples were observed by SEM and the presence of Ti was determined by EDS (SEM
LEO EVO 40XVP-M Zeiss; EDS INCA Energy 250, Oxford Analytical Instr.). The EDS
analysis in Fig. 6 shows that a very small amount of TiO2is still present in the samples
taken from the external face of the pillars, directly exposed to rain (samples A, C), while
samples B and D, taken from the sheltered faces show a notably higher TiO 2amount.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 5: Sampling points (and heights) in the two treated pillars.
Fig. 6: EDS spectra of the surfaces of the collected samples (area analysed 3.5 mm2).
3.3. Sandstone ashlars of Palazzo Podestà in Bologna
The application of a TiO2nanodispersion identical to that used for marble samples in the
laboratory tests was carried out (on 24th July 2015) in some sandstone ashlars of Palazzo
Podestà, a XVI Century building which faces the central square of Bologna and is one of
the most prominent monuments in the city. Despite the dark yellow colour of the stone, no
visible colour change was observed after two subsequent spraying applications (Fig. 7). The
monitoring of the presence of TiO2 is presently in progress.
Fig. 7: The sandstone before (left) and 30’ after the TiO2 application (right).
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4. Conclusions
The laboratory tests show that the aqueous dispersions of nano-TiO2 exhibit some photocatalytic behaviour even after few hours of UV exposure. Nevertheless, depending on the
amount of nanoparticles deposited on the surface (higher for render than for marble) and
the technology used for promoting nanoparticles adhesion (none for marble, fixing through
lime carbonation for render), artificial rain significantly affects TiO 2 permanence. In fact,
artificial rain decreases the TiO2 amount in both substrates, but more markedly for marble.
The on-site tests highlight the aesthetical compatibility of the treatments, but show that,
depending on the method used for enhancing the nanoparticles adhesion, rain may
differently affect TiO2 removal. In the Istrian stone sculpture a primer was used before the
TiO2 application and a thin layer of titania is still present after 3 years. Conversely, in the
repair render directly exposed to rain (where the treatment was applied on the carbonated
lime paint) a limited amount of TiO2 was found, despite the high substrate porosity. Further
monitoring of the buildings is presently in progress.
References
Dietrich, L. A. S., et al., 2012, Experimental study of TiO2nanoparticle adhesion to silica
and Fe (III) oxide-coated silica surfaces, Chemical Geology, 332, 148-156.
Franzoni, E., et al., 2014, Compatibility of photocatalytic TiO2-based finishing for renders
in architectural restoration: a preliminary study, Build Environ, 80, 125-135.
Graziani, L., et al., 2014, Durability of self-cleaning TiO2 coatings on fired clay brick
facades: Effects of UV exposure and wet & dry cycles, Building and Environment,
71, 193-203.
Kaegi, R., et al., 2008, Synthetic TiO2nanoparticle emission from exterior facades into the
aquatic environment, Environmental Pollution 156, 233–239.
La Russa, M.F., et al., 2012, Multifunctional TiO2 coatings for Cultural Heritage, Progress
in Organic Coatings, 74, 186–191.
Licciulli, A., et al., 2011, Photocatalytic TiO2 coatings on limestone, J of Sol-Gel Science
and Technol, 60, 437–444.
Munafò, P., et al., 2014, Durability of nano-engineered TiO2 self-cleaning treatments,
Construction and Building Materials, 65, 218-231.
Munafò, P., Goffredo, G.B. and Quagliarini, E., 2015, TiO 2-based nanocoatings for
preserving architectural stone surfaces: An overview, Construction and Building
Materials, 84, 201–218.
Pinho, L., et al., 2013, A novel TiO2–SiO2nanocomposite converts a very friable stone into
a self-cleaning building material, Applied Surface Science, 275, 389–396.
Quagliarini, E., et al., 2013, Self-cleaning materials on Architectural Heritage:
compatibility of photo-induced hydrophilicity of TiO2 coatings on stone surfaces, J
of Cultural Heritage, 14, 1–7.
768
THE IMPACT OF SCIENCE ON CONSERVATION PRACTICE:
SANDSTONE CONSOLIDATION IN SCOTTISH BUILT HERITAGE
C. Gerdwilker1*, A. Forster2, C. Torney1 and E. Hyslop1
Abstract
Scotland’s extensive sandstone-built heritage is an irreplaceable cultural and material asset
which suffers increasing weathering decay that necessitates the consolidation of friable
surfaces to delay material loss. Many academic studies of sandstone consolidants have been
carried out but long-term field performance monitoring is rarely undertaken. Currently only
two types of consolidants, the acrylic resin Paraloid B72 and alkoxy silanes, are commonly
applied to sandstone, both associated with inherent risks that could irreversibly accelerate
decay. Scotland’s conservation community has the technology and expertise to carry out
compatibility and performance testing of consolidants but is hampered by typical
restrictions on access, project funding and time. The use of science in the context of risk
assessment rather than guarantee of compatibility is suggested to enable timely and solution
orientated results that inform the decision-making process. The research highlights the need
for conservation science to be routinely and more effectively integrated into conservation
planning and processes from the outset. The architect’s role as client representative and
project manager is identified as critical to achieving this. Training, outreach activities and
an accessible platform for the collation and dissemination of research and treatment
documentation are considered possible means of improving collaboration between scientists
and conservators and advancing conservation technology and processes.
Keywords: sandstone, consolidation, compatibility, risk assessment, conservation planning
1. Introduction
Scotland’s Historic Environment Audit 2012 identifies 90% of pre- 1919 buildings as
requiring some repair (Historic Scotland, 2012), the vast majority of these adopting mass
sandstone construction (Urquhart, 2007). Climate change is likely to accelerate the decay of
masonry due to moisture transfer mechanisms and long term saturation in porous materials
(Smith et al., 2011) caused by increasing levels of rainfall and low potential evaporation
associated with a northern maritime climate. Given that almost all the quarries that
historically supplied Scottish building stone are currently closed this places greater pressure
to arrest decay, and a presumption to consolidate as opposed to replace stone may be
favoured. These decisions also aid application of the philosophical and technical
1
C. Gerdwilker*, C. Torney and E. Hyslop
Historic Environment Scotland, United Kingdom
christa.gerdwilker@hes.scot
2
A. Forster
Heriot Watt University, United Kingdom
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
requirements associated with best practice conservation (BS7913, 2013; ICOMOS, 2013),
and more specifically issues surrounding minimal intervention and authenticity.
Price (2006) describes consolidation as ‘the process of strengthening and reinforcing’ and,
given the potential scale of application Panagiotis et al. (2008) consider consolidation as a
major conservation activity which presents particular risks due to the irreversibility of the
consolidation processes affecting the stone matrix (De Clerq et al., 2008; Ferreiro Pinto &
Delgado Rodrigues, 2008). Subsequently, a clear evidence-based understanding of the
benefits and risks associated with the application of consolidants is necessary for objective
and informed treatment decisions to be taken. This research aims to identify how
conservation science supports Scotland’s building conservation community in their
decision-making process in regards to the use of stone consolidants. The research identifies
factors impacting on effective collaboration between conservators and scientists and means
of improvement.
2. Method
A review of recent literature determined key requirements for and evaluated currently used
sandstone consolidation treatments. Means of testing the efficacy and compatibility of
consolidants were identified. The applicability of the review findings for the Scottish stone
conservation sector was tested during subsequent questionnaires and interviews. A small,
yet representative group of six practising stone/building conservators and six conservation
scientists in Scotland from different public and private organisations were chosen as
interviewees and grouped into scientists and conservators. The interview process combined
small scale quantitative with qualitative research to gain understanding of:
the type and extent of consolidation treatments carried out in Scotland,
the extent to which they are determined and evaluated by scientific investigations,
the type of investigations used,
their impact on the treatment decision making process and
respective attitudes towards and experiences of collaboration between conservation
scientists and conservators.
A meta-synthesis examined six conservation project case files of properties throughout
Scotland. Their study compared the interview findings with the factual application of
conservation science in relation to stone consolidation in Scotland.
2.1. Literature research
Examination of current literature identified key requirements for sandstone consolidants as
to not alter the physical and visual nature and behaviour of the stone in the short or
long-term (Young et al., 2003; Doehne & Price, 2010).
being effective in slowing down the rate of decay (Price, 2006).
the ability to penetrate to a sound core (Weber & Zinsmeister, 1991).
Given the great variability of sandstones, the review surprisingly identified only two types
of currently prevalent sandstone consolidation treatments: the acrylic resin Paraloid B72 is
used to re-adhere surface delaminations, while alkoxy silanes are applied to soft powdering
sandstone surfaces As an irreversible surface-applied material, alkoxy silanes have the
greatest potential to cause harm and are the most tested type of consolidant (Weber &
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Zinsmeister, 1991; De Clerq et al., 2008). The main advantages of silanes are their
chemical compatibility with sandstone and potential ability to achieve deep penetration
(Price, 2006). While useful on disaggregating stonework their brittle and non-adhesive
nature cannot achieve the re-adhesion of delaminating surfaces. This common problem is
overcome by the theoretically reversible acrylic resin Paraloid B72. Its disadvantage is that
the resin has poor penetration and significantly reduces the permeability of consolidated
stone. It is also noted for poor performance in damp settings (Price 2006; Odgers & Henry,
2012).
Ultrasound velocity (US), infrared (IR) thermography and measuring water adsorption are
identified as effective non-destructive field techniques to monitor the impact of
consolidants (Haake et al., 2004; Ruedrich et al., 2004; Ferreiro Pinto & Delgado
Rodrigues, 2008; Moropoulou et al., 2013). A rebound hammer can also provide
information on surface hardness (Török, 2010). The difficulty and importance of
correlating laboratory and field test results, to ensure the former relates to practical
situations and the latter are correctly interpreted, are highlighted. Thin section petrography
of core samples is seen as an important initial step in understanding stone petrology and
decay phenomena (Nwaubani & Dumbelton, 2001) while drill resistance (DRMS) can
detect a hardness profile (Cnudde et al. 2007; Pamplona et al., 2008). Furthermore, the
above are often combined with strength, permeability and colorimetric tests (Young et al.,
2003). Academic research also allows access to more sophisticated laboratory equipment,
e.g. neutron radiography and X-ray tomography (Cnudde et al., 2007; Graham et al, 2014).
In spite of the evidently available technology and academic research, little published field
data is available on the long-term performance of project applied consolidants (Calia, 2004;
Wheeler, 2005).
2.2. Interviews
2.2.1 Interviews with conservators
The conservators represent the private and public sector in equal measure and carry out the
bulk of stone conservation in Scotland. Consolidation forms 25 – 50% of all conservation
work and >75% of consolidation treatments are applied to sandstone. The conservators
most commonly use Paraloid B72 and non-hydrophobic silanes as sandstone consolidants.
Conservators rarely commission material testing due to lack of funding, time or the
inability to take destructive samples. If undertaken, this usually involves thin section
petrography to identify decay mechanisms. More commonly, comparative hardness and
water absorption tests are carried out by the conservators themselves. While all
conservators keep and archive treatment records, these are not generally accessible to others
and rarely include long term performance monitoring results as this is usually also
prevented by lack of funding, access to the site and restraints on destructive sampling.
Four of the six conservators wish to work more closely with conservation scientists while
two question the scientists’ ability to relate their findings to the context of their projects.
They also bemoan a lack of conclusive answers to their questions on treatment
compatibility within project timeframes and budgets. Limited awareness of available
investigative technology is singled out as inhibiting their collaboration with conservation
scientists by the majority of conservators, followed by restricted funding and access to
scientists. The commercial conservators in particular feel that their clients’ lack of
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awareness of conservation science impacts on their willingness to pay for such services and
client development is identified as key to improving collaboration, combined with ‘access
to conservation science research’ and ‘access to scientists’ themselves.
2.2.2 Interviews with conservation scientists
Six building conservation scientists are interviewed, representing approximately 60% of the
sector in Scotland. One scientist works in the commercial sector while the remainder are
employed by academic and public institutions. All scientists spend over 75% of their time
on conservation related work, three scientists primarily on academic research while the
other three are conservation project focused. Combined, the scientists are able to offer all of
the analytical techniques identified by the literature research as potentially useful for
consolidant testing. Nonetheless, they confirm that such testing is very rare. Only the three
most experienced scientists have ever tested consolidants and only one scientist has applied
such findings to conservation projects while the other tests form part of academic research.
Petrographic analysis, water absorption and hardness are considered the most effective
stone consolidant tests to have been used by each of the above three scientists. In addition,
DRMS followed by US are seen as potentially useful techniques, but had not been used.
Like the conservators, the conservation scientists see performance monitoring of
consolidation treatments as imperative but the interviews reveal that this tends to be carried
out only in response to treatment failures and positive outcomes are likely to go uninvestigated. Nonetheless, the scientists feel that their research findings influence
conservation practice and agree that effective conservation science research requires
involvement in practical conservation projects. Limited contact and communication
difficulties, due to lack of funding, are identified as the biggest obstacles to collaboration
between conservation scientists and practitioners. Four main themes recur when asked how
collaboration between conservators and conservation scientists might be improved:
education, communication, contact and funding; with time being considered only a minor
factor.
2.3. Meta-synthesis of conservation projects
The meta-synthesis examines six stone conservation projects carried out over the last
approximately 30 years in Scotland to compare stone consolidation practice with interviews
and literature review findings (Tab. 1).
The meta-synthesis aims to identify:
- the investigative processes involved,
- their impact on the decision making process,
- the consolidation treatment and application methodology,
- the decision makers in these processes,
- whether performance monitoring is carried out, and
- treatment outcome.
Analytical investigations were carried out in 80% of the examined cases to determine decay
causes but rarely to test consolidant compatibility. Paraloid B72 is the main consolidant
used with silane being the only other identified substance in use, confirming the findings of
the interviews and literature review. The cases indicate that consolidants do not return stone
to ‘as new’ condition but that they might only last a few years before requiring retreatment. Thin section petrography followed by moisture related investigations are the
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primary means of establishing decay causes, but X-ray diffraction (XRD) and IR
thermography are also commonly used. Hill House is the only project to have involved
consolidant testing but, seemingly, findings were not applied to the project. Performance
monitoring tends to be limited to visual observations. As a preventive alternative to
remedial consolidation treatment, stabilisation of environmental conditions appears to have
slowed down the decay of internal stone at Skara Brae and this approach is currently being
trialled and monitored at Skelmorlie Aisle. While stone conservators determine treatments,
their decision tends to require the approval from the architect (as client representative) as
well as statutory bodies when applied to listed buildings and scheduled monuments.
Tab. 1: Summary of meta-synthesis.
Hill House
Linlithgow
Palace
Skara Brae
Holyrood
Abbey
Petrography
Petrography
Petrography
Petrography
Porosity
Sorptivity
Moisture
survey
Moisture
survey
IR
thermography
IR
thermography
XRD
XRD
Moisture
content (MC)
Melrose
Abbey
No
Petrography
Strength
Analysis
XRD
Environmental
Applied to
project
No
Treatment
Silane
injection
Decision
maker
Architects
Visual
Performance
monitoring
Skelmorlie
Aisle
Yes
Yes
N/A
Yes
Paraloid B72 Environmental
Paraloid B72
Paraloid B72
Silane
Environmental
Architect
Conservator
Inspector
Conservator
Conservator
Architect
Conservator
Scientist
Visual
MC
Yes
Environmental
Architect
Conservator
Inspector
Visual
Visual
Visual
Environmental
Visual
Environmental
XRD
Laser scan
IR
thermography
Outcome
Failed
Re-treated
Slowing of
decay rate
No access
Paraloid
partially
failed;
Silane stable
Too early
3. Discussion
Currently only two products are applied to address two main forms of sandstone decay:
granular de-cohesion and surface delamination. Of these, Paraloid B72 has been shown by
the literature review and meta-studies to have poor long-term performance, particularly in
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exterior settings. Like all other resinous consolidants, Paraloid B72 is an impermeable
adhesive and was never developed as a consolidant. At the same time, silanes are unable to
re-adhere detached surfaces. Consolidation is a major conservation activity yet,
investigating its impact on sandstone has been shown as not being routinely carried out, in
spite of available technology and expertise. Impregnation depth, hardness, water
absorbency and strength have been identified as key parameters for the compatibility
assessment of consolidants. A lack of awareness by budget holders and subsequent failure
to commission compatibility testing, combined with constraints on site access, time and
sampling from heritage sites, mean that these consolidant parameters are rarely known in a
project context and treatment decisions are predominantly influenced by user familiarity as
opposed to most effective testing regime and treatment. The short-term effect of most
consolidation treatments is seen as positive but without monitoring, misleading
assumptions about their long-term performance might be made which puts remote or
inaccessible parts of buildings or monuments at particular risk of unobserved decay. The
limited life span of consolidants necessitates periodic re-treatment which will undoubtedly
pose new compatibility problems.
The research reveals a discrepancy between the conservator perceived lack of access to
conservation science research and the conservation scientist’s feeling that their research
informs conservation practice. The majority of research participants would like to see more
project collaboration to support each other’s work which would resolve this discrepancy.
4. Conclusion
The long-term effects of consolidants on heterogeneous sandstone masonry in Scotland are
poorly understood due to a lack of compatibility and performance testing. Given the limited
range of consolidants, such testing might only seek to answer whether to consolidate or not.
Research and testing of other potentially suitable or adaptable products and the
development of new commercially available and purpose-designed products is urgently
required.
Science cannot necessarily clearly answer, within a project restricted timeframe, whether
consolidation is going to be effective and compatible. Realistic expectations of what
consolidants can achieve and what questions scientists can usefully answer within a given
timeframe need to be established.
Consequently, conservation science might be more realistically used as an evidence-based
risk assessment tool to reduce treatment uncertainty by identifying existent risk factors in
the stone e.g. low strength, high porosity, presence of clays etc. in relation to prevalent
environmental factors e.g. soluble salts, moisture content, climatic conditions, etc. to
produce a stone decay risk factor. By subsequently assessing the physical properties of
consolidated stone in the context of improved environmental conditions, the risk factors of
treated and un-treated stone might be compared, taking the intrinsic and extrinsic properties
of stone into consideration.
The routine integration of purposeful analytical investigations into conservation projects
from the start would permit effective planning of resources to allow informed treatment
decisions to be made. This should involve both analyses prior to treatment as well as post
treatment and longer term monitoring. The significance of architects and other
professionals influencing this process must be recognised and addressed to improve
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awareness of how conservation science can aid their client’s project outcomes, e.g. through
outreach events, formal training, publications and guidance. The lack of long-term
performance monitoring of consolidants leads to high-risk treatments with potentially
costly outcomes and results in missed opportunities to learn from past experiences. The
combined collation and dissemination of conservation science research and conservation
case studies through accessible and non-judgmental publications and online portals is
advocated but has both a resource and administrative requirement.
References
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Cultural Significance, 2013 (http://australia.icomos.org/wp-content/uploads/TheBurra-Charter-2013-Adopted-31.10.2013.pdf, accessed 20.04.14) articles 3.1, 4.
BSI Group. BS 7913:2013. Guide to the conservation of historic buildings - 2013,
paragraphs 6.5 – 6.7.
Calia A., Lettieri M., Quarta G., Laurenzi Tabasso M., Mecchi A. M., 2004, Documentation
and assessment of the most important treatment carried out on Lecce stone
monuments in the last two decades. In: Kwiatkowski D., Loefvendahl R. (eds.),
10th International Congress on Deterioration and Conservation of Stone, 27 June –
2 July 2004, Stockholm Vol. 1, ICOMOS Sweden, pp. 431 – 438.
Cnudde V., Dierick M., Vlassenbroeck J., Masschaele B., Lehmann E., Jacobs P., Van
Hoorebeke L., 2007, Determination of the impregnation depth of siloxanes and
ethylsilicates in porous material by neutron radiography. Journal of Cultural
Heritage, 8, Elsevier, pp. 331 – 338.
De Clerq H., De Zanche S., Biscontin G., 2008, TEOS and Time: Influence of Application
Schedules on the Effectiveness of Ethyl Silicates Based Consolidants. In: Delgado
Rodrigues J. , Mimoso J. M. (eds.) Proceedings of the International Symposium
Stone consolidation in cultural heritage – research and practice, 6 – 7 May 2008,
Laboratorio Nacional de Engenharia Civil, Lisbon, pp. 399 – 408.
Doehne E., Price C. A., 2010, Stone Conservation – an overview of current research’, 2 nd
edition, Getty Institute, Los Angeles, pp. 39, 36, 40.
Ferreira Pinto A. P., Delgado Rodrigues J., 2008, Stone consolidation: The role of treatment
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Graham C., Martin L., Vernon P., Young M., 2014, Conserving Scotland’s Built Heritage:
A Petrographic Investigation on the Effects of Deicing Salts on Scottish
Sandstones , Engineering Geology for Society and Territory, Vol. 8, pp 487 – 490.
Haake S., Simon S., Favaro M., 2004, The Bologna Cocktail – evaluation of consolidation
treatments on monuments in France and Italy after 20 years of natural ageing. In:
Kwiatkowski D., Loefvendahl R. (eds.), 10 th International Congress on
Deterioration and Conservation of Stone, 27 June – 2 July 2004, Stockholm Vol.
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Scotland, Scotland’s Historic Environment Audit 2012, pp. 3,9;
(http://www.historic-scotland.gov.uk/sheareport2012-2.pdf, accessed 27.10.2015).
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Moropoulou A., Labropoulos K. C,. Delegou E .T., Karoglou M., Bakolas A., 2013, Nondestructive techniques as a tool for the protection of built cultural Heritage.
Construction and Building Materials, 48, Elsevier, pp. 1222 – 1239.
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Heritage, London, p. 222.
Pamplona M., Kocher M., Snethlage R., Wendler E., 2008, Consolidation effectiveness of
TEOS on Ança limestone from Portugal. In: Delgado Rodrigues J. , Mimoso J. M.
(eds.) Proceedings of the International Symposium Stone consolidation in cultural
heritage – research and practice, 6 – 7 May 2008, Laboratorio Nacional de
Engenharia Civil, Lisbon, pp. 183 – 192.
Panagiotis T., Karatasios I., Stefanis N. A., 2008, Performance Criteria and evaluation
parameters for the consolidation of stone. In: Delgado Rodrigues J. , Mimoso J. M.
(eds.) Proceedings of the International Symposium Stone consolidation in cultural
heritage – research and practice, 6 – 7 May 2008, Laboratorio Nacional de
Engenharia Civil, Lisbon, pp. 279 – 288.
Price C., 2006, Consolidation. In: Henry A. (ed.) Stone Conservation – Principles and
Practice, Donhead Publishing, Dorset, pp. 102, 104, 107.
Ruedrich J., Hertrich M., Just A., Siegesmund S., Yaramanci U., Jacobs F., 2004,
Construction physics of the market gate of Miletus discovered by non-destructive
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Deterioration and Conservation of Stone, 27 June – 2 July 2004, Stockholm Vol.
2, ICOMOS Sweden, pp. 745 – 752.
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commentary on climate change, stone decay dynamics and the ‘greening’ of
natural stone buildings: new perspectives on ‘deep wetting’. Environmental Earth
Science, 63, pp. 1691 – 1700.
Török Á., 2010, In situ methods of testing stone monuments. In: Boştenaru Dan M, Přikryl
R, Török Á (eds.) Materials, Technologies and Practice in Historic Heritage
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Urquhart D., 2007, Stonemasonry skills and materials - a methodology to survey sandstone
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Weber H., Zinsmeister K., 1991, Conservation of Natural Stone – Guidelines to
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776
USE OF LOCAL STONE IN THE MIDWESTERN UNITED STATES:
SUCCESSES, FAILURES AND CONSIDERATIONS
E. Gerns1* and R. Will1
Abstract
Until relatively recently, locally available stone was used almost exclusively in
construction, due to availability, limited transportation options and economics. Historically,
naturally formed field stone was used for foundations, localized cladding features and in
some instances entire building façades. Stone, perhaps more than any other natural building
material, has numerous varieties and characteristics within its broader classifications. Many
of these local stones were not necessarily appropriate for some applications and
environmental conditions. Since around 1880, and continuing for perhaps 40 years, as
quarrying techniques mechanized, the use of some local stones in larger and thinner
individual units as cladding in multi-wythe exterior wall systems were replacing traditional
monolithic field stone wall systems. As these “newer” wall systems have aged, these
applications introduced challenges including unanticipated weathering characteristics,
residual stresses and detrimental inclusions. Where and how these unique local stones are
installed as well as climate and weathering patterns certainly contribute to the potential
deterioration and serviceability challenges. This paper will focus on three local limestones
used in the Midwestern United States between the 1850s and early 1900s that have variable
performances in various applications.
Keywords: façade cladding, Joliet limestone, Carthage marble, Platteville limestone
1. Introduction
Stone has been used as a building material for thousands of years. Its aesthetics and sense
of permanence have made it a popular material, especially among builders and architects.
Many of the significant buildings throughout history have been constructed of stone. Early
stone monuments constructed of non-local material have been the source of numerous
theories regarding how this material was transported over great distances. In reality, the
method of extracting and transporting may be as simple as basic physics, in combination
with inexpensive and available labor and the expectation that construction can be a
generational endeavour, rather than the highly accelerated pace required in today’s
economic climate. The days of monumental royal constructions are mostly long over, but
the desire to construct buildings using stone remains universal. The evolution of stone clad
buildings closely parallels the evolution of building construction and technologies.
Monolithic wall assemblies were the standard for thousands of years. Modern construction
techniques attempt to minimize the amount of stone used to maintain the aesthetics a
particular stone provides, to save weight and money. This change is a result of the evolution
1
E. Gerns* and R. Will
Wiss, Janney, Elstner Associate, Chicago, Illinois, United States of America
*corresponding author
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of structural and manufacturing technology allowing stone to be used and quarried in
thinner applications than had historically been feasible. Historic quarrying and fabrication
techniques relied on both local labor forces, local stone sources and basic transportation
systems.
Historically stone was used for both decorative and functional purposes. With few
exceptions, building systems incorporate inexpensive backup materials in combination with
more expensive facing. Early stone structures were typically solid, multi-wythe, load
bearing assemblies combining high quality facing stone finished to very tight tolerances
with a looser rubble or brick backup. Once again, economics was critical to the
development of exterior enclosure systems.
The Industrial Revolution of the mid-19th Century dramatically changed the building
industry. Economics certainly still was the primary driving factor in almost all building
construction, but mechanization provided advancements in the construction industry from
machines to transportation. This resulted in the wider use of stone since it was now more
economical in some respects. Transportation remained a major factor in the selection and
use of stone throughout the world.
2. Midwestern United States geology
In the Midwestern United States large stores of limestone exist. Beginning in the 1850s, the
use of locally quarried limestone for civil structures and building foundations became
common. The stone was readily available and the physical properties were found to be
desirable for civil and foundation applications. In these applications, the stone was quarried
in relatively large blocks and installed with the bedding planes oriented parallel to the
ground (naturally oriented).
Unlike foundations, when some of these sedimentary stones were used for cladding, the
geological composition of the stone became more critical to the durability and workability
and therefore appropriateness of the applications. As a cladding, the desire to use the stone
in less natural applications was greater, thus resulting is situations with higher exposure and
less redundancy in the material. Workability with respect to carving, and the desire for
larger units used in alternate aesthetics to random coursing, began to expose the limited
durability of some of the stone.
3. Midwestern United States stone
This paper will focus on three commonly used stones in the Midwestern region of the
United States between 1850 and 1910 including Joliet Limestone, Platteville Limestone and
Carthage “Marble”. Each is extensively used in civil and building applications between
1850 and 1910 in the areas close to their natural source. The material was rarely transported
out of the area for use in other parts of the United States. Use of these stones as a building
stone has all but stopped, but many examples remain in each respective area of their natural
formations.
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3.1. Joliet limestone
In the Chicago area, a cream-colored dolomitic limestone known as Joliet limestone was
widely used prior to 1870. Laid down during the Silurian age, roughly 425 million years
ago, the stone was often marketed as marble to improve the perception of quality of the
material. Joliet limestone was first encountered when the I&M Canal was being built in the
late 1830s. The density and low absorption characteristics of the stone were ideal for lining
the walls of the canal. Being local, the stone was relatively inexpensive and readily
available. Buildings built adjacent to the canal were often constructed using the stone
(Kubal 2013). The Great Chicago Fire of 1871, however shifted the popularity of Joliet
limestone toward Indiana limestone. Newspaper accounts from the time unbelievably
reported that during the fire, limestone ‘seemed as though [it] actually burned like
wood.’ Certainly not the case. By the 1870s exposed applications of the stone revealed that
Joliet limestone was subject to exfoliation and weathering. Thus, many of the older
buildings of the time that used the stone for the exterior walls were showing signs of age
that also put a damper on new construction (Kubal 2013). Further, many of the stone
masons that had worked with the stone since it was first used were no longer in the industry
having retired or passed away. Thus, the rise of popularity of Indiana limestone occurred
since the stone provided a more uniform appearance, had good weathering characteristics,
was easier to work with and was more consistent with the change of architectural aesthetic
that was beginning around 1890. In addition, Joliet limestone became more popular and
economical as an aggregate rather than a building stone since the processing and skilled
labor force required was less than that of building stone. With few exceptions, the stone has
not been used as a building stone since around 1910.
Many examples of Joliet Limestone buildings and structures remain throughout the Chicago
area to this day including the I&M canal, the Chicago Water tower, the Scottish Rite
Cathedral, and Second Presbyterian Church (Fig. 1).
Common characteristics of the stone that often must be addressed in repair work is
exfoliation and face bedding. Few options exist to address these issues and often substitute
stone is used to replace deteriorated components. The weathering of the stone can be
mitigated to an extent by maintaining or improving the water shedding characteristics of the
building with the use of gutters and downspouts. Watertables and drip courses often were
constructed of regional sandstone (Fig. 1) in-lieu of the limestone since it was easier to
work, but more expensive to procure. These features tend to exhibit more deterioration
from run off, requiring higher percentages of repair and replacement than units within the
field of the wall. Replacement material that is similar to the original remains available when
replacement is necessary.
Another unique nature feature is asphaltic inclusions in the stone giving the stone the
mistaken appearance of being stained by roofing mastics or careless repair activities.
Understanding that this is a natural occurring feature of the stone is critical to developing
appropriate and necessary repairs rather than ill-advised approaches such as surface
treatments or aggressive cleaning techniques. Even gentle cleaning methods, such as water
soaking, can cause significant levels of the friable surface to release from buildings clad
with Joliet limestone as the stone begins to soften and ‘protective’ crust formed by years of
atmospheric soiling is removed.
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Fig. 1: Representative example of Joliet limestone with sandstone drip course. Image on the
left is of the Chicago Water Tower (1869) and the image on the right is from Second
Presbyterian Church (1874) also located in Chicago. Note the asphaltic inclusions that are
common in some of the limestone quarried in the area of Joliet Illinois.
3.2. Carthage “Marble”
In Missouri, a metamorphic limestone, known as Carthage marble was popular for both
foundations and cladding beginning in the 1880s. Carthage deposits are part of the
Burlington group of the Mississippian Carboniferous strata that was formed during the
Silurian and Carboniferous periods, roughly 360 million years ago. The ledges are
horizontal and vary from three to twelve feet thick, the thickness increasing with depth. The
ledges are separated by mud seams (Strong 1908). The peak of production for Carthage
marble was the early 1900s at which point more than 750,000 cubic feet were quarried per
year which was second in the United States only to Indiana limestone (Hiller 1910).
The stone in the Carthage quarries has a gray and bluish-gray color, and the lithologic
characteristics of the quarry beds. Stylolites are prominent in the ledges and usually lie in
the direction of the planes of bedding. They are spaced in vertical intervals that vary in
thickness from 1 to 18 inches. The texture of the stone is essentially of uniform
crystallinity, with only slight variations in grain sizes in the stone between the stylolite
‘veins’ (Perazzo 2015).
Carthage marble is similar to limestone in appearance with the exception of the pronounced
stylolites and bedding planes (Fig. 2). When used in exterior wall applications, face spalling
and visible pronounced stylolites are susceptible to freeze-thaw related deterioration in
areas of high exposure. Carved building elements are also more susceptible to weathering
since more of the bedding planes and stylolites are exposed. In addition, random hairline
map cracks are common. These cracks are likely the result of the residual stresses in the
stone being released during quarrying operations. The combination of the factors listed
above resulted in a relatively short use of the stone for building applications. Once again,
the use of Indiana limestone usurped a locally available stone. Most of the original quarries
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have been converted to gravel facilities. Repair of this stone introduces similar challengers
as Joliet limestone. Water shedding façade features can be protected by installing a metal
flashing or cap on the top exposed surfaces of the features. With few exceptions,
replacement material options are limited to higher quality and more consistent limestone. A
common approach that helps maintain the aesthetics and original building fabric is to
replaced architectural features, such as water tables and drip courses, in their entirety with
similar matching material. While all of the stone in a particular feature may not be
significantly deteriorated, the likelihood of such deterioration is often unavoidable. By
replacing the features, these areas of high weathering achieve a much greater service life
cycle.
Fig. 2: Representative example of Carthage marble. Photograph is of the Missouri State
Capitol (1917). Note pronounced bedding planes in image on the right.
3.3. Platteville limestone
In the Minneapolis area, a dolomitic limestone, known as Platteville limestone was widely
used for foundations and cladding beginning in the 1880s. Platteville Limestone is part of
the Ordivician limestone formation and overlies a layer of Glenwood Shale, which overlies
a much thicker layer of Saint Peter Sandstone. Platteville limestone was deposited during
the Ordovician period of the Paleozoic era, roughly 485 million years ago. Platteville was
used widely in the Minneapolis for a period of about 30 years. The lower bed of the
formation was first used for building stone as early as 1823 and was generally characterized
to consist of interlaminated dense or semicrystalline blue-gray limestone with irregular
shaly bands. The upper bed which is fine-grained limestone was found to be more durable
than the lower layers but its use was still limited to foundations and walls not exposed to
view (Sardeson 1914). Over time, in wall applications, all layers of the limestone have not
performed well in a severe cyclical climate such as Minneapolis. When used in a confined
application, such as foundation walls, the stone has performed reasonably well over the
years. In unconfined applications that are exposed to water, the inclusions in the bedding
planes form calcium sulfate dihydrate (gypsum) that will expand when exposed to moisture,
resulting in often dramatic displacements and bowing of building components such as
window sills and parapets (Fig. 3). The gypsum will also result in efflorescence forming on
the surface of the stone as it dries. Like the other two stones, little can be done to address
the stone itself in these instances and replacement is often the only viable repair option.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 3: Representative examples of Platteville limestone. Image on the left is of the Stone
Arch Bridge (1883) located in Minneapolis, Minnesota; image on the right is from the
Pillsbury A-Mill (1881) also in Minneapolis.
4. Causes of deterioration
All stone is susceptible to deterioration from various causes including: moisture shedding
characteristics, lack of proper maintenance, organic growth, inappropriate previous repairs,
and inappropriate cleaning techniques. Freeze-thaw durability has long been known as a
source of stone deterioration and a significant issue in the Midwestern United States. In the
case of dolomitic limestones, clay laden bedding planes are far more susceptible to freezethaw deterioration than oolitic limestone as the clay will readily absorb water (Winker,
1997). Most importantly, relative to the stone described above is a general vulnerability of
the materials based on application. This issue is further exacerbated when the stone is
installed in a face-bedded orientation. Face-bedding is an economic-driven fabrication
method that is commonly used when the proportions of the stone are greater in elevation
than in plan. This creates a greater potential for face delamination and exfoliation of units
when exposed to temperate weathering patterns. While the stones presented above provided
an economical solution for particular application in localized areas of the Midwestern
United States, time has provided the best indication that there are clear disadvantages to
using these local stones in many applications.
5. Repair approaches
While it is often desirable from a preservation philosophy perspective to replace as little
deteriorated stone with the same stone as necessary, yet in some instances this is not
practical or appropriate. Often, the stone is no longer available and for good reason.
Replacing severely deteriorated units or façade elements with an alternate stone in most
instances is the accepted approach. In the case of the stones presented in this paper, a stone
that is often substituted for Platteville and Joliet limestone is known as Lannon stone. First
quarried in the 1830s, Lannon was used in throughout the Midwestern United States. The
stone is a dolomitic limestone quarried in southeast Wisconsin and is part of the Niagara
Escarpment from the Silurian Period (Young 2012). The stone is generally a gray to cream
color and is quarried close to the surface and has excellent durability and very low
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
absorption. This stone has been found to blend well with the both Joliet and Platteville
limestone (Fig. 4). Indiana limestone has been found to be good substitute for Carthage
marble, aside from some of the aesthetic concerns regarding uniformity described above.
The material has a long successful track record of successful applications and the color is
generally consistent Platteville and Carthage with the exception of the lack of pronounced
bedding planes and styolites. Using these alternate stones for water shedding façade
elements as well as deteriorated façade features enable many of the buildings clad with
these poor performing stones to remain in service.
Fig. 4: Representative examples Lannon stone used as a substitute for Platteville stone.
Image on the left is a replacement sill and image on the right is a reconstruction of a
parapet.
As with any building façade repair project, developing an appropriate repair approach is a
multi-faceted process. A typical investigation should include a review of available
documents related to the façade including drawings, maintenance records and previous
reports, a thorough inspection, an investigation of concealed conditions and field and
laboratory testing of the constituent façade components including the stone and mortar.
Based on the findings of the investigation, appropriate repairs, scope and prioritized
phasing can be developed. These repairs may principally include stone replacement, but in
addition consideration of envelope water management provisions, including roof drainage,
repointing and crack repair are often necessary. Finally, appropriate cleaning and biogrowth
treatment often helps to mitigate accelerated deterioration, yet in the Joliet limestone could
cause further deterioration. Other repairs that are sometimes considered include patching,
application of consolidants, pinning and re-sculpting of weathered elements. Each of these
need to be approached with great care. Often times these techniques are ineffective at best
and in some instances detrimental to the stone.
6. Conclusions
When considering these three stones or other local stones that have not been recently used
in building construction, it is critical to understand the properties which make them unique.
This understanding helps to prioritize repairs and determine the appropriateness of using
the same material, if it is available, or using an alternate material without significantly
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compromising aesthetic and providing proven durability. Because stone is not a man-made
product, its physical and aesthetic characteristics can vary significantly even within the
same quarry, thus just because it appears to be the same material, does not mean it will
behave as such.
Traditionally recognized stone properties include compressive, flexural, shear, and tensile
strengths, density, abrasion resistance, coefficient of thermal expansion, and modulus of
elasticity and rupture. In addition to these established properties, other properties that are
frequently overlooked can contribute to premature failure of a stone cladding system.
These properties include permanent volume change or hysteresis, freeze-thaw weathering,
chemical weathering, thermal weathering, effects of stone finish, orientation and
permeability. Simply stated, these properties may reduce the strength and durability of the
particular stone, which can lead to significant maintenance and repairs of the stone façades
in the not-so-distant future.
References
Hiller, J. C., 1910, “Annual Report of the Bureau of Labor Statistics, the State of
Missouri..., Volume 32”, Hugh Stephens Printing Company, Jefferson City, MO,
p. 627, https://books.google.com/books?id=7RkoAAAAYAAJ,
(accessed November 1, 2015).
Kubal,
J.,
2013,
“One
Stone
to
Another”,
http://www.esconi.org/
esconi_earth_science_club/2013/04/what-do-you-know-about-joliet-lemontlimestone-.html, (accessed November 1, 2015).
Perazzo, P., 2015, “Stone Quarries and Beyond”, http://quarriesandbeyond.org/
states/mo/Missouri.html, (accessed November 1, 2015).
Sardeson, F., 1914, “Description of the Minneapolis and St. Paul District”,
pubs.USGS.gov/gf/201/text.pdf, p. 13, (accessed November 1, 2015)
Strong, R. S., 1908, “Carthage Limestone: Its Production and Characteristics”, Mine and
Quarry, Chicago, pp. 179-182.
Winkler, E. M., 1997, “Stone in Architecture: Properties Durability”, p.254
Young, E. 2012, “Home-grown Limestone”, Masonry Edge, Masonry Advisory Council,
https://masonryedge.com/site/mim-archives-thestorypole-vol-38-no-6/372homegrown-limestone, (accessed November 1, 2015).
784
LASER YELLOWING OF HEMATITE-GYPSUM MIXTURES: A
MULTI SCALE CHARACTERISATION
M. Godet1*, V. Vergès-Belmin1, C. Andraud2, M. Saheb3,
J. Monnier4, E. Leroy4 and J. Bourgon4
Abstract
Nd:YAG Laser cleaning at 1064 nm of limestone monuments covered by black gypsum
crusts is sometimes associated with yellowing. This unwanted yellow discoloration is still
not fully explained by the scientific community. During laser irradiation of black crusts a
lot of particles are ablated, forming a visible smoke. One possible explanation of the
yellowing phenomenon is that some yellow iron-rich nanoparticles formed by irradiation
and present in the smoke are redeposited on the surface of stone during the cleaning. To
investigate this hypothesis, previous research has been conducted on simplified model
crusts containing only gypsum and hematite. However this research always focuses on the
analysis of the substrate after cleaning and never on the ablated particles. In the
investigation presented here, we have characterised the particles ablated during the laser
cleaning of a model gypsum crust containing hematite. As the particles of interest are rare
and submicronic we have elaborated a multi-scale analytical methodology. Light digital
microscopy reveals that the ablated particles are essentially gypsum crystals with a slightly
yellow hue, plus red and black micro-particles interpreted as being hematite and magnetite.
When focusing on the yellow gypsum crystals at the nanoscale, electron microscopy allows
us to highlight the presence of two types of iron-rich nanoparticles covering the surface of
gypsum crystals. One type of nanoparticle measure several tens of nanometres and contain
iron, calcium and oxygen whereas the other type of nanoparticles measure less than ten
nanometres and seem to contain only iron and oxygen. These results ascertain the link
between the presence of iron containing nanoparticles and the yellowing effect.
Keywords: laser, cleaning, gypsum crust, nanoparticle, iron yellowing, TEM
1
M. Godet* and V. Vergès-Belmin
Laboratoire de Recherche des Monuments Historiques (CRC-LRMH USR 3224), France
marie.godet@culture.gouv.fr
2
C. Andraud
Centre de Recherche et Conservation des Collections (CRC-CRCC USR 3224), France
3
M. Saheb
LISA, UMR CNRS 7583, Université Paris-Est Créteil and Université Paris-Diderot, France
4
J. Monnier, E. Leroy and J. Bourgon
Université Paris-Est, ICMPE Institut de Chimie et des Matériaux Paris-Est, UMR 7182
CNRS-UPEC, Thiais, France
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
1. Introduction
The Nd:YAG (1064 nm) laser cleaning of historical monuments covered by black gypsum
crusts sometimes induces a yellowing of the underlying stone (Pouli, 2012). In the 2000s,
this yellowing phenomenon raised a widespread aesthetic controversy (Délivré, 2003),
especially in France where the market of laser cleaning for historical monuments has almost
totally disappeared nowadays (Vergès-Belmin et al., 2014). Since 2001, many studies on
the yellowing effect have been conducted on model gypsum crusts (Klein et al., 2001; De
Oliveira et al., 2015; Gracia et al., 2005). As a reminder, a natural black crust is a complex
system composed of a gypsum matrix entrapping soot, iron oxides, ashes; basically all the
particles present in the atmosphere. Thus studying the interactions between this system and
the laser beam is difficult. The problem has therefore been simplified by focusing on
simplified model crusts. Model crusts studied to date are mixtures of synthetic gypsum and
lamp black, graphite, or hematite with various quantities of each component. These
mixtures are applied as a coating on various substrates such as marble or plaster. By
irradiating these model crusts, scientists have managed to simulate in a very simplified way
the laser induced yellowing obtained on site. The irradiated model crusts have then been
analysed with various techniques. For instance for model crusts containing only hematite, it
was found with SEM-EDS that the surface of the post-irradiated yellow substrate was
covered by iron-rich nanoparticles measuring a few tens of nanometres (Klein, 2001).
During laser irradiation of black crusts, a lot of particles are ablated, forming a visible
smoke (Vergès-Belmin et al., 2003). One possible explanation of the yellowing
phenomenon is that some yellow iron-rich nanoparticles are redeposited on the stone
surface during cleaning. To investigate this hypothesis, yellow phases may be searched for
either on the substrates or in the smoke itself. Most of the researches conducted to date
focus on the analysis of the substrate and never on the ablated particles (Klein et al., 2001;
Gracia, 2005; Potgieter-Vermaak et al., 2005).
The only investigations performed on smoke are related to health hazards. Feely et al.
(2000) and Kush et al. (2003) for instance, have evidenced the presence of micro to
nanoparticles in the smoke generated by laser during natural black crust elimination. They
had to face the difficulties of developing a pertinent observation methodology as the
particles are present in very low quantities. These studies were not focussed on yellowing,
and in any case a great number of phases not implicated in the yellowing phenomenon may
be generated in such conditions. Starting from this statement we have decided in the present
study to simplify the system and to focus on particles ejected from a model crust based on
gypsum and hematite. We have elaborated a multiscale approach wherein the morphology
and the structure of the ejected particles were analysed at a macro- to nanometric scale
using complementary analytical tools in order to link these multi-scale observations with
the yellowing effect.
2. Materials and methods
2.1. Sample preparation
The sample used in this study is a model gypsum crust elaborated with a procedure already
described by De Oliveira et al. (2015). A white gypsum plate (7×3 cm) is synthesised by
hydration of a powder of calcium sulphate hemihydrate CaSO 40.5H2O (ALDRICH 97%)
in distilled water. Before the plate becomes totally dry, a mixture of the same calcium
sulphate hemihydrate and red hematite α-Fe2O3 (ALDRICH 99%) powders (70:30 wt %) is
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
sprinkled over the plate through a coarse-meshed sieve (about 1 mm). The remaining water
in the plate is absorbed by the powder and leads to the crystallization of a gypsum crust
entrapping particles of hematite. The crust is left to dry for 24 hours. The name of the
sample is GH30 for Gypsum-Hematite-30wt%.The amount of iron oxide has been
deliberately chosen much higher than the amount present in a natural black crust (1-2 wt%
according to Ruffolo et al. (2014)) in order to increase the probability of the detection of
the yellow particles. Indeed De Oliveira et al. (2015) has shown that the more concentrated
in hematite the model crusts are, the more yellow they become after laser irradiation. We
operate under the assumption that the more yellow is the surface of model crusts, the larger
will be the amount of particles responsible of the yellowing. Particulate materials from the
sample GH30 are obtained using a Nd:YAG laser. The irradiation conditions have been
chosen because they are similar to those used by restorers-cleaners. (see Tab. 1).
Tab. 1: Experimental parameters for laser irradiation of model black crust GH30.
Parameters
Unit
Value
Energy
J
0.4
Frequency
Hz
10
-
Duration/cm²
mincm ²
3
Fluence
Jcm-²
0.4-0.6
The laser is operating at a wavelength of 1064 nm and producing discrete pulses of laser
energy up to 0.4 J with a pulse length of 15×10 -9 seconds. The pulse is delivered using an
articulated mirrored arm and a hand-piece equipped with a 70 cm focal converging lens.
The fluences used slowly increase from 0.4 to 0.6 Jcm-² during the cleaning with a
frequency of 10 Hz and a duration of irradiation of three minutes per cm². In other words,
about 1800 pulses per centimetre are used to clean the sample. The surface is water sprayed
before irradiation. The particles are collected on a clean glass slide (76×26 mm) and a
round adhesive carbon tab (diameter: 6 mm) put vertically aside the sample at a distance of
about 1 cm. (see Fig. 1). The slide and the carbon tab are then stored in an airtight box to
prevent contamination.
Fig. 1: Experimental set-up used to collect particles ejected from the model crust.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
2.2. Characterization techniques
The morphology and colour of particulate materials have first been observed with a light
digital microscope Keyence 3D VHX-5000. We then use scanning electron microscopy
(SEM) to study the morphology at a micro and sub-micron scale. The SEM observation is
performed with a SEM-FEG MERLIN coupled with an energy dispersive X-ray
spectrometer Aztec EDS Advanced to give a first approximation of the chemical
composition. The adhesive carbon tab covered by ablated particles is directly put in the
microscope. Transmission electron microscopy (TEM) analysis is used to identify the
chemical composition and the structure of the particles at a nanoscale. TEM analysis is
performed at 200 keV with a FEI TECNAI F20 equipped with a STEM device coupled with
an EDS spectrometer EDAX R-TEM Sapphire and with a Gatan GIF 2001 Electron Energy
Loss Spectrometer (EELS). The EELS and EDS capabilities are used to determine the
chemical compositions of the particles. Energy-filtered transmission electron microscopy
(EFTEM) technique is also used to select a precise range of electron energies to provide
elemental maps. The sample is prepared by rubbing gently the surface of the glass slide
with a copper grid covered with a holey amorphous carbon film.
3. Results and discussion
3.1. Digital microscope
During laser cleaning of model black crust, the surface of the cleaned sample GH30
becomes yellow (see Fig. 2) and a lot of particles are ablated and are transferred to the glass
slide or the adhesive carbon tab.
Fig. 2: GH30 sample before (red) and after (yellow) laser irradiation.
With naked eye observation, we are able to see a dust deposit. The digital microscope
observation reveals the simultaneous presence of various particles together with a high
quantity of euhedral gypsum crystals having a slightly yellow colour (see Fig. 3). In
addition to the gypsum crystals we can see two other types of particles:
-
-
Irregular agglomerated red particles ranging from a few to several tens of
micrometers interpreted as being hematite which has not reacted with the laser
beam.
Sub-rounded and often agglomerated black particles ranging from a few to several
tens of micrometers interpreted as being magnetite formed from the transformation
of hematite under the laser beam (Da Costa, A. R., 2002; Gracia, 2005).
The gypsum crystals are recognizable thanks to their morphology: they usually form long
and white transparent rods or platelets as shown by De Oliveira et al. (2015). In our case,
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
most ablated gypsum rods or platelets show a diffuse yellow colour but the microscope
resolution is too low to see more clearly their details. It seems therefore that, during laser
irradiation, at least two transformations take place: the hematite transforms into magnetite
and the white transparent gypsum rods acquire a yellow hue.
Fig. 3: Ejected particles collected on a glass slide (digital microscope picture).
3.2. Scanning electron microscope
The SEM investigation we conducted permitted to better understand the structure of the
yellow hue observed with the digital microscope. The ablated yellow gypsum platelets are
actually covered by two types of objects: a large number of spherical nanoparticles and a
rough nanometric film. The size of the nanoparticles is very variable: they range from
several tens of nanometres to more than a few hundreds of nanometres. The rough
nanometric film is covering irregularly the surface of gypsum rods and platelets (see
Fig. 4). The SEM resolution is too low to distinguish more clearly the morphology of the
nanometric film. Based on EDS analyses, we found that the surface of the ablated gypsum
rods and platelets contains calcium, sulphur, oxygen and iron.
Fig. 4: Nanoparticles and rough nanometric film at the surface of a gypsum platelet (SEM
picture, secondary electron mode).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Our SEM observations are in line with those made by Klein et al. (2001) and De
Oliveira et al. (2015) on model gypsum crusts containing hematite which present a yellow
hue after laser irradiation. The two authors have shown that after irradiation the surface of
the gypsum substrate is covered by nanophases containing iron. Here we found that the
laser ablated gypsum crystals presenting a slight yellow hue are covered by nanoparticles
and by a rough nanometric film both containing iron. Our SEM analysis thus tends to
indicate that the yellow hue observed on the gypsum substrate and on the ejected gypsum
crystals after laser irradiation may both originate from the formation of similar nanometric
phase(s) containing iron.
3.3. Transmission electron microscope
TEM analysis was conducted to explore the surface of the gypsum rods and platelets at the
nanoscale. Two types of particles were observed (see Fig. 5):
-
Spherical nanoparticles measuring several tens of nanometres which we will call
“big” nanoparticles.
Sub-rounded nanoparticles measuring less than ten nanometres which we will call
“small” nanoparticles. The small nanoparticles are often agglomerated and may
cover a big nanoparticle.
The big nanoparticles observed by TEM probably correspond to what was described as
“nanoparticles” on SEM observation. The small nanoparticles most probably correspond to
the basic unit of the rough nanometric film previously described.
Fig. 5: a) Small nanoparticles agglomerated on the surface of a gypsum rod; b) Isolated
big nanoparticles covered by a lace of small nanoparticles (TEM pictures); note: the grey
network observed behind the nanoparticles corresponds to the carbon holey film.
The chemical composition of some nanoparticles was determined using EDS and/or EELS.
We mostly looked for isolated nanoparticles to avoid the contribution of gypsum chemical
components to their chemical composition. The localized isolated nanoparticles have
probably detached from the gypsum rods or platelets when we rubbed the copper grid on
the glass slide surface. Two types of particles were detected: nanoparticles containing iron
and oxygen and nanoparticles containing iron, oxygen and calcium. The TEM image in
Fig. 6 shows a big nanoparticle partially covered with an aggregate of small nanoparticles.
The EFTEM maps of calcium, iron and oxygen clearly show that the big nanoparticle
contains iron, oxygen and calcium while the small nanoparticles contain iron and oxygen.
The absence of calcium may be due to the fact that calcium is present in too low quantity to
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
be detected. The absence of sulphur is most probable, as sulphur was not detected by EDS
and it cannot be detected by the EFTEM set up because sulphur energy is too low for the
electron energy loss spectrometer (GIF GATAN) we worked with. However as sulphur is
very difficult to detect at the nanoscale we do not exclude the possibility of its presence.
TEM picture
Ca
Fe
O
Fig. 6: EFTEM cartography of an isolated big nanoparticle
covered by an aggregate of small nanoparticles.
4. Conclusion
In order to understand the laser-induced yellowing phenomenon, we have studied the
ablated materials ejected during the laser irradiation of a model crust composed of gypsum
and hematite. We used a multi-scale approach to link the colour to the morphology at a
micro and nanoscale. The digital microscope aids the identification of yellow gypsum
crystals in the form of rods or platelets associated with red and black micro-particles
interpreted as being respectively hematite and magnetite. SEM/EDS analysis enabled us to
observe the surface of the ablated yellow gypsum rods or platelets at a sub-microscale.
Those crystals are covered with isolated nanoparticles and a rough nanometric film both
containing iron. TEM analyses show that in addition to the isolated nanoparticles observed
with SEM, the presence of smaller nanoparticles measuring less than ten nanometres is
ascertained. These smaller nanoparticles may correspond to the basic unit of the rough
nanometric film observed with SEM but it has not been evidenced yet. Using TEM coupled
with EDS, EELS and EFTEM techniques we have determined the chemical composition of
the observed nanoparticles. The composition seems to depend on the size of the particle: the
“small” nanoparticles measuring less than 10 nanometres contain iron and oxygen whereas
the “big” nanoparticles measuring 20 to 100 nanometres contain iron, oxygen, calcium and
possibly sulphur. The next step of the investigation on those neoformed nanophases is now
to link these multi-scale observations with the yellow colour observed on the surface of
gypsum rods. Further study will undoubtedly reveal more information about the precise
identification of the nanophases and their relation with the yellow colour. Understanding
the laser induced yellowing is a major challenge as it will help the laser manufacturers to
build new cleaning lasers which will not discolour the stone and thus give the cleaning
method a fresh start.
Acknowledgements
Many thanks to the SILLTEC company which is partly funding this PhD research.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
References
Da Costa, A. R., 2002, Ultra-fast dehydration and reduction of iron oxides by infrared
pulsed radiation, Scripta Materialia, 47, 327-330.
Délivré, J., 2003, Laser cleaning: Is there specific laser aesthetics?, Journal of Cultural
Heritage, 4, 245-248.
De Oliveira, C., Vergès-Belmin, V., Demaille, D. & Bromblet, P., 2015, Lamp black and
hematite contribution to laser yellowing: a study on technical gypsum samples,
Studies in Conservation, online DOI:10.1179/2047058415Y.0000000003
Feely, J., Williams, S., Fowles, S., 2000, An initial study into the particulates emitted
during the laser ablation of sulphation crusts, Journal of Cultural Heritage, 1, 6568.
Gracia, M., Gavino, M., Vergès-Belmin, V., Hermosin, B., Nowik, W. & Saiz-Jimenez, C.,
2005, Mössbauer and XRD Study of the Nd-YAG Laser Irradiation at 1.06 µm on
Haematite Present in Model Samples, Proceedings of the Laser in the
Conservation of Artworks Congress (LACONA V), Dickmann, K., Fotakis, C. and
Asmus, J. F. (eds.), Osnabrueck, Germany, 341-346.
Klein, S., Fekrsanati, F., Hildenhagen, J., Dickmann, K., Uphoff, H., Marakis, Y. &
Zafiropulos, V., 2001, Discoloration of Marble During Laser Cleaning by
Nd:YAG Laser Wavelengths, Applied Surface Science, 171(3–4), 242–51.
Kusch, H.-G., Heinze, H., Wiedemann, G., 2003, Hazardous emissions and health risk
during laser cleaning of natural stones, Journal of Cultural Heritage, 4, 38s-44s.
Pouli, P., Oujja, M., Castillejo, M., 2012, Practical issues in laser cleaning of stone and
painted artefacts : optimisation procedures and side effets, Applied Physics A :
Materials Science & Processing, 106, 447-464.
Potgieter-Vermaak, S.S., Godoi, R.H.M., Van Grieken, R., Potgieter, J.H., Oujja, M.,
Castillejo, M., 2005, Micro-structural characterization of black crust and laser
cleaning of building stones by micro-RAMAN and SEM techniques,
Spectrochimica Acta Part A, 61, 2460-2467.
Ruffolo, S., Comite, V., La Russa, M., Belfiore, C., Barca, D., Bonazza, A., Crisci, G.,
Pezzino, A., Sabbioni, C., 2014, An analysis of the black crusts from the Seville
Cathedral: A challenge to deepen the understanding of the relationship among
microstructure, microchemical features and pollution sources, Science of the Total
Environment, 502, 157-166.
Vergès-Belmin, V., Wiedemann, G., Weber, L., Cooper, M., Crump, D., Gouerne, R., 2003,
A review of health hazards linked to the use of lasers for stone cleaning, Journal of
Cultural Heritage, 4, 33-37.
Vergès-Belmin, V., De Oliveira, C., Rolland, O., 2014, Investigations on yellowing as an
effect of laser cleaning at Chartres Cathedral, France, Proceedings of the ICOMCC 17th Triennial Conference, Bridgland, J. (eds.), Melbourne, art. 1703.
792
THE USE OF HYDROXYAPATITE FOR CONSOLIDATION OF
CALCAREOUS STONES: LIGHT LIMESTONE
PIŃCZÓW AND GOTLAND SANDSTONE
(PART I)
A. Górniak1, J.W. Łukaszewicz2*, B. Wiśniewska1
Abstract
Carbonate stones have been widely used to create works of art and architecture, due to their
mineral composition which is extremely sensitive to weathering mechanisms. The corrosion
processes results in density reduction and loss of mechanical integrity, often accompanied
by an increase in porosity. Structural consolidation aims at restoring the original physical
properties of the stone and at the same time making them more resistant to weathering
agents. Since the second half of the 20th century, after many years of using organic,
synthetic resins for this purpose, there is now a tendency to return to inorganic
consolidants, which are chemically compatible with stone building minerals. One goal of
this research is to examine the possibility of using diammonium hydrogen phosphate (DAP)
for consolidation of light limestone and calcareous Gotland sandstone, often used in Polish
architecture and sculpture. Another aim is to determine the best conditions for the
procedure.
Keywords: Pińczów limestone, Gotland sandstone, consolidation of calcareous stone,
hydroxyapatite, diammonium hydrogen phosphate (DAP), SEM/EDS
1. Introduction
Apatite coatings have been identified on ancient monuments. Good preservation of these
layers and the stone underneath, was an impulse to start research on consolidation and
increasing acid dissolution resistance by causing formation of apatite in the structure of
carbonate stones. These works commenced in 2009 by a research team under the direction
of Professor George W. Scherer, Princeton University, New Jersey, USA.
This paper investigated the possibility of using diammonium hydrogen phosphate (DAP) as
a consolidant for a structural treatment of Pińczów limestone and Gotland sandstone.
Conditions affecting the effectiveness of the reaction between DAP and calcium carbonate
and its impact on the properties of treated stones were defined.
1
A. Górniak and B. Wiśniewska
conservator-restorer
2
J.W. Łukaszewicz*
Department for Conservation of Architectonic Elements and Details, Faculty of Fine Arts,
Nicolaus Copernicus University, Toruń, Poland
jwluk@umk.pl
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The effectiveness of structural consolidation is affected by stone properties, like their
chemical and mineralogical nature, type of porous structure (pore distribution, their
diameter and shape) and also by the method and materials used. The most significant
requirements for consolidants are (Łukaszewicz 2002, s. 63-64):
- Short time of solution penetration, depending on its low viscosity;
- Evenly distributed in stone structure, lack of migration to the surface;
- High degree of amplification of the disintegrated material, while maintaining the porosity;
- Not affecting any visual changes, especially on the surface;
- Absence of harmfull side effects, like introduction of water-soluble salts;
- Highresistance to erosion and corrosion factors, like water, UV radiation, air pollution,
biological agents.
The method of carbonate stone consolidation with hydroxyapatite (HAP) is based on
exposing calcite to an diammonium hydrogen phosphate (DAP) solution, as schematically
shows the chemical reaction (Kamiya et al. 2004, s. 56)
10CaCO3 + 5(NH4)2HPO4 → Ca10(PO4,CO3)6(OH,CO3)2 + 5(NH4)2CO3 + 3CO2 + 2H2O
The structure of the final product depends on many factors including solution
concentration, temperature, pH and presence of foreign ions. During this transformation
intermediate, metastable phosphate phases other than hydroxyapatite are formed
(identification of their structure will be studied in Part II of current research).
In this study the impact of the type of the stone, DAP solution concentration and
temperature on the possibility of reaction between calcium carbonate contained in Pińczów
limestone and DAP was investigated.
2. Methodology
2.1. Materials
2.1.1. Stone samples
Two types of carbonate stones were used, both popular in Polish monuments and
sculptures, Pińczów limestone and Gotland sandstone. Pińczów is a porous light limestone
with bulk density d= 1.73 g/cm3, water penetration up to 5 cm within 30-36 min., water
absorption N= 13.9%, open porosity Po=22.61% and compressive strength Rc=10.9 MPa.
Gotland is a porous sandstone with carbonate binder with varying amount of calcium
carbonate, with bulk density d= 2.11 g/cm3, water penetration up to 4 cm within 2860 min., water absorption N= 5.9-6.2%, open porosity Po=12.7% and compressive strength
Rc=17.9 – 38.2 MPa. In this research two types of Gotland sandstone were used, one with
8.42-10.67% calcium carbonate content, and another with 13.32 – 14.02%.
Ground Pińczów limestone fractions <0.16 mm, 0.16-0.25 mm and 0.25-0.40 mm were
used. The crushed limestone was placed in cylindrical containers having 3.5 cm diameter
and 5cm high. In the second part of the research cubic samples were used (5 side).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
2.1.2. Consolidant
Both stones were consolidated with water solution of diammonium hydrogen phosphate
(DAP) - (NH4)HPO4, purchased from Polskie Odczynniki Chemiczne S.A., Gliwice, 5%
and 15% solutions were prepared.
2.2. Consolidation
Ground Pińczów limestone was impregnated by capillarity with 5% and 15% DAP
solutions. After a fully saturation, part of the cylindric containers were placed in a tightly
covered vessel for 48h in laboratory conditions (293-294 K) and the second part in a heat
chamber (303K). This treatment was repeated 1, 2, 3 and 5 times. Pińczów limestone and
Gotland sandstone cubic samples were consolidated by partial immersion with 5 in 15%
DAP solutions. Calcium phosphate phases and bridges between grains formed after
treatment were assessed with ATR-FTIR and SEM/ EDS. The effectiveness of the
consolidation was evaluated by the capillary impregnation time change and impregnability
change after treatment, also by improvement of mechanical properties and freezing
resistance of the stone.
3. Results
3.1. Impact of DAP solution concentration and multiple saturation on properties of
ground Pińczów limestone
After just one saturation cycle with 5% DAP in every ground cylindric sample bridges
between grains emerged as a product of DAP and calcium carbonate reaction. This merger
allowed samples to be released out of the cylindric containers and to be cut in pieces
(Fig. 1). An increase in weight occurred, depending on aggregate fraction, from 0.54%
(<0.16 mm) to 1.08% (0.25-0.40 mm), due to different solution absorption of the samples
of different grain size. The sharp increase of phosphate phases content in the samples
occurred after repetition of the saturation and increasing the concentration of DAP (Tab. 1).
Fig. 1: GroundPińczów limestone after consolidation.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Influence of concentration and numbers of DAP application
on time of capillary rise, absorption and changes in weight.
Fraction of
aggregates
Number of
application of
DAP
Time of capillary
rise up to 4 cm
Absorption
Increase of
weight
s
%
%
I
58
43.99
0.82
0.16-0.25
II
36
40.08
3.08
5% DAP
III
31
38.39
3.97
V
26
35.68
4.62
I
1’21”
54.04
5.94
0.16-0.25
II
46”
32.50
12.51
15% DAP
III
35”
32.23
13.31
V
37”
30.53
14.26
mm
The decrease of capillary penetration time and absorption during the subsequent
impregnation of ground limestone is clearly demonstrated. The number of separated
phosphate phases depends on both the concentration of the solution as well as the number
of impregnation cycles, with the highest value (14.26%) for fivefold impregnation with
15% DAP solution. Samples after triple impregnation with 15% DAP were analyzed by
SEM/EDS to determine their texture, identify phosphate phases and define their distribution
in micro regions (Fig. 2 to Fig. 4). The results indicate that phosphate phase distribution is
evenly throughout the sample, also on the surface of limestone and in free spaces between
grains.
Fig. 2: Texture of limestone grain before treatment.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 3: Texture of treated limestone grains by 15% DAP – middle part of the sample.
Fig. 4: Distribution of phosphorus.
ATR-FTIR was used as an analysis method to investigate the newly formed phosphate
phases. As an comparative model untreated ground Pińczów limestone and calcium
phosphates synthesized in the reaction of lime water and a 15% solution of DAP were used.
For carbonates analytical bands with wave number 1396 cm-1, 871cm-1, and for phosphates
1031 cm-1, 560 cm-1 were adopted. With increasing degree of conversion into phosphate
phases the carbonate absorbance bands decreased whilst phosphates were increasing. The
Fineness of Pińczów limestone together with the solution concentration clearly influences
this process. Addtionally, temperature has also a small effect on the conversion of
carbonates into phosphate phases.
3.2. The impact of stone type on consolidation effectiveness
3.2.1. Stone impregnation
Pińczów limestone and Gotland sandstone were impregnated by capillarity from a partial
immersion in 5% and 15% DAP solution. Impregnation time of the limestone was quite
short, but the solutions moved slower in the sandstone (Tab. 2). It depends on the type of
stone but also on the concentration of the solutions. An extremely long time was needed for
the 15% DAP solution to saturate Gotland sandstone. Absorption of DAP solutions in
different concentrations and water absorption were similar (approx. 13% for Pińczów
limestone and approx. 6.2% for Gotland sandstone). It must therefore be concluded that
these two lithotypes were fully saturated with the investigated solutions, regardless of their
concentration.
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Tab. 2: Influence of type of stone for consolidation possibility.
Stone
Limestone
Sandstone
Concentration of
DAP solution
Capillary rise
up to 4 cm
Absorption of
DAP solution
Increases of
weight
%
min.
%
%
5
39
13.19
0.16
15
46
13.19
0.33
5
44
6.05
0.14
15
151
6.16
0.40
After impregnation a slight increase in weight of the samples was noted, depending on the
DAP solution concentration used. Despite the fact that after impregnation the samples were
kept in a closed system, the reaction products migrated to the surface, having a significant
impact on esthetic values of the stone, which is difficult to accept. Surfaces of both, the
limestone and the sandstone were covered with a white coating (Fig. 4 and Fig. 5), also the
color of the stones was darker. The standard tests for color changes in a L*a*b system
showed a large color change after consolidation for Pińczów limestone (ΔE from 5.6 to
6.5).
Fig. 4: White coatings after consolidation of limestone (right),
before consolidation (left).
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Fig. 5: White coatings after consolidation of Gotland sandstone by 15% DAP.
2.1.1. Properties of consolidated stones
Properties of consolidated stones were investigated on Pińczów limestone impregnated one
and two times with 5% and 15% DAP, and Gotland sandstone impregnated with 5% DAP.
15% DAP solutions were abandoned in Gotland sandstone impregnation due to a strong
crystallization of reaction products on the surface of the stone, hence the inability to use
this solution concentration in conservation practice. The effectiveness of the process is
obtained by changes in water absorption, porosity, compressive strength (Rc) and breaking
strength (Rb). The results are presented in Tab. 3.
Tab. 3: Properties of treated stones.
Stone Concentration Increase
Water
Decrease Open Decrease
of DAP
of
absorption
of
porosity
of
solution/
weight
water
porosity
Number of
absorption
applications
Limestone
Sandstone
Rc
ΔRc
%
%
%
%
%
%
MPa
%
5%/2×
0.18
12.47
4.15
21.84
3.41
13.51
24.17
15%/1×
0.33
12.74
2.6
22.21
1.78
13.67
25.64
15%/2×
0.68
12.52
4.28
21.85
3.36
16.47
51.38
5%/1×
0.14
5,75
7.56
12.01
4.93
31.38
6.32
Rb=
0.45
25
The use of DAP to consolidate Pińczów limestone and Gotland sandstone, and as a
consequence formation of calcium phosphates phases inside the stone pores (with not fully
examinated chemical structure) caused only a slight decrease in water absorption and
porosity of both stones, which should be considered as an advantage of the proposed
method. Mechanical strength increase depends on the amount of phosphate phases
introduced into the pores of the stone. Increasing numbers of phosphate phases were
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obtained by increasing the concentration of DAP solution and the number of solution
applications. There was a greater percentage increase in mechanical strength of limestone
than sandstone, which is connected to the initial high, but also diverse mechanical
properties of the sandstone. This occurrence is known and confirmed in other studies on
Gotland sandstone, where breaking strength had a slightly higher gain than presented in this
paper, due to lower initial values.
4. Conclusions
The current study shows that the use of diammonium hydrogen phosphate (DAP) to
structural consolidation of porous carbonate stones is possible, the method fulfils many of
the criteria stated in the introduction. It does not require the use of environmentally harmful
toxic solvents, aqueous DAP solutions move relatively quickly in the pores, allowing a
complete saturation. Seasoning after the procedure takes only two days during which no
substances harmful for the stones are emerged, the consolidated materials also retain their
hydrophilic properties.
The research has shown that the phosphates forms were evenly distributed throughout the
volume of all treated samples, wherein the water absorption and the open porosity
decreased only slightly, which allows resaturating the consolidated stone in the future if
needed. However, a partial migration of the reaction products to the surface, especially in
Gotland sandstone, has caused reliable sealing of the surface and produced white coatings,
and darkening of the surface of both stones, which of course is harmful. The mechanical
properties depend on the number of newly created phosphate phases, which form in the
pores of the stones, and their number depends on the concentration of the DAP solution and
the number of repetitions of the process. The highest increase in compressive strength was
obtained after a double impregnation of 15% DAP solution, 51%, with 0.68% weight
increase after the treatment. Consolidation of Gotland sandstone also gives good results.
Preliminary studies on freezing resistance of treated stones showed that samples of
consolidated limestone after 25 freezing-thawing cycles endured it better than not
consolidated samples. The decrease in mechanical properties in the first case was 33%,
while in the second 42%.
With increasing reaction temperature the degree of conversion of calcium into phosphate
forms in Pińczów limestone increases, therefore the treatment should be carried out, if
possible, at higher temperature (approx. 25-40°C).
In conclusion:
- Diammonium hydrogen phosphate (DAP) solutions can be interesting consolidates
for Pińczów limestone and Gotland sandstone.
- Time of capillary rise of DAP solutions depends on their concentration and the
structure of the stone.
- Reaction effectiveness depends on the mineralogical composition of the treated
stones and the conditions of seasoning after treatment.
- Increase in mechanical strength properties depends on the concentration of the
solution and the number of procedures performed.
- Due to migration of phosphate phases to the surface, which follows its seal and
coatings forming, at this stage of the research the method cannot be used in
conservation practice.
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Future research should be continued, primarily on further explaining the mechanism of
DAP and calcium carbonate reaction in different stones (including the impact of metal ions
presence) and the reduction of phosphate phases migration to the surface.
Acknowledgements
The authors would like to thank Dr.Grażyna Szczepańska (Instrumental Analysis
Laboratory, Faculty of Chemistry, NCU) for helping with the SEM-EDS analysis and Mr.
Krzysztof Lisek for technical assistance during the project.
References
Kamiya M., Hatta J. Shimada E., Ikuma Y., Yoshimura M., Monma H., 2004, AFM
analysis of initial stage of reaction between calcite and phosphate, Materials
Science and Engineering B, 111.
Łukaszewicz J. W., 2002, Badania i zastosowanie związków krzemoorganicznych w
konserwacji zabytków”, Wydawnictwo UMK, Toruń, ISBN 83-231-1445-5,
pp. 257.
Rodrigues J. D., Pinto A. P. F., 2015, Laboratory and onsite study of barium hydroxide as a
consolidant for high porosity limestones, Journal of Cultural Heritage,
paper in press.
Sassoni, E., NaudiS., Scherer, G. W., 2010, Preliminary Results of the Use of
Hydroxyapatite as a Consolidant for Carbonate Stones, Paper WW4.5, Materials
Research Society Symposium WW, Materials Issus in Art and Archaeology IX,
November 29 - December 2, Boston, s. 189-196.
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802
MARBLE PROTECTION BY HYDROXYAPATITE COATINGS
G. Graziani1*, E. Sassoni1, E. Franzoni1 and G.W. Scherer2
Abstract
Hydroxyapatite (HAP) based treatments have been proposed for the protection of marble
artifacts against acidic rain corrosion, because of the much lower dissolution rate and
solubility of HAP with respect to calcite. Results obtained so far are promising, but
optimization is necessary to make the treated layer complete, non-cracked and non-porous.
In this study, ethanol addition was proposed to enhance surface coverage while avoiding
crack formation, thus increasing the acid attack resistance of the substrate. The
investigation of the best formulation and treatment procedure to be used was determined on
calcite powders, then the acid resistance of the most promising treatments was evaluated on
Carrara marble specimens by a specifically designed simulated rain apparatus, allowing to
drop a continuous flux of acidic solution onto the samples, thus being closer to real
weathering conditions on site. Results obtained show that HAP is a valuable option for
marble protection, being able to slow down marble decay due to acid rain and exhibiting a
better performance than ammonium oxalate, currently the most investigated inorganic
protective for marble.
Keywords: calcium phosphate, acid attack, ammonium oxalate, calcite, dissolution
1. Introduction
Dissolution of marble surfaces due to the interaction with rain is a severe issue regarding
cultural heritage preservation, as it results in the loss of precious material from stone
artworks. Marble dissolution is linked to the solubility of calcite, its principal constituent
(Naidu et al. 2015; Bonazza et al. 2009). However, all stone protectives currently available,
both organic and inorganic, exhibit drawbacks that limit their efficacy. For this reason the
research for a suitable product to be employed for stone protection is a primary goal in
cultural heritage conservation.
The use of hydroxyapatite (HAP) as a protective for marble has been recently investigated
(Naidu et al. 2014; Naidu et al. in press), as HAP has a very low solubility and dissolution
rate compared to calcite. For this reason, creating a layer of HAP on top of marble would
prevent calcite dissolution, provided that the layer is continuous, non-porous and uncracked. HAP can be formed by a mild chemical route by reacting diammonium hydrogen
1
G. Graziani*, E. Sassoni and E. Franzoni
Department of Civil, Chemical, Environmental and Materials Engineering (DICAM),
University of Bologna, Italy
gabriela.graziani2@unibo.it
2
G.W. Scherer
Department of Civil and Environmental Engineering (CEE), Princeton University,
United States of America
*corresponding author
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phosphate (DAP) with calcium ions (Sassoni et al. 2011), deriving either from partial
dissolution of the stone or externally added. Results obtained so far were very promising,
but the treatment still needs to be optimized.
Ethanol has been found to be a calcite growth modifier and to adsorb on calcite and HAP
(Ji et al., 2015, Sand et al. 2010). For this reason, in this study, ethanol addition to the DAP
solution was investigated, with the aim of increasing surface coverage without causing
crack formation, and hence improving acid resistance of HAP-treated marble. Solutions of
DAP and ethanol in different concentrations and in single and double applications were
used and their efficacy was compared. At this step, treatments were applied to calcite
powders and acid attack testing was performed by exposing samples to a finite volume of
acid solution. Powders, having very high specific surface, undergo much faster dissolution,
so this method allowed faster evaluation of the treatments. Moreover, it allowed exposure
of a high number of grains that differ in crystallographic orientation and impurities, which
otherwise would have required a high number of coarse samples. First, the most suitable
ethanol concentration and treatment procedure were selected based on resistance to acid
attack. Results were compared to those obtained by treating samples with ammonium
oxalate (AmOx), currently the most used inorganic material for marble protection. Mixtures
of AmOx and HAP were investigated too, with and without ethanol addition, as AmOx is
effective in uniformly covering the substrate, but its solubility is significantly higher than
that of HAP. Morphology and composition of the coatings were also investigated. The most
promising coatings were applied on Carrara marble prisms, to get closer to the real
situation, and a different type of acid attack test was used, consisting in a simulated runoff
apparatus. Cycles, each consisting in continuous dripping of acidic solution over the
samples followed by drying, were performed to prevent too high an accumulation of
calcium ions near the dissolving marble surface, which would reduce the marble dissolution
rate (Kaufmann G., et al., 2007, Sjcoberg E.L. et al., 1985).
2. Materials and Methods
Calcite powders (30-50 White, Imerys) were sieved to select the fraction with particle size
between 500 and 595 µm. Particles in this range would allow several nucleation sites on
each particle, while providing a high specific surface area for dissolution tests. Carrara
marble samples (Imbellone Michelangelo s.a.s.) had 30×30×20 mm3 size. DAP (> 99%,
Sigma Aldrich), calcium chloride (assay > 99.0%, Sigma Aldrich), ethanol (FisherScientific) and ammonium oxalate (≥ 99.99%, Sigma Aldrich) were used for the treatments.
Prior to treating and characterization, powders and prisms were rinsed with water and
ethanol to remove possible surface impurities and dried overnight.
2.1. Treatments on calcite powders
Reference samples were treated with a 0.1 M DAP solution (sample D0.1M) and with a
5 wt.% AmOx solution, according to Doherty et al., 2007 (sample AmOx). To evaluate the
effect of ethanol on the formation of HAP, ethanol was added in different concentrations to
the 0.1 M DAP solution and its effects were evaluated (samples with the letter “E”). To
boost surface coverage, ethanol addition was tested in combination with higher DAP
concentration (namely 1M, samples D1E) and in double treatments (samples D1E+D1). In
all DAP-treated samples (with and without ethanol addition), calcium ions were externally
added by adding CaCl2 to the solution, to prevent dissolution of the substrate. All
treatments were performed by immersion (reaction time 24 hours). Compositions of the
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most significant solutions are presented in Tab. 1. Second treatments were performed
exactly as the first ones, but on pre-treated powders. Surface coverage, morphology and
composition of the layers were investigated for the most promising treatments by FT-IR
(Nicolet 6700) and SEM/EDS (FEI Quanta 200 FEG ESEM with Oxford EDS probe).
Tab. 1: Composition and nomenclature of the most significant treatments.
Specimen
D0.1
D0.1E
D1E
AmOx
AmOxE
Treating solution
0.1 M DAP + 0.1 mM CaCl2
0.1 M DAP + 0.1 mM CaCl2 + 0.5 wt.% ethanol
1 M DAP + 1 mM CaCl2+ 0.5 wt.% ethanol
5 wt.% Ammonium Oxalate
5 wt.% Ammonium Oxalate+ 0.5 wt.% ethanol
The efficacy of the treatments was evaluated in terms of acid attack resistance, determined
by exposing powders to an aqueous solution of HNO 3 at pH 5, such pH being chosen based
on current and future values of rain pH (Bonazza et al., 2009a, Bonazza et al., 2009b).
Powders were put in a beaker with the acidic solution kept stirring at a constant speed and
pH variations in time were recorded. Morphology was re-examined for relevant samples.
2.2. Treatments on Carrara Marble prisms
Treatments D0.1M, D0.1ME and double treatment D0.1ME+0.1M were applied on Carrara
Marble prisms. Untreated and AmOx treated samples were also examined for comparison's
sake. Treatments were performed by immersion as for the powders.
As calcite dissolution depends on the concentration of Ca 2+ ions in the solution, a custom
designed setup providing a continuous dripping of solution onto the samples was preferred
for the acid resistance test. Deionized water (at initial pH 6.8) was dripped onto the samples
at a rate of 500 mL/h, alternating periods of dropping (2.5 h) and drying. After 24 wet/dry
cycles (2 cycles per day), each sample had been exposed to an average solution volume of
29 L. Considering the annual average rain in Bologna (800 mm) and the size of the
specimens, this volume of solution corresponds to about 40 years of rain. Runoff water was
collected at each cycle and Ca2+ and PO43- concentrations in the solutions were determined
after cycles 1, 2, 8 and 24, to evaluate the dissolution of both the substrate and the coating.
Ca2+ concentration was determined by HPLC, PO43- by spectrometer. SEM/EDS was
performed after the acid resistance test on the most promising formulation, to evaluate the
treated layer morphology after artificial weathering.
3. Results and discussion
The treatment efficacy was evaluated on powders in terms of acid resistance (Fig. 1). The
acid resistance of samples treated with 0.1M DAP solution is not satisfactory and
accordingly several uncoated areas can be observed when powders are examined by SEM
(Fig. 2a). These areas can act as preferential points for acid attack and, in fact, after acid
attack it is visible that acid has undercut the substrate under the coating (Fig. 3b).
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When ethanol is mixed to the solution, acid attack resistance of samples remarkably
increases (Fig. 1a). Ethanol additions are beneficial in terms of acid resistance; no benefits
are obtained by increasing the concentration above 0.5 wt.-%, while values of 20 wt.-%
make the solution too diluted and the acid resistance decreases; hence 0.5 wt.% was the
selected concentration. SEM observations of ethanol-treated samples show that surface
coverage has been remarkably improved by ethanol addition; however, some sparse
uncoated areas can still be spotted (Fig. 2a). For this reason, ethanol-doped solutions at
higher DAP concentration were tested.
Fig. 1: Acid resistance (pH vs. time) for: a) different concentrations of ethanol in single
and double treatments, b) different DAP concentrations, c) AmOx and DAP combined
treatments, d) double treatments with and without ethanol addition. In e) the composition of
the treated layer of the most promising formulations is investigated by FTIR.
In terms of acid resistance (Fig. 1b), D1E samples are much more resistant than D0.1E
samples. However, when the morphology of the treated layer is observed, cracks are
evident (Fig. 2c) thus raising concerns about long time performance of the coating. Cracks
might occur during drying due to excessive thickness of the coating. Hence, double
treatments were investigated, with the aim of creating two superimposed layers of reduced
thickness instead of a thicker one, so as to avoid the crack formation. Double treatments
with and without ethanol addition were investigated and the best one in terms of acid
resistance was selected (Fig. 1c and d). Double treated samples at 0.1M concentration
(D0.1+D0.1) have a better acid resistance than single D 0.1M treatment with and without
ethanol addition (Fig. 1b). However, the efficacy can be further enhanced by ethanol
addition: the most promising formulation being that where ethanol is used in the first layer,
as no further increases in acid resistance were obtained by ethanol addition in the second
layer (Fig. 1d). Double treatments at higher ethanol concentration in the first layer were
also examined, as well as double treatments at higher DAP concentration (Fig. 1b). None of
the tested treatments exhibits a better behaviour with respect to D0.1E+D0.1, which was
then selected as the most promising and subjected to further characterization.
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Fig. 2: Morphology of treated powders: a) sample D0.1; b) sample D0.1E; c) sample D1E;
d) sample D1E+D1; e) sample D0.1E+D0.1; f) sample AmOx.
Fig. 3: Morphology of treated powders after acid attack test: a) untreated powder; b)
sample D0.1; c) sample D0.1E+D0.1.
Acid resistance of D0.1E+D0.1 sample is much higher than that of ammonium oxalate
treated samples, despite the uniformity of AmOx coating on powders (Fig. 2f), due to high
solubility of calcium oxalate with respect to HAP and to the porosity of the layer. AmOx
and HAP mixed treatments exhibit a better behaviour than AmOx treatment alone.
However, they are still more soluble than D0.1E+D0.1 treated samples. No substantial
benefits were obtained by adding ethanol to ammonium oxalate (Fig. 1c). When sample
D0.1E+D0.1 morphology was examined by SEM, the coating appeared continuous and uncracked (Fig. 2e). After acid attack, however, some sparse uncoated areas were found close
to the grain edges (Fig. 3c). The composition of the treated layer was determined for the
most promising samples: D0.1, D0.1E and D0.1E+D0.1 by FT-IR (Fig. 1e). Bands relative
to HAP formation can be assessed for all of the samples. These treatments were then
applied to massive samples, again in comparison with AmOx, using the described dripping
apparatus, so that data would not be affected by the finite volume of acid. Dissolution of
samples was evaluated by determining the Ca2+ concentration in the runoff solution; values
are reported in Tab. 2 and Fig. 4.
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Tab. 2: Ca2+ concentrations (values are averages for duplicates samples).
Specimen
Ca2+ (mg/L)
Untreated
2.59±1.34
D0.1
2.21±0.69
D0.1E
1.97±0.98
D0.1E+D0.1
1.64±0.65
AmOx
2.69±1.18
Fig. 4: Ca2+ion concentration in the runoff solutions for duplicate samples.
Fig. 5: Ca2+and PO43- ion concentrations in the runoff solutions for duplicate samples.
The lowest calcium ions concentration can be assessed for samples D0.1E+D0.1, thus
indicating slower dissolution (Fig. 4). Ethanol addition alone results in an improvement
with respect to the sample treated with 0.1M solution but, for massive samples, its effect is
much less visible than for powders. D0.1E+D0.1 also exhibits the lowest standard deviation
between the two samples and in the different cycles, indicating that the behaviour is more
dependent on that of the coating than the substrate. Phosphate concentration was also
investigated to assess whether the dissolution would affect only the substrate or also the
coating (Fig. 5). As HAP is expected to be insoluble for the given pH, high PO43- contents
indicate the presence of soluble phases together with HAP. Non-negligible phosphate
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
amounts in sample D0.1E might hence suggest that soluble phases have formed together
with HAP, hence Ca2+ ions found in the solution might derive from the dissolution of both
the substrate and the coating. Sample D0.1E+D0.1 exhibits the lowest dissolution and a
negligible presence of PO43- ions, hence indicating that HAP and not soluble phases were
obtained by the treatment. In particular, Ca2+ concentration is much lower than that of
AmOx samples, where, however, Ca2+ ions in solution derive from dissolution of both the
substrate and the coating, given the higher solubility of AmOx with respect to HAP.
Fig. 6: Morphology of samples after simulated rain test: a) untreated marble, b) AmOx,
c,d) D0.1E+D0.1; e) EDS on sample D0.1E+D0.1 in one area that seems uncoated.
Ca2+ ion concentration in D0.1E+D0.1 is lower than that of untreated marble; however, as
some dissolution occurs in the samples, SEM was performed after the simulated rain test
(Fig. 6). Images of untreated marble and AmOx are also reported for sake of comparison.
After acid attack, untreated samples appear etched, as does AmOx, where the surface seems
essentially bare, thus suggesting that both dissolution of the coating and of the substrate has
occurred. After acid attack, large areas of D0.1E+D0.1 appear uncoated and etched, though
etching seems less severe than in the untreated reference. Some thick areas of the coating
remain visible. However, when EDS is performed, phosphorous signal is detected in all the
areas of the sample, including those that seem bare. For this reason it might be presumed
that a layer of nanometric thickness is preserved: this would be consistent with the fact that,
despite the treated layer being almost entirely consumed, the dissolution of the sample is
still lower than that of the untreated reference, hence some protection is still maintained.
Further tests are currently in progress to verify the presence of this layer and for further
optimization of the treatment.
4. Conclusions
A novel HAP-based treatment for marble protection was proposed: ethanol addition was
investigated to enhance surface coverage and acid resistance of the coating. The treatment
proposed (D0.1E+D0.1), consisting in a double application of the solution with ethanol
addition in the first layer, was successful in providing good coverage on powders without
leading to the formation of cracks and hence to slow down dissolution.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The treatment gave promising results also when applied to Carrara Marble specimens,
slowing down the dissolution of treated samples. The treatment still offered protection after
prolonged simulated rain (corresponding to a period of 40 years in Bologna, Italy):
however, further optimization is currently in progress to enhance the coating resistance.
Acknowledgements
We thank Dr. J. Schreiber for assistance on SEM analysis and Prof. A. Bocarsly and Dr. J.
Pander for FT-IR analysis (Princeton University), M.Eng. M. Glorioso for collaboration on
dripping tests and Dr. L. Guadagnini on HPLC (University of Bologna).
References
Bonazza, A. Sabbioni C., Guaraldi C., De Nuntiis P., 2009a, Climate change impact:
Mapping thermal stress on Carrara marble in Europe, Sci Total Environ, 407,
4506-4512.
Bonazza A., Messina P., Sabbioni C., Grossi C.M., Brimblecombe P., 2009b, Mapping the
impact of climate change on surface recession of carbonate buildings in Europe,
Sci Total Environ, 407, 2039-2050.
Doherty B., Pamplona M., Selvaggi R., Miliani C., Matteini M., Sgamellotti A., Brunetti
B., 2007, Efficiency and resistance of the artificial oxalate protection treatment on
marble against chemical weathering, Appl Surf Sci, 253, 4477-4484.
Ji X., Su P., Liu C., Li J., Tan H., Wu F., Yang L., Fu R., Tang C., Cheng B., 2015, A novel
ethanol induced and stabilized nanorods: hydroxyapatite nanopeanut, J Am Ceram
Soc, 98, 1702-1705.
Kaufmann G., Dreybrodt W., 2007, Calcite dissolution in the system CaCO 3-H2O-CO2 at
high undersaturation, Geochim Cosmochim Acta, 71, 1398-1410.
Matteini M., 2008, Inorganic treatments for the consolidation and protection of stone
artifacts, Conserv Sci Cult Herit, 8, 13–27.
Naidu, S., Liu C., Scherer G.W., 2015, Hydroxyapatite based consolidants and the
acceleration of hydrolysis of silicate-based consolidants, J Cult Herit, 16, 94-101.
Naidu, S., Scherer G.W., 2014, Nucleation, growth and evolution of calcium phosphate
films on calcite, J Colloid Interf Sci, 435, 128-137.
Naidu, S., Blair J., Scherer G.W., Acid attack mechanism on Carrara marble and efficacy of
a protective hydroxyapatite film, J Am Ceram Soc (in press).
Sand K.K., Yang M., Makovicky E., Cooke D.J., Hassenkam T., Bechgaard K., Stipp
S.L.S., 2010, Binding of ethanol on calcite: the role of the OH bond and its
relevance to biomineralization, Langmuir, 26, 15239-15247.
Sassoni E., Naidu S., Scherer G.W., 2011, The use of hydroxyapatite as a new inorganic
consolidant for damaged carbonate stones, J Cult Herit, 12, 346-355.
Sjcoberg E.L., Rickard D.T., The effect of added calcium on calcite dissolution kinetics in
aqueous solutions at 25°C, Chem Geol 49, 1985, 405-413.
810
USE OF CONSOLIDANTS AND PRE-CONSOLIDANTS IN
SANDSTONE WITH SWELLING CLAY AT THE
MUNCIPAL THEATRE OF SÃO PAULO
D. Grossi1*, E.A. Del Lama1 and G.W. Scherer2
Abstract
Swelling clay is a problem in the stone cultural heritage of some countries, such as the
United States, Germany and Switzerland. This expansive mineral increases the rate of stone
degradation and puts the monuments at risk. As such, we need to test products for
increasing the durability of these stones. Itararé Sandstone was used to build important
historical and cultural heritage buildings, such as the Municipal Theatre of São Paulo – a
100-year-old building that has undergone three restorations. Ethylenediamine anhydrous
and 1.3 Diaminopropane (DAA) were used as pre-consolidants, and tetraeth oxysilane
(TEOS) and diammonium hydrogen phosphate (DAP) were used as consolidants. The
results showed that the products closed the pores slightly and the stones become resistant to
water degradation.
Keywords: swelling clay, Itararé sandstone, pre-consolidants, consolidants, surfactants
1. Introduction
Sandstones with swelling clays used in heritage buildings and monuments constitute a
challenge for conservation. This is due to a rain-induced wetting-and-drying phenomenon,
and to increasing moisture levels causing movement of the clay layers and generating a
granular disintegration and weakening of the structure of the rock, causing the rock to
degrade faster. The object of study is Itararé Sandstone, which is a layered rock, formed in
a deltaic environment and of a fine-to-coarse grain. Mineralogically, it is a feldspathic
sandstone with a clayey matrix consisting of clay minerals of the smectite group, including
chlorite and illite. This rock is a constituent of the Municipal Theatre of São Paulo – an
important building in the history of the development of the city – which is used for events
up to the present day. As an attempt to inhibit or reduce the clay swelling behaviour, we
pre-consolidated the rock using surfactants, ethylenediamine anhydrous and
1.3 diaminopropane (DAA).
Jiménez González and Scherer (2004) evaluated the use of surfactants to decrease the
expansion of rocks that contain swelling clays, and found good results for Portland
Brownstone. Wangler and Scherer (2008) worked on understanding the behaviour of the
1
D. Grossi* E.A. Del Lama
Institute of Geosciences, University of São Paulo, Brazil
danigrossi@usp.br
2
G.W. Scherer
Department Civil & Environmental Engineering, Princeton University, United States of America
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
clays and identified two main types of expansion, with intracrystalline expansion causing
more damage. The latter authors developed a method for the characteriza tion of this type
of expansion in sandstones.
Water is considered one of the most damaging agents for stone. The harm is greater when
the stone has small pores, which increasing capillarity and carry the water deep into the
stone. This behaviour is most harmful when the water freezes or when the stone has salts or
swelling clays.
The methods used for the evaluation of the products were ultrasonic velocity measurement,
dilatometry, sorptivity, mercury porosimetry and wetting and drying cycles. With these
tests, performed on fresh and treated samples, it was possible to compare the action of
products, simulating the passage of time and the deterioration caused by water.
2. Itararé Sandstone
Itararé Sandstone is poorly consolidated, deposited in a deltaic environment between the
Paleozoic and Mesozoic eras. Today the quarry from which the samples were taken is a
nature conservation area, known as National Forest of Ipanema. It is located in the
municipality of Iperó, in the state of São Paulo (Brazil). The stone is a yellow sandstone,
with fine-to-coarse grains, formed in a deltaic environment. Petrographically, Itararé
Sandstone is feldspathic, with clayey matrix constituted by the smectite group with illite
and chlorite (Del Lama et al., 2009).
3. Methodology
The fresh samples were cut and dried before treatment with pre-consolidants, consolidants,
or pre-consolidants and consolidants sequentially. The pre-consolidants are aminoalkanes
with hydrocarbon chains of varying lengths (DAA). The aim of this phase was to decrease
the volume and the depth of water penetration and increase the resistance of the clays in
contact with water without the application of the hydrophobic products that prevent the
ingress of the water and sometimes close the pores, making retreatment or application of
other products impossible. The consolidants were diammonium hydrogen phosphate (DAP)
prepared at 1 molar concentration and oligomers of tetraethoxysilane (Conservare 100,
PROSOCO), hereafter identified as TEOS, diluted in 99.5% ethanol in the proportion 1:3.
The products were applied by capillary rise to penetrate the stone and avoid trapping air
inside it. After it rose to the top, the samples were covered by the product and left to
impregnate for 24 hours. After that, they were removed from the liquid and left to dry in a
chemical hood. In the case of TEOS, the manufacturer indicates that the hydrolysis takes
three weeks. After three weeks, the samples were submerged in a solution of
1:4 ethanol:deionized water for 24 h to complete the hydrolysis of the TEOS and render the
sample hydrophilic (Naidu et al., 2015). After this period, the samples were left to dry
naturally under the fume hood. The product was completely hydrolyzed when the weight of
the sample stabilized.
To summarize, the treatments were two pre-consolidants (DAA) successively, DAP only,
DAA + DAP, TEOS only and DAA + TEOS.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3.1. Mercury porosimetry
Mercury porosimetry was used to measure the pore sizes and the cumulative intrusion
volume, aiming to compare the results of untreated and treated samples. The size tested was
1×1×1.5 cm.
3.2. Sorptivity
The equipment to perform this test was used by Jiménez González and Scherer (2002). The
sample is suspended from a balance and its bottom surface is in contact with water, so the
balance shows the weight gain caused by the ingress of water into the pores. The sorptivity
is calculated from the slope of the curve of weight gain versus square root of time.
Measurements were made parallel to the bedding and perpendicular to the bedding. The
size of the samples was 1×1×1.5 cm.
3.3. Ultrasound velocity
The velocity of sound decreases on passing through fractures, larger pores and any kind of
discontinuity, so it is a good parameter for following the degradation of stone. The
equipment measures the transit time, t (s), of the sound wave through the sample, and the
velocity, V (m/s), is given by V = d/t, where d = sample thickness (m). The equipment used
was a Pundit machine with 54kHz transducers. The size tested was 2.5×2.5×8.5 cm.
3.4. Wetting-and-drying cycles
To simulate the stress caused by hygric expansion, wetting-drying cycles were performed in
a machine developed by Jiménez González and Scherer (2006). Samples are attached to a
belt that passes through a bath containing tap water to saturate the stone and then under a
set of fans to produce rapid drying. The samples were submerged in water for 20 minutes
and dried for 40 minutes in each cycle. This process was repeated for one month, which
amounts to about 700 cycles. The ultrasonic velocity was measured before and after the
cycles. The samples size was 2.5×2.5×8.5 cm.
4. Results and Discussion
Mercury porosimetry showed that the total porosity was not affected by the products, but
the TEOS closed the small pores (diameters near 10 nm) (Fig. 1), and drastically reduced
the volume of pores with diameters near 1 µm. All the results are shown in Tab. 1.
The sorptivity of the bare stone was about 0.0045 g/cm2•min1/2 perpendicular to the
bedding, and varied by about a factor of 2 parallel to the bedding (from a value similar to
that perpendicular to the bedding to about half as much). The DAA increased the sorptivity
from 0.0038 g/cm2min1/2 (fresh) to 0.0060 g/cm2min1/2 perpendicular to the bedding and
from 0.0043 g/cm2min1/2 (fresh) to 0.0051 g/cm2min1/2 parallel to the bedding direction.
This may reflect expansion of the body as DAA intercalates into the clay in the stone
(Wangler and Scherer, 2008). DAP reduced swelling by 29% perpendicular to the bedding
and raised it 23% parallel to the bedding direction. Treatment with DAA + DAP reduced
swelling by 91% perpendicular to the bedding, and TEOS reduced it by 42% perpendicular
to the bedding and by 10% parallel to the bedding. DAA + TEOS reduced the sorptivity by
50% perpendicular to the bedding direction and increased it by 27% parallel to the bedding.
(Tab. 2). The greatest decrease was caused by the treatment with DAA+DAP, which is in
contrast to results on other stones (e.g., Naidu et al., 2015), where the silicate consolidant
caused a much greater change.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 1: Comparison of mercury intrusion curves for fresh stone and sample consolidated
with TEOS.
Tab. 1: Results of mercury porosimetry.
Porosity (%) –
Porosity (%) –
(100 – 10000 nm)
(10 – 100 nm)
Bare
17.09
14.15
DAA
16.09
15.13
DAP
29.66
14.39
DAA + DAP
17.01
9.65
TEOS
13.09
1.80
DAA + TEOS
14.53
10.80
Treatment
We tested six samples for each treatment in wet and dry cycles, totalling 30 samples. The
best results were obtained by using aminoalkanes followed by silicate-based and phosphatebased products (Fig. 2). The range of ultrasonic wave velocity before wetting-and-drying
cycles was 2.7 to 3.6 km/s and 1.9 to 3.1 after the cycles. The sample treated with
DAA + DAP shows the highest velocity before and after the treatment. Even though it did
lose a lot of stiffness after cycling, it is still much better than the untreated stone, and better
than the one treated with TEOS. The biggest negative factor for DAP is the decrease in
sorptivity, which probably indicates that it reacted with the DAA and precipitated a product
that blocks the pores. In all cases, the velocity decreases following wetting-drying cycles
were lower for treated stones than for fresh samples. It shows that all products were of
benefit to the stone. The DAA + TEOS was not cycled, because the sorptivity result
showed that this product blocked the pores.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 2: Results of sorptivity.
Treatment
Bedding direction
Sorptivity
(g/cm2•min1/2)
Average
(g/cm2•min 1/2)
Perpendicular
0.0057
Perpendicular
0.0043
Perpendicular
0.0026
Perpendicular
0.0025
Parallel
0.0043
Parallel
0.0039
Parallel
0.0050
Parallel
0.0040
Perpendicular
0.0050
Perpendicular
0.0069
Parallel
0.0042
Parallel
0.0060
Perpendicular
0.0027
0.0027
Parallel
0.0053
0.0053
Perpendicular
0.0004
0.0004
Perpendicular
0.0017
Perpendicular
0.0027
Parallel
0.0039
Perpendicular
0.0024
Perpendicular
0.0014
Parallel
0.0043
Parallel
0.0067
0.0038
Bare
0.0043
0.0060
DAA
0.0051
DAP
DAA+DAP
0.0022
TEOS
0.0039
0.0019
DAA+TEOS
0.0055
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
4.0
3.5
3.0
2.5
2.0
Ultrasonic velocity before and after cycle machine
Fig. 2: Ultrasonic wave velocity before and after wetting-and-drying cycles. B: Before, A:
After the cycles. The line represents the range of values and the triangle is the average.
5. Conclusions
Treatment with diaminoalkane (DAA) is expected to suppress swelling of the clay, but it
had a negligible effect on the stiffness of the stone and on the retention of stiffness after
cycling. When used in combination with diammonium hydrogen phosphate (DAP), there
seems to be a detrimental chemical reaction that reduces the sorptivity, but it provides a
considerable increase in stiffness, much of which is retained after cycling. The best results
were obtained with TEOS alone, which caused less reduction in sorptivity than
DAA + DAP and had higher stiffness than untreated stone after cycling. All of these tests
were performed on unweathered stone, which may account for the modest impact of the
treatments on the properties. Future studies will focus on samples that have already been
damaged by hydric or thermal cycles.
Acknowledgements
The authors thank FAPESP (2012/24067-4 and 2013/24833-1) for the financial support.
References
Del Lama, E.A., Dehira, L.K., and Reys, A.C., 2009, Visão geológica dos monumentos da
cidade de São Paulo, Revista Brasileira de Geociências, 39 (3), 409-420.
Jiménez González, I. and Scherer, G.W., 2002, Hygric Swelling of Portland Brownstone.
MRS Proceedings, 712, II 2.4.
Jiménez González, I. and Scherer, G. W. 2004, Effect of swelling inhibitors on the swelling
and stress relaxation of clay-bearing stones, Environmental Geology, 46, 364-377
Jiménez González, I. and Scherer, G.W. 2006, Evaluating the potential damage to stones
from wetting and drying cycles, in Measuring, Monitoring and Modeling Concrete
Properties, Konsta-Gdoutos M.S. (ed.), Springer, 685-693.
Naidu, S., Liu, C. and Scherer, G.W., 2015, Hydroxyapatite-based consolidant and the
acceleration of hydrolysis of silicate-based consolidants, J. Cultural Heritage, 16,
94-101.
Wangler, T. and Scherer, G.W. 2008, Clay swelling mechanism in clay-bearing sandstones,
Environmental Geology, 56, 529-534.
816
ASSESSING THE IMPACT OF NATURAL STONE BURIAL UPON
PERFORMANCE FOR POTENTIAL CONSERVATION PURPOSES
B.J. Hunt1* and C.M. Grossi2
Abstract
Historic England is researching the performance of natural stone subjected to burial. The
primary reason driving the research is a need to reduce the costs of preserving natural stone
monuments and structures where there may not be the immediate funds to carry out more
extensive preservation works. Stone burial is poorly researched and the possible benefits
and risks are neither known nor understood. The research involves testing designs for
burial, known as clamps, over a minimum three-year period to determine the optimum
design. A range of stone types is being tested to develop guidance as to when such an
approach is appropriate. Clamps have been set up at an exposed site using four different
burial media for eight different stone types set at both shallow and deeper levels. Probes set
within the stone blocks directly measure the temperature and moisture contents, which is
being compared with data from a weather station at the test area. Two sets of the stone
blocks have also been left out in the open, one set being free of ground contact, the other
simply sitting upon the ground. Exposure began in November 2014 and this paper considers
the first nine months of readings. It is already indicated that the stone blocks do not easily
dry out within clamps once saturated and that shallow buried stones undergo more rapid
freezing than deeper buried stones. Current indications are that the depth of burial along
with the ability of a stone to take on board and retain moisture will be critical. Thus
suggests that burial sites will need to be well drained and ventilated with direct moisture
contact reduced.
Keywords: stone, burial, frost, monitoring, preservation, cultural heritage
1. Introduction
Funds for the upkeep of the many buildings and monuments of historical importance that
come under the auspices of Historic England rarely are sufficient. Unfortunately there are
many situations where the building fabric is left unprotected whilst funds for necessary
major interventions are awaited. To this end Historic England considered ways in which
fabric deterioration could be slowed whilst awaiting such intervention. Part of the solution
has been the removal of fabric to controlled storage facilities, which can involve substantial
capital costs and significant limitations to what can be achieved effectively. The other part
1
B.J. Hunt*
IBIS Limited, 10 Clarendon Road, South Woodford, London, E18 2AW, United Kingdom
barry.hunt@ibis4u.co.uk
2
C.M. Grossi
School of Health Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
of the solution has been the on-site burial of fabric in what have become known as
‘clamps’.
Clamps are believed to provide protection from the principally maritime environment of the
UK, especially cyclic frost attack, allowing fabric to be stored until funds can be made
available for proper intervention. The need for storage for many structures is believed to be
measurable in decades. Therefore, clamps may buy considerable time for a structure whilst
significantly reducing long term preservation costs. Having received enquiries from
owners of historic structures concerning the use of clamps Historic England realised that
there was no tangible research or other technical backup available to support the promotion
of clamp use without taking a significant unknown risk. Therefore in late 2005 Historic
England undertook the burial in sand of some 600 stone elements at Riveaulx Abbey,
incorporating sensors to monitor the burial environment. A principal conclusion of this
initial research was that further and more in depth research was required; this prompted the
current project.
A literature search reveals a lack of significant research into the conditions and
performance of buried natural stone. There has been some work concerning archaeological
site reburial (Canti & Davis, 1999) and research into the geochemical conditions of
archaeological sites and effects upon various materials (Lillie & Smith, 2006) but this is of
minimal relevance to the current study. Apocryphal stories from stone quarriers about the
protection by burial of stone over winter periods and general geological observation of
natural stone resources within the UK environment were thus used to formulate how clamps
might be constructed in order to provide protection from the elements. General experience
of how different stones and the structures built from them suffer deterioration was also
considered. Thickett et al (2008) carried out X-ray fluorescence and near infrared
spectroscopy on a variety of sandstones in order to rank their potential durability prior to
burial and to help monitor the stone condition once buried. This non-destructive approach
had only very limited use.
The two principal factors believed to exert the greatest influence upon a clamp environment
were considered to be stone temperature and moisture content. How these two factors
interacted over time, particularly with respect to the degree of saturation at the time of
freezing, and possibly the rate of freezing, was considered to be important. The amount of
cover to the stone and the nature of the burial media were believed to be significant
controlling factors of both the moisture content and temperature, so some variation in these
was required. The most obvious variation was the stone itself and thus eventually eight
stones representing a range of British types were selected for testing. It was considered that
the clamps needed to be drained whilst the top surface of the burial media remained
uncovered. Two sets of control stones were deployed, one set sitting 200 mm off the ground
on a wooden pallet and thus exposed on all sides, and another set laid directly upon the
ground and thus exposed on five sides.
The monitoring comprises combined temperature/moisture sensors set into two of the eight
stone types taking readings on the hour that will continue for a period of at least three years.
These readings are being compared with those from a small weather station set up within
the area of the test clamps. The readings include air temperature, humidity, rainfall, wind
speed, wind direction and sunlight. Statistical analyses are being applied to the results in
order to assess the number of actual freezing events inside the clamps, and the influence of
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
temperature lag, moisture changes and other potential factors. At the end of the monitoring
period in early 2018 the stones will be assessed for changes using petrography and electron
microscopy, and possibly using mercury porosimetry at different levels from surfaces.
2. Trial set-up
2.1. Principal considerations
There were believed to be five principal considerations for setting up the trial variables:
1) an apocryphal history of stone burial suggested this provided protection; 2) deeper burial
would provide more stable temperatures and potentially a lower number of freeze-thaw
cycles; 3) different burial media might increase/decrease the rate of saturation, the level of
saturation, and the rate of drying: 4) different burial media might exhibit differences in
lateral moisture creep and 5) the variables were applicable to porous stones. Assessments of
the level of damage to the various stone test blocks will only be undertaken at the end of the
trial. Assessment of the current findings is based on comparison of data and the limited
visual observations that have been made so far.
2.2. Stone selection
The majority of historical structures built in England used local stones that inevitably
included sandstone and/or limestone. The following eight stone types were selected to
represent the range of available materials. Included are basic descriptions along with
density (D, g cm-3), water absorption (W, %) and saturation coefficient (S) values as
appropriate.
Jordan's Whitbed Portland limestone: medium grade, oolitic (D: 2.16 W: 6.3 S: 0.73)
Jordan's Basebed Portland limestone: medium grade oolitic (D: 2.18 W: 6.9 S: 0.76)
Appleton sandstone: high grade, arenitic (D: 2.38 W: 2.9 S: 0.63)
Stanton Moor sandstone: medium grade, arenitic (D: 2.32 W: 3.8 S: 0.67)
St Bees sandstone: medium grade, calcareous (D: 2.09 W: 6.8 S: 0.66)
Red Lazonby sandstone: medium grade, iron-rich (D: 2.34 W: 2.4)
Creeton Hard White limestone: low grade, oolitic (D: 2.25 W: 7.0 S: 0.93)
Cadeby White Magnesian limestone: medium grade (D: 2.17 W: 7.3 S: 0.83)
Blocks of a significant size (300 mm length, 200 mm width and 200 mm height) were used,
given that in practice masonry blocks to be buried typically would be relatively large.
Larger blocks would also allow the taking of samples at the end of the monitoring period
whilst leaving significant material to continue the burial exercise if required. The blocks
were also cut to ensure that the natural bedding would run perpendicular to the small end
faces.
2.3. Site and burial media
The test site is located in Helmsley, North Yorkshire, and has an oceanic climate. The
nature of the burial media was considered to be a potential factor in the performance of the
clamps, especially in relation to moisture transmission in and out of the clamps. Four
different stone burial media were selected for the clamp construction as follows:
a) coarse 20 mm single sized crushed granite with poor packing and low absorption;
b) coarse 20 mm single sized crushed limestone with poor packing and high absorption;
c) crushed igneous rock fines with good grading but poor packing, and
d) natural building sand with continuous grading and good packing.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
A bed of 150 mm depth was laid first before the lower layer of stone test blocks was
installed by simply placing them on top of that layer. The stone test blocks remained
isolated from each other. The area around the stone test blocks was then filled with the
aggregate and this was continued until the stone test blocks were completely covered by a
150 mm thick layer of the aggregate. The upper layer of stone test blocks was then placed
upon the aggregate, the area around them filled and the stone test blocks finally covered to
at least 150 mm. Additionally, two sets of the eight stones were placed outside of the
clamps. One set was left sitting upon the ground via a thin bed of the building sand to
ensure full contact. The other set was left sitting upon a wooden pallet about 200 mm above
the ground and exposed.
2.4. Monitoring Equipment
The temperature and moisture content of the stone within the clamps and on the outside set
in contact with the ground were monitored using Delta-T SM300 sensors set into the
samples. A pair of nominal 7 mm diameter holes were drilled into each stone test block, the
centres 25 mm apart, and the wire probes inserted into the holes and set using a proprietary
masonry grout to ensure full contact with the stone fabric. A weather station was set up at
the centre of the clamps that incorporated instrumentation supplied by Delta-T: a) RHT2nl02 Relative Humidity/Precision air temperature sensors (2K Thermistor); b) RG2+BP-06
Raingauge, Compact; c) ES2-05 Solar Energy Flux Sensor, and d) AN-WD2 combined
wind speed and direction sensor. The instrumentation of the clamps and weather station
was linked to a Delta-T DL2e Data Logger that was set to take measurements every hour.
With a total of 43 measurements being taken each hour, a total of 1,130,040 measurements
would be obtained over the course of a continuous three year monitoring period.
2.5. Clamp design
It was assumed that any clamps to be constructed realistically would require a location that
was either free-draining or with some form of drainage installed. It was considered that the
retention of moisture within a clamp would be a function of the trickle down of moisture
from above and the absorption and packing of the burial media. Ideally it would have been
preferred to construct the trial clamps within a pit that was then drained, but this created a
number of serious problems at the proposed trial site. It was agreed that the clamps could be
constructed above ground, which was considered to be potentially a straightforward and
more realistic methodology for constructing actual clamps. Fig. 1 below shows how the
clamps were constructed, with some of the materials stripped away. The use of exposed
sides was considered to be potentially more realistic but likely to increase the damage
potential due to an increased rate of heat loss and reduced ground heat storage effects. The
base of the clamps was left in direct contact with the ground so that moisture was able to
flow out from the construction. The top of the clamps was left open, leaving the possibility
that at some time the clamps might be covered and the findings before and after covering
them might be compared and contrasted.
3. Data analysis
A descriptive statistical analysis of the stone temperature and moisture content in the
different situations and their variation during the time of exposure was carried out. Time
series analysis was used to compare stone temperature and moisture with air temperature,
relative humidity and precipitation by estimating autocorrelation and cross-correlation of
the stones and their lags with the environmental parameters. The percentage of frost hours
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
was determined by counting the hours where temperatures were lower than 0º C. Clustered
multivariable regression models with robust standard errors using the channel as panel
variable (16 clusters) were carried out. The response variables were stone temperature,
stone moisture as continuous variables, and frost event in the stone as a binary variable (yes
or no). The stone type (Appleton or Creeton), type of clamp (limestone, sand, granite sand
or crushed granite) and levels (upper or lower) were used as covariates. Linear regression
was used for the analysis of stone temperature and moisture and logistic regression was
used for frost occurrence. The statistical analysis was carried out using STATA 14
software.
SM300 sensors to
data logger
Fig. 1: design of the trial clamps using four different burial media and four of the eight
stones set at two different levels; typical positioning of the SM300 sensors is shown.
4. Initial results
4.1. Monitoring
Monitoring was begun on 05 November 2014, just prior to the winter period and before the
first frosts occurred. At the time of writing monitoring has been carried out for nine months,
to 27th August 2015, with a total of 7073 hourly records. During this monitoring period the
number of freezing events affecting the external environment numbered 48 and the total
number of hours with temperature ≤ 0◦C (and potential frost occurrence) totalled 289.
Precipitation totalled 501 mm, the daily average being 1.69 mm.
One of the most important occurrences affected the Creeton limestone left sitting upon the
ground, which obviously suffered relatively catastrophic breakdown. This demonstrated
that the local climate over the winter period had been particularly harsh. It was also
apparent that this would provide a good basis for comparison with the performance of the
Creeton limestone within the various clamps under the different storage and exposure
conditions.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
4.2. Current indications
The temperature within the clamps is both strongly auto-correlated and correlated with the
air temperature. The clamp temperature also varies according to the level with the upper
level exhibiting temperatures closer to the air temperature than those of the lower level. The
time lag in temperature change is smaller in the upper level than in the lower level (Tab. 1).
The percentage of variance by stone type is very small and this does not appear to be a
significant factor (Tab. 2). Changes in humidity also appeared to be more stable within the
finer burial materials.
Tab. 1: Summary of winter temperature (November to February).
Levels
Number of
observations
Mean
St Dev
Min
Max
◦C
Corr
with
Air T
Lag
with
Air T**
◦C
◦C
◦C
Air T
2,767
4.9
3.7
-5.5
14.5
--
--
Overground
5,534
4.1
3.6
-5.1
13.1
0.99
0
Upper level
22,136
3.9
2.8
-2.0
10.8
0.77
5 (2)
Lower level
22,136
4.3
2.5
-0.2*
9.9
0.67
9 (3)
* Lower level: temperatures < 0° C were only recorded in the coarse limestone clamp;
** Mean and Poisson standard deviation (brackets); Lag = Number of hours to reach the best correlation between
Air and clamp temperature (i.e. time of response to external temperature conditions).
Tab. 2: Regressions of T, moisture and frost occurrence vs type of stone, clamp and level.
Temp*
Temp
Coef
P > |t|
Coef
P > |t|
O.R.
P > |t|
base
0.06
--0.468
base
4.78
--<0.001
base
1.07
--0.880
Clamp CC limestone
Building sand
Granite sand
CC granite
base
-0.11
0.002
0.17
--0.486
0.988
0.245
base
2.38
2.53
5.00
--0.102
0.091
0.009
base
0.41
0.45
0.45
--0.263
0.181
0.063
Level
base
-0.37
0.01
--0.001
---
base
-1.35
0.58
--0.173
---
base
16.2
---
--0.002
0.10
Stone
Appleton
Creeton
Lower
Upper
R2
Moisture* Moisture
Frost
Frost
occurrence** occurrence
* Clustered linear regression with robust errors;
** Clustered logistic regression with robust errors
No autocorrelation or environmental factors were included in these regressions. Freeze events coded as No-Yes.
P values ≤ 0.1 indicate significant relationship with 10% error. O.R. are odds ratios where O.R. > 1 indicate
positive relationship and O.R. < 1 indicate negative relationship. Coefficients > 0 indicate positive relationship and
coefficients < 0 indicate negative relationship.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The upper levels of the clamps were more susceptible to the outside frost events (Tab. 3)
mostly due to the shorter time lag in temperature change. The clamp that employed the
coarse limestone burial material appeared to achieve freezing conditions more rapidly.
The stones within the clamps initially took on board moisture, which then stabilised to a
degree and then slowly reacted to outside moisture variations (Fig. 2). Drying occurred only
very slowly during prolonged drying periods. The indications are that over the period of
monitoring the moisture content has been slowly growing, especially within the Appleton
sandstone. Outside of the clamps the Appleton sandstone was more reactive to the changes
in the amount of precipitation.
The Creeton limestone placed externally that suffered breakdown saw a disruption in the
temperature data, probably suggesting a loss of contact between the stone and grout, and
possibly other factors. It also appeared the Creeton limestone within the clamps may have
failed at the same time, most likely within the coarse limestone and granite burial media,
and potentially in the granite sand clamp.
Tab. 3: Cross-tabulation of the external environment frost occurrence (number of hours
with T ≤ 0º C) and frost occurrence at different exposures from Nov 2014 to Feb 2015*.
Air Frost
occurrence
Overground stones
T≥0
T≤0
Air T ≥ 0
4837
203
Air T ≤ 0
6
488
**
%
99
Upper level clamps
T≥0
T≤0
19714
446
1718
258
**
%
13
Lower level clamps
T≥0
T≤0
20122
38
1969
7
%**
0.35
* Freeze events in the lower level only were registered in the coarse crushed limestone clamps. ** Number of
hours with stone T ≤ 0 ºC / number of hours with Air T ≤ 0º C as percentage (e.g overground stones =
488/(488+6) x100), two significant figures.
Fig. 2: Moisture content of the trial clamps for Appleton and Creeton stones
at lower and upper levels during the first nine months of exposure.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
5. Initial Conclusions and Recommendations
The findings to date suggest that a burial environment does alter the effects of local weather
upon the stone by slowing the rate at which a frost event occurs. This may increase the
ability of stone to combat the potential build up of internal pressures and subsequent
damage experienced. Therefore there is already strong evidence that clamp environments
do provide protection, though the potential level of this protection is yet to be determined.
It would appear that leaving the upper surface uncovered has made the stones within the
clamps more susceptible to taking on board moisture, which then takes a long time to
reduce during drier periods. It is indicated that more deeply buried stone takes longer to dry
out. This reduction in the rate of drying out may counteract some of the apparent benefits
of burial, which needs to be investigated further.
During the second half of the current monitoring period it is proposed to incorporate a
cover to the clamps and to direct moisture away from the buried stones. This may help to
better determine whether different burial media produce different burial climates, especially
in response to possible lateral transfer of moisture.
The rate of take up and release of moisture and temperature changes at different depths
from the outer surface of a stone block may be important factors in the assessment of the
long term performance. Future research might incorporate probes at different positions
within larger and differently shaped pieces of masonry to assess such potential effects. The
moisture content readings will require conversion to actual moisture content values, which
will be undertaken at the end of the monitoring period.
Acknowledgements
The Authors would like to thank Historic England for the opportunity to carry out this
research on their behalf, and also the opportunity to produce this on-going summary of the
findings. The Authors would also like to thank Zoë Davis for her assistance with the
manuscript. Thanks also go to various staff members of Albion Stone, Cadeby Stone,
Marshalls and Stancliffe Stone for the supply of stone materials for the project, and
especially to Gordon Hines and Michael Poultney.
References
Canti M.G. & Davis, M., 1999, Tests and Guidelines for the Suitability of Sands to be used
in Archaeological Site Reburial, J. of Archaeological Science, 26, 775-781.
Lillie, M. & Smith, R., 2006, The in situ preservation of archaeological remains: using
lysimeters to assess the impacts of saturation and seasonality, J. of Archaeological
Science, 34, 1494-1504.
Thickett, D., Lambarth, S. and Wyeth, P., 2008, Determining the stability and durability of
archaeological materials, 9th International Conference on NDT of Art, Jerusalem,
Israel, 25-30 May 2008.
824
STUDY OF PROTECTIVE MEASURES OF STONE MONUMENTS
IN COLD REGIONS
T. Ishizaki 1*
Abstract
In cold regions, stone monuments located outside deteriorate due to the freeze and thaw
cycles in winter. The main factors for the deterioration of stone are material property, water
content and temperature. The stone deteriorates severely if the stone is frost susceptible.
There is a stone gateway (Torii in Japanese) at the entrance to a Shinto shrine in Yamagata
city. The stone gateway was built in Heian Period (from 8 to 12 centuries ago) and is
designated as an important cultural property. For the protective measures, the stone
gateway is covered with plastic film with insulation and straw mat in winter. In order to
measure the temperature of the stone surface, the temperature sensor was set on the stone
surface inside of the cover. The environmental temperature decreased to -5.3 ºC at the end
of January, but the surface temperature of the stone was -0.8 ºC. The experimental result
showed that a large amount of water was not frozen at -1 ºC. Therefore, it can be said that
the freezing pore water in stone in the winter cover did not have big effect on the stone
damage during this period. From these results, this is considered to be a quite effective
method for the protective measures of stone monuments in cold regions. The present author
observed the microclimate condition in the glass shelter for the stone monument in
Hokkaido. The shelter is quite effective to reduce the water content of the stone
monuments. The laboratory experiment showed that the freezing temperature decreases
greatly with the decrease of the water content of the stone. In this condition the water
content of the stone monument is kept quite low, which leads to low freezing temperature
and results in low risk of frost damage.
Keywords: frost damage, frost heave phenomenon, protective measure, water content,
shelter
1. Introduction
In cold regions, stone monuments deteriorate due to the freezing and thawing cycles in
winter season. The degree of the deterioration depends on the stone type, moisture content
and temperature. The freezing temperature decreases with decreasing moisture content of
the stone. Therefore it is one of the protective measures to reduce the moisture content of
the stone. The installation of a shelter around a stone monument or applying water repellent
material on the monument is an effective protective measure to prevent deterioration.
Another protective measure is to avoid the exposure of the stone to low temperatures by
using thermal insulation material.
1
T. Ishizaki*
Institute for Conservation of Cultural Property, Tohoku University of Art & Design, Japan
ishizaki.takeshi@aga.tuad.ac.jp
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
For these purposes in Germany stone monuments made of marble are covered with wood
shelter during the winter season. In Japan one example of protective measures is to cover
stone monuments with straw mat. Fig. 1 shows the stone shrine gate with winter cover in
Motoki, Yamagata city. The stone shrine gate was built around 1000 years ago in Heian
Period and it was designated as an important cultural property in Japan. The procedure for
the winter cover is as follows. First the stone was covered with vinyl sheet with insulation
layer, then covered with straw mat and finally covered with vinyl sheet. To evaluate the
validity of this winter cover, temperatures of stone surface and cover surface were
measured in winter season. The temperature and relative humidity of the environmental
condition were also measured. The time lapse camera was installed to take photos of the
stone gate to observe the snow accumulation on the stone gate.
Fig. 1: Stone shrine gate with winter cover in Motoki, Yamagata city.
2. Results of Temperature Measurement
Air temperature and relative humidity of the surrounding environment were measured for
two month from January 26 to March 27, 2015. The air temperature around the stone gate is
shown in Fig. 2a. Based on the temperature measurement, the air temperature recorded
minimum value of -5.3 ºC at 5:30 on January 29. The stone surface temperature inside the
winter cover is shown in Fig. 2b. The surface temperature on the stone surface inside the
winter cover recorded -0.8 ºC at 3:30 on January 29. On February 5, the minimum air
temperature was -4.3 ºC and the temperature on the stone surface inside the winter cover
was -0.2 ºC. Fig. 3 shows daily minimum air temperature and the minimum surface
temperature of the stone surface inside the winter cover. In this figure, positive temperature
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
values were omitted. During this period, the minimum air temperature was -5.3 ºC and the
minimum temperature on the stone surface was -0.8 ºC.
a)
b)
Fig. 2: a) Air temperature change around the stone shrine gate in Motoki,
Yamagata city; b) Temperature change of the stone surface inside the winter cover.
Fig. 3: Daily minimum air temperature (●) and
daily minimum surface temperature (■)
3. Discussion
The stone deteriorates due to the freezing and thawing cycles. Based on the laboratory
experiment, Fukuda (1984) concluded that the number of temperature change cycles
between +4 and -4 ºC is important for the frost damage of the stone. Ishizaki (2000) curried
out measurement of unfrozen water content of Oya tuff stone which was used for the stone
monument in Japan by the pulsed NMR technique. The experimental result showed that
large amount of water was not frozen at -1 ºC. Therefore, it can be said that the freezing
pore water in stone in the winter cover did not have big effect on the stone damage during
this period based on the temperature data shown in Fig. 2b and Fig. 3. As shown in Fig. 3,
the surface temperature of the stone was around 4 ºC higher than the air temperature. The
reason can be due to the winter cover in which straw mat was covered with vinyl sheet on
both sides. This structure prevented cold air to flow into the winter cover. Therefore this
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
method is simple and effective way to reduce the risk of frost damage of stone monument
in winter.
The minimum air temperature in Yamagata city was -7.5 ºC on December 28, 2014 based
on the meteorological data from Yamagata Meteorological Agency. This method of winter
cover is considered to be effective in the area where winter temperature is not so low, such
as in Yamagata city. However, it would be difficult to reduce the risk of frost damage by
this winter cover method in the area where winter coldness is much severe. In Hokkaido
area, where the minimum temperature reaches -20 ºC and stone freezes even if the stone
monument is covered with insulation materials.
For further studies, it is necessary to obtain thermal properties of stone and materials used
for the winter cover and carry out thermal analysis for the precise estimation of the stone
surface temperature change with environmental conditions.
The present author has been doing research on the frost damage of earthen wall of Shiwa-jo
in Morioka City, Iwate prefecture (Fig. 4). The degree of damage to the earthen wall
depended on the volumetric water content of the soil. The earthen wall was damaged
greatly where the volumetric water content measured by TDR (Time Domain
Reflectometer) apparatus exceeded 30%. The earthen wall was not damaged where the
volumetric water content was low. Laboratory experiments were carried out to clarify the
relationship between the freezing temperature of the soil and the volumetric water content
(Ishizaki, 2015). From these research results, it was found that the risk of frost damage
becomes low if the water content of the earthen wall is kept at lower value than 20%.
Fig. 4: Earthen wall of Shiwa-jo in Morioka City, Iwate prefecture
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
4. Conclusions
Use of plastic film with straw insulation in winter keeps the surface temperature of the
stone around 4 ºC higher than the air temperature. This is a simple and effective way to
reduce the risk of frost damage to stone monuments in winter, if the climate is not severe.
For further studies, it is necessary to obtain thermal properties of stone and materials used
for the winter cover and carry out thermal analysis for the precise estimation of the stone
surface temperature change with environmental conditions.
Acknowledgement
The present Author would like to thank Ms. Kaoru Uematsu and people in Board of
Education of Yamagata city to help this research for the preservation of stone monument.
References
Fukuda, M., 1984, Frost shattering of the carving in Temiya Cave, Otaru, Low Temperature
Science, Ser. A, 43, 171-180.
Ishizaki, T., 2000, Frost deterioration of historical stone monuments and brick buildings
and its preventive measures, Proc. of the international Symposium on Ground
Freezing and Frost Actions in Soils, Belgium, 79-83.
Ishizaki, T, 2015, Deterioration of cultural properties with earthen materials and their
protective measures, Proc. 2015 International Symposium on Conservation of East
Asian Cultural Heritage in Nara, 26-29.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
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830
STUDY OF CONSOLIDATION OF POROUS AND DENSE
LIMESTONES BY BACILLUS CEREUS BIOMINERALIZATION
J.M. Jakutajć1, J.W. Łukaszewicz2* and J. Karbowska-Berent2
Abstract
The research was focused on the evaluation of the possibility of using commercially
available materials and biomineralisation technology, which is based on the ability of
Bacillus cereus to precipitate calcium carbonate for consolidating high porous stones and
infilling micro-cracks in dense limestones. The effectiveness of the treatment was verified
indirectly by the evaluation of physical properties of consolidated stones and directly by
identification of calcium carbonate on sandstone slabs with SEM/EDS analysis. The results
show that the bacteria are able to induce calcium carbonate precipitation and the new
cement alters the strength properties of the stone. Nevertheless the consolidating effect is
superficial and biomineralisation procedure is linked with some side effects. The evaluation
of suitability of this treatment for use on dense stones demonstrated that it is possible to fill
micro-cracks and create colour patina on the stone surface.
Keywords: biomineralisation, bacillus cereus, consolidation, infilling cracks,
carbonate stones, porous and dense limestone
1. Introduction
Carbonate stones are very susceptible to decay due to the chemical nature of their main
component – calcite. Symptoms of weathering and corrosion of limestones may cause
defacing of a relief and a sculpture form or may even lead to full destruction of a stone
artwork (ed. Domasłowski 2011). Consolidation treatment is needed in some cases to avoid
such damage. Since the second half of the 19 th century, consolidation of stone artworks has
been one of the basic conservation problems. Since that time, a wide variety of materials
have been used for strengthening weathered monuments. A majority of these materials are
inorganic: lime, nano-lime (Ziegenbalg 2008), barium hydroxide (Lewin 1971) and organic
polymers: epoxy resins (Domasłowski, Strzelczyk 1986), acrylic polymers (Domasłowski,
Łukaszewicz 1983), alkoksysilanes (Łukaszewicz 2002). Unfortunately, some of these
materials are not effective enough or may cause irreversible changes in the chemical
structure of a stone. The research towards new treatments based on compatibility of the
consolidant with the stone substrate has led to the development of an alternative
conservation treatment based on the phenomenon of MICP (Microbially Induced Calcite
1
J.M. Jakutajć
Conservator – Restorer, Poland
2
J. W. Łukaszewicz* and J. Karbowska-Berent
Department for Conservation and Restoration of Architectonic Elements and Details,
Faculty of Fine Arts, Nicolaus Copernicus University, Toruń, Poland
jwluk@umk.pl
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Precipitation). MICP has been investigated for consolidation and protection of sculpture
and architecture made from carbonate stones for more than twenty years (Castanier et al.
1999, Le Metayer-Levrel et al. 1999, Rodriguez-Navarro et al. 2003, De Muynck et al.
2010). The method known as calcium carbonate biomineralisation or biodeposition is the
development of the lime-water treatment, the purpose of which is to recreate the binder in
deteriorated calcareous stones. The first biomineralisation technology was developed and
industrialised by the French research group (Adolphe and Billy 1974, Adolphe et al. 1989,
1990, Castanier et al. 1999) which was patented as Calcite Bioconcept (CB) technology,
where the Bacillus cereus activity is used. The success of the method encouraged different
research groups to develop alternative approaches for the bacterial biomineralisation. A
Spanish research group proposed the use of Myxococcus xanthus (Ro×driguezNavarro et al. 2003) or the use of microorganisms inhabiting the stone (JimenezLopez et al. 2007) to consolidate carbonate stones. Another main biomineralisation
technology was developed by the Ghent University research group, which proposed the
microbial hydrolysis strategy to obtain a calcite layer by Bacillus sphearicus (De
Muynck et al. 2010).
2. Materials and methods
2.1. Stone samples
In this experiment two groups of stones were chosen: porous stones (Pińczów limestone,
Żerkowice sandstone) and nonporous stones (Rosso Verona marble, Dębnik limestone).
The Pińczów limestone is one the most popular Polish carbonate stones, which was widely
used in architecture and sculpture, especially in the 16 th century. It is a fine-grained
limestone of ecru or light beige colour with high porosity (25-27%) and high water
absorption (14-18%) (ed. Domasłowski 2011). The Żerkowice sandstone is a Polish coarsegrained sandstone with clay binder, porosity 12-14% and water absorption 6-7.5% (ed.
Domasłowski 2011). The porous stones were used for the examination of the consolidation
effect of microbial induced calcite precipitation. Considering the superficial nature of
strengthening effect due to the biomineralisation (De Muynck et al. 2010, RodriguezNavarro et al. 2003), the research on the changes of physical properties of stones was
conducted on slabs 0.4-0.5×1×10 cm in size, as the bacteria could penetrate the whole
structure of the sample. To enable the detection of newly formed calcite crystals in the
stone structure by SEM/EDS analysis, the sandstone samples were used. In the experiment
concerning the possibility of infilling cracks and fissures in dense limestones, the decayed
slabs of the Dębnik limestone and the Rosso Verona marble were chosen. The samples
were devoid of polish and were rich in micro-cracks and fissures. Considering the real
conditions of historical stones, the treatment was applied on non-sterile stone slabs.
2.2. Biodeposition procedure
The study was based on the CB biomineralisation technology (Adolphe et al. 1990). The
bio-preparation used in the experiments consists of two compounds: freeze-dried bacteria
isolates – Bacillus cereus and dry culture medium (nutrition). The compounds were
hydrated by distilled water and applied on the stone samples using a brush or spray,
according to the five-day procedure that was recommended by the producer. The
application procedure is shown in Tab. 1. The new liquids were prepared daily due to the
risk of undesired growth of microorganisms from the air.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: The application programme of Calcite Bioconcept treatment.
Day
Compounds
Amounts
0.25 g bacteria
1
Inoculation of Bacillus cereus
in liquid nutrition
1.25 g nutrition
50 cm3 distilled water
2
Application on stone of 16h old
inoculated culture medium (CB+)
–––––––
3
2× Application on stone of
sterile culture medium (CB-)
2.5% in distilled water
4
1× Application of CB-
2.5% in distilled water
5
1× Application of CB-
2.5% in distilled water
Considering the possibility of creating a colour patina due to CB technology (Le MetayerLevrel et al. 1999), the use of the biomineralisation with pigments for infilling cracks and
fissures in the dense stones was proposed. In this experiment, pigments matched to the
colour of the stone were added to the culture medium during the 3rd, 4th and 5th day of the
biomineralisation procedure. The coloured liquids were applied on the stone surfaces by
spraying, brushing, or local application into cracks by syringe. An extra test was performed
to evaluate the effect of bio-patina and cracks filling, when the colour liquid is applied
before the biomineralisation procedure.
All the experiments were performed in laboratory conditions at a temperature between 2030°C. In contrast to the original method, the condition of increased relative humidity of the
air (70-80%) was proposed during the application procedure and 7 days after to retard water
vaporisation from the stone surfaces. Considering the high content of soluble salts in the
culture medium, a desalination procedure (24 hour in the static bath in distilled water) was
proposed three weeks after the end of the biomineralisation procedure.
Tab. 2: An overview of the types of treatment.
Humidity conditions
Trials
conditions of normal humidity
(40-50%)
CB treatment
conditions of increased humidity
(70-80%)
CB treatment
CB treatment and desalination procedure
CB treatment and desalination procedure
2.3. Evaluation methods
To investigate the changes on Bacillus cereus cells during the biomineralisation process the
Scanning Electron Microscope (LEO Electron Microscopy – model 1430 VP) was used.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The consolidation effect of the biomineralisation technique was evaluated by the
verification of physical properties of treated Pińczów limestone: colour changes, weight
increase, soluble salts content, and mechanical properties.The colour changes were verified
by comparison of treated samples and control samples. The total weight increase was
calculated from the difference in weight before and after the treatment on samples dried to
constant mass at 60°C. The hypothetical weight increase of calcium carbonate was
calculated from the difference in the dry weight before treatment and after the desalination
of treated samples. The contents of soluble salts were measured by the conductometric
method before and after the treatment and also after the desalination of treated samples. To
verify mechanical properties of the treated samples, the resistance to bending was measured
by using the “Dynstat” instrument. The measurement was performed two months after the
biomineralisation procedure for the control samples, treated samples and treated desalinated
samples. Considering the heterogeneous texture of the stone slabs the investigation was
conducted on 44 consolidated samples and two highest and two lowest results were
rejected. The mechanical properties were calculated using the formula:
𝑅𝑧𝑔 =
6𝑀 ∗ 98.07
bh2
(Eq. 1)
where Rzg is the resistance to bending, M is the bending moment, b is the width of the
sample and h is the thickness of the sample. The detection of newly formed calcium
carbonate and the evaluation of penetration depth of the new carbonate cement was
performed on the treated Żerkowice sandstone samples by SEM/EDS analyses (Quantax
200 with the XFlash 4010 detector, Bruker AXS). The evaluation of the filling of cracks in
the dense stones was based on the microscopy conducted before and after the treatment.
3. Results
3.1. Observation of Bacillus cereus growth
The inoculation of Bacillus cereus in CB culture medium results in very fast growth of the
bacteria. After 16 hours of incubation, most of the bacteria are still in a spore phase
(Fig. 1a), which allows to introduce them deeper to the structure of the stone; however,
after the 2nd day of the procedure all of the bacteria are already in the advanced stage of
evolution (Fig. 1b). The vegetative bacteria cells always arrange themselves around the
organic matter from the nutritional solution (Fig. 2a). The bacteria firstly organize
themselves into chains, but then establish structures, sometimes highly organized. The SEM
observation showed that 4 days after inoculation of bacteria in the culture medium, the solid
products (in the form of patches) start to appear on the bacteria cell walls (Fig. 2b).
a)
b)
Fig. 1: a) Bacillus cereus at the spore phase, b) Bacillus cereus
at the the evolution stage (zoom ×100).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 2: a) Congregating of Bacillus cereus bacteria around organic matter,
b) inorganic precipitants on the bacterial cell wall.
3.2. Changes of physical properties of Pińczów limestone
Colour changes: After the treatment, the darkening and yellowing of the specimens were
reported mostly on the evaporation side of the stone samples. Less visible changes of colour
were noticed on the specimens treated in the conditions of increased relative humidity of
the air (70-80%). After the desalination the visual aspects of the stone surfaces returned to
the original.
Weight increase: The CB treatment resulted in significant weight increase of Pińczów
limestone samples (2-3%). The bigger changes of mass properties were noticed on the
samples treated in the conditions of normal relative humidity of the air (40-50%).
Nevertheless, after the desalination procedure the weight increase amounted to about 0.2%.
Soluble salts content: The content of soluble salts was significant for all of the treated
specimens (Tab. 3). The treatment in normal conditions of air humidity resulted in twice as
high a content of soluble salts when compared to the treatment that was performed in
conditions of increased humidity. After the desalination, the soluble salts content decreased
to 0.4%.
Fig. 3: Crystallisation of NaCl in the porous structure of the limestone.
Mechanical properties: The CB treatment increased resistance to bending for all the
limestone samples. The highest strengths were obtained for the samples treated in normal
humidity (5.72 MPa). After the desalination, the resistance to bending decreased but was
still 15-16% higher than before the treatment. After the desalination, the change in humidity
did not result in significant influence on the mechanical properties.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 3: Summary of changes of physical properties of Pińczów limestone
according to CB procedure.
Condition
laboratory
increased
humidity
Specimen
Total
weight
increase
CaCO3
weight
increase
Soluble
salt
content
Resistance
to
bending
Increase
of bending
resitance
%
%
%
MPa
%
untreated
-
-
0.05
2.85
-
treated
3.17
-
2.44
4.63
62
treated and
desalinated
-
0.21
0.37
3.3
16
treated
2.17
-
1.18
5.72
101
treated and
desalinated
-
0.21
0.2
3.29
15
3.2.1. Identification of calcium carbonate
The SEM/EDS analyses showed the presence of calcium carbonate crystals on the surface
of treated sandstone samples. The accumulation of the calcium carbonate is especially
apparent on the superficial layer up to 300 µm in depth.
Calcium carbonate
crystals on the surface
Cross-section of the
sandstone treated
sample:
Concentration of
calcium carbonate
on the depth to
Fig. 4: Żerkowice sandstone.
3.3. Infilling cracks and fractures in dense stones
The CB treatment with the addition of the pigments gave different outcomes depending on
the method of application. The pouring of the coloured culture medium resulted in a more
homogeneous effect of patina on the stone surface than applying it by brush. Microscopy
showed that the micro-cracks were partially or completely infilled. Nevertheless, the
created patina was not resistant to abrasion. The local application of bio-preparation using
the syringe did not increase the effectiveness of the micro-cracks infilling. The application
of the pigments mixed with distilled water before CB procedure resulted in the creation of
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
homogenous colour patina and its resistance to abrasion; however, the filling of microcracks was not completed. A side effect was noticed during and after the procedure: white
crystals of salts were precipitated on the stone surfaces after the water evaporated.
Fig. 6: The filling of micro-cracks on the Rosso Verona marble and the
Dębnik limestone due to the biomineralisation procedure
4. Discussion
The CB biomineralisation treatment had significantly altered the physical properties
(weight, strength) of the Pińczów limestone. Nevertheless, structural consolidation was not
obtained due to the superficial effect of calcite precipitation. Moreover, the procedure was
linked to some side effects, like the colour changes and the soluble salt crystallisation due
to the composition of the culture medium. However, the desalination procedure, proposed
in this research, made it possible to remove them. After the desalination, the stone samples
returned to their original colour and were still more resistant to bending (15-16%) than the
untreated ones. The introduction of the conditions of increased humidity limited colour
changes of the stone. The high humidity of the air retards the vaporisation of water from the
stone structure and may decrease migration of the unused nutritional solution to the stone
surface, which can cause the colour change. The present preliminary study shows that
biomineralisation is able of infilling micro-cracks on the surface of dense stones. The
micro-cracks were probably infilled by the grains of pigment bonded by the calcium
carbonate cement. However, the homogenous colourful patina was difficult to obtain due to
the separation of the suspension of the pigments in the culture medium. Among the
negative effects were the crystallisation of the soluble salts (NaCl) and the lack of
resistance to abrasion. It might have been a result of the insufficient yield of the calcium
carbonate precipitation to bind all the grains of pigments. The biggest homogeneity and
resistance of the patina was obtained in the treatment where the pigments were applied on
the stone surface before the CB procedure. Although the filling of micro-cracks was not
complete, it is believed that the repetition of the procedure may bring better results.
5. Conclusion
The CB procedure results in a very fast growth of Bacillus cereus and the precipitation of
inorganic crusts on the bacteria cell walls. In the porous stone the calcium carbonate
precipitation is obtained only on the surface up to 300 µm. The changes of physical
properties of the Pińczów limestone due to the CB were evident, although it was attended
by precipitation of a significant amount of soluble salts. The desalination treatment
removed this side effect, but caused a decrease in the mechanical properties compared to
the value obtained after the CB treatment. It may be a result of the finely crystalline
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
structure of the calcium carbonate, which elutes from the stone along with the salts. The
further research should be concerned with the evaluation of the harmfulness of the soluble
salts introduced to the stone during the biomineralisation procedure. An explanation for the
decline of the mechanical properties after the desalination procedure should also be
investigated.
References
Adolphe, J.-P., Loubie`re, J.-F., Paradas, J., Soleilhavoup, F., 1990. Proce´de´ de traitement
biologique d’une surface artificielle, European patent No. 90400G97
Castanier S., Le Metayer-Levrel G., Perthuisot J-P., 1999, Ca-carbonates precipitation and
limestone genesis – microbiogeologist point of view, Sedimentary Geology, 126.
De Muynck W., De Belie N., Verstraete W., 2010, Microbial carbonate precipitation in
construction materials: A review, Ecological Engineering, 36, 118-136.
Domasłowski, W. (ed.), 2011, Zabytki kamienne i metalowe, ich niszczenie i konserwacja
profilaktyczna, Toruń.
Domaslowski W., A. Strzelczyk, 1986, Evaluation of applicability of epoxy resins to
conservation of stone historic monuments, Case Studies in the Conservation of
Stone and Wall Paintings: Preprints of the Contributions to Bologna Congress, ed.
N. S. Brommelle and P. Smith, 126-132.
Domasłowski W., Łukaszewicz J. W., 1983, Badania nad strukturalnym wzmacnianiem
wapienia pińczowskiego termoplastycznymi żywicami sztucznymi, AUNC
Zabytkoznawstwo i Konserwatorstwo X, Nauki Humanistyczno-Społeczne, 129,
Toruń.
Jimenez-Lopez, C., Rodriguez-Navarro,C., Pinar,G.,. Carrilo-Rosua, F. J., RodrigezGallego, M., Gonzalez-Munoz, M.T., 2007, Consolidation of degraded ornamental
porous limestone by calcium carbonate precipitation induced by mikrobiota
inhabiting the stone, Chemosphere, 68 (10), 1934.
Le Metayer-Levrel G., Castanier S., Orial B., Loubiere J-F., Perthuisot J-P., 1999,
Applications of bacterial carbonatogenesis to the protection and regeneration of
limestones in buildings and historic patrimony, Sedimentary Geology, 126, 25-34.
Lewin, S. Z., 1971, Recent experience with chemical techniques of stone preservation, The
Treatment of Stone, Proceedings of the Meeting of the Joint Committee for the
Conservation of Stone, Bologna, Italy.
Łukaszewicz J. W., 2002, Badania i zastosowanie związków krzemoorganicznych w
konserwacji zabytków kamiennych, Toruń, Poland.
Rodriguez-Navarro, C., Rodriguez-Gallego, M., Ben Chekroun, K., Gonzalez-Munoz, M.
T., 2003, Conservation of ornamental stone by Myxococcus Xanthus – induced
carbonate biomineralization, Applied Environmental Microbiology, 69 (4).
Ziegenbalg, G., 2008, Colloidal calcium hydroxide: A new material for consolidation and
conservation of carbonatic stones, Proceedings of the 11th International Congress
on Deterioration and Conservation of Stone.
838
ASSESSMENT OF DOLOMITE CONSERVATION BY
TREATMENT WITH NANO-DISPERSIVE
CALCIUM HYDROXIDE SOLUTION
F. Karahan Dağ1*, Ç.T. Mısır1, S. Çömez1, M. Erdil1, A. Tavukçuoğlu1,
E.N. Caner-Saltık1, B.A. Güney1 and E. Caner2
Abstract
In recent years, compatible stone consolidation treatments have gained a special
importance. This study concerns the treatment of microcrystalline dolomite, a building
stone that has been widely used in Anatolian monuments, with nano-dispersive calcium
hydroxide solutions and monitoring the efficiency of those treatments. Sound dolomite
pieces from the new quarries of Midyat-Mardin were used for the experiments. Samples
were cut to the sizes of 5×5×2 cm. A nano-dispersive calcium hydroxide solution in ethyl
alcohol prepared in the laboratory was applied through the surface of stone samples by
capillary suction. The aim was to establish a compatible calcite network within the
dolomite structure. The efficiency of the treatment was assessed by using standard
laboratory tests through monitoring the progress in main physical and physicomechanical
properties of samples in terms of bulk density, total porosity, water absorption capacity,
water vapour permeability, thermal and moisture expansion, ultrasonic pulse velocity and
modulus of elasticity before and after treatments. Depth of consolidation and calcite
formation in the microstructure of dolomite were examined by using SEM/EDS, XRD and
optical microscopy. Treatment with a nano-dispersive calcium hydroxide solution resulted
in considerable increase in ultrasonic pulse velocity of dolomite indicating improvements in
physicomechanical properties. No significant change in water vapour permeability and
dilation properties after treatment promise advantages for future compatibility of treated
and untreated parts of stone. Microstructural investigations with optical microscopy and
SEM/EDS at high magnification showed integration of newly formed calcite crystals with
existing dolomite crystals of the stone. Additional investigations with repeated treatments
will help for further evaluation of treatments for historical dolomitic structures
Keywords: dolomite, consolidation, efficiency tests for conservation treatment, nanodispersive calcium hydroxide solutions, XRD, SEM/EDS
1
F. Karahan Dağ*, Ç.T. Mısır, S. Çömez, M. Erdil, A. Tavukçuoğlu, E.N. Caner-Saltık and
B.A. Güney
Middle East Technical University (METU Materials), Department of Architecture, Ankara, Turkey
flykarahan@gmail.com
2
E. Caner
Department of Conservation and Restoration of Cultural Heritage, Pamukkale University Denizli,
Turkey
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
1. Introduction
Stone consolidation treatments have a major role in the field of conservation science. Stone
consolidation treatments are expected to slow the decay mechanisms, be compatible with
the stone structure in the long run and improve physical and physicomechanical properties
of the deteriorated stone. Consolidation of the historic stones by the formation of a
compatible network within the microstructure of the stone is a requirement for the
compatibility of the treatment. However, there is limited knowledge on the efficiency of
various consolidation products in terms of their performance, compatibility and durability
in relation to the stone type and state of deterioration. Therefore, it was necessary to
develop some tests to assess the effectiveness of stone consolidation treatments by
measurable parameters before their application and prove their success in time.
There are numerous studies on application of calcium hydroxide solutions on several
materials like limestones, wall-paintings, mortars or plasters (Daehne and Herm, 2013,
Caner et al., 2013, Caner, 2011, Daniele et al., 2008, Dei and Salvadori, 2006, Giorgi et al.,
2000, Ambrossi et al., 2001). Treatments with nano-dispersive calcium hydroxide solution
are favourable due to their high penetration depth, the final product calcium carbonate
having the same chemical and mineralogical composition with limestone, lime mortars and
plasters.
Carbonation of calcium hydroxide is closely affected by relative humidity of the
environment, its CO2 enrichment, the type of dispersing medium, and the calcium
hydroxide concentration. Tests that are performed before and after treatments are expected
to show the changes in physical and physicomechanical properties and the microstructure
of stone. The results of the tests should be directly correlated with the compability and
durability properties of stone.
In this study, nano-dispersive calcium hydroxide solution was applied to dolomite samples
obtained from quaries of Midyat-Mardin and some tests were conducted to evaluate
effectiveness and compability of treatment. Dolomite mineral has a unit cell of
rhombohedral shape with chemical formula CaMg(CO3)2. Minerals of dolomite are similar
in structure to those of calcite having unit cell of rhombohedral shape. Dolomite has layers
of carbonate alternating with layers calcium and magnesium. The insertion of magnesium
atom for half of the calcium atoms makes dolomite with a lower degree of symmetry
compared to calcite. The regular alternating layers of calcium-magnesium in its unit cell
make dolomite a difficult mineral to be synthesized in the laboratory under normal
atmospheric conditions. Even though, it is a very stable mineral thermodynamically, its
formation is not favored in terms of kinetic factors (Morrow, 1982). Since the treatment of
dolomite with dolomite nanoparticles has not yet been achieved, nano-dispersive calcium
hydroxide solution was used for the treatment of dolomite where the carbonation product,
calcite, having similar crystalline shape can be an appropriate choice for the consolidation
of dolomite.
2. Materials and Methods
Dolomite samples were obtained from Midyat-Mardin. They were cut to the size of
5×5×2 cm. Those samples were used in all experiments before and after the treatments.
Nano-dispersive calcium hydroxide solution in ethyl alcohol was prepared at METU
Materials Conservation Laboratory with the concentration of 30g/L. The size of the nano-
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
dispersed particles was measured by Malvern Nano ZS90 instrument. The average particle
size was found to be in the range of 350-600nm (Caner, 2011, Caner et al., 2013).
Samples were treated by putting them on filter papers saturated with nano-dispersive
calcium hydroxide solution. By this way, the solution penetrated through samples by
capillary suction. Samples were left on filter paper for half an hour. Treated samples were
then kept in a chamber (Thermo Scientific MIDI 40 CO2 incubator) under 90% relative
humidity and 20% CO2 environment during one month and then dried in oven at 60°C.
Effectiveness of consolidation treatment in dolomite samples were studied by examining
them for their physical, physicomechanical and microstructural properties before and after
the treatments. Bulk density (), porosity () of samples were determined by RILEM
standards (RILEM, 1980). Ultrasonic pulse velocity (UPV direct) in dry condition was
measured via PUNDIT Plus 220Hz equipment. Modulus of elasticity was calculated
indirectly by using average UPVdirect values and densities of dry samples (RILEM, 1980;
Topal & Doyuran, 1995) (Tables 1 and 2). Water vapor permeability properties of stone
samples were determined according to the standards (RILEM,1980, Teutonico, 1988). An
experimental set up was constructed and equivalent air thickness of vapor permeability
(SD) and water vapor diffusion resistance coefficient (μ) of treated and untreated stone
samples were determined (Tab. 3). Linear expansion-shrinkage behaviour of dolomite
samples (5×5×2 cm dimensions) were observed at a dry ambient environment having a
constant relative humidity (30%) during cooling from 40 to 20°C and then immersing in
water (Fig. 1) by recording the movement vs time with sensitive probes of LVDT (Linear
Variable Differential Transformer) which works with a data collector (ASTM D5335-14:
2010). Mineralogical and microstructural properties of dolomite samples before and after
the treatment were studied by XRD (Bruker D8 Advance Diffractometer), stereomicroscope
(Leica Z16 APO A model stereomicroscope), and SEM/EDS analyses.
3. Results and Discussion
Effectiveness of consolidation with nano-dispersive calcium hydroxide solution in ethyl
alcohol was evaluated through comparison of basic physical and physicomechanical
properties, water vapour permeability, linear dilation properties and microstructural views
before and after the treatments.
3.1. Physical and Physicomechanical Properties
Average bulk density of untreated dolomite samples were 1.890.02 gcm-3, porosity values
being 27.60.9% by volume. Those properties were not measured after the treatment to
avoid damage to treated samples. Samples were thoroughly examined for their ultrasonic
pulse velocity characteristics by direct UPV measurements in three axes. Average UPVdirect
values of dry samples were between 3127219 ms-1 (Tab. 1). Values for modulus of
Elasticity, Emod, calculated by using bulk density and UPVdirect were found to be
19.62.7 GPa (RILEM, 1980; Topal & Doyuran, 1995). Average UPVdirect values of treated
samples in three axes did not show any significant difference in the samples treated with
nano-dispersive calcium hydroxide solution (Tab. 2). Although the changes in average
ultrasonic velocity values were near the range of standard deviation, some increase was
noticed in the capillary direction after the treatments (4%-15%). Obtaining variable changes
in UPVdirect values in three axes indicated heterogeneous distribution of nano-dispersive
solution in the sample by capillary suction.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Physical and physicomechanical properties of dolomite samples.
Stone sample
-3
Dolomite (M)
UPVdry
Emod
-1
gcm
Vol.-%
ms
GPa
1.890.02
27.60.9
3127219
19.62.7
Tab. 2: Average UPV values of dolomite samples before and after treatment with nanodispersive Ca(OH)2 solutions.
Stone
samples
Direct UPV values
before treatment
Direct UPV values
after treatment
Rel. Change
UPV*
UPVZ **
UPV*
UPVZ**
UPV*
UPVZ**
ms-1
ms-1
ms-1
ms-1
%
%
MII-1
3331
3430
3187
3583
-4
4
MII-2
3491
3498
3537
4006
1
15
MII-3
3538
3435
3373
3877
-5
13
MII-4
3463
3365
3364
3826
-3
14
Average
3455
3432
3365
3823
* average UPV values of x-y-z directions
** UPV values in z direction being parallel to the direction of capillary suction
Water vapor permeability of the samples before and after the treatments was thought to be a
useful parameter to show the compatibility between the treated and untreated parts of stone
in consolidation applications for the evaluation of treatment’s compatibility. It was
observed that water vapor permeability characteristics of untreated and treated samples
were in quite the same range indicating that the treatment did not significantly affect the
breathing behavior (Tab. 3).
Tab. 3: Water vapor permeability properties of treated and untreated dolomite samples.
Stone samples
S0*
SD**
m
m
***
MII
Untreated(average)
0.0197
0.199
10.39
MII-1
Treated
0.0195
0.247
12.68
* thickness of sample
** equivalent air thickness of water vapor permeability (SD)
*** water vapor diffusion resistance coefficient (μ)
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3.2. Linear Thermal Expansion Properties Related to Thermal Changes
Linear expansion/shrinkage behavior of dolomite related to temperature and water suction
changes were first examined with a preliminary experiment during cooling from 40°C to
20°C followed by immersion in water. Considerable shrinkage during cooling from 40°C to
20°C was observed, whereas, the immersion of the sample in water did not cause any
dimensional change (Fig. 1). Those results indicated that linear expansion behavior of
dolomite samples related to thermal change was more important.
Fig. 1: Linear shrinkage of 5 cm dolomite sample during cooling from 40°C to 20°C and
immersion in water.
Therefore linear expansion of the dolomite samples related to thermal changes was
examined before and after the treatment with nano-dispersive solution. Before treatment,
dolomite samples of 5 cm length had linear expansion of about 0.015 mm during heating
from 10°C to 50°C. Expansion of the same sample after the treatment was observed to be
around 0.016 mm. The results indicated that treatments did not cause any significant
difference in the expansion properties of dolomites during temperature changes (Fig. 2).
The results showed the treatment’s compatibility in terms of linear expansion.
Fig. 2: Thermal expansion graph of dolomite sample before (left) and after (right)
treatment.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3.3. Mineralogical and Microstructural Characteristics
Mineralogical composition of dolomite was identified by XRD. The dolomite samples
obtained from new quarries of Midyat-Mardin, are purely dolomite as followed by XRD
traces. Impurities within the dolomite were more likely to be in minor amounts.
Microstructural changes by the treatments were followed by stereomicroscope and
SEM/EDS. Untreated and treated samples were viewed by a stereomicroscope at its highest
zoom, It was observed that calcite crystals formed by nano-dispersive Ca(OH)2 solution
gathered within the bigger pores; covering the areas with a white layer whereas in untreated
samples, large dolomite crystals belonging to original stone were observed within the pores.
Fig. 3: SEM images of treated dolomite cross-sections: General view (×100) of bigger
pores (left); Detailed view (×10000) of crystals inside the pores (center); Dolomite crystals
(×40000) can be observed in structure after treatment (right).
Fig. 4: SEM images of treated dolomite cross-sections: General view (×100) of bigger
pores (left); Detailed view (×10000) of crystals inside the pores (center); Nano calcite
crystals (×40000) can be observed in structure after treatment (right).
The changes in the microstructure of dolomite were better observed in secondary electron
images of gold /palladium coated samples before and after treatments. Cross-section views
of big pores before the treatments are seen in Fig. 3. Micritic size dolomite crystals are well
observed in the pores of the stone. Cross-section views of big pores after the treatments are
seen in Fig. 4. Newly formed calcite crystals after the treatments are well observed in the
pores as being integrated with the dolomite crystals. Straight lines of crystal edges are
indicative of surface controlled precipitation of calcite by treatment with nano-dispersive
Ca(OH)2 solution. Dissolution and precipitation reactions of calcium carbonate are
supposed to be controlled by surface reactions in a wide pH range of 4 to 14 (Morse and
Arvidson, 2002). Alkaline solutions at pH larger than about 13.5 are considered to be in
favor of aragonite precipitation (Kitamura et al., 2002). Aragonite formation is also favored
in presence of magnesium ions (Bischoff and Fyfe, 1968., Lipmann, 1973). Morphological
characteristics of precipitated calcium carbonate in SEM images indicate the presence of
rhombohedral calcite but not orthorhombic aragonite. The precipitation of calcite must have
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
occurred in a medium with pH lower than 13.5 and where magnesium ion concentration
was not noticeable. Therefore, dedolomitization of dolomite was unlikely to occur during
the treatments with nano-dispersive Ca(OH)2 solution (Caner et al., 1985).
4. Conclusion
In this study, consolidation of dolomite with nano-dispersive calcium hydroxide solution in
ethyl alcohol was studied in terms of its effectiveness and compatibility with the stone
structure. The treatment with nano-dispersive solution improved its physicomechanical
properties. The treatments did not affect the stone’s water vapour permeability and thermal
dilation characteristics showing compatibility of treated parts with the untreated parts of the
stone. Formation of calcite crystals within the microstructure of the stone and their
integration with its dolomite crystals were examined by SEM which showed the success of
the treatments. Further studies with repeated treatments as well as treatments of deteriorated
dolomites need to be done for the development of this method as a treatment for historical
dolomitic structures.
5. Acknowledgement
In this study, financial support of The Scientific and Technological Research Council of
Turkey (TUBİTAK) is gratefully acknowledged.
References
Ambrossi, M., Dei, L., Giorgi, R., Neto, C., Baglioni, P., 2001, Colloidal Particles of
Ca(OH)2 Properties and Applications to Restoration of Frescoes, Langmuir, 17,
4251-4255.
ASTM D5335-14: 2010 - Standard test method for linear coefficient of thermal expansion
of rock using bonded electric resistance strain gauges, 7p. American Society for
Testing and Materials.
Bischoff, J.L., and Fyfe, W.S., 1968, Catalysis, imbition and the calcite-aragonite problem,
Part 1, The aragonite-calcite transformation, Am. Jour. Sci., 266, 65-79.
Caner, E.N., Demirci, Ş. and, Türkmenoğlu, A.G., 1985, Deterioration of Dolomite by
Soluble Salts in Divriği Great Mosque-Turkey, V th. International Congress on
Deterioration and Conservation of Stone, Ed. G.Felix, 1, 299-305, Ecole
Polytechnique Federale de Lausanne, Lausanne, Lausanne,
Caner, E., 2011, Limestone decay in historic monuments and consolidation with
nanodispersive calcium hydroxide solutions, Middle East Technical Univeristy,
Phd Thesis.
Caner, E., Caner-Saltık, E.N., 2013, Deterioration mechanisms of historic limestone and
development of ıts conservation treatments wıth nanodispersive Ca(OH) 2
solutıons, 8th International Symposium on the conservation of Monuments in the
Mediterranean Basin, 3, 54-72.
Daehne, A., Herm, C., 2013, Calcium hydroxide nanosols for the consolidation of porous
building materials, Heritage Science, 1(11).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Daniele, V., Taglieri, G., Quaresima, R., 2008, The Nanolimes in cultural heritage
conservation: characterization and analysis of the carbonation process, Journal of
cultural heritage, 9, 294-301.
Dei, L., Salvadori, B., 2006, Journal of cultural heritage, 7, 110-115.
Giorgi, R., Dei, L., Baglioni, P., 2000, A new method for consolidating wall paintings
based on dispersion, of lime in alcohol, Studies in Conservation, 45, 154- 161.
Kitamura, M., Konno, H., Yasui, A., Masuoka, H. 2002, Controlling factors and
mechanism of reactive crystallization of calcium carbonate polymorphs from
calcium hydroxide solutions, Journal of Crystal Growth, 236, 323-332.
Lippman, F., 1973, Sedimentary Carbonate Minerals, Springer Verlag, Berlin.
Morrow, D.W., 1982, Diagenesis 1. Dolomite-Part 1. The chemistry of dolomitization and
dolomite precipitation, Geosicience Canada, 9(1), 5-13.
Morse, J. W., and Arvidson, R. S., 2002, The dissolution kinetics of major sedimentary
carbonate minerals, Earth Science Reviews, 58, 51-84.
RILEM, 1980, Tentative Recommendations, Comission-25-PEM, Recommended tests to
measure the deterioration of stone and to assess the effectiveness of treatment
methods, Materaux et Constructions, 13(75):173-253.
Teutonico, J.M., 1988, A Laboratory Manual for Architectural Conservators, ICCROM,
Rome, p.32-122.
Topal, T. and Doyuran V., 1995, Ultrasonic Testing of Artificially Weathered Cappadocian
Tuff. Preservation and Restoration of Cultural Heritage, 205-211.
846
EUROPEAN PROJECT
“NANO-CATHEDRAL: NANOMATERIALS FOR CONSERVATION
OF EUROPEAN ARCHITECTURAL HERITAGE DEVELOPED BY
RESEARCH ON CHARACTERISTIC LITHOTYPES”
A. Lazzeri1, M.-B. Coltelli1, V. Castelvetro2, S. Bianchi2, O. Chiantore2,
M. Lezzerini3, L. Niccolai4, J. Weber5, A. Rohatsch6,
F. Gherardi7 and L. Toniolo7*
Abstract
Europe has significant cultural and environmental diversity together with an exceptional
ancient architecture and built environment. From the point of view of conservation, this
architectural excellence and heritage may present degradation problems related to the
variety of stone materials used for their construction. In the present project five different
medieval cathedrals and a contemporary opera theatre were selected as they may be
considered as representative of both different environmental conditions and types of stones
(limestones, sandstones and marbles) in Western Europe. The project aims at developing
new materials, technologies and procedures for the restoration and conservation of stone in
ancient cathedrals and monumental buildings, with a particular emphasis on the
preservation of the originality of the building materials and on the development of tailormade approach to tackle the specific problems. The original materials will be analysed and
classified, evaluating their connection with historical exploitation of quarries as a source of
building materials. Nanomaterials suitable for the consolidation and protection of stones
will be developed aiming at providing the best technological answer for the preservation of
different types of stones, according to porosity and mineralogical and chemical features.
The exploitation of the project will bring about the adoption of best practices for the
preservation of the cathedrals and high quality buildings by selecting the most advanced
nanotechnologies.
1
A. Lazzeri and M.B. Coltelli
INSTM - Department of Civil and Industrial Engineering, University of Pisa, Italy
2
V. Castelvetro, S. Bianchi and O. Chiantore
INSTM - Department of Chemistry and Industrial Chemistry, University of Pisa, Italy
3
M. Lezzerini
INSTM - Department of Geosciences, University of Pisa, Italy
4
L. Niccolai
Colorobbia Consulting S.r.l., Italy
5
J. Weber
University of Applied Arts Vienna, Austria
6
A. Rohatsch
Institut für Geotechnik, Technische Universität Wien, Austria
7
F. Gherardi and L. Toniolo*
INSTM - Department of Chemistry, Materials and Chemical Engineering, Politecnico di Milano,
Italy
lucia.toniolo@polimi.it
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Keywords: architectural heritage, nanomaterials, stone conservation, consolidation,
protection
1. Introduction
1.1. Project “Nano-cathedral”
In the framework of the EC Horizon 2020 Nano-Cathedral project1 launched in 2015,
nanomaterials for the preservation of stone based monuments have been designed as a
result of a collaborative effort of European research Centers, companies involved in the
development and production of engineered inorganic nanoparticles, Conservation
Institutions and Foundations managing monumental buildings. The general objective of the
three-year project is the design, production and evaluation of different types of inorganic
and polymeric nanoparticles as well as nanoparticles based formulations, to be applied as
protective and/or consolidation treatments onto different lithotypes on European
monuments characterized by a variety of environmental exposure conditions. In particular,
the Cathedral of Pisa (Italy) and the Cathedral of Santa María of Vitoria-Gasteiz (Spain) are
representative of south European “Mediterranean” climate in coastal and continental
regions, respectively; the Sint-Baafs Cathedral of Ghent (Belgium), the Cathedral of St.
Peter and Mary of Cologne (Germany) and the St. Stephen's Cathedral (Vienna), are
included as representative of a Central-North European climate in continental regions.
Moreover, the Oslo Opera House (Norway) was considered as an example of a
contemporary building cladded with white Carrara marble. The stones used for the
construction of the buildings have been analysed and classified, evaluating their connection
with historical exploitation of quarries as a source of building materials, thus improving the
knowledge of the architectural and artistic heritage and the connections with the regional
context. For this purpose a general protocol has been defined for the identification of the
petrographic and mineralogical features of the stone materials, the evaluation of their state
of conservation, the identification of correlations among the relevant state of decay, the
material properties and the local macro and microclimatic exposure. The innovative
nanomaterials, that will be developed, will be applied on stone materials taken from
quarries representative of the selected lithotypes, and they will be tested before and after
application of the consolidation and/or protection products to evaluate the effectiveness of
the treatments, following a protocol of laboratory tests which include microscopic
observations, colorimetry and spectroscopic analyses. Finally, the best formulations of
consolidants and protective treatments will be applied on pilot-areas selected in each
building and non-destructive tests will be carried out to monitor their effectiveness and
durability.
1.2. Nanomaterials for stone conservation
Since ‘80s, the scientific research has been devoted to the development of nanomaterials to
be applied in a wide range of fields, including the conservation of Architectural Heritage.
Compared to traditional materials and methods, the innovative nanomaterials show
enhanced effectiveness in their main properties as their higher surface area make them more
reactive. Regarding the class of stone consolidants, one of the first synthesized
1
H2020 Grant Agreement N.646178; NMP-2014-2015/H2020-NMP-2014-two-stage
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
nanomaterial is nanolime, that is a water or alcoholic dispersion of Ca(OH) 2 nanoparticles.
Nanolime has been used for the consolidation of calcareous stone and wall paintings, since
it presents different advantages compared to traditional limewater: higher reactivity, deeper
penetration in the substrate, reduction of carbonation time and higher stability
(Chelazzi et al. 2013, Rodriguez-Navarro et al. 2013). Different commercial nanolime and
dispersions of nano-SiO2 are available on the market and their use is becoming more
common among restorers, despite nowadays the most used consolidants are alkoxy-silane
and oligomers. In order to overcome the drawback of alkoxy-silanes related to the
formation of cracks of the silica gel, particle-modified consolidants, based on the
introduction of different nanoparticles in pre-polymerized tetraethoxysilane, have been
proposed (Miliani et al. 2007, Kim et al. 2009). Another interesting nano-consolidant is the
one proposed by Verganelaki, which consists in the incorporation of nanoparticles of
amorphous calcium oxalate monohydrate in TEOS to form a crack-free nanocomposite,
with a good penetration depth inside the substrate, able to increase the strengthening
properties of calcareous building stones and cement mortars (Verganelaki et al. 2015).
Nanotechnology is also applied for the synthesis of protective treatments for stone
materials, realized by adding different nanoparticles (SiO2, SnO2, Al2O3) inside polymeric
media (poly(methyl methacrylate), functionalized perfluorinated polyether and
polyalkylsiloxane) to increase the stone surface roughness (Manoudis et al. 2009, Facio and
Mosquera 2013). These nanocomposites are able to confer super-hydrophobic (water
contact angle > 150°) and self-cleaning properties to the stone. Moreover, TiO2
nanoparticles have been used for the synthesis of self-cleaning consolidants and protective
treatments because of their photocatalytic property to promote the degradation of inorganic
and organic pollutants and their ability to create superhydrophilic surfaces (Munafò et al.
2015). Among TiO2-based self-cleaning coatings for Cultural Heritage stone surfaces, two
different categories can be identified. The first one includes hydrophilic nano-TiO2
dispersions (Quagliarini et al. 2013), whereas the second one comprises hydrophobic and
superhydrophobic nanocomposites (Kapridaki et al. 2014).
The results of the current and more recent literature demonstrates the potential of
nanostructured consolidants and protective treatments for the conservation of architectural
heritage, since they can overcome the open challenges related to durability, adhesion on the
substrates, effectiveness and transparency issues.
2. Survey on commercial and research stone consolidants and protective
coatings
One of the activities of the Project concerns the realization of a survey to setup a database
of the most applied commercial products and the most relevant research products from the
current scientific literature in Europe for the consolidation and the protection of natural
decayed stones. The collected data are coming from the Project Partners on the basis of
their professional and research experience and the elaborated data are strictly connected to
this provenance; therefore, the database is not an exhaustive collection of all the
commercial or research products available. Among commercial products, the total number
of different consolidant materials is 37. They can be divided in three main chemical classes:
alkoxy-silane and oligomers, acrylics and low molecular weight inorganics. 12 of them
contain nanoparticles in the formulation, in particular Ca(OH) 2, SiO2, ZrO2, Al2O3 (Fig. 1).
Regarding the dispersing media, the most used ones are organic solvents. Among
commercial products, the total number of different protective coatings is 21, 2 of which
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
have antifouling properties. They can be divided in 5 chemical classes: alkyl-alkoxy-silane
oligomers, alkyl-aryl-polysiloxanes, fluorinated or partially fluorinated polymers, low
molecular weight inorganics and vegetable polysaccharides. Among them 5 contain
nanoparticles in the formulation, in particular Ag, SiO 2, TiO2, ZnO nanoparticles (Fig. 1).
Organic solvents are the most used in the formulations.
Among research products the total number of consolidants is 39, 2 of which have also
antifouling properties. They can be divided in 4 main chemical classes: alkoxy-silane and
oligomers, acrylics, low molecular weight inorganics and products of biomineralization. A
wide range of nanoparticles have been used in the formulation but nano-SiO2 is the most
used one. Organic solvents are the most used in the formulations, which have been applied
on different stone substrates, following different application methods. The total number of
protective coatings is 27, 4 of which show antifouling properties and 2 of which show both
properties. They can be divided in 4 main chemical classes: alkyl-alkoxy-silane oligomers,
alkyl-aril-polysiloxanes, acrylic polymers, fluorinated or partially fluorinated polymers,
oxalates, low molecular weight inorganics and aliphatic polyesters. Also for research
protective coatings, a wide range of nanoparticles have been used in the formulation among
which nano-TiO2 is the most used one. Organic solvents are the most used in the
formulations, which have been applied on different stone substrates, following different
application methods.
Fig. 1: Nanoparticles present in commercial consolidants (left) and
protective coatings (right).
3. Selection of lithotypes
For each cathedral one lithotype has been selected (except for Cathedral of Cologne, for
which two lithotypes have been selected) taking into account its petrographic properties and
its representability for the building but also with respect to the European context, to grant a
large scale application of the project results. The selected lithotypes are summarized in
Tab. 1.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Selected lithotypes for the full characterization and application of
consolidation and protection formulations.
Building
Stone name
Lithotype
Ajarte
Fossil limestone
Balegem
Sandy limestone
Obernkirchen
Sandstone
Schlaitdorf
Sandstone
Cathedral of Vienna
St. Margarethen
Calcareous
arenite
Cathedral of Pisa and
Oslo Opera House
Carrara marble
Marble
Cathedral of Vitoria-Gasteiz
Cathedral of Ghent
Cathedral of Cologne
4. Innovative consolidants and protective coatings
4.1. Aqueous Nanocalcite dispersions as consolidant
Nanoparticles of calcium carbonate are produced by a novel process involving colloidal
particle stabilisation with either citrate or a block copolymer of poly(ethylene oxide) with
poly(citrate). The optimisation of the synthetic procedure for the aqueous nanoparticle
dispersions is targeting the smallest achievable particle size, since these nanocarbonates
(calcite, vaterite which is a polymorph of calcium carbonate) are expected to penetrate to
some extent into the porous network of degraded calcareous stones. The citrate anion plays
a key role both as a nanoparticle stabiliser (it adsorbs efficiently onto the surface) and as a
promoter of adhesion of the nanoparticle onto the calcareous stone surface (or inner pore
surface) thanks to its ability to “chelate” the Ca2+ ion. Combinations of the obtained
nanocalcite with conventional silane consolidants (e.g. based on TEOS) will also be
explored, as it is expected that a “nanoparticle-modified consolidant” may improve the
performance of simple TEOS-based treatments in terms of achieved stone cohesive strength
and lower long-term damage (e.g. by shrinkage-induced micro-cracks in the silica-like
material resulting from TEOS-based consolidation).
4.2. Water-borne polymeric and hybrid polymer/inorganic nanoparticle formulations
New self-stabilized amphiphilic or hydrophobic copolymers are being synthesized, as
components of either consolidant or protective formulations, respectively. In particular, the
composition and structure of the (acrylic) copolymers are designed to provide one or more
of the following features:
i) Enhanced stability to photo-oxidative aging, by inclusion of comonomer units bearing the
2,2,5,5-tetramethylpiperidine (or Hindered Amine Light Stabilizer, HALS) group in the side
chain;
ii) A combination of acrylic and methacrylic comonomers (e.g. methyl methacrylate, butyl
acrylate) in a mole ratio providing the required balance of thermal and mechanical
properties, while keeping the polymer photooxidative sensitivity at a minimum;
iii) Side-chain semifluorinated comonomers for enhanced hydrophobicity and chemical
stability;
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
iv) One terminal hydrophilic short “block” of either poly(acrylic acid) (PAA) or poly(ethylene
oxide) (PEO) to provide the polymer particle with the required colloidal and storage
stability, without the addition of low molecular weight surfactants.
Depending on the expected performance and material requirements, the aqueous colloidal
dispersions are synthesised according to one of the following two methods:
a) Conventional free radical emulsion polymerisation, yielding a high molecular weight
random copolymer with uncontrolled comonomer distribution and requiring addition of a
molecular surfactant for colloidal stabilisation during and after synthesis;
b) The so-called “ab initio” controlled RAFT (Reversible Addition Fragmentation Transfer)
polymerisation, which may be performed in “soapless” conditions (without added
surfactant) and leads to the formation of amphiphilic block copolymers, self-assembling
into polymer nanoparticles of controlled size (typically within the 50-150 nm range). In this
case the presence of a hydrophilic PAA or PEO block is mandatory, and may contrast the
hydrophobic contribution of the remaining polymer structure. However, the PAA block may
contribute to “anchoring” the polymer either to the stone surface, thus providing
consolidation effectiveness, or to inorganic nanoparticle surface in hybrid formulations used
as protectives. An advantage of the PEO block, on the other hand, is its inertness towards
carbonatic stones and its photodegradation behaviour leading to fragmentation and
eventually self-removal of this hydrophilic component from the polymer layer.
The specific contributions of these structural features to the ultimate polymer properties are
assessed by a broad range of analytical techniques to fully characterize the relevant
structural (by spectroscopies), morphological (by Dynamic Light Scattering and electron
microscopy) and film surface (by contact angle, Zeta potential, and ATR-FTIR analyses)
features.
5. Conclusions
The main objectives of this Project are: innovation in materials technology and
rationalization of the conservation policy, affording a renewed knowledge of the complex
system - treatment/stone substrate and of the durability threshold of these treatments.
The wide experience and literature on the nanostructured materials in the field, the
multidisciplinary approach and the inclusion of industrial partners – Colorobbia Consulting
Srl, Chem-Spec srl, Tecnologia Navarra de nanoproductos sl – will grant the possibility to
set-up new affordable conservation treatments.
In the first semester of the Project, a decisive state of the art about the use of
nanotechnologies for the consolidation of stone materials was carried out, assessing
nano-SiO2 and nanolime as the most used nanostructured materials. In the field of
protection and water-repellent treatments for stone surfaces, TiO2 and ZnO nanoparticles
are the most employed in dispersions or formulations.
In the framework of this Project, some different new nanomaterials have been already
designed and prepared. An important achievement is the set-up of the new synthetic
procedure for nanocalcite which will be used and tested as simple dispersion, which can
easily penetrate the porosity of calcareous stone materials, or will be used as an additive in
particle modified consolidants (i.e. modified TEOS) and improve the adhesion of the
system to the crystalline substrate. New self-stabilized amphiphilic or hydrophobic
copolymers have been already synthesized to be used as protective treatments or in hybrid
system covering nanoparticles of different nature.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
A short testing protocol will be carried out in the following months to assess the most
promising nanomaterials. Actually, the Technology Readiness Level of the project should
be at least 5, as the developed technologies will be validated in lab and in situ, that is on the
selected monuments.
Aknowledgements
The research project is supported by the European program Horizon 2020 Call NMP21- AC
646178.
References
Chelazzi, D., Poggi, G., Jaidar, Y., Toccafondi, N., Giorgi, R., Baglioni, P., 2013,
Hydroxide nanoparticles for cultural heritage: Consolidation and protection of wall
paintings and carbonate materials, Journal of Colloid and Interface Science,
392(0), 42-49.
Facio, D.S., Mosquera, M.J., 2013, Simple Strategy for Producing Superhydrophobic
Nanocomposite Coatings In Situ on a Building Substrate, ACS Applied Materials
& Interfaces, 5(15), 7517-7526.
Kapridaki, C., Pinho, L., Mosquera, M.J., Maravelaki-Kalaitzaki, P., 2014, Producing
photoactive, transparent and hydrophobic SiO2-crystalline TiO2 nanocomposites at
ambient conditions with application as self-cleaning coatings, Applied Catalysis
B: Environmental, 156–157(0), 416-427.
Kim, E.K., Won, J., D,o J-y., Kim, S.D., Kang, Y.S., 2009, Effects of silica nanoparticle
and GPTMS addition on TEOS-based stone consolidants, Journal of Cultural
Heritage, 10(2), 214-221.
Manoudis, P.N., Karapanagiotis, I., Tsakalof, A., Zuburtikudis, I., Kolinkeová, B.,
Panayiotou, C., 2009, Superhydrophobic films for the protection of outdoor
cultural heritage assets, Appl Phys A, 97(2), 351-360.
Miliani, C., Velo-Simpson, M.L., Scherer, G.W., 2007, Particle-modified consolidants: A
study on the effect of particles on sol–gel properties and consolidation
effectiveness, Journal of Cultural Heritage, 8(1), 1-6.
Munafò, P., Goffredo, G.B., Quagliarini, E., 2015, TiO 2-based nanocoatings for preserving
architectural stone surfaces: An overview, Construction and Building Materials,
84, 201-218.
Quagliarini, E., Bondioli, F., Goffredo, G.B., Licciulli, A., Munafò, P., 2013, Self-cleaning
materials on Architectural Heritage: Compatibility of photo-induced hydrophilicity
of TiO2 coatings on stone surfaces, Journal of Cultural Heritage, 14(1), 1-7.
Rodriguez-Navarro, C., Suzuki, A., Ruiz-Agudo, E., 2013, Alcohol dispersions of calcium
hydroxide nanoparticles for stone conservation, Langmuir, 29(36), 11457-11470.
Verganelaki, A., Kapridaki, C., Maravelaki-Kalaitzaki, P., 2015, Modified
Tetraethoxysilane with Nanocalcium Oxalate in One-Pot Synthesis for Protection
of Building Materials, Industrial & Engineering Chemistry Research, 54(29),
7195-7206.
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854
NEW POLYMER ARCHITECTURES FOR ARCHITECTURAL
STONE PRESERVATION
A. Lazzeri1, S. Bianchi2, V. Castelvetro2*, O. Chiantore3, M.-B. Coltelli1, F. Gherardi4,
M. Lezzerini5, T. Poli3, F. Signori1, D. Smacchia2 and L. Toniolo4
Abstract
A series of multifunctional polymeric systems have been designed, synthesized and their
effectiveness in modifying the surface properties of different stone types have been
evaluated. Both the synthetic strategy and the design of the macromolecular structures are
aimed at achieving maximum flexibility in the introduction of structural features that are
required to provide the resulting polymers with a range of potential properties. For this
purpose, the controlled free radical polymerization of acrylic monomers by the so-called
RAFT (Reversible Addition Fragmentation Transfer) technique has been adopted to obtain
amphiphilic block copolymers. These may be used either as such in the modification of
aqueous dispersions of inorganic nanoparticles (silica, titania, zirconia, zinc oxide among
others), resulting in hybrid nanocomposite treatment materials, or as self-assembling
reactive precursors for ab initio emulsion polymerizations, leading to the formation of
colloidal aqueous dispersions of nanostructured multifunctional polymer nanoparticles.
Among the innovative features of the polymers under investigation, the self-stabilisation
against photooxidative degradation is worth mentioning as the durability of organic
polymers is a well-known open issue in conservation. To achieve enhanced stability, free
radical scavenging groups such as Hindered Amine Light Stabilizers (HALS) are
introduced in the polymer structure through copolymerization with HALS derivatives. In
addition, combination of polymers and UV-blocking inorganic particles (ZnO, TiO2) are
also expected to greatly enhance durability. These polymeric materials, and other presently
under development, are intended as components of either protective or consolidant
treatments to be tested first at a lab scale on various stones (both carbonatic and silicatic),
then in situ on 5 different cathedrals distributed throughout Europe and on a contemporary
opera theatre.
Keywords: block copolymer, hybrid latex, self-stabilisation, protection, consolidation
1
A. Lazzeri, M.B. Coltelli and F. Signori
INSTM - Department of Civil and Industrial Engineering, University of Pisa, Italy
2
S. Bianchi, V. Castelvetro* and D. Smacchia
INSTM - Department of Chemistry and Industrial Chemistry, University of Pisa, Italy
valter.castelvetro@unipi.it
3
O. Chiantore and T. Poli
INSTM - Department of Chemistry, University of Turin, Italy
4
F. Gherardi and L.Toniolo
Department of Chemistry, Materials and Chemical Engineering, Politecnico di Milano, Italy
5
M. Lezzerini
INSTM - Department of Geosciences, University of Pisa, Italy
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
1. Introduction
The stone materials undergo different kinds of alterations and degradation upon aging due
to the different chemical, physical and mechanical characteristics of the stone and to the
peculiar outdoor exposure. In the EU H2020 “NanoCathedral” project launched in 2015
five different medieval cathedrals and a contemporary opera theatre (Fig. 1) were selected
as representative of both different macro- and micro-climatic conditions - continental vs.
coastal; arid vs. humid - and different lithotypes - limestones, sandstones and marbles.
Fig. 1: Selected cathedrals within the Nanocathedral” H2020 project: Pisa (Italy) and
Santa María of Vitoria-Gasteiz (Spain) exposed to south European climate in coastal and
continental regions, respectively; Sint-Baafs (Ghent, Belgium), St. Peter and Mary
(Cologne, Germany) and St. Stephen (Wien, Austria) exposed to North European climate in
either coastal or continental regions. Oslo Opera House, dipping into the North Sea.
The project aims at providing innovative consolidant and protective products tailored for
the specific stone-environment combination, while granting improved effectiveness and
durability. In particular, a wide range of inorganic nanoparticles, innovative polymeric
structures, and their hybrid combinations are being investigated. The best products and
formulations, selected according to their performance and durability tests performed in
three different laboratories and on stone specimens representative of those present in the
different monumental buildings (fig. 1), will be applied during the second year of the threeyear project on the participating Cathedrals for in situ evaluation.
A key requirement for consolidants is its effective penetration by capillarity into the stone
porous network; this is often not achieved, as shown by the failure of many past
consolidation treatments causing damage by formation of surface scales. Lack of
chemical/physical compatibility or uncontrolled reactivity with the stone substrate is
another reason of failure; poor durability of the consolidant a third one. Last but obviously
not least, a consolidant material has to perform its main role of strengthening the microstructure of the decayed stone by replacing lost original mineral bridges, partially
recovering lost mechanical properties, and in some cases even converting unstable material
into stable one (e.g. soluble into insoluble salts). Several reviews report on the state of art in
stone consolidation (Clifton, 1980; Doehne and Price, 2010). Alkoxysilanes are currently
the most commonly used consolidating materials, followed by acrylics. While the former
may perform poorly due to bridging capacity limited to narrow fissures, long term
shrinkage causing the formation of a secondary porosity, hydrolytic instability and poor
chemical affinity with carbonatic stones, acrylics may develop better bridging properties
but, as most organic polymers, their durability is poor and degradation products may be
detrimental to the stone substrate.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Novel nano-materials may overcome penetration depth issues, while their extremely large
surface area may promote the reactivity required to build up cohesive and adhesive forces.
Nano-lime systems, also applied in combination with alkoxysilane treatments, have shown
encouraging results, although the penetration and durability of such treatment has not been
clearly demonstrated yet (Daehne and Herm, 2013). The so-called (nano)particle modified
consolidant (PMC), typically based on tetraethoxysilane (TEOS) formulations with silica
nanoparticles, can reduce the internal stone damages caused by the shrinkage and cracking
during sol-gel condensation of TEOS (Ksinopoulou et al., 2016). However, shortcomings
are still related to the hydrolytic sensitivity and poor control of the time evolution of the
consolidant nanophase during the sol-gel process. On the other hand other types of
inorganic nanoparticles (e.g. Ti, Zn, Al, Si oxides or hydroxides) and hybrid organicinorganic systems have been much less extensively investigated, although they may provide
additional useful features such as biocidal (Gómez-Ortíz et al., 2013) and self-cleaning
properties, synergistic mechanical reinforcement, hydrophobicity, etc..
When dealing with hydrophobic protection the main open issues are durability inertness
towards the stone substrate and lack of undesired aesthetic modifications upon and after
application. Even in this case the limited durability of organic polymers is raising major
objections, among conservators, against their application, although they are undoubtedly
superior materials in providing hydrophobic and even self-cleaning surfaces. Even in this
case, however, novel polymeric, hybrid or nanocomposite systems may provide solutions to
overcome these drawbacks and even introduce additional useful features such as e.g.
biocidal activity (van der Werf et al., 2015). Among the various materials under
development within the H2020 Nanocathedral project, here the design and synthetic
approach to novel polymeric structures and their water based formulations will be
presented, along with the preliminary results concerning their characterization and the
evaluation of their performance and durability.
2. Approach and Results
2.1. Design of multifunctional polymer structures
The underlying criteria for the newly developed polymers are:
a) A synthetic approach that may allow easy adaptation of the polymer structure
according to the specific requirements of either consolidation or protection;
b) Self-dispersibility in water (i.e. without added low molecular weight surfactants)
in the form of nanoparticles with controllable (< 100 nm) size, for solvent-free
application and effective penetration within the porous stone network;
c) Functional groups for enhanced durability, water repellency, specific interaction
and binding with inorganic nanoparticles (for nanocomposite treating materials)
and with the stone substrate, respectively.
For such purposes, a synthetic scheme for multifunctional acrylic copolymers based on the
controlled RAFT (Radical Addition–Fragmentation-Transfer) free radical polymerization is
adopted. The relatively recent RAFT technique (Wang A.R. and Zhu S., 2003) has become
very popular in recent years due to its tolerance towards most functional groups (thus
allowing the synthesis of multifunctional polymers) and solvents (from hydrocarbon to
water). Besides, the so-called “ab initio” RAFT emulsion polymerisation, may be
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
performed in “soapless” conditions (without added surfactant) by using amphiphilic RAFT
mediators, leading to the formation of amphiphilic block copolymers self-assembled into
nanoparticles of controlled size (typically 50-150 nm) (Chenal et al., 2013).
With the above approach, water-based polymer dispersions with controlled composition
and a range of functional groups have been prepared, for desirable properties such as:
colloidal stability (for extended shelf life and easy application), by using a RAFT
mediator leading to the formation of polymers with a short “block” of either
poly(acrylic acid) (PAA) or poly(ethylene oxide) (PEO) at one chain end;
adhesivity by incorporation of comonomers with either Ca 2+ binding (e.g.
carboxylate, for carbonatic stones) or sol-gel reactive (e.g. trialkoxysilyl groups for
specific bonding to silicatic stones) functional groups;
film cohesivity, by balancing the main copolymer composition (methyl
methacrylate/butyl acrylate) for a polymer glass transition, T g, slightly below room
temperature, while keeping the polymer photooxidative sensitivity at a minimum;
self-stabilisation against photo-oxidative aging, by incorporation of HALS group
in the side chain (stabilisation against UV-induced photooxidation is based on a
cyclic deactivation of photogenerated free radicals and peroxiradicals, followed by
regeneration of the free-radical scavenging nitroxyl-amine active species.
water repellency, by introduction of semifluorinated comonomers (in progress).
2.2. Polymer synthesis
The general synthetic scheme starts with an amphiphilic trithiocarbonate RAFT mediator
extended with a short hydrophilic oligomer through controlled free radical polymerization.
The obtained RAFT-active amphiphilic oligomers (Fig. 2) can then be used as block
copolymer precursors of functional polymer nanoparticles (Fig. 3).
Fig. 2: RAFT-active amphiphilic block copolymer precursors.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
< 100 nm
Fig. 3: synthetic scheme for self-stabilized multifunctional block copolymer nanoparticles
by ab-initio RAFT emulsion polymerization of amphiphilic precursors.
3. Materials and characterizations
3.1. Latex Polymers
A selection of the functional polymer dispersions (polymer latexes) prepared during the
first year of the project is listed in Tab. 1. Macro-RAFT is the alkyl-dithiocarbonate
terminated oligo (acrylic acid) (PAA-TTC) or oligo(ethyleneglycol) (MPEG-TTC) of
Fig. 2, used as a reactive surfactant and RAFT mediator in the ab initio emulsion
polymerization of the butyl acrylate/methyl methacrylate (BM) mixture. The polymer latex
acronyms indicate the amount of hydrophilic PAA or MPEG block (1 to 5 wt.- %) and of
the HALS comonomer (1 and 3 wt.-% in H1 and H3 samples, respectively).
Tab. 1: Water borne polymer particles.
Polymer Latex
MacroRAFT
PMPMA
Solids
content
Particle
size
wt.-%
wt.-%
wt.-%
nm
BM-PAA5-H1
(DS4)
PAA-TTC
1
7.8
170
BM-PAA3-H1
(DS7)
PAA-TTC
1
9.0
143
BM-PAA1
(DS10)
PAA-TTC
//
9.1
188
BM-PAA1-H1
(DS11)
PAA-TTC
1
9.2
55
BM-PEG5
(DS9)
MPEG-TTC
//
8.0
79
BM-PEG5-H1
(DS12)
MPEG-TTC
1
7.9
181
The latexes were cast to clear films, and after dilution to 1 wt.% solids were applied by
capillarity to Carrara marble and Schleitdorf sandstone (Cologne), respectively, to a
nominal 1 m-thick coating (actually thinner due to absorption into the porous stone). The
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
water contact angles (Tab. 2) and the surface Zeta potential data (Fig. 4) show that even at
low concentration and without structure optimisation, these relatively hydrophilic materials
are effective hydrophobic modifiers.
Tab. 2: Static water contact angle on polymer films and treated stones.
Polymer Latex
Smooth polymer film
Sandstone
Marble
deg
deg
deg
35.2 ± 2.3
35.2 ± 2.0
Untreated stone
BM-PAA1
(DS10)
90.0 ± 2.0
105.3 ± 3.5
99.4 ± 5.4
BM-PAA1-H1
(DS11)
86.5 ± 0.8
104.5 ± 5.6
81.7 ± 7.0
BM-PEG5
(DS9)
91.6 ± 0.2
100.5 ± 8.6
67.7 ± 7.4
BM-PEG5-H1
(DS12)
97.2 ± 0.9
113.9 ± 5.8
99.8 ± 3.8
Fig. 4: ζ potential of uncoated and coated stone surfaces (measured with the Anton PAAR
SurPASS® Electrokinetic Analyser).
3.2. Ageing tests
The FT-IR spectra of fig. 5 were recorded on cast films of selected polymers (DS#, as listed
in Tab. 1) and of their nanocomposites with TiO2 nanoparticles (DS#n), before and after the
first 250 hours of simulated solar irradiation (Hereus Suntest CPS solar box, Xenon lamp,
300 nm cutoff filter, 750 W/m2). The preliminary results indicate that:
After 250 hours of ageing only a slight oxidation is detected from the appearance
of weak OH absorptions at 3220 cm-1 and of a shoulder at 1640 cm-1 due to
chain-end double bonds (compare DS9 in Fig. 5a, and DS10 in Fig. 5b,
before and after agieng).
The HALS moiety inhibits the oxidation phenomena, as shown by the further
reduction of the weak OH absorption at 3220 cm-1 (compare DS12 with DS9 in
Fig. 5a, and DS11 with DS10 in Fig. 5b)
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The photocatalytic action of TiO2 promotes polymer oxidation phenomena
(compare DS9 and DS9n in Fig. 5a) as shown by the growth of a broad
absorption above cm-1 due to formation of hydroxy groups, irrespective of the
presence of HALS groups (compare DS12 and DS12n in Fig.5a).
Fig. 5: FT-IR transmission spectra of films on silicon wafer.
4. Conclusions
A range of amphiphilic block copolymers and of self-stabilized, surfactant-free colloidal
polymer dispersions (polymer latex) with small particle size (< 100 nm, for improved
capillary absorption into the stone porous network) and reactive functional groups
(carboxylate, for polymer anchoring onto stone substrates or inorganic nanoparticles) have
been synthesized by means of the RAFT controlled polymerization method.
The amphiphilic block copolymers may be useful as modifiers of inorganic nanoparticles
(ZnO and TiO2 for protection, calcite, ZrO2 and hydroxyapatite for consolidation) and as
precursors of multifunctional latex particles or water-borne nanocomposite materials.
Encouraging results have already been obtained from preliminary tests of application of the
colloidal polymer dispersions onto sandstone and marble different stone samples (,
respectively). In particular, very low amounts of applied polymer are sufficient to make the
stone surface hydrophobic.
Aging tests have confirmed the foreseen stabilizing effectiveness of the HALS groups
introduced by means of functional comonomers. On the other hand, the photocatalytic
activity of embedded TiO2 nanoparticles was shown to cause, as expected, accelerated
degradation of the polymer matrix in nanocomposite films. Finally, a better understanding
of the stone-polymer and stone-nanoparticle interaction and distribution at and within the
porous stone surface may be achieved thanks to a combination standard (water absorption,
water vapour permeability, contact angle) and less conventional techniques; among them,
the Zeta potential may provide useful insights on the effectiveness of a treatment and on the
evolution of the treated stone surface upon aging.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Aknowledgements
The research project is supported by the European program Horizon 2020 Call NMP21-AC
646178: “Nanomaterials for conservation of European architectural heritage developed by
research on characteristic lithotypes (NANO-CATHEDRAL)”
References
Chenal M., Bouteiller L. and Rieger J., 2013, Ab initio RAFT emulsion polymerization of
butyl acrylate mediated by poly(acrylic acid) trithiocarbonate, Polym. Chem. 4,
752-762.
Clifton J.R., 1980, Stone Consolidating Materials-A Status Report. U.S. National Bureau of
Standards Technical Note 1118, Washington, D.C. (http://cool.conservationus.org/byauth/clifton/stone/ , accessed 30th June 2016).
Daehne A. and Herm C., 2013, Calcium hydroxide nanosols for the consolidation of porous
building materials - results from EU-STONECORE, Herit. Sci. 1, 11.
Doehne E. and Price C., 2010, Stone Conservation – An Overview of Current Research,
The
Getty
Conservation
Institute,
Los
Angeles,
2nd
ed.
(http://openarchive.icomos.org/1097/1/37730.pdf, accessed 30 th June 2016).
Gómez-Ortíz N., De la Rosa-García S., González-Gómez W., Soria-Castro M., Quintana P.,
Oskam G. and Ortega-Morales B., 2013, Antifungal coatings based on Ca(OH)2
mixed with ZnO/TiO2 nanomaterials for protection of limestone monuments, ACS
Appl. Mater. Interfaces 5, 1556−1565.
Ksinopoulou E., Bakolas A. and Moropoulou A., 2016, Modifying Si-based consolidants
through the addition of colloidal nano-particles, Appl. Phys. A, 122, 267
van der Werf I.D, Ditaranto N., Picca R.N., Sportelli M.C. and Sabbatini L., 2015,
Development of a novel conservation treatment of stone monuments with
bioactive nanocomposites, Herit. Sci. 3, 29
Wang A.R. and Zhu S., 2003, Modeling the reversible addition–fragmentation transfer
polymerization process, J. Pol. Sci.: Part A: Polym. Chem., 41, 1553-1566
862
TRIALS OF BIOCIDE CLEANING AGENTS ON ARGILLACEOUS
SANDSTONE IN A TEMPERATE REGION
E. S. Long1* and D.A. Young2
Abstract
Trials of biocide cleaning agents were carried out on an argillaceous sandstone to determine
the efficacy of different application methods, to review any residual effect in the warm
temperate conditions of Sydney, Australia and to compare products available on the local
market. The trials were carried out on a significant public building which was designed in
the Art Deco style and completed in 1952. The building does not have traditional detailing
like cornices which discourage water from running down the façade. As a consequence, the
upper courses of stone have become heavily marked by dark biological growths. Two
commercial biocides containing benzalkonium chloride, but different co-formulants, were
used in the trials. Following previous studies by others it was decided not to use any
mechanical cleaning (scrubbing) in conjunction with the biocide treatment, but to trial a
range of techniques including brush and poultice application and applying them to dry and
to pre-wet surfaces. Monitoring the trials over two and a half years has demonstrated that
effective biological control is attainable without scrubbing and that pre-wetting did not
appear to make a significant difference in these conditions. Though initially it appeared that
poultices preformed better, it was found that run-off from untreated horizontal surfaces
above the trial panels obscured the effects of different treatments.
Keywords: biological growth, biocide, benzalkonium chloride, poultice
1. Introduction
This investigation was prompted by cleaning the exterior of the building in 2012 and 2013.
The work had been specified to include cleaning with water under low pressure, subject to
site trials. During the works, despite repeated interventions by the conservation staff
inspecting the cleaning, it became apparent that the pressure was too high for the surface, as
evidenced by the amount of particles (from the stone surfaces) that washed off the façades.
The building had been cleaned previously in 2002 using water under high pressure. The
specification said “nominally 2000 psi” (13,790 kPa), a pressure sufficient to cause
considerable damage to this type of stone, even after the effects of pressure decrease from
the pump to wall surface have been taken into account.
1
E.S. Long*
Sydney Living Museums, Sydney, Australia
elishal@sydneylivingmuseums.com.au
2
D.A. Young
Heritage Consultant, Melbourne, Australia
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
A review of photographs from the time of construction until 2012 suggested a very slow
build up in biological growth after the completion of the building in1952, presumably as the
stone weathered and the surface gradually became more open. Dark patches in areas of
water run off first become noticeable in relatively small areas during the 1980s.
The review of photographs also suggested that the biological regrowth became more
extensive, that is darker and over larger areas, after the cleaning programme in 2002 than it
had been before. By 2012, the stone was again very dark on the upper wall surfaces and
parapets, with growths more extensive on the southern, i.e. most-shaded, surfaces.
Concern about the rapid regrowth since 2002, the loss of surface grains when cleaned and
the ongoing effect of cleaning at ever shorter intervals led to a review of the approach to
cleaning sandstone and alternative methods of controlling micro-biological growths.
2. Climate
Sydney’s warm temperate climatic conditions are favourable to micro-biological growth on
stone: mild winters and warm humid summers. Summer highs average between 25-31o C
(71-88o F) and winter highs average between 15-20o C (59-68o F). Winter lows are rarely
below 5o C (41oF). Biological regrowth on porous surfaces can be rapid.
Fig. 1: View of the east face of the Museum of Contemporary Art building, Sydney.
Trials were conducted on the inside faces of the parapets of the balcony at right.
3. The substrate
Much of the sandstone of the Sydney region is characterised by a warm golden colouring
due to the presence of iron minerals in the matrix. The colouring makes them attractive
building stones and characterises the architecture of historic Sydney. However, stones of
the region typically have relatively high clay contents, where higher contents are linked to
poor durability. Samples from the quarry from which this stone was taken have been shown
to contain 15–22 % clay (Franklin, 2000).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Magnification of the surface using a field microscope showed that the surface of the stone
was extremely open and porous. It is assumed that some of this loss of surface in such a
young building may be due to past cleaning programs, and possibly to a post-construction
wash down with acid, intended to remove mortar spills, and perhaps to intensify the yellow
colour. Unfortunately, there are no records of such cleaning.
4. The biofilm
Before carrying out the trials, the biofilms on the building were reviewed in-situ by a
botanist. It was found that the growths varied over the upper surfaces of the building. Red
and green algae and various types of lichens, were identified (Archer, pers. comm.). As
expected, lichens are more common on the horizontal surfaces and there are greater
concentrations of algae on the shaded vertical surfaces.
5. Location of site trials
The trials were undertaken on the inside of the parapet walls of a roof-top balcony on the
north-east corner of the building (Fig. 1 and Fig. 2). The choice was driven by the presence
of significant levels of biological growth which were easily accessible for both application
and monitoring, and which would not affect the outwards appearance of the building for the
period that the trials were underway. The trials were applied to three parapet walls so that
the effect of different orientations could be observed.
Fig. 2: The eastern wall of the balcony, 23 months after treatment. The dark area left of
centre is the untreated control panel; to its left are panels treated by poultice application of
biocide. Note the wide zones around the mortar joints showing a biocidal effect of the
alkaline jointing material.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
6. Biocides
Biocides, chemical compounds which kill or control micro-biological growth, are an
accepted part of stone conservation. The most common active ingredient of biocidal agents
for masonry is benzalkonium chloride, which is also a common ingredient in domestic
disinfectants and swimming pool algaecides. Benzalkonium chloride is a quaternary
ammonium compound, which are also known as ‘quats’. They are used at very low dilution
rates, e.g. 2% in water (Caneva, et al., 2008; Nugari & Salvadori, 2003).
Two biocides that are common on the Australian market were trialled:
Biocide One: ‘Wet and Forget’
This product is supplied as a blue liquid concentrate in which the active ingredient is
benzalkonium chloride. The concentrate was diluted on-site to produce a 2%
solution (i.e. 20 grams per litre).
Biocide Two: ‘Boracol 100RH’
This product is supplied as an already diluted clear liquid. The active ingredients are
benzalkonium chloride present at a rate of 22g/L, boron present at a rate of 23g/L
and ethylene glycol at 109 g/L.
7. Methodology
Following the work of Charola et al. (2012) who found that pre-wetting improved the
cleaning effect, the methodology provided for the application of both biocides by brush
with three different surface conditions:
•
dry surfaces;
•
pre-wet with water on the day of application;
•
double pre-wet with water: i.e. on the day before application and on the day of
application.
One of the biocides was also applied within a commercially available absorbent poultice.
The aim of testing the use of the poultice was to assess whether the longer contact time
improved the effectiveness of the treatment. The same three surface conditions: dry, single
pre-wet and double pre-wet were used with the poultice applications.
Ethylene glycol, a component of Biocide Two, was added to one trial of Biocide One to test
whether the solvent improved the biocidal effect. Ethylene glycol is also used as a
fungicide, particularly for treating rot in timber. Isopropyl alcohol was added to another of
the Biocide One trials to test whether its presence improved penetration of the biofilm.
Tab. 1 sets out the different biocides, application methods and surface conditions. The
complete scheme was applied three times, once each to the north and south walls in 0.5
metre wide panels, and once to the east wall in one metre wide panels. Untreated control
panels were left at the end of each wall and were included in the middle of the range of trial
panels. Poultices were covered with polyethylene film for five days and then allowed to dry
naturally. All the trial panels were kept covered for 14 days to prevent them being affected
by rain. The poultices were taken off when the coverings were removed.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Biocide trials testing scheme.
No
Biocide
Application
Surface condition
1
Biocide One
brush
dry
2
Biocide One
brush
single pre-wet
3
Biocide One
brush
double pre-wet
4
Biocide One
Cocoon poultice
double pre-wet
5
Biocide One
Cocoon poultice
single pre-wet
6
Biocide One
Cocoon poultice
dry
7
Control
—
—
8
Biocide Two
brush
dry
9
Biocide Two
brush
single pre-wet
10
Biocide Two
brush
double pre-wet
11
Biocide One + 10% Ethylene Glycol
brush
double pre-wet
12
Biocide One + 10% Isopropyl Alcohol
brush
double pre-wet
13
Biocide One
brush
double pre-wet
8. Monitoring and recording of trials
The trials have now been monitored and reviewed for 2.5 years (30 months). Observations
made at approximately six-monthly intervals have included visual inspections and digital
photography. A field microscope has been used to assess whether there has been any
regrowth.
9. Complicating factors
A range of factors have influenced the appearance of the trial panels and complicate
assessment of the results. These include:
•
orientation of the trial panels, which face north, west and south, leading to
different micro-environmental conditions for the biological growths, and
different photographic recording conditions, both making comparison between
walls difficult;
•
the influence of mortar joints — alkaline mortars have had a biocidal effect
which extends some distance from the joints (Fig. 2);
•
run-off from the uncleaned horizontal tops of the parapet which intensifies
growths in some locations, and may be contributing to regrowth;
•
previous cleaning — now visible as diffuse horizontal bands from high-pressure
washing (Fig. 2);
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
•
other treatments — which have left various marks on the stone surfaces, some of
which have become apparent only after the cleaning trials have removed much of
the biofilm;
•
location of trial panels too close the walls of the main building — which has
resulted in less-effective cleaning due to additional water run-off and splash from
the wall surfaces;
•
untreated control panels have continued to accumulate biological growths,
increasing the contrast between treated and untreated panels, and so complicating
assessment of the degree of cleaning achieved (Fig. 3).
10. Results
Bearing in mind the complicating factors, the following results have been found:
•
both biocides were effective in controlling the biofilm, with little discernible
difference between the two, and little or no loss of surface from the sandstone;
•
separate additions of ethylene glycol and isopropyl alcohol to one of the biocides
show no discernible differences;
•
pre-wetting in this instance does not seem to have increased the efficacy of the
biocides;
•
the cleaning effect of the treatments continued to improve for at least eleven
months after treatment, and is retained at 23 months;
•
poultice applications left a residue which washed off most areas within one year,
though some residue can still be seen with a field microscope after two years;
•
untreated control panels have continued to accumulate biological growths.
11. Discussion
Following completion of the biocide applications, all treatments were left untouched so that
any residual effects and changes over time would become apparent. As observed by
Charola et al. (2012), the cleaning effect continued to improve for at least eleven months
after treatment. Fig. 3 shows a sequence of images, which demonstrate improvement in
panels treated by both poultice and brush applications until 11 months.
Also apparent in Fig. 3 is a white residue from the paper poultice, which is still visible after
eleven months, but is almost gone at 23 months. Such a residue would not be acceptable in
a full scale cleaning project, and so further trials should test different clean-up procedures
and their timing.
The results of the different application methods were mixed, with some panels showing
little difference between brush and poultice application (see Fig. 3), others suggesting
benefits from poultices. A closer review of these results at 30 months showed that regrowth
was concentrated where the horizontal surface of the parapets above the treated panels had
not been cleaned, thus providing a source of further micro-organisms. Trial panels which
had no microbiological growth in the catchment area above remained clean to a visual
inspection after 30 months. This is an aspect that will be monitored during future
inspections.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Pre-wetting was done with a hand-pumped sprayer which may not have delivered sufficient
water to adequately ‘wet’ the biofilm in what can be a hot and windy environment. In
future, multiple applications should be trialled.
Fig. 3 Sequence of images taken 0.5, 11, 23 and 30 months after treatment, of a section
of north-facing wall. The cleaning effect of the two treatments shown is similar, both
improving until at least eleven months. Note the white residue from the paper poultice
at left, which washes off with time; and the intensification of the dark biofilm
in the untreated control panel.
12. Conclusions
The trials confirm that in these conditions:
•
Effective biological control is attainable using biocides without scrubbing;
•
There was no loss of surface material from the sandstone, unlike previous cleaning
programmes;
•
Biocide application must begin at the top of the building, or rain catchment surface,
in order to prevent spores washing down and starting new growths;
•
Effectiveness of the different methods of application were obscured by regrowth
from the wash-down.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
•
Pre-wetting did not appear to improve the outcome in the particular circumstances of
the trials.
The existing trials should continue to be monitored until the cleaning effect of the biocides
declines. Future trials should:
•
Ensure that trial panels are cleaned to the full height of their catchments;
•
Test pre-wetting with greater quantities of water;
•
Test methods of ‘opening-up’ the biofilm (e.g. light brushing with a stiff nylon
bristled brush) prior to the main biocide application;
•
Test a range of clean-up procedures and their timing for poultice applications.
Acknowledgements
Dr Alan Archer FRSC, Honorary Research Associate, National Herbarium of NSW, who
investigated the biofilms. Niall Macken, Head of Heritage, Sydney Harbour Foreshore
Authority, who sponsored the trials and their ongoing monitoring. NSW Public Works
Centennial Stone Program, which funded the initial development of the biocide testing
scheme.
References
Caneva, G., Nugari, M.P. and Salvadori, O., (eds.) 2008, Plant biology for cultural heritage:
biodeterioration and conservation, Getty Conservation Institute, Los Angeles,
ISBN 9780892369393, 408pp.
Charola, A.E., Wachowiak, M., Webb, E.K., Grissom, C.A., Vicenzi, E.P., Chong, W.,
Szczepanowska, H. and DePriest, P., 2012. Developing a methodology to evaluate
the effectiveness of a biocide, in proceedings of the 12th International Congress on
Deterioration and Conservation of Stone, Columbia University, New York.
Franklin, B., 2000, Sydney dimension sandstone: the value of petrography in stone
selection and assessing durability, in Sandstone city: Sydney’s dimension stone
and other sandstone geomaterials, Proceedings of a symposium held on 7th July,
2000, McNally, G.H and Franklin, B.J. (eds) EEHSG Monograph 5, Geological
Society of Australia, ISBN 1876315229, 98-116.
Nugari, M.P. and Salvadori, O., 2003. Biocides and treatment of stone: limitations and
future prospects, in Art, biology and conservation: biodeterioration of works of art,
Koestler, R.J., Koestler, V.H., Charola, A.E. and Nieto-Fernandez, F.E., (eds) The
Metropolitan Museum of Art, New York, ISBN 1588391078, 518-535.
870
DEVELOPMENT OF A METHODOLOGY FOR THE
RESTORATION OF STONE SCULPTURES USING MAGNETS
X. Mas-Barberà1*, M.A. Rodríguez1, L. Pérez2 and S. Ruiz2
Abstract
Nowadays, the structural joining of stone fragments of sculptures present, in some cases,
reversibility problems. In this work, we present a new system based on the use of magnetic
materials which is more reversible than present technologies. This technology is less
invasive and, therefore, more respectful to the original artwork. We have used different
materials normally used in sculpture (plaster gypsum, calcarenites from Novelda and
marble from Macael). NdFeB magnets have been fixed to the different materials and the
joints have been tested by different mechanical methods. From these experiments, a
theoretical model based on Classical Mechanics has been proposed, a model that allows the
prediction of the best choice of magnets and their optimal location in the piece to be
restored. The external magnetic field created by the magnet has been calculated using finite
elements simulations to minimize it, avoiding the contamination of the materials by
magnetic particles suspended in the atmosphere. A system to separate the joint pieces in a
reversible way has also been developed.
Keywords: magnets, fragments, unions, sculpture, magnetism
1. Introduction
Nowadays, the structural assistance in restoration of sculpture and ornaments are made with
synthetic adhesives that, in some cases, are reinforced by rods of different materials
(Ivorra et al., 2013; Contrafatto and Cosenza, 2014; Raftery and Whelan, 2014), such as
fiberglass (Polacek and Jancar, 2008), stainless steel (Rosewitz et al., 2016), and other
materials (Mas-Barberà, 2011; Quagliarini et al., 2016). In most cases, when the piece has a
complicated position or its weight is high, there is a conflict of interest in which the
stability of the artwork is faced with the principle of minimal intervention and reversibility,
as inserting rods is usually a fairly invasive work on the original artwork. The use of
magnetic materials in this type of intervention could be an interesting alternative pathway,
in order to have better reversibility being less invasive.
The use of magnetic materials in Conservation and Restoration is relatively recent. They
are used as display system for paper and textile work (Spicer, 2010), as their use is non1
X. Mas-Barberà and M.A. Rodríguez
Conservation and Restoration of Cultural Heritage Department, University Institute of Restoration
of Heritage, Polytechnic University of Valencia, Spain
jamasbar@upvnet.upv.es
2
L. Pérez and S. Ruiz
Departamento de Física de Materiales, Universidad Complutense de Madrid, Spain
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
invasive and reversible. In addition the magnetic force can be controlled, which is essential
to avoid distortions and brands. One good example of this application is the use of magnets
by the Montreal Museum of Fine in the work of Betty Goodwin (Potje, 1988). Magnetic
materials have also being used as a tool in the field of restoration such as sculpture and
architecture (Watson, 2011), easel painting and archeology. In particular, they can be used
as straightening system to remove distortions (Bestetti, 2005), to remove cleansing gels in
which metallic filler has been incorporated or to locate metallic cores or sediment.
Magnetic materials has also been proposed as binding system for fragments and
reconstructions, although not many works can be found in this direction. Probably, one of
the most representative one is the marble Christ from Andrea Sansovino (Oddy, 1999). The
present paper provides a systematic study of these magnetic junctions, proposing a model to
design this kind of systems for any artwork to be repaired and, therefore, opening an
interesting path in the field of Conservation and Restoration (Rodríguez et al., 2014, 2015).
2. Experimental methodology
2.1. Materials
In this work, we have used two different cylindrical NdFeB magnets supplied by
Supermagnete, with 10mm (S-10-05-N) and 15mm (S-15-05-N) in diameter and 5 mm of
height, magnetized parallel to the cylinder axis. The magnets were fixed to the different
materials using Paraloid B-72 and Araldite epoxy resin.
We have used three different types of stone materials: calcarenite, marble and plaster
gypsum. The Calcarenite, also called stone Novelda Bateig and supplied by Bateig Stone
(Alicante), it is a natural biocalcarenite rock type, extracted from the Middle Vinalopó area
with a high porosity (between 12.7% and 20,4%) (Fort et al., 2002). The marble, supplied
by Gonzalo Esteban Fernandez (Almeria), is a white marble, mined in Macael (Almería). It
has a total porosity of 2.5% and hardness 3 in the Mohs scale (Bello et al., 1992; SáezPérez and Rodríguez-Gordillo, 2009; Luque et al., 2010). Finally, we have used the plaster
gypsum "Alamo 70" supplied by AGM (Valencia), prepared by mold casting using a
plaster/water ratio of 1/1.86.
2.2. Characterization of permanent magnets
Although the manufacturer provides us with a data sheet containing information about the
magnetic force of the magnets, this force is normally measured between the magnet and a
piece of iron. In this work we have use magnet-to-magnet junctions, so we need to
characterize the maximum force between pairs of magnets i.e. the maximum force in each
magnetic junction between the pieces to restore. We have determined the attraction force of
the magnets by tensile experiments using a Lhomargy ADAMEL traction machine
DY 30 model with the configuration presented in Fig. 1a. To determine the maximum
operating temperature of the magnets we have slightly modified the measurement
configuration by adding a thermocouple and a heating device, thus allowing for adjusting
the temperature between 25°C and 140°C.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 1: Schematics of the different experimental set-ups: a) tensile experiment; b)
determination of the static friction coefficient; c) static experiment.
We have also study the reversibility of the junction by measuring the minimum temperature
necessary to separate it. For that, we have covered the different pieces with aluminum foil
to protect them and homogenize the temperature and, afterwards, applied heating with a
resistive belt. The internal (close to the magnets) and outside (on the edge of the piece)
temperatures were monitored with thermocouples.
2.3. Measurement of static friction coefficients
The friction coefficient is a key parameter to understand the static behavior of materials. In
general, it is tabulated for a wide range of materials. However, the different stone materials
are generally included within a group called “stone”, without making differences among
them. We have considered necessary to carry out experimental measurements of the friction
coefficient for the three groups of stone materials under study. For this purpose, we placed
together two pieces of the same material, tilting the pieces until the upper test piece slid on
the lower piece (see Fig. 1b). The friction coefficient can be calculated as µ=tan(α), being α
the angle at which the sliding begins.
2.4. Static studies
Before making a junction, it is compulsory to develop a model to predict the configuration
of magnets required to make a connection between fragments. To establish the model, we
performed various tests on model specimens. Different model configurations were selected,
combining a rectangular block (10×10×15 cm) with two different suspended blocks
(rectangular and truncated) of similar weight and dimensions (see Fig. 1c). The tests were
performed using two magnets placed 3 cm from the top and 2 cm from each side of the
rectangular block.
To perform the tests, we have been placed normalized weights on the suspended block,
varying the distance between the test weights and the union, thus increasing the total mass
supported by the junction as well as the distance from the center of mass of the assembly to
the pivot axis. This is equivalent to add longer pieces to the junction, validating the joining
for different geometries.
2.5. Magnetic field simulation
Considering that we are adding magnets to a sculpture, it is essential to guarantee that the
magnetic field outside the artwork is low enough to prevent contamination by magnetic
particles, which would lead to an aesthetic problem. For that, we have used a Finite
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Element Calculation using Comsol Multiphysics software. Considering the stone is not
ferromagnetic, the relative permeability of the stone materials could be approximated by the
one of the air. The magnetic parameters to introduce in the input of the program have been
extracted from the data-sheet of the magnets as well as from their characterization as
described in section 2.2.
3. Results
3.1. Characterization of permanent magnets
The maximum value of strength obtained with the traction machine corresponds to the
maximum force of attraction between the magnets before they separate. The mean value of
this force is 33.6 ± 1.0 N for magnets 10 mm diameter and 5 mm in height, which is 43%
greater than the data provided in the data sheet. For the rest of the magnets, we have
obtained values similar or even higher than those of the date sheet. Therefore, we can use
the values provided by the manufacturer in calculations and models because they guarantee
enough strength to hold the fragments, providing a margin of safety.
To study the maximum working temperature, we have performed the same tensile tests in
the traction machine, after heating the magnets in-situ at different temperatures. For heating
treatments below 80°C, the magnets fully recover their magnetic properties when cooled.
However, when the temperature increases above 100°C, magnets begin to lose their
magnetic properties permanently. For example, after a treatment at 140°C, the maximum
force is reduced by 52%. Therefore, we can consider that 80°C is the safety temperature for
NdFeB magnets. This temperature is more than enough for applications in sculpture
restoration in both outdoor and indoor environments.
One of the most important features of the magnetic joints is the possibility of separating the
pieces in a reversible way. In order to separate the magnetic junction making minimal
mechanical force without damaging the original work, we apply heating while separating
the pieces. We have already proved that, if the heating is below 80°C, the magnetic force is
reduced without degrading the magnets.
Test specimen of plaster with magnets S-10-05-N and test specimen of marble with
magnets S-15-05-N were heated. The temperature required to separate the pieces is, in all
cases, close to 63°C outside the pieces. The temperature in the magnets is approximately
12°C lower. Once the pieces are cooled down, and therefore, the magnetic force is
recovered, we repeated the tests. We observed that, after the third heating cycle, some loss
of clamping force is appreciated. It is therefore recommended not recycle magnets more
than twice after removing the junction. It should be noted that the stone material is
unaffected by the heating. Therefore, this magnetic joint system is reversible and does not
damage the artwork.
3.2. Measurement and calculation of static friction coefficients
Tab. 1 shows the value of the static friction coefficient measured in different faces of the
studied materials. There is a clear dispersion between the different measurements, due to
the fact that the friction coefficient depends greatly on the state of the surface. It is
important to note this dispersion when defining the required values of strength in the union
to use always a range of values of μ in the calculations that ensure a reasonable margin of
safety.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Friction coefficients measured in the different faces of the materials
used in this work.
Block type
Material
Friction coefficient
Standard deviation
Calcarenite from
Novelda
0.57
0.02
Plaster-gypsum
0.86
0.03
Marble from
Macael
0.78
0.04
Block
Truncated Block
3.3. Static studies
The static studies helps to model the behavior of the system and predict the best
configuration of magnets to ensure a safe and reversible joining between the different
pieces to restore in a sculpture. Fig. 2a shows a static study carried out in a joint made with
Plaster-Gypsum. The test was repeated 5 times to ensure reproducibility.
a)
b)
Fig. 2: a) Static study carried out in Plaster-Gypsum model probes; b) Simulated magnetic
field at distances from the magnets for parallel (up)
and antiparallel (down) magnet configurations.
Two interesting results can be extracted. First, there is a maximum weight supported by the
union, which coincides with extra weight place in the closest position related to the
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
junction. Therefore, when the center of mass of the piece to be joined is close to the
junction, the weight of the piece is the only parameter to consider developing a safe
junction. Second, when the extra weight is placed far from the junction the weight
supported is considerably lower. This configuration is equivalent to have longer suspended
pieces in which the center of mass is more separated from the junction. In this case, it is
also extremely important to consider the equilibrium of momenta.
3.4. Magnetic field simulation
By using Finite Element Simulations, we have calculated the magnetic field created by
magnets placed in parallel and in antiparallel configurations. From the simulations, it is
noted that the field in the antiparallel configuration attenuates much faster with distance
(Fig. 2b). Considering that both configurations produce the same clamping force, the
antiparallel configuration is more interesting for these applications because produces a
smaller external field and therefore it reduces the potential for environmental
contamination.
4. Theoretical model
We have developed a theoretical model that collects all the above exposes results. This
model is based on the considerations of Statics, using the equilibrium of forces and
momenta using the scheme shown in Fig. 3.
Fig. 3: Schematics of the model used to develop the theoretical calculations.
We start considering the balance of forces. The weight of the piece and the added weight
are counteracted by the friction force:
Piece weight + Added weight = Friction force = μ Magnet strength.
In addition, the equilibrium of momenta should be also considered:
Magnet strength d1 – piece weight l/2= Added weight x.
This behavior corresponds to the hyperbolic behavior observed in the static tests.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
5. Conclusions
To conclude, we have developed a reversible system based on magnets for restoration of
stone sculpture. This model can be satisfactory applied to real artwork. A theoretical model
based on Classical Mechanics allows choosing the magnets and calculating their position to
ensure a safety union. Simulations, carried out using a finite elements model, allow
selecting a configuration that minimizes the magnetic field outside the artwork. We have
also proved that the system is reversible under the application of moderate heating.
Acknowledgment
This work has been partially supported by Spanish Ministry of Economy and
Competitiveness under grant HAR2011-29538.
References
Bello, M. A., Martin, L. and Martin, A., 1992, Identificación microquímica de mármol
blanco de Macael en varios monumentos españoles / Microchemical identification
of Macael white marbie in some spanish monuments in Materiales de
construcción, Vol. 42, n.° 225, 23-30.
Bestetti, R., 2005, Risarcimento strutturale trattamento delle lacune il caso del dipinto
giardini romani di Giacomo Balla of the ICC Congreso Nazionale IGIIC lo stato
dell’arte, Palermo, 336-343.
Contrafatto, L. and Cosenza, R., 2014, Behaviour of post-installed adhesive anchors in
natural Stone in Construction and Building Materials 68, 355–369.
Fort, R., Bernabéu, A., García del Cura, M.A., López de Azcona, M. C., Ordóñez, S. and
Mingarro, F., 2002, La Piedra de Novelda: una roca muy utilizada en el patrimonio
arquitectónico / Novelda Stone: widely used within the spanish architectural
heritage in Materiales de construcción. Vol. 52. nº 66, 19-32.
Ivorra, S., García-Barba, J., Mateo, M., Pérez-Carramiñana, C. and Maciá, A., 2013, Partial
collapse of a ventilated stone façade: Diagnosis and analysis of the anchorage
system in Engineering Failure Analysis 31, 290–301.
Luque, A., Cultrone, G., Mosch, S., Siegesmund, S., Sebastian, E. and Leiss, B., 2010,
Anisotropic behaviour of White Macael marble used in the Alhambra of Granada
(Spain). The role of thermohydric expansion in stone durability in Engineering
Geology 115, 209–216
Mas-Barberà, X., (2011), Conservación y restauración de materiales pétreos: diagnóstico y
tratamientos. Valencia, UPV. ISBN 978-8483635834, 190 pp.
Oddy, A., and Carroll, S., (1999), Reversibility – does it exist? (British museum occasional
Papers), London, British Museum Press, ISBN 978-0861591350, 179 pp.
Polacek, P., Jancar, J., 2008, Effect of filler content on the adhesion strength between UD
fiber reinforced and particulate filled composites in Composites Science and
Technology 68, 251–259.
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Potje, K., 1988, A Traveling Exhibition of Oversized Drawings Montreal in The Book and
Paper Group Annual. Volume seven (on line) http://cool.conservationus.org/coolaic/sg/bpg/annual/v07/bp07-09.html consultation date 01/04/2016.
Quagliarini, E., Monni, F., Bondioli, F. and Lenci, S., 2016, Basalt fiber ropes and rods:
Durability tests for their use in building engineering in the Journal of Building
Engineering 5, 142–150.
Raftery, G.M. and Whenlan, C., 2014, Low-grade glued laminated timber beams reinforced
using improved arrangements of bonded-in GFRP rods in Construction and
Building Materials 52, 209–220.
Rodríguez M.A., Mas-Barberà. X. and Pérez L., 2014, Optimización de sistemas
magnéticos en la restauración de esculturas y elementos ornamentales of the XIII
Congreso Nacional de Materiales, J. M. Guilemany (ed.), Barcelona, Sociemat, 75.
Rodríguez, M.A., Mas-Barberà. X. and Pérez, L., 2014, Estudio para optimizar las uniones
de fragmentos en escultura y ornamentos mediante sistemas magnéticos of the
Jornadas Emerge 2014: Jornadas de Investigación Emergente en Conservación y
Restauración de Patrimonio, M. V. Vivancos, M. T. Domenech, M. Sánchez and
M. J. Osca (eds.), Valencia, UPV and IRP, 471-477.
Rodríguez, M.A., Mas-Barberà. X., Pérez, L. and Ruiz-Gómez, S., 2015, Estudio de
sistemas magnéticos a base de imanes para uniones de fragmentos y prótesis a la
obra original escultórica of the La Ciencia y el Arte V. Ciencias y tecnologías
aplicadas a la conservación del patrimonio, consejo editorial IPCE (eds.), Madrid,
IPCE and Museo Centro de Arte Reina Sofía, 121-135.
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study of pinning selection for restoration of a historic statue in the Materials and
Design 98, 294–304.
Sáez-Pérez, M. P. and Rodríguez-Gordillo, J., 2009, Structural and compositional
anisotropy in Macael marble (Spain) by ultrasonic, x-rd XRD and optical
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Spicer, G., 2010, Defying gravity with magnetism, in AIC News, volume 35, Nº 6, 1-5
Watson Adsit, K., 2011, An Attractive Alternative: The Use of Magnets to Conserve
Homer by John Chamberlain in WAAC Newsletter. Volume 33. Nº 2, 16-21.
878
THE ROCK RELIEFS “STEINERNE ALBUM” OF GROßJENA,
GERMANY – PROBLEMS OF DETERIORATION AND
APPROACHES FOR A LASTING PRESERVATION
J. Meinhardt1*, T. Arnold2 and K. Böhm2
Abstract
The baroque stone album consists of 12 reliefs of biblical motifs concerning viniculture,
carved out of the bedrock. In their entirety these are the biggest stones reliefs of the
European cultural area. The outcrop represents different varieties of Triassic sandstone. As
a result of harmful environmental influences, especially during the GDR past, massive
damage processes - caused by sulphur oxide emissions - began on the reliefs. The seriously
affected stone album was restored between 1997-1999. After the restoration, a monitoring
and care concept was established. Soon after restoration, strong sanding and flaking in
combination with massive efflorescences were observed on some of the reliefs. The
deterioration proceeds quite quickly, probably also because of unsuitable care measures.
The monitoring care concept that has been agreed upon needs to be reviewed. Using
wireless, minimally invasive sensors, the actual reservoir of soluble components in the
depth profile and their migration depending on moisture penetration in the bedrock and the
climate are currently being monitored. First data reflect significant fluctuations of humidity
and impedance. On several sample areas different poultices for salt reduction measures
were applied. The permanent covering of the endangered reliefs using poultices has been
assessed as particularly promising. Initial results regarding the efficiency of the different
materials are presented in the paper. A great challenge in this context is the forming of the
poultices, considering the value of the monument.
Keywords: KSE, bedrock, salt reduction, poultices, monitoring and care concept
1. Introduction
The rock carvings of the “Steinerne Album” (Stone Album) are situated in central Germany,
near Naumburg. It is about 25 km southwest of a major chemical site during the GDR past
(Leuna, Buna and Bitterfeld). Due to the unprotected exposure, the carvings were
contaminated with pollutants with an anthropogenic origin (sulphur oxide emissions). This
contamination still has an impact today. During the restoration in the 1990s, no salt
reduction measures were carried out. There were concerns that the theoretically constant
supply of salts makes the reduction at the surface useless. On some stone reliefs the
1
J. Meinhardt*
Institute for Diagnosis and Conservation of Monuments in Saxony and Saxony-Anhalt,
Halle/Saale, Germany
meinhardt@idk-denkmal.de
2
T. Arnold and K. Böhm
State Office for Heritage Management and Archaeology Saxony-Anhalt, Halle/Saale, Germany
*corresponding author
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weathering proceeds very quickly. Most likely, this is to be seen in the context of the salt
content in the region near the surface and the direct connection to the bedrock. Despite
periodic monitoring and care measures, the weathering progress cannot be slowed down
significantly. Therefore the care concept needs to be modified, especially with regard to salt
reduction measures.
The aim of the project is to find an appropriate approach for dealing with cultural heritage
objects integrated in masonry (e.g. epitaphs) or directly connected to the bedrock, where the
supply of moisture and salt is difficult to control. These objects are permanently exposed to
these damage stimulating factors from their surroundings. The intention is to identify
suitable compositions of salt storage mortars from the projects sample areas which have the
potential of a long-term care measures. An important requirement of these mortars is their
durability and their visual appeal. If the concept is successful, the outcomes of the current
research project will be suitable for numerous other comparable objects.
2. The “Steinerne Album” of Großjena
2.1. History
In 1777, on the occasion of the 10th anniversary of the regency of Duke Christian, his court
jeweler Johann Christian Steinauer had the Steinerne Album built on his vineyard by
different stonemasons. The baroque stone album consists of 12 reliefs of biblical motifs
concerning viniculture, carved out of the bedrock. The figures are partly larger than life
size. In their entirety, these are the biggest stones reliefs of the European cultural area
(see Fig. 1). Over time, the Steinerne Album fell slowly into oblivion and was only known
among experts. More or less in the 1990s, the Stone Album was rediscovered and returned
to the public awareness.
Fig. 1: Section of the Stone Album, located at the foot of the vineyard.
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2.2. Geological conditions
The outcrop of the album represents three different varieties of Triassic sandstone - red and
grey fine-grained and yellowish coarse-grained material. The reliefs represent the transition
between Hardegsen- and Solling-Formation (Chirotheriensandstein) of the Middle
Buntsandstein (Siedel 1998). The sandstone is clayey-siliceous bound with fluctuating
decay stability. Hardegsen-Formation is clayey to poor siliceous and at the base also
carbonatic bound (Rey 1975). Cement of the Chirotheriensandstone is also clayey to poor
siliceous (Rey 1975). In some places lenses of clay occur. Clay-rich areas are accompanied
by a worse weathering resistance of the material. Furthermore, an outflow of water (stratum
water) can be observed in some parts of the outcrop.
The stone reliefs are situated close to the lower parts of the river Unstrut, about 10 to 12
metres above the river level. In the 1990s examinations regarding the origin of the salts in
the Stone Album were carried out. Nearby, in the lower Unstrut valley, Permian salt springs
are described where prehistoric salt-mining was carried out (Clasen & Sommerwerk 2003).
In Großjena, the village in which the Steinerne Album is situated, hydrogeological
investigations led to the conclusion that modern dewatering measures disrupted former
saline-discharge in this area (Clasen & Sommerwerk 2003) thus, this salt spring discharge
could have theoretically led to a contamination of parts of the stone reliefs. But isotope
investigations had shown clearly that the sulphates stem from an urban environment and
cannot be assigned to any Triassic rock formation (Siedel & Klemm 2001).
For several years now, the vineyard has been used as it was originally intended. In this
context fertilisers have been applied which probably endanger the historic substance
additionally.
2.3. Previous restorative and conservation measures
As a consequence of harmful environmental impacts, especially during the GDR past,
massive damage processes caused by sulphur oxide emissions began. In the sulphuric acid
environment, the dolomitic cement was transformed to the destructive salt Magnesium
sulphate. Even though the stone reliefs are situated in a rural area, the proximity to one of
the most popular chemical sites during the GDR past (Leuna, Buna and Bitterfeld) led to a
massive contamination of the monuments in Central Germany by dry and wet deposition.
The strongly affected rock carvings were restored between 1997 and 1999 as a part of a
project founded by the German Environmental Foundation (DBU) (Meinhardt 2013, 2015).
The emphasis was placed on the conservation and protection of the historic substance. The
12 stone reliefs were strengthened using KSE almost entirely. In order to avoid an overstrengthening of the surface, the infusion method was applied in most areas. Using specially
developed stone replacement mortars, the protection of detached parts was subsequently
carried out. Furthermore, a plaster with high salt storage capacity was applied. This plaster
acts as a storage container for the salts. When any moisture diffuses out through the render,
it leaves the salts that were dissolved in it behind.
In the period between years 2008-2010, the Stone Album was part of the nationwide
research project founded by the DBU: Stone monuments under the influence of
anthropogenic environmental impacts - Development of methods and criteria for the longterm control of weathering and conservation. In this context the condition of the stone
reliefs and in particular the durability of the applied conservation and restorative measures
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were checked using a standardised methodology of natural stone monitoring (Auras et al.
2010).
At the time of these investigations, particularly in the lower parts of the endangered reliefs,
strong sanding in combination with a massive salt load and flaking could be observed. In
these areas mortar applications are often delaminated. Furthermore, efflorescences were
covering areas with salt storage mortar, an indication of the depletion of the available pore
space.
2.4. Monitoring and care concept
A monitoring and care concept was established right after restoration. The care concept
comprises containing the adjoining vegetation, dry cleaning (brush) of the stone surfaces,
removing efflorescences (brush), control and repair of the mortar applications using a stone
replacement mortar (soft) on a pure mineral base (Remmers® Restoration Mortar), visual
and haptic control of the surface strength and, if necessary, re-strengthening by using
solvent-free stone strengthener on a silicic acid ethyl ester base (gel deposit rate: approx. 30
%) (Remmers®). Furthermore colour retouching was carried out in some parts (pigments
dissolved in water). The same restorer who was already responsibly involved in the
restoration carries out the monitoring and care measures every year. Because of the small
amount of available money, only two or three stone reliefs can be inspected in closer detail
each year.
Despite the improvement of the environmental conditions the stone reliefs are still
permanently exposed to the environment due to their prominent position on the weather
side of the vineyard and because of moisture transport in the slope.
2.5. Current state of damage
Regarding sustainability, some of the stone reliefs should be critically evaluated. Partly, the
surfaces are overstrengthened. There is a thin crust, more like a skin, with burst pustules
and flaking can be observed. The cohesion of the crust with the stone substrate is weak. The
stone under this crust is weathered.
The status of the stone reliefs “Duke Christian” and “Marriage in Cana” is of particular
concern. An explanation could be that the more endangered reliefs are in a completely
vertical position and sheltered to some extent by a small overhang (see Fig. 2, left).
Fig. 2: Vertical relief “Duke Christian” (left) in comparison to inclined areas (right).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
This could be associated with the fact that they stay dry longer during light showers. Thus,
the salts cannot be reduced as in the case of reliefs with slight inclination (backwards)
(see Fig. 2, right), which are obviously not in much danger. In both situations (vertical and
inclined) the salts are already activated by a high relative humidity. But the reliefs in
vertical position do not benefit from salt leaching as often as the inclined parts. Only in the
case of a strong rain shower will they get completely wet. A further problem, especially in
the context of recognisability, is the biological growth. The interested visitors are not
allowed to get close to the Stone Album, it being located in a private section. The distance
between the path and the reliefs is about 40-50 metres. Additionally to the different colours
of the stone varieties, an intensive biological growth hinders the perceptibility significantly.
3. New approach to long term preservation
3.1. Modification of the care concept
During the comprehensive restoration in the 1990s no salt reduction measures were carried
out. The main reason for the decision made at that time was the postulated ongoing
transport of soluble components from the bedrock. Now, experience in the field of salt
reduction measures on natural stone is so advanced that a renewed conservation approach
on the basis of different salt reduction cycles is promising. Monitoring of the water
transport and the salt content near the surfaces depending on environmental conditions was
regarded as useful. Therefore sensors, working on the basis of electrical impedance
measurements, were installed in one of the endangered stone reliefs. On the basis of the
information about the real reservoir of soluble components and their transport - depending
on moisture penetration in the bedrock and on the climate (precipitation) - a salt reduction
concept can be established. In this context sample areas with different long-term poultices
were prepared. The aim is to slow down the weathering process and to increase the
sustainability of the conservation. Furthermore, the figures should become more easily
recognised.
3.2. Electrical impedance measurement
In order to choose appropriate care measures for the stone reliefs and for a proper
estimation of the effectiveness of the salt reduction measures, the salt content along the
depth profile and the development of humidity in dependence on environmental conditions
should be determined. To monitor the water transport and the accumulation of salts in
historic structures continuously, a wireless impedance measurement system was developed
by the MPA at the University of Stuttgart and TTI GmbH - TGU Smartmote (Krüger and
Lehmann 2011). The electrical impedance of a porous material is influenced by both its
moisture content and its salt concentration. High levels of moisture and high amounts of
salt correspond to low impedances and vice versa. As both factors influence the impedance
in a similar way, it may not be possible in situ to distinguish which parameter has changed.
However, by observing the impedance over time continuously, it is possible to draw
conclusions about the moisture source and, more importantly, the accumulation of salts
(Krüger and Lehmann 2011). For the determination of the salt and water content, a
representative area within a stone relief which is particularly endangered was chosen for the
measurement. Because of recurring efflorescences or salt crystallisation, the surface of the
relief is at risk. The devices were installed in a deteriorated and an un-deteriorated area in
comparison directly next to each other. For the permanent investigations, two sets of six
holes, each having a diameter of 6 mm, were drilled in each of the two areas (see Fig. 3)
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
with the aim of determining moisture and salt content at different depths. The available
measuring devices unfortunately allow only data recording up to 10 cm. Furthermore, drill
powder was taken for moisture and chemical analysis in depth profiles > 10 cm towards the
interior. These results represent the starting point of data recording and they are helpful for
a proper interpretation of the electrical impedance. These measurements strongly depend on
temperature. Therefore it is logged additionally at all three depths. The measured values
and climatic parameters can be collected remotely. Initially, measurements will be carried
out on an annual cycle. First results, after four months, are shown in section 4 of this paper.
Fig. 3: Position of the boreholes for determining moisture, temperature and impedance
(boreholes 1-3 below, left of the head and 4-6 above). Depth indicates the position of the
sensors (graphic design by F. Lehmann, MPA Stuttgart).
3.3. Application of different long-term poultices
On the stone relief “Joshua and Kaleb”, in the inscription field in the lower part, where
significant damage was already observed, sample areas with different poultice materials
were applied (spray gun, multilayer) (see fig. 4, right). Previously, in adjacent areas without
rock carvings the salt and moisture content along several depth profiles was determined. In
order to get information about the general ability for fluid absorption, capillary water
absorption tests were also carried out on the sample areas (w-values 0.8 - 1.8 kg/m²√h). Of
course, a special focus is on the effectiveness regarding salt reduction. But furthermore the
poultice application is also intended as a protective layer on the endangered surface and to
enhance the recognisability of the reliefs (see Fig. 4, left) especially by an optical
harmonisation of the different colours of the weathered surfaces (stone varieties, biological
growth, replacement mortars).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 4: Relief “Joshua and Kaleb” where different sample areas (right) were applied in the
lower part. Recognisability is obviously enhanced by the poultices (left). Details of the
relief underneath can be seen clearly.
By combination of protection (relocation of the reaction front out of the stone), permanent
measures (salt reduction) and optimisation of the presentation, a promising long-term care
concept can be achieved. By means of the different sample areas these parameters and the
subsequent handling with the stone surface should be studied. The following poultice
formulations were applied either using a funnel gun (8 mm) or with a trowel. Application
with the funnel gun led to a smoother surface and therefore a better distinctness of the
underlying relief. Whether the cohesion between poultice and stone surface is better than
with trowel application will be derived from the results after the long-term exposition of the
different poultices. By using a trowel, greater thickness of the material can be achieved.
1.) FEAD-poultice after FEAD GmbH Berlin: 1P (parts, weight) Bentonite;
4P fire-dried quartz sand 0-2 mm; 10P fire-dried quartz sand 0.1-0.5 mm;
2P quartz powder QM 1600 and 6P Arbocel®PWC500
2.) 0.5P Bentonite, 4P fire-dried quartz sand 0.1-0.5 mm, 2P Arbocel®PWC500
3.) 2P Kaolin, 1P fire-dried quartz sand 0-2 mm
4.) 2P sand 0-2 mm, 1,5P fire-dried quartz sand 0-0.7 mm, 0.3P Sepiolithe
(after C. Pieper)
5.) 0.5P sand 0-2 mm, 1P fire-dried quartz sand 0-0.7 mm,
1P Poraver®foam glass 0.25 – 0.5 mm, 1,25P Poraver®foam glass 0.5-1 mm,
3P Arbocel® PWC500, 0.5P bentonite and 1P binder (slaked lime and NHL 5)
(after lab E. Wendler)
6.) Remmers® desalination poultice Art.1070.
To ensure better sustainability of the poultices, all formulations are combined with slaked
lime, except recipes 4 and 6. A covering slurry containing 2.5P fire-dried quartz sand 00.7 mm, 0.5P kaolin, 1P Otterbeiner® lime (NHL 5), 1P fire-dried quartz sand 0-2 mm and
1P slaked lime + methylcellulose was applied on sample areas 1-3 using a funnel gun (8
mm). Finally, Remmers®Silicone Resin paint LA, transparent (diluted with distilled water)
was applied on all sample areas for a better weathering resistance and a colour adjustment.
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4. First results
4.1. Poultices
At the moment, a final statement regarding the effectiveness of the different poulticemortars cannot be given. The samples should remain on the relief for about 12 months. But
for a first orientation initial results were determined four months after application (see
Tab. 1). Therefore two samples 10×10 cm were cut off the sample fields of every poultice
formulation.
Tab. 1: First results regarding efficiency of the different poultice formulations (two samples
per material type) (For all formulations the content of soluble components was determined
on control samples. It was <0.12 M.-%).
Poultice
(see section 3.3)
Content of soluble components after
four months [M.-%]
1
0.16 and < 0.12
2
0.34 and < 0.12
3
0.26 and < 0.12
4
0.18 and < 0.12
5
0.30 and < 0.12
6
< 0.12
Tab. 1 indicates that efficiency of the poutices is different, even within one material type.
Up to now in all sample fields, except material 6, a reduction of soluble components from
the underground into the poultice can be determined. To get an idea of the real
contamination in the adjacent areas of the sample fields, two depth profiles taking drill
powder were set up. At a depth of 0-1 cm contents between 1.9-2.5 M.-% were detected.
Between 1-2 cm contents of 0.8-1.4 M.-% were measured. Behind this superficial zone the
content of soluble components decreases significantly. Between 2-5 cm 0.5 M.-% were
determined. Obviously, a considerable contamination exists in the stone surface which can
be reduced by appropriate poultices. Final evaluation of the different poultices should be
drawn after one year. A statement regarding the quality of the connection to the stone
surface comparing funnel gun and manual application cannot be given after this quite
limited exposition time. For an objective conclusion regarding this matter, 12 months
should first pass. The assessment of the visual impression showed that the application using
the funnel gun led to much better surfaces than the manual application. The finer the
components in the poultice, the smoother the surface of the mortar is, and details of the
figuration are much more recognisable. Experience shows that in the case of a higher salt
content in the object, better salt reduction can be achieved with thicker poultices. Proper
relation between the thickness of the poultices and the recognisability of the 3D
underground is required.
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4.2. Electrical impedance measurement
After four months, first results of data recording can be given. Relative humidity at the
different depths is very high during the logged period. A dependency from the ambience is
not evident (see Fig. 5). In contrast, temperatures in the different depths follow the outside
climate rather directly.
Fig. 5: Relative Humidity in the different bore holes and depths.
Furthermore, logged data reflect significant differences of the impedance in the different
bore holes and depths (see fig. 6). In boreholes 1-3 (left) the impedance near the surface is
much higher than in 25 and 100 mm. At the second measuring point (boreholes 4-6) the
impedance is lower in all three boreholes and the difference between the depths is smaller
(rigth).
Fig. 6: Measured impedance at 10 kHz in the different boreholes
(1-3 left and 4-6 right) and depths.
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References
Auras, M., Meinhardt, J. and Snethlage, R., 2010, Leitfaden Naturstein-Monitoring,
Nachkontrolle und Wartung als zukunftsweisende Erhaltungsstrategien,
Fraunhofer IRB, Stuttgart, Germany.
Clasen, S. and Sommerwerk, K., 2003, Die (hydro)geologischen Voraussetzungen für die
prähistorische Salzgewinnung im Unteren Unstrut-Tal, Jahresbericht für
Mitteldeutsche Vorgeschichte, Bd. 86,85-96.
Krüger, M. and Lehmann, F., 2011, Wireless impedance measurements to monitor moisture
and salt migration in natural stone, Proceedings of the European Workshop on
Cultural Heritage Preservation, Berlin, September 2011, Fraunhofer IRB.
Meinhardt, J. 2013, Das Steinerne Album in Großjena – Die Pflege eines barocken
Kleinods in der Kulturlandschaft Saale-Unstrut. Denkmalpflege in SachsenAnhalt, Heft 1 (2013), ed. Landesamt für Denkmalpflege und Archäologie
Sachsen-Anhalt.
Meinhardt, J. 2015, Sicherung und Erhaltung der Felsreliefs des Steinernen Festbuchs bei
Großjena – neue Ansätze der Restaurierung der barocken Sandsteinbilder,
Abschlusskolloquium
Modelhafte
Konservierung
der
anthropogen
umweltgeschädigten Felsenkapellen St. Salvator (Schwäbisch Gmünd),
proceedings.
Rey, S. 1975, Die Natursteinvorkommen im Bezirk Halle und ihre Eignung als Werk- und
Dekorationsstein in Vergangenheit und Gegenwart, Dissertation, Martin-LutherUniversity Halle-Wittenberg: III + 139 pp, Halle (Saale), unpublished.
Siedel, H. and Klemm, W. 2001, Salzausblühungen auf der Oberfläche von
Sandsteindenkmalen und auf anstehenden Sandsteinen in Aufschlüssen –
natürliche oder anthropogene Ursachen? Special Edition Geologica Saxonica,
Proceedings of the Symposium in honour of Hanns Bruna Geinitz, Abhandlungen
des Museums für Mineralogie und Geologie Dresden, Bd. 46/47, 203-208.
Siedel, H. 1998, Petrographische Untersuchungen an Sandsteinproben vom „Steinernen
Festbuch“ Großjena, internal report 10/98 Institute for Diagnosis and Conservation
on monuments in Saxony and Saxony-Anhalt.
888
ETHYL-SILICATE CONSOLIDATION FOR POROUS LIMESTONE
COATED WITH OIL PAINT – A COMPARISON OF APPLICATION
METHODS
M. Milchin1*, J. Weber2, G. Krist2, E. Ghaffari2 and S. Karacsonyi1
Abstract
Ethylsilicates (TEOS) are frequently used to consolidate porous limestones usually by full
immersion in a consolidation bath or by run-off application in situ. For porous limestones
with their high level of capillarity these methods are sufficient to achieve reasonable results
as long as the surface is uncoated. However, when covered with oil-based paints or similar
coatings stone surfaces effectively become impervious, which prevents consolidants from
penetrating into the material, so alternative ways of application are required. This paper
describes the case of a 19th century sculpture from Vienna, Austria. It was carved out of a
porous calcareous arenite and originally painted with oil colour; over time several
secondary layers of paint have been added. Some areas of the stone sculpture were in a very
bad condition; the goal of the treatment was to consolidate the stone, but to preserve the
original polychrome paint layer. Tests were conducted on dummies to achieve optimum
penetration of the consolidant through the surface layers by three approaches, namely (1)
total immersion, (2) run-off application, and (3) a patented low-pressure impregnation
treatment known as VCP (Vacuum-Circling-Process) (Pummer 2007). The test specimens
were coated with an oil-based paint prior to their laboratory treatment with TEOS in the
mentioned ways. Penetration depth and drilling resistance were assessed and samples for
polished thin sections were taken, on which polarizing light and scanning electron
microscopy was performed. This latter group of analyses provided significant results in
respect to the deposition of the silicate gel after consolidation. Based on the results, the
sculpture itself was treated with the VCP-method and the effect was verified. It can be
concluded that the VCP application is suitable for the consolidation of stone objects with a
surface of inhomogeneous or reduced permeability.
Keywords: consolidation, TEOS, application, porous limestone, vacuum
1
M. Milchin* and S. Karacsonyi
Institute of Conservation, University of Applied Arts Vienna, Austria
marija.milcin@uni-ak.ac.at
2
J. Weber , G. Krist and E. Ghaffari
Section of Conservation Sciences, Institute of Art and Technology, University of Applied Arts
Vienna, Austria
*corresponding author
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1. Introduction
For several decades ethylsilicates (TEOS), primarily developed and marketed to strengthen
siliceous sandstones, have likewise been used for the consolidation of porous carbonate
materials such as soft limestones from the Tertiary Leithakalk formation. These lithotypes
play a predominant role for sculptural and architectural stonework in eastern Austria (see
e.g. A. Kieslinger 1951, A. Török et al 2004, and A. Rohatsch 2005). TEOS is known to
stabilize decohesive grain textures in these limestones and is thus widely used by
conservators. However, its efficacy is frequently questioned by materials scientists (see e.g.
C.A. Price&E. Doehne 2011 and G. Wheeler 2008); the chemical diversity between
carbonate substrate and silicate consolidant is sometimes interpreted as a “chemical
incompatibility” between both systems. This fact seems to account for the frequent
observation by SEM that silica gel from TEOS treatments of limestones or mortars though
precipitated in pores and cracks, show a rather poor contact with the calcitic mineral grains.
Based on SEM observations alone, some scientists tend to doubt the ability of TEOS to
consolidate limestones in general, notwithstanding the proven physico-mechanical effects
of such treatments. Efforts have been made in the recent past to produce modified TEOS
specialised for the consolidation of limestones. These specialised products were not part of
the present study but have shown some problems on their own and should certainly be
looked at more closely in future.
Some of the earlier applications of TEOS on façades in Vienna have caused problems in
recent years. Strong delamination parallel to the surface can be observed. However, in most
cases such failure is linked to either wrong application methods (e.g. spray or brush), or the
application of TEOS on wet stones, or even the use of water (!) as a diluting agent.
In general the use of TEOS for the consolidation of porous Leithakalk limestones proved a
good practice as long as the surfaces are permeable and the consolidant is not restricted
from entering the structure. A critical situation emerges when porous limestone objects
have their surfaces sealed such as when stones are covered with paint layers or coatings. In
such situations the substrate is often very porous and in need of a consolidation, the coated
surface however prevents the consolidant from penetrating. If the layer sealing the surface
is of no historic or artistic value, its removal can be a possible solution, although the risk to
damage the stone underneath may necessitate a number of additional measures on
beforehand. In case the layer shall be kept e.g. because it represents an original paint, the
problem becomes more difficult to handle. This is the case with the object presented in this
paper, where a sculpture made out of a highly porous limestone, coated with layers of paint,
most of which are oil bound was in great need of a structural consolidation.
2. The sculpture
The object of concern is a life-sized sculpture depicting the Madonna with Child (Fig. 1),
carved out of a highly porous calcareous arenite. It is carved from Au Stone - named after
the locality of extraction in the Southeast of Vienna – which is one of the softest lithotypes
of the Tertiary Leithakalk formation. Formed in coastal areas of the shallow shelves of the
Miocene Paratethys, this stone type was extracted from numerous quarries located in
Eastern Austria, Southern Moravia and Western Hungary (Török et al. 2004). Rohatsch
(2005) describes Au Stone as detrital limestone composed of fossil fragments (mainly
Corallinaceae) and foraminifera at a grain size of below 2 mm. Feebly cemented by sparitic
calcite, the average total porosity of the sound stone is well above 30% by volume, and its
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
water uptake amounts to about 17% by mass. From the 14th to the late 19th century, Au
Stone was probably the most appreciated Leithakalk variety for sculptural stonework in
Vienna and surroundings.The sculpture is dated to the middle of the 19th century, and was
produced by the Viennese sculptor Joseph Käßman (1784-1856). It was originally painted
with a linseed oil based paint containing lead white as pigment, accented with some gilded
sections (crown and details of the dress). The sculpture was placed on a façade in the
seventh district of Vienna where it remained on site until it was first moved for
conservation in 2012; earlier interventions consisted in frequent repainting, according to the
fashion of the time. While most of these secondary layers are also oil bound, the most
recent ones are based on acrylic emulsion as binding medium.
Fig. 1: Thesculpture of a Madonna with Child, 19 th Cent., Vienna, by Joseph Käßman
During the recent campaign, the sculpture had to be removed from the façade because of its
instability and the danger of losing pieces. When delivered to the atelier, the most exposed
parts such as sections from the drapery and the feet were already heavily cracked or broken
in many pieces. Initial analyses by light microscopy confirmed the presence of an original
paint layer. Drilling resistance showed the poor condition of the stone underneath. It was
therefore decided that the sculpture had to be consolidated. Based on the drilling resistance
profiles, it was obvious that a deep penetration was essential. To this end, the consolidant
had to penetrate through the craquele in the oil paint layer, or find its way through the few
lacunae.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3. Methods
In view of the above, it was decided to perform a small laboratory program in order to test
different application methods of TEOS consolidant on test specimens that were prepared in
a way to imitate the presence of an impervious layer with just a few defects. Cubes of
approx. 40×40×40 cm were cut out of a block of a Leithakalk limestone similar, though not
identical to the original stone, since that exact type is no longer available. The cubes were
coated with a commercial white oil paint. An area of 10×10 cm was left uncoated,
simulating the usually unpainted underside. A split line was prepared on 4 sides before the
paint layer was applied in order to facilitate the splitting of the cubes after consolidation.
After the curing of the paint layer, different types of defects were produced in order to
simulate those found on the object. Three drilling resistance profiles before consolidation
were measured for all of the cubes on three different faces.
The blocks were then consolidated using different application methods. The test of the runoff method consisted of applying consolidant by means of a wash bottle in a way that it was
left to freely flow over the surfaces until no more liquid was absorbed. In addition, the
impregnation by total immersion in a bath was tested. With this test, the specimen was
placed in the solution in such a way that first the consolidant was absorbed by capillarity
before it was fully immersed until no more air bubbles were released. The final method was
a patented method known as VCP or Vacuum-Circling-Process(Pummer 2007)and was
employed by the patent holder. This procedure, frequently used in situ, is based on the
airtight packing of the stone element, which is then subject to a regime of under-pressure to
which the consolidant is injected. More details are given elsewhere in this volume
(Pummer 2016).The TEOS product used in all three cases was Funcosil-300E by
Remmers, Germany, a concentrated elastified ethyl silicate with a gel precipitation rate of
300 g/L. For the VCP treatment this consolidant is modified to facilitate the process of
hydrolysis.
Immediately after the application of the consolidant, the cubes were separated along a
predetermined split line. The penetration depth was measured and photographically
documented. Afterwards the fragments were reassembled to cubes using force loops and a
tape, in order to re-establish as far as possible the initial conditions. After a period of 6
weeks, a time span commonly considered sufficient for the hydrolysis of TEOS, the drilling
resistance was again measured and compared to the initial readings. Additionally small drill
cores were taken for polished petrographic thin sections, which were produced after
vacuum impregnation with a blue-dyed epoxy resin. These sections were analysed in a
polarizing light microscope as well as by SEM under low vacuum. Based on the SEM-BSE
images obtained in which the precipitated TEOS silica gel is revealed by a specific grey, its
distribution in depth as well as its precise topographic position in the pore structure was
visualized in pseudo colour. This not only allows for easier apprehension of the distribution
of the consolidant in the micrographs, but would also enable digital image calculation of
relevant parameters such as the degree of pore filling in selected areas of a depth profile, a
procedure not followed however in frame of the present study.
In general, the information gained from the micrographs in combination with the readings
from the drilling resistance and the penetration depth measured on the split planes all
contributed to the final decision regarding the treatment of the sculpture.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
4. Results
4.1. Test Series on Dummies
The first test results were based on the observation of the penetration depth along the split
faces. The cubes that had been treated in a consolidation bath and by the VCP method,
respectively, appeared fully soaked with the consolidant. On the contrary, the cube treated
in the run-off test showed very low penetration depths of 0-7 cm (Fig. 2).In particular, the
penetration was dependant on the condition of the paint layer in a specific area. Where the
colour was scratched or lacunae were present, the consolidant could penetrate the stone
fairly well. In areas with intact paint-layer the penetration depth was either very small or
not determinable.
Fig. 2: Low and irregular penetration depth of the consolidant
applied to the outer faces of the cube by run-off
The measurement of drilling resistance proved to be of limited use in the case of the
dummies. This is probably due to the lack of strength profiles in the unweathered
specimens before treatment. The cubes that were consolidated by total immersion and the
VCP method had a uniform increase of the resistance after the treatment, while the cubes
treated by the run-off method showed no relevant strength increase. On the contrary,
drilling measurements yielded highly significant results for the sculpture with its obvious
weathering profile (see 4.2).
Observations by optical microscopy and SEM revealed not only differences in the
penetration depth of the consolidants for different modes of treatment (Fig. 3), but also
showed that the specific places in the pore system where the silica gel preferentially
precipitated or accumulated were likely governed by the method. As expected, virtually no
silica gel could be detected in the sample from the cube that was treated by the run-off
method, whilst the samples treated both by total immersion and by the VCP-method
revealed significant amounts of silica gel in the full length of the drill core. In either case,
however, the amounts of precipitate decreases with depth. In respect to the preferential
position of gel precipitation, the consolidant was able to penetrate in smaller pores and
thinner cracks when applied by the VCP method than in the case of total immersion, though
the differences seem to be slight and further tests with more samples must be performed to
clarify whether these observations are of relevance. Another observation relates to the
deposition of the gel on the surface. While no silica could be detected on the surfaces of the
sample consolidated by the VCP-method, the full immersion test left behind a surface coat
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
of gel even though the surface of the cube had been dried with a tissue after removal from
the bath. It is likely that this layer had formed in the course of backwards migration of the
consolidant during evaporation, a process that would have not taken place in the VCP test,
either because the gel was preferentially trapped in smaller pores, or because of the
reaction-facilitating additive.
Fig. 3: In-depth distribution of silica gel (in pseudo colour) in the dummy stone subject to
laboratory treatments (a) run-off, (b) immersion, and (c) VCP. SEM-BSE of polished thin
sections, surface on top, depth of scanned area ca. 8 mm
4.2. Consolidation of the Sculpture
Following the results from the laboratory test series, the decision was made to consolidate
the sculpture using the VCP method, which was performed by the company that holds the
patent. After the curing period, drilling resistance measurements were conducted in six
areas of the sculpture that had shown different degrees of decay, and were compared to
drillings that had been made in the same areas before consolidation. Fig. 4 graphs this
comparison and shows a significant increase in strength post-consolidation, with the
greatest effect in the outermost 3 or 4 centimetres that had been in an extreme state of poor
cohesion.
Just one core of 2 cm in diameter could be drilled out of the sculpture at its back side to
check the consolidants precipitation in a polished thin section by polarizing light
microscopy and SEM. Figures 5a and b illustrate the position of the gel at a depth of 2 cm
from the surface. The findings support the drill resistance profile in that the VCP treatment
of the sculpture has produced good results of consolidation.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 4: Drilling resistance, before and after treatment, sculpture Madonna with Child. The
graph shows an example representative of a total of six measurements taken in different
places of the sculpture
a)
b)
Fig. 5: Silica gel in the pores of the sculpture of Madonna with Child after the
consolidation by the VCP method, approximate depth: 2 cm beneath the surface; (a) SEM
image, (b) silica gel in pseudo colour
The amount of gel gradually decreases with the increase in depth. This finding, supported
by the steady graph of the drilling resistance, correlates with the decreasing need for
consolidant in the depth where the stone is in better condition. While quantitative values
typically are not producible to establish the efficacy of a consolidation treatment along a
gradient, one can try to estimate trends achieved by a treatment. The effect shown in our
case was that the pronounced strength gradient before the consolidation has been partly
flattened out, showing that the strength of the subsurface zone of the stone was significantly
increased.
5. Conclusions
The results from the laboratory test series as well as from the treatment of the sculpture
itself point to the fact that the consolidation with TEOS using the VCP-method is a very
good possibility to consolidate porous limestone objects coated with layers of low
permeability. The VCP-method offers one possibility to master these problems. In the
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present case, the surface of the sculpture was covered with oil paint, but the results seem to
be relevant to similar stones with different kinds of surface sealing coatings. The total
immersion in a consolidant bath also proved to be a useful method when executed properly.
The limitation of the size of the object is more relevant to the total immersion treatment
than to the VCP-method. In recent years rather large objects have been treated with this
method. Another advantage of VCP is that it can be done on site without dismantling any
structures, as opposed to the full immersion technique that must be done in a studio, which
can be difficult if not impossible for large structures.
Acknowledgements
Thanks are due to G. Fleischer from the Austrian Research Institute (ÖFI) for the
measurements and data processing of drilling resistance on the sculpture as well as on the
test cubes. Thanks go also to A. Baragona for editing the language of the text.
References
Kieslinger, A., 1951,Gesteinskunde für
Gewerbeverlag, Vienna, Austria.
Hochbau
und
Plastik,
Österreichischer
Price, C. A., and Doehne, E. 2011. Stone conservation: an overview of current research.
Getty Publications.
Pummer, E., 2007, Steinkonservierung; Die Kremser Dreifaltigkeitssäule, Selfpublished,
Rossatz, Austria.
Pummer, E. 2007. European Patent no. 1295859 Vacuum Circular Consolidation Method.
Owner Erich Pummer GmbH.
Pummer, E., 2016,Vacuum-Circling Process: Innovative Stone Conservation Method. In:
Proc. 13th International Congress on the Deterioration and Conservation of Stone,
Glasgow, 6-10 September 2016 (this Volume)
Rohatsch, A., 2005,Neogene Bau- und Dekorgesteine Niederösterreichs und des
Burgenlandes, In: Mitt. IAG BOKU, Institut für Angewandte Geologie,
Universität für Bodenkultur Wien, Nutzbare Gesteine von Niederösterreich und
Burgenland - „Junge Kalke, Sandsteine und Konglomerate – Neogen, Vienna,
Austria.
Siedel, H., Wichert, J. and Frühwirt, T., 2016, Application of ethyl silicate based
consolidants on sandstone with negative pressure - a laboratory study. In: Proc.
13th International Congress on the Deterioration and Conservation of Stone,
Glasgow, 6-10 September 2016 (this Volume).
Török, Á., Rozgonyi, N., Prikryl, R., and Prikrylová, J., 2004,Leithakalk: the ornamental
and building stone of Central Europe, an overview. Dimension stone. Balkema,
Rotterdam, 89-93.
Wheeler, G., 2008,Alkoxysilanes and the consolidation of stone: Where we are now, - In:
Stone Consolidation in Cultural Heritage: Research and Practice; Proceedings of
the International Symposium, Lisbon, 6–7 May 2008, ed. J. Delgado Rodrigues
and J. M. Mimoso, 41–52. Lisabon: LNEC (LaboratórioNacional de Engenharia
Civil)
896
ELECTRO-DESALINATION OF SULFATE CONTAMINATED
CARBONACEOUS SANDSTONE – RISK FOR SALT INDUCED
DECAY DURING THE PROCESS
L.M. Ottosen1*
Abstract
Sodium-sulphate is known to cause severe stone damage. This paper is focused on removal
of this salt from carbonaceous sandstone by electro-desalination (ED). The research
questions are related to possible stone damage during ED and subsequently suction cycles
are made in distilled water before, during and after ED. During suction in water the salts are
concentrated in the upper part of the sandstone. After 2 days of treatment the average water
soluble SO42- concentration was half the initial and for this sample corners were damaged
as was the case for the reference stone. After 4 days of ED the average SO 42- concentration
was 15% of the initial, and here no stone damage was seen from the suction cycles. This
result shows that the damaging salts are removed and that no new harmful salts are formed
during ED in the actual case. Acid is produced at the anode during ED. The acid is buffered
in the poultice with carbonate. The acid would be highly damaging to the carbonaceous
sandstone as the binder-CaCO3 is soluble in acid. From pH measurements of the poultice it
seems as if the acid is buffered well, as pH is still slightly alkaline after ED, but this is a
measurement of the average pH and thus it was decided to measure the compressive
strength of the stones after ED. The lowest compressive strength was measured for the
reference stone, which had not been treated by ED (but had the highest salt content). Thus
from this investigation there is an indication, that dissolution of carbonates in the stone did
not happen, though the data material is too scarce to make a final conclusion. In summary,
this investigation did support that ED removes the salts without new damaging side effects
in the stone.
Keywords: electro-desalination, salt decay, sulphate, sandstone
1. Introduction
When water accesses the pore network of a stone, it may carry various salts in solution.
Several mechanisms can subsequently cause crystal growth and crystallization-dissolution
cycles, which can result in severe stone damage. The damaging effect varies between salts
and salt mixtures, and not all salts are equally harmful, e.g. Rodriguez-Navarro & Doehne
(1999) showed that evaporation from a saturated Na2SO4 solution caused more damage in
limestone than evaporation from a saturated NaCl solution, because Na 2SO4 easily forms
supersaturated solutions, which is a mechanism for the generation of stress (Steiger &
Asmussen 2008). According to Price and Brimblecombe (1994), at 20°C Na2SO4·10H2O is
1
L.M. Ottosen*
Department of Civil Engineering, Technical University of Denmark, Brovej, Building 118,
2800 Kgs. Lyngby, Denmark
LO@byg.dtu.dk
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
the stable form of sodium-sulphate at relative humidity (RH) between 71 % and 93 %.
Na2SO4·10H2O occupies a 314 % larger volume than the anhydrous salt. Thus the volume
of sodium-sulphate changes significantly with changes in RH, which is likely to be a major
factor involved in the development of crystal pressure. The topic of the present paper is
removal of Na2SO4 from carbonaceous sandstone by electro-desalination (ED).
The carbonaceous sandstone is Gotlandic sandstone, a soft, grey stone with approximately
20 % porosity and a fairly high degree of homogeneity, which makes it suitable for
sculptures. The sandstone is sensitive to outdoor conditions due to the quite high porosity
and the CaCO3 bonding. The calcite can chemically be transformed to gypsum when
exposed to acid-rain (Suneson 1942). Based on samplings from two monuments built of
Gotlandic sandstone Nord and Tronner (1995) observed that rain dissolved calcite and
decreased the Ca concentration in the stone. The dissolved Ca concentrated at the surface
where a hard, thin gypsum crust was formed.
ED is based on application of an electric potential gradient and electromigration of the ions
from the damaging salts out from the stone. During ED electrodes are placed externally on
the surface of the salt infected stone. The electrodes are placed in a poultice in which the
ions from the salts concentrate during the treatment. When the poultices are removed after
the desalination, the ions of the salts are removed with them. At both electrodes there are
pH changes due to electrolysis reactions:
At the anode:
H2O → 2H+ + ½ O2 (g) + 2 e-
(Eq. 1)
At the cathode:
2 H2O + 2e- → 2OH- + H2 (g)
(Eq. 2)
As seen from (1) and (2) pH decreases at the anode and increases at the cathode. It is
necessary to neutralize the pH changes to prevent severe pH changes of the stone.
Herinckx et al. (2011) and Skibsted (2014) underlined the importance of avoiding stone
acidification, as in experiments without pH neutralization; the stones were severely
damaged next to the anode. Calcite rich clay poultice can be used for neutralization of the
pH changes at the electrodes (Rörig-Dalgaard, 2009). The calcite buffers the pH changes
and the clay gives workability, so the poultice can have optimal contact to the surface of the
object to be desalinated. When the calcite buffers the acid from the anode, Ca 2+ ions are
released. If these ions do not precipitate with anions, they can be transported into the
limestone by electromigration, and possibly precipitate with dissolved SO42-. Should this
happen, it may hamper the desalination and the formation of calcium- sulphates may even
contribute to further salt weathering. In the present work it is investigated whether the stone
is weakened during ED or at increased risk for salt decay during the process.
2. Materials and methods
2.1. Stone for the experiments
The Gotlandic stone pieces for the investigation were cut out of a former window frame
from Kronborg Castle, Denmark. The original window frame had been removed and
replaced during a renovation action. The outer parts of the stone were discharged, and the
stone pieces for the experimental work (size 2.8×2.8×5.2 cm) were cut as seen in Fig. 1.
The stone pieces were dried at 105°C. The pieces were vacuum saturated by 30 g/l Na2SO4
in a desiccator prior to the ED experiments.
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Fig. 1: The stone pieces were cut from a removed window frame.
2.2. Stone characterization
Two extra sandstone pieces were cut from the window frame (4×4×5 cm3) for measurement
of capillarity, porosity and density. Capillarity: The samples were dried at 105°C. The dry
samples were weighed and placed in a tray with distilled water with 5 mm height on the
stone. The sandstones were weighed after 1, 2, 4, 6, 8, 16, 30, 60, 120, 180, 240 and 360
min. The samples were dried at 105°C again. They were vacuum saturated in a desiccator
and the stones were weighed above and below water as it is required to calculate porosity
and density.
2.3. ED experiments
Electrode compartments with the size 3×3×3 cm3 were placed at each end of the sandstone
piece (Fig. 2A). The frame of the electrode compartments were folded in thin plastic and
jointed with tape to fit the ends of the stones. The frames were filled with poultice; a
mixture of kaolinite and CaCO3 (Rörig-Dalgaard, 2009). Inert electrode meshes (electrodes,
which do not take part in the electrode processes themselves) were placed at the end of each
electrode compartments, see Fig. 2a. The sandstone and electrode compartments were
wrapped in plastic film to hinder evaporation. A constant current of 2 mA was applied. The
durations of the ED experiments were 2, 4 or 7 days (denoted ED 2, ED4 and ED7
respectively).
a)
b)
Fig. 2: a) ED setup with clay poultice and electrode mesh; b) segmentation of the stone
after ED.
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Each of the ED experiments was made in doublet. Concentration profiles were made on
basis of one set of experiments, whereas suction cycles and compressive strength tests were
made with the other set to evaluate the salt damage. See procedures below.
2.3.1. ED and concentration profiles
After ED the stones were segmented with hammer and chisel into five segments; numbered
from the anode end (Fig. 2b). A reference stone (Ref.) was segmented directly after vacuum
saturation by 30 g/l Na2SO4 to get the concentration profiles before ED. The water content
in the five segments was measured and calculated as weight loss after drying at 105°C per
dry weight. The dried segments were grinded in a mechanical mortar. Following 10 g
powder was suspended in 25 ml distilled water and agitated for 24 h. The samples settled
for 10 min and pH was measured. The samples were filtered through 0.45 μm filter. Na
concentrations were analysed by ICP-OES. SO42- (and for the reference sample also Cl)
concentrations were analysed by ion chromatography (IC, Dionex DX-120). For each
segment the concentrations were measured as double determinations.
2.3.2. ED and stone decay
The present experimental work focuses on stone decay caused by calcium sulfate formed
during ED and since this salt has a low solubility it will not necessarily be seen in the
concentration profiles measured in the suspension of powdered sandstone in water. Thus it
is necessary to evaluate the ED process based also on the decay pattern. Two
drying/wetting cycles were preformed just after ED: the stone pieces were dried to constant
weight at 50°C. They were placed in distilled water to a height of 1 cm (Fig. 3). The surface
where the cathode poultice had been placed was placed in the water. The water level in the
beaker was kept constant manually. When water had been sucked all the way through the
stone piece, the stones were left for 1 day in the setup. The stones were dried again to
constant weight at 50°C and the suction procedure was repeated. After the second suction
was completed, the stone pieces were inspected visually and compressive strength tests
were performed.
Fig. 3: Suction test after ED.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3. Results and discussion
3.1. Porosity, density and capillarity
The porosity of the experimental stone is 20.5% and the dry density 2120 kg/m2. In less
than 2 hours water is sucked into the stone to full height (5 cm) and stable water content.
The capillarity of the sandstone is high 5.98 kg/(m2 s½).
3.2. Removal of Na and SO42- during ED
The Gotlandic stone for the investigation had been exposed to the outdoor environment at
Kronborg Castle, which is situated just next to Øresund with salt water. As the stones thus
potentially can be infected by Cl, the concentrations of Cl were measured in the five
segments of the reference stone: 60.2 ± 7.2 mg Cl/kg. Thus the Cl concentration of the
stone pieces for the ED experiments is low and thus the major salt is the Na 2SO4 in which
the stones were submerged.
Fig. 4 shows the concentration profiles of SO42- and Na through the stone piece at the end
of the ED experiments. It is seen, that SO42- electromigrated towards the anode and Na
towards the cathode, as it could be expected. The initial concentrations (Ref.) were 1950 ±
35 mg SO42-/kg and 940 ± 80 mg Na/kg. At the end of ED 7 the concentrations were
decreased to 36 ± 4 mg SO42-/kg and 49 ± 5 mg Na/kg. This corresponds to removal
percentages of 98% SO42- and 95% Na during 7 days.
Ref SO4
Concentration, mg/kg
2500
Ref Na
2000
ED2 SO4
1500
ED2 Na
1000
ED4 SO4
ED4 Na
500
ED7 SO4
ED7 Na
0
1
2
3
4
5
Fig. 4: SO42- and Na concentration profiles of Ref and ED stones.
Skibsted et al. (2015) reported that the ED removal rate per valence for SO 42- was 75% of
the ED removal rates for Cl– and NO3- regardless the ionic mobility of SO42– is slightly
higher than that of the monovalent anions. The main reason for the lower removal rate for
SO42– was found to be the chemical interaction with Ca2+, which entered the brick from the
poultice in the anode chamber. The concentrations of Ca 2+ and SO42– in the pore solution
decreased after 5 days of ED and precipitation of gypsum was thus not considered as a
permanent problem. Simulation results were congruent with those obtained experimentally
The present experimental work (Fig. 4) support this conclusion, however, in case calciumsulfate salt with low solubility is formed during ED, it will not necessarily be seen in the
concentration profiles of figure 4, because the concentrations shown here are measured in a
suspension of powdered sandstone in water after filtration. The salt crystals will be
removed from the sample during the filtration process if not dissolved. Thus it is necessary
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
to evaluate the ED process also on the decay pattern, which was done by suction cycles, see
section 3.3 of this paper.
Electro neutrality is fulfilled all the time and thus during ED other anions than SO 42- ensures
the electro neutrality in relation to the Na+ concentration profile, as the concentration of this
cation is high close to the cathode where the SO42- concentration is low. In Paz-Garcia et al.
(2013) it is suggested from numerical-chemical simulations that these are mainly OH- ions
(experimentally it is also often seen that pH increases slightly from the cathode side, which
was also the case in the present work see section 3.4). There may thus be precipitation of
Ca(OH)2 in the material if Ca2+ from the anode poultice and OH- from the cathode meet
inside the stone. Over time Ca(OH)2 may react with CO2 from air and form CaCO3, but
neither Ca(OH)2 nor CaCO3 are considered damaging, because aqueous solutions of
calcium hydroxide (limewater) have been used for many centuries to protect and
consolidate limestone, and CaCO3 is present in the original carbonaceous stone.
3.3. Decay of ED treated stone evaluated after suction cycles
Pictures of the stones Ref and ED´s after two cycles of water suction are shown in Fig. 5.
Some of the thin white layer on the upper horizontal surface originates from the poultice
(see also Fig. 3). During the suction, the soluble salts are transported towards the top of the
stone, which means a concentration of salt in this part and a lower concentration in the
remaining stone. It is seen that the upper corners were damaged for the Ref and ED 2
experiments whereas similar damage was not seen for ED4 and ED7 revealing that the
overall concentration was lowered sufficiently after 4 days.
Ref
ED2
ED4
ED7
Fig. 5: Ref and ED stones after two water suction cycles.
It is noticed, that the soft material/crystals at the damaged corners of the Ref and ED 2 stone
differs. At the Ref. it has the colour of the sandstone and at ED 2 the salt crystals are white.
It might be different salts responsible to the decay in the two cases, but it is not determined
in this investigation. In the Ref stone the Na2SO4 in which the stone was submerged is
considered the major salt, whereas in ED2 also Ca2+ may have been transported from the
anode poultice into the stone. The calcium sulphate will dissolve again as long as Ca 2+ and
SO42- are removed from the pore solution in the applied electric field as equilibrium
supports the dissolution. The lack of crystals on ED 4 and ED7 support this hypothesis.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3.4. Compressive strength of ED treated stone
The average pH in the segments from Ref. was 8.9 ± 0.05 and for ED 7 9.0 ± 0.3. The
overall pH in the stone piece did thus not change significantly during ED. The pH remained
the same in the anode end as initially, whereas the pH increase from the cathode was not
buffered to the same extent, as pH in the segment closest to the cathode was increased to
9.5, which is though not considered a problematic level.
The fact that the pH did not change from the anode side is not a proof that H + did not
electromigrate into the stone. Gotlandic sandstone has a buffering capacity towards acid as
it is calcite bound, which was shown experimentally in Skibsted (2014). In case an
acidification had occurred during the ED treatment, this would decrease the compressive
strength of the stone as result of dissolution of calcite. Thus it was decided to make
compressive test measurements. The compressive strength tests were conducted after the
suction cycles, and the stone compressive strength could be influenced from both
acidification and salt weathering. The result is shown in fig. 6 and 7. A quite large variation
in compressive strength was observable between the four stones. The Ref. stone had the
lowest compressive strength of all four stones, which may indicate that ED does not lower
the strength significantly by dissolving the bonding calcite phases, but the data are too
scarce to make a final conclusion on this point. Fig. 7 shows that the pattern with which the
stones were broken during the compressive strength tests differed. The pattern was linked
to the compressive strength in that for the Ref and ED 7 stones with the lowest compressive
strength, the stones were damaged by flaking from the surface, whereas the two stronger
stones ED2 and ED4 were broken in the expected pattern hourglass figure for a
homogeneous sample.
Compressive
strength, MPa
40
30
20
10
0
Ref
ED2
ED4
ED7
Fig. 6: compressive strength after ED and 2 suction cycles (single determinations).
Ref
ED2
ED4
ED7
Fig. 7: The stones after compressive strength measurements.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
4. Conclusions
Carbonate bound sandstones are weak and sodium-sulphate a highly damaging salt. ED was
tested for removal of sodium-sulphate from Gotlandic sandstone, which is carbonate bound.
The focus was on possible damaging side effects, such as dissolution of the carbonate phase
or formation of new damaging salts, during the treatment. No indications of these side
effects were seen. The compressive strength of the stones were measured and it was not
decreased during ED, though this determination eas only made in single determinations and
the result must be taken with caution. The ED treatment followed by suction cycles did not
show any stone damage after ED during 4 days, which was on the contrary to before
treatment.
References
Herinckx S, Vanhellemont Y, Hendrickx R, Roels S, De Clercq H., 2011, Salt removal
from stone building materials using an electric field. In: I. Iannou & M.
Theodoridou (eds.) Proceedings from the international conference on salt
weathering on building and stone sculptures, Cyprus 19-22 October, 357-364.
Nord, A.G., Tronner, K., 1995, Effect of acid rain on sandstone: The Royal palace and the
Riddarholm Church, Stockholm. Water, Air and Soil Pollution, 85,2719-2724.
Paz-Garcia, J.M.P.; Johannesson, B.; Ottosen, L.M.; Ribeiro, A.B.; Rodroguez-Maroto, M.,
2013, Simulation-based Analysis of the Differences in the Removal Rate of
Chlorides, Nitrates and Sulfates by Electrokinetic Desalination Treatments.
Electrochimica Acta. 89, 436-444.
Price, C.; Brimblecombe, P., 1994, Preventing salt damage in porous materials, In Eds A.
Roy and P. Smith, Preventive conservation: Practice, theory and research" Ottawa
Congres, 12-16 Sep., 90-93.
Rodriguez-Navarro, C.; Doehne, E., 1999, Salt weathering: Influence of evaporation rate,
supersaturation and crystallization pattern, Earth Surf. Process. Landforms, 24,
191-209.
Rörig-Dalgaard, I., 2009, Preservation of masonry with electrokinetics – with focus on
desalination of murals. PhD Thesis. Department of Civil Engineering, Technical
University of Denmark.
Skibsted, G., 2014, Matrix changes and side effects induced by electrokinetic treatment of
porous and particulate materials, PhD Thesis, Department of Civil Enginering,
Technical University of Denmark.
Skibsted, G.; Ottosen, L.M.; Jensen, P.E.; Paz-Garcia, J.M., 2015, Electrochemical
desalination of bricks - Experimental and modeling. Electrochim. Acta, 181, 2430.
Steiger, M.; Asmussen, S., 2008, Crystallization of sodium sulfate phases in porous
materials: The phase diagram Na2SO4 ∙ H2O and the generation of stress,
Geochimica et Cosmochimica Acte, 27, 4291-4306.
Suneson, E., 1942, Bygningsmaterialer, 3. Bind: Natursten. Jul. Gjellerups Forlag, 117139.
904
PERMEABLE POSS-BASED HYBRIDS: NEW PROTECTIVE
MATERIALS FOR HISTORICAL SANDSTONE
A. Pan1, S. Yang1 and L. He1*
Abstract
Although much effort has been dedicated to the development of advanced materials and
techniques, only a relatively small part of conservation science has focused on the
production of innovative materials that can be applied to repair ancient stone. Because soft
nanomaterials do not alter the original physical and chemical properties of artefacts, we
report two kinds of well-designed polyhedral oligomeric silsesquioxanes (POSS)-based soft
materials of ap-POSS-PMMA-b-P(MA-POSS) (P1) and PDMS-b-PMMA-b-P(MA-POSS)
(P2) prepared for protecting historic stones. Their assembled soft nanoparticle, surface
wettibility, water adsorption and themal properties are investigated. P1 gives lower water
adsorption (Δf=-600 Hz) and viscoelasticity (ΔD=75×10-6) but higher thermostability
(Tg=124 C and Td=400 C. P2 shows a silicon-rich surface, strong storage modulus
(648-902 MPa), higher water adsorption amount (Δf=-2300 Hz) and surface rigidity
(ΔD=26×10-6). Therefore, two POSS-based hybrids are recommended to the protective
performance of sandstone with different porosity as D1 (23.66%) and D2 (21.57%),
evaluated by the colour variations, capillary water absorption, water vapour permeability,
water static contact angles, salt-tolerance crystallization cycles and freeze-thaw cycles. All
the results indicate that the colour variation of the treated stones is within the permitted
range. Under the condition of invariable pore size distribution, the water resistance is
obviously improved and the water permeability is slightly reduced, and P1 does better than
P2. On the other hand, P2 is realized much better in salt-tolerance and freeze-thaw recycles
than P1. The smaller pore size diameters (less than 2 μm) have been covered but the middle
pore size is narrowed at 200-900 μm. The weathering behaviours also indicate good
resistance to anti-salt and anti-freeze/thaw after 9 salt crystallization cycles and 50 freezethaw cycles. Therefore, P1 and P2 are suggested as protective materials to the historical
stones.
Keywords: soft nanomaterials, POSS-based copolymer, permeability, film properties,
protective performance
1
A. Pan, S. Yang and L. He*,
Department of Chemistry, School of Science, Xi’an Jiaotong University, China
heling@mail.xjtu.edu.cn
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
1. Introduction
Soft nanomaterials have been considered for protecting application of ancient stones
(Baglioni et al. 2015, Son et al. 2009) based on their extraordinary surface properties,
excellent film-forming properties (Zhang et al. 2013, Licchelli et al. 2013), high
mechanical and anti-chemical properties (Cappelletti et al. 2015, Verganelaki et al. 2015,
Xu et al. 2015), and undisturbed the original physical and chemical properties of artefacts.
Actually, silica-based nanomaterials have been reported for sandstones protection with
reinforcement and surface protective due to the better compatibility with the sandstones
(Luo et al. 2015, Baglioni et al. 2013), such as “TEOS-SiO2-ST-PDMS-OH” hybrid by
combining TEOS, colloidal silica (200 nm) and polydimethylsiloxane (PDMS-OH) used
for stone consolidation (Salazar-Hernández et al. 2010). The colloidal silica (200 nm) is
favour of the micro-porous and mesoporous structures, and the organic segments of PDMS
could improve the elasticity of the gel by chemical bonding with TEOS which could also
improve the surface wettability. Recently, introduction of polyhedral oligomeric
silsesquioxanes (POSS) particles, the smallest SiO2, into organic matrix is used to improve
properties of soft nanomaterials, based on that POSS with silsesquioxane cage ((SiO1.5)n, n=
8-14) and organic functional groups (Kuo et al. 2011) could disperse in nanoscale and give
higher reactivity in obtaining new nanomaterials (Tada et al. 2012). Actually, POSS-based
nanomaterials present low surface energy surface and highe mechanical properties without
changing the surface structures and gas permeability (Kota et al. 2012).
Therefore, this work presents the well-designed two POSS-based block-structured
nanomaterials and their protective application to historic stones. They are separately
synthesized by aminopropylisobutyl POSS (ap-POSS, cages structure) and mono-carbinol
terminated polymethylsiloxane (PDMS-OH, soft segments) initiating methylmethacrylate
(MMA) and methacrylisobutyl polyhedral oligomeric silsesquioxane (MA-POSS) by ATRP
technique to obtain ap-POSS-PMMA-b-P(MA-POSS) (named as P1; Yang et al. 2014) and
PDMS-b-PMMA-b-P(MA-POSS) (named as P2; Yang et al. 2015). 1H,1H,2H,2Hheptadecafluoro-1-decanol (CFH2CH2(CF2)8OH) is also used to initiate MMA and MAPOSS to gain F-PMMA-b-P(MA-POSS) (named as P3) for comparison (Pan et al. 2015).
The differences of their self-assembly in solutions, surface morphology, wettability and
thermo-stability are compared. Their protective efficiency onto two stones is evaluated by
the colour variation, water absorption, permeability, surface contact angles, pore size
distribution and salt/freeze/thaw decay behaviour.
2. Experimental section
2.1. Materials
Details of the used materials of (ap-POSS-PMMA-b-P(MA-POSS; Yang et al. 2014) and
PDMS-b-PMMA-b-P(MA-POSS; Yang et al. 2015) are provided in Tab. 1. Their
assembled nano-particle from molecular blocks prepared by casting 1 wt% homogeneous
solutions in chloroform (CHCl3) and the corresponding particle size distribution
areinvestigated by TEM and DLS (Fig. 1). The ap-POSS-PMMA-b-P(MA-POSS) (Fig. 1a)
behave 200 nm core-shell structured micelles (the inner dark core and out light shell) as the
dark core of ap-POSS and P(MA-POSS), and the light shell of PMMA (Yang et al. 2014).
The similar micelles are observed for F-PMMA-b-P(MA-POSS) in Fig. 1c. While, PDMSb-PMMA-b-P(MA-POSS) in CHCl3 solution form 200-500 nm opposite core-shell micelles
Fig. 1b with the white PMMA core, and 50 nm thickness of the black shell formed by
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
PDMS and P(MAPOSS; Yang et al. 2015). However, the micelles (150 nm) are much
smaller than ap-POSS-PMMA-b-P(MA-POSS) (200 nm), this is possible due to the poor
solubility of F segments which could shrink the micelles. As we all known that the
micellization behaviour is mainly controlled by the solvent and the interaction of solvent
with the copolymer blocks. So another reason is that CHCl3 solution has the smaller
dielectric constant (ε = 4.81) which could decrease the repulsive between the segments, and
improve the affinity of PDMS and P(MA-POSS).
Tab. 1: The molecular weights of prepared samples by SEC.
Samples
Chemical composition
Mw/ Mn
×104
Micelles
Surface
Si
size/nm
roughness, element,
TEM/DLS
(nm)
(wt%)
2.83/2.44 200-500/295
0.83
8.68
P1
ap-POSS-PMMA152-b-P(MA-POSS)8.4
P2
PDMS-b-PMMA408-b-P(MA-POSS)8.2 5.36/4.41 100-300/283
P3
a)
F-PMMA200.8-b-P(MA-POSS)9.06
3.02/2.74 100-300/135
b)
2.48
14.62
1.69
6.34
c)
Fig. 1: TEM morphology of P1 (a), P2 (b) and P3 (c) in CHCl3 solution.
2.2. Protection of historic sandstone
Sample preparations: The historic stone samples are collected from DaFoSi Grottoes (Red
Stones) and Zhongshan Grottoes (Gray Stones) of Shaanxi province, famous Great Buddha
Grotto in China. The stone samples are cut into 2×2×1 cm3 (cube) and 4.2×1.0 cm2
(cylindrical) approximately, washed with deionized water, dried at 110°C up to constant
weight (24 h), and then stored in silica gel desiccators before treatment. The historic stone
samples are immersed in P1 or P2 solutions (1 wt%) until no air bubbles (about 1h). The
treated stone samples are kept a 3-week interval for reaching constant weight.
Assessment method and process: The colour variation of stone surface is evaluated by
colorimetric measurements using a Konica Minolta Colorimeter (CR-400). The
measurements of water absorption are conducted by using the gravimetric method
according to total completely immersion. Water capillary absorption is performed
according to the Italian Standard UNI 10859. The capillary absorption coefficient is
calculated at the end of the test for all the samples. The water vapour permeability is
processed by the cylinder sandstone samples (4.2×1.0cm2). The surface morphology of
treated stones is investigated by SEM. The surface contact angles measurements are
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
conducted on an OCA-20 DataPhysics Instruments GmbH with SCA 20 software at 25°C.
The stone porosimetry is used to measure the pore size distribution of the macropores on an
Autopore IV9500 Micromeritics Instrument. The anti-salt decay behaviour of stone samples
is processed as total immersion into a saturated solution of Na 2SO4 for 24 h and then drying
at 105-110°C for 24 h. This cycle is repeated until obvious damage appeared. The freezethaw cycle is done as total immersion in deionized water at 20-25°C for 4 h and then
freezing at -4°C for 4 h. This cycle is repeated up to twenty times. The weight loss
percentage of the samples (measured at the end of cycle) is taken as a measure of the
damage.
3. Results and discussion
3.1. The colour variation and surfaces wettability of protective stones
Table 2 shows the colour variation ΔE of the treated stone samples. P3-treated stone surface
shows the biggest ΔE (3.57 for red stone and 3.74 for gray stone) due to the poor
compatibility with the silicate-based stones. P1-treated surface presents the smallest colour
variation (ΔE=1.69 for red stone and 3.21 for gray stone). All of the stones treated by the
materials are within acceptable limits (not larger than 5).
Tab. 2: Colour variation ΔE and water contact angle of the treated stone samples.
ΔE
Samples
P1
P2
P3
Red stone
1.69
2.31
3.57
Gray stone
3.21
3.46
3.74
Water contact angle in degrees
Red stone
Gray stone
128.6±3.6
122.9±2.1
138.9±2.4
128.7±1.6
127.2±3.1
120.2±1.7
The surface wettablilty is evaluated by water contact angles (WCA) in Table 2. All the
stones samples treated provide the high-hydrophobic surface (WCA=120°-139°). When the
water droplets contact the stone surface, the droplets are absorbed quickly for the untreated
stones. However, the water droplets on the treated samples could keep for a long time. The
WCA values show that P2 provide 138.9±2.4° for red stone (the biggest WCA) and
128.7±1.6° for gray stone, and P3-treated stones have the smallest WCA (127.2±3.1° for
red stone and 120.2±1.7° for gray stone). All the results demonstrate markedly the surface
wettability. As is well-known that surface wettability is controlled by the surface structure
and morphology. Take red stone as example, POSS cages are able to grow into big crystals
when they contact the silicate-based stones (regarded as the crystal-seed) (Fig. 2b), but P2
wearing PDMS chains with much better flexible and movement has better permeability and
strong combination with the stones (Fig. 2c), while P3 do not influence the surface
structures (Fig. 2d). All the results demonstrate that the stones surface keep un-changed and
clear-outline surface without changing the surface structures after treated which could
improve the surface wettability.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
a)
b)
c)
d)
Fig.2. SEM images of untreated red stone (a) and treated by P1 (b), P2 (c) and P3 (d).
3.2. Water absorption and permeability
The water capillary absorption also reveals the water-resistant property of the treated stone
samples. Figure 3 shows the water capillary absorption, and the capillary absorption
coefficients calculated by the slope of initial 15 min of the capillary absorption curves. The
untreated stones absorb rapidly a great amount of water, but this tendency is reduced by
every treated sample, which indicates that the wettability has been improved after
protective treatment. For red stones, all the samples show the similar capillary absorption
coefficient of 7.89×10-5 g·cm-2·s-1/2 for P1, 6.58×10-5 g·cm-2·s-1/2 for P2 and 5.95×10-5
g·cm-2·s-1/2 for P3, and similar water-absorption of 2.46% for P1, 2.22% for P2 and 2.72%
for P3, which is much lower than the untreated samples (1.53×10 -3 g·cm-2·s-1/2, 6.89%
water-absorption). This is because that the red stones have much bigger interspaces which
is in favour of the similar water-absorption. However, as for the gray stones, all the treated
samples show the lower absorption speed (capillary absorption coefficient is 1.98×10 -3
g·cm-2·s-1/2 for P1-, 1.47×10-4 g·cm-2·s-1/2 for P2 and 1.77×10-3 g·cm-2·s-1/2 for P3) than the
untreated samples (2.50×10-3 g·cm-2·s-1/2, 11.15% water-absorption). And P2-treated stone
presents the lowest capillary absorption coefficient 1.47×10 -4 g·cm-2·s-1/2 and water
absorption (5.95%). P1- and P3- treated stones have the similar tendency which is much
lower than the untreated stone, but much higher than P2-treated samples. Actually, the gray
stone have the smaller interspaces but the P2 could penetrate into the stones easier than
other materials to decrease the water-absorption.
Furthermore, the water vapour permeability of treated stones is compared. For the red
stones, all the treated red stones show the similar tendency and lower water vapour
permeability (1.03-1.53 g·m-2) than the untreated red stone (2.52 g·m-2). P1 shows the
highest water vapour permeability but P2 gives the poorest one. This is because P1 provide
most POSS cages than P2 and P3 which is much better for water vapour permeability. As
for gray stone, all the samples show the similar tendency with the red ones and P1 shows
the highest water vapour permeability. Due to the compact structure of gray stones, it water
vapour permeability (0.206-0.274 g·m-2) is much lower than the red ones. The water vapour
permeability results demonstrate that all the treated samples increase their wettability but
decrease a little of water vapour permeability. It is concluded that much better water vapour
permeability is supported by the more POSS cages in P1.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
a)
b)
d)
c)
e)
Fig. 3: a) Capillary absorption coefficient; b) Water absorption; c) Water vapour
permeability, d) Weight loss percent after salt crystallization, e) Freeze-thaw cycles.
3.3. Pore size distribution
The pore size diameters of all treated stone samples are measured and are compared to the
untreated one. For red stones, three different kinds of pore size diameters are observed:
200-900 μm, 3.5-40 μm and <2 μm (Fig. 4). All the pore size diameters at 200-900 μm for
three treated red stones have not changed, but the pore size diameters at less than 2 μm of
P1-treated stone has disappeared and has become narrow as 10-30 μm compared to
untreated one (3.5-40 μm; Fig. 4a). The pore size diameters of P2-treated stone show the
similar tendency (0.2-2 μm). But P3-treated stone gives a specific peak of pore size
distribution appeared at 7-9 μm. All results demonstrate that after protective treatment, the
smaller pore size diameters (< 2 μm) has been blocked and the middle pore size distribution
become narrow but the pore size at 200-900 μm have never been changed.
As for gray stones, the untreated stones show three different pore size distributions at
20-900 μm, 0.3-20 μm and smaller than 300 nm in Fig. 4b. The pore size diameters of P1treated stone at 200-900 μm has changed to 100-800 μm and the pore size diameters at
0.3-20 μm and less than 2μm has been replaced by 0.2-10 μm. However, only one pore size
diameter happened at 30-800 μm could be seen for P2- and P3-treated stones. Therefore,
the smaller pore size diameters and the middle pore size distribution has been covered and
the pore size at 200-900 μm have never been changed after treatment.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
a)
b)
Fig. 4: Pore size distribution of red stone (a) and gray stone (b).
3.4. Salt and freeze/thaw cycles
Figure 5 shows the surface appearance of stone samples after salt crystallization cycles and
freeze-thaw cycles. It is observed that the untreated red sample is damaged after one salt
crystallization cycle. However, all the three treated samples are well preserved after the
6 salt crystallization cycles. After 9 salt crystallization cycles, the surface of both red and
gray stone samples have the slightly damage in P3-treated red-stone (Fig. 5a, the last one),
and the P-treated stone begins to be damaged. But P2-treated stone is still well preserved
even after the continuing 9 salt crystallization cycles.
a)
b)
c)
d)
Fig. 5: The surface appearance of stone samples after 9 salt crystallization cycles (red-a
and gray -b) and 50 freeze-thaw cycles (red-c and gray-d).
The weight loss percents of samples after 9 salt crystallization cycles are listed in Fig. 3.
Compared with the big weight loss of the reference stones (60.94%), P2-treated stones
provide the best resistance to salt crystallization (the weight loss is only 0.07%), and P3treated samples has the poorest effect (the weight loss is 41.53%). On the other hand, all the
gray stones show the similar resistance to salt crystallization (20.23% for P1, 23.88% for P2
and 19.67% for P3, respectively), which is a little better than the untreated-gray-stone
(24.66%; Fig. 5b). While, after 50 freeze-thaw cycles, only some matrix powder in water
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
and some cracks happened in the surface of untreated stone sample with a higher weight
loss percent (0.62%), while the other treated stone samples keep integrity with lower
weight loss percents (0.13-0.31%) shown in Fig. 3 which indicate a good resistance to
freeze-thaw.
4. Conclusion
Three well-designed POSS-based nanomaterials are prepared for the protection of historic
stones, their properties and protective performance onto two stone specimens are evaluated.
The protective efficiency demonstrates that all the colour variation of the treated stones is
within acceptable limits (△E≤5). P2-treated surface provide the biggest water-resistant
property (WCA=138.9-128.7). After treated by three nanomaterials, the middle pore size
distribution become narrow and the pore size at 200-900 μm has never been changed. The
protective behaviour indicates a good resistance to anti-salt and anti-freeze/thaw after 9 salt
crystallization cycles and 50 freeze-thaw cycles. Therefore, P1 and P2 are able to be
suggested as protective materials to the historical stones.
Acknowledgment
This work has been financially supported by the National Basic Research Program of China
(973 Program, No.2012CB720904), the National Natural Science Foundation of China
(NSFC Grants 51373133, 51573145), and the International Cooperation Project of Shaanxi
Province (No.2014KW11). The authors also wish to express their gratitude for the MOE
Key Laboratory for Non-equilibrium Condensed Matter and Quantum Engineering of Xi’an
Jiaotong University.
References
Baglioni, P., Carretti, E., and Chelazzi. D., 2015, Nanomaterials in art conservation, Nature
Nanotechnol, 10(4), 287-90.
Son, S., Won, J., Kim, J.-J., Jang, Y. D., Kang, Y. S., and Kim, S. D., Son, S., 2009,
Organic-inorganic hybrid compounds containing polyhedral oligomeric
silsesquioxane for conservation of stone heritage, ACS Appl Mater Interfaces,
1(2), 393-401.
Zhang, H., Liu, Q., Liu,T., Zhang, B., 2013, The preservation damage of hydrophobic
polymer coating materials in conservation of stone relics, Progress in Organic
Coatings, 76(7-8), 1127-1134.
Licchelli, M., Malagodi, M., Weththimuni, M. L., Zanchi, C., 2013, Water-repellent
properties of fluoroelastomers on a very porous stone: Effect of the application
procedure, Progress in Organic Coatings, 76(2-3), 495-503.
Cappelletti, G., Fermo, P., and Camiloni, M., 2015, Smart hybrid coatings for natural
stones conservation, Progress in Organic Coatings, 78, 511-516.
Verganelaki, A., Kapridaki, C., and Maravelaki-Kalaitzaki, P., 2015, Modified
tetraethoxysilane with nanocalcium oxalate in one-pot synthesis for protection of
building materials, Industrial & Engineering Chemistry Research, 54(29), 71957206.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Xu, F., et al., Xu, F., Wang, C., Li, D., Wang, M., Xu, F., Deng, X., 2015, Preparation of
modified epoxy–SiO2 hybrid materials and their application in the stone
protection, Progress in Organic Coatings, 81, 58-65.
Luo, Y., Xiao, L., and Zhang, X., 2015, Characterization of TEOS/PDMS/HA
nanocomposites for application as consolidant/hydrophobic products on
sandstones, Journal of Cultural Heritage, 16(4), 470-478.
Baglioni, P., Chelazzi, D., Giorgi, R., and Poggi, G., 2013, Colloid and materials science
for the conservation of cultural heritage: cleaning, consolidation, and
deacidification, Langmuir, 29(17), 5110-5122.
Salazar-Hernández, C., , María J. P. A., Patricia S., and Jorge C., 2010, TEOS-colloidal
silica-PDMS-OH hybrid formulation used for stone consolidation, Applied
Organometallic Chemistry, DOI 10.1002/aoc.1646
Kuo, S.-W., and Chang, F.-C., 2011, POSS related polymer nanocomposites, Progress in
Polymer Science, 36(12), 1649-1696.
Tada, Y., Yoshida, H., Ishida, Y., T., Hirai, Bosworth, J. K., Dobisz, E., Ruiz, R.,
Takenaka, M., Hayakawa, T., and Hasegawa, H., 2012, Directed self-assembly of
POSS containing block copolymer on lithographically defined chemical template
with morphology control by solvent vapour, Macromolecules, 45(1), 292-304.
Kota, A.K., Kwon, G., Choi, W., Mabry, J. M., and Tuteja, A., 2012, Hygro-responsive
membranes for effective oil-water separation, Nat Commun, 3, 1025.
Yang, S., Pan, A., and He, L., 2014, POSS end-capped diblock copolymers: synthesis,
micelle self-assembly and properties, J Colloid Interface Sci, 425, 5-11.
Yang, S., Pan, A., and He, L., 2015, Organic/inorganic hybrids by linear PDMS and caged
MA-POSS for coating, Materials Chemistry and Physics, 153, 396-404.
Pan, A., Yang, S., and He, L., 2015, POSS-tethered fluorinated diblock copolymers with
linear- and star-shaped topologies: synthesis, self-assembled films and
hydrophobic applications, RSC Adv., 5(68), 55048-55058.
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914
DIFFERENTIAL EFFECTS OF TREATMENTS ON THE
DYNAMICS OF BIOLOGICAL RECOLONISATION OF
TRAVERTINE: CASE STUDY OF THE TIBER’S EMBANKMENTS
(ROME, ITALY)
S. Pascucci1, F. Bartoli1, A. Casanova Municchia1 and G. Caneva1*
Abstract
Monuments exposed to the environment are subject to numerous causes of degradation,
including the action of biological organisms forming patinas and crusts of various colour
and different aggressiveness. However, these patinas can be used in contemporary art for
the creation of drawings, as in William Kentridge’s project, along the embankment of the
Tiber River, illustrating the “Triumphs and Laments” of Rome history. More than eighty
figures will be created through selective cleaning of the black biological patina on
travertine, which is much used in Rome but little studied in biocide tests. The aim of this
study is to understand which chemical treatments could delay the biological growth in the
cleaned area, extending the lifetime of the images. Three commercial biocides
(Algophase®, Biotin R®, Preventol R80®) and two water-repellents (Hydrophase superfici®,
Silo 111®) were chosen and tested in situ (30 tests areas, with three repletion) using
different concentrations and mixtures, in accord with the safety of users and environment.
In order to limit the re-colonization after treatments, colour measurements and portable
optical microscope were conducted both on the bare surface of the stone (the control test)
and on the stone after chemical treatments.The results show that each product has different
biocidal efficacy and a different colorimetric response. The preventive treatment of
Preventol R80® with subsequent application of biocides in mixture had the best results in
preventing re-colonisation. The use of water repellents alone was revealed to be ineffective
in preventing biological recolonization and also determined colorimetric alterations in
terms of brightness.The experimental data has provided an improved understanding of the
effects of chemical treatments on travertine and of the phenomena of biological
recolonization dynamics.
Keywords: biocide, cyanobacteria, biodeterioration, travertine, water repellent
1. Introduction
Outdoor stone monuments are subject to many forms of alteration and degradation, among
which is the biodeterioration that takes place when biological organisms forming patinas
and crusts varying in colour and different aggressiveness (Tomaselli and Pietrini, 2008;
Caneva et al., 2008). These biological patinas have recently been used in contemporary art
(Bio-art) as a basis for the creation of drawing and figures. During the late 90s some artists
1
S. Pascucci, F. Bartoli, A. Casanova Municchia and G. Caneva*
Roma Tre University, Science Department, Rome, Italy
giulia.caneva@uniroma3.it
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
became increasingly interested in the use of the tools of modern biology. There are several
example of Bio-artist, such as Diego Scroppo with his project involving the bioluminescent
fungus Panellus stipticus, Jun Takita with many different bioluminescence project, or the
bio-art created through bacteria design at the American Microbiology Society.
An interesting case study is represented by the embankment of the Tiber River (Rome),
where the diffuse blackening of the surface is due by a biological colonization, and not to
chemical cause (Bellinzoni et al., 2003; Kumbaric et al., 2012). In 2005 this biological
patina present on the embankment was used in the creation of twelve figure representing
Roman wolves. These figures, of about 8 meters high, were created by applying a stencil
onto the surface and subsequently removing the biological patina through a pressure washer
and sandblasting processes, forming the final figure in negative (see Fig. 1a).
Unfortunately, three years later the figures had been obscured by biological re-colonization
(see Fig. 1b).
a)
b)
Fig. 1: a) The figure of a wolf on the Tiber embankment (2005);
b) The same figure three years later.
In April 2016 the artist William Kentridge together with TEVERETERNO foundation will
realise a project for the city of Rome entitled “Triumphs and Laments”, a procession of
eighty figures along the embankment of the Tiber River, between Ponte Sisto and Ponte
Mazzini, using the same technique as the wolves. Based on previous experience, our
research project is aimed to make long lasting in time this contemporary frieze by choosing
the most suitable methodologies for preventing or slowing down the biological growth in
the areas subjected to removal of the biological patina. There is an extensive literature on
the effectiveness of water-repellents and biocides to prevent the re-colonization on the
stone, tested overall in laboratory conditions (Nugari et al., 1993; Tiano et al., 1994; Urzì
and De Leo, 2007; Bartolini and Ricci, 2009; Moreau et al., 2008; Delgado and Charola,
2011; Pinna et al., 2012). However, little has been reported on outdoor conditions,
particularly with regard to travertine substrata.
Considering such lack in the literature, the aim of this study is to understand which
chemical treatments could delay the biological growth in the cleaned area, extending the
lifetime of the images, and the re-colonization dynamic process in different condition test.
2. Materials and Methods
2.1. Case study
The Tiber embankments are composed of load bearing walls, which are extremely deep and
about 10 meters high, covered with travertine slabs of varying sizes. The travertine stone is
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a sedimentary and limestone rock characterised by a low porosity but with a high number of
macro-pores, which can increase the water content. Field tests were carried out in the
stretch of the Margherita bridges.
The porosity combined with the inclination of the wall, along with input water, influence
the amount of water contained in the substrate, contributing significantly to the rate of
biological growth on the embankments. The blackish patina found on embankments walls is
composed mainly of cyanobacteria and green algae species. In detail, Chroococcus
lithophilus, Myxosarcina spectabilis, Tolypothrix byssoidea and Synechocystis pevalekii,
occur frequently, while rarely Synechococcus aeruginosus, Muriella terrestris,
Chlorococcum sp. and Scytonema julianum. Nostoc punctiforme and Desmococcus vulgaris
appear rarely (Bellinzoni et al. 2003, Kumbaric et al. 2012). The maximum coverage of
these patinas was found in the northern areas with no tree cover.
2.2. Tests with biocides and water repellents
The present study involves a series of tests using of mixtures of three chemical biocides and
two water-repellents in various concentrations (Algophase® + Hydrophase superfici®,
Biotin R® + Silo 111® and with pre-treatments by Preventol R80®), and the application of
water repellents alone. These biocides were selected according to the low toxicity and the
safety for the users and environment (Caneva et al., 2008). The mixtures of biocides with
water repellents were selected according to their effectiveness against the biological recolonization on stone in outdoor conditions (Charola et al., 2007; Urzì and De Leo, 2007;
Pinna et al., 2012) (Tab. 1).
Tab. 1: Features of products applied on test area.
Biocides:
Product
Active principle
Concentration
Preventol R80®
alkyl-dimethyl-benzylamine chloride
4% in distilled water
Algophase®
2,3,5,6-tetrachloro-4-methylsulfonylpyridine
5% and 3% of
Algophase directly in
Hydrophase Superfici
OIT and Carbamate
4% and 3% of Biotin
R directly in silo 111
Active principle
Concentration
Methylethoxy polysiloxane
10% in white spirit
alkyl alcoxy silane
40% in isopropyl
alcohol
Biotin R®
Water repellents:
Product
Silo 111®
Hydrophase
Superfici®
One biocide (Preventol R80® (4% v/v)) was applied alone, while the other two biocides,
Algophase® (5% v/v and 3% v/v) and Biotin R® (4% v/v and 3% v/v), were applied in
different concentration in mixtures with water repellents, respectively in Hydrophase
Superfici® (ready to use 40%) and Silo 111® (ready to use 10%).
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In order to choose the best products, the appropriate mixture and the right concentration, 10
tests were performed in three series of repetitions on the embankments walls. For 4 tests
(T1, T2, T3 and T4) a preventive treatment with Preventol R80 ® was applied, followed by
the application of a biocides and water repellents mixture, for another 4 tests (T5, T6, T7
and T8) we applied the biocides and water repellents mixtures only and finally, 2 further
tests (T9 and T10) looked at water repellents alone. All products were applied with a
paintbrush until the entire surface was thoroughly saturated with the solutions.
2.3. Application of treatments
Close to Ponte Regina Margherita, 8 areas of cleaning of overall size of 64×64 cm were
prepared. Each area consisted of a frame enclosing a circular or quadrangular cleaning test
area, and the cleaning tests were carried out with a gently pressure washer (Fig. 2). For the
purpose of the experiment, the cleaning tests areas were divided into 30 individual test
areas (10.5×4 cm each) onto which the products were applied, and 4 areas were left
untreated as a control.
a)
b)
Fig. 2: Two examples of quadrangular (B) or circular (A) cleaning test area.
At the beginning: 3 tests areas were treated with Preventol R80 ® and Algophase® 5% v/v
plus Hydrophase superfici® (T1); 3 tests areas were treated with Preventol R80 ® and
Algophase® 3% v/v plus Hydrophase superfici® (T2); 3 tests areas were treated with
Preventol R80® and Biotin R® 4% v/v plus Silo 111® (T3); 3 tests areas were treated with
Preventol R80® and Biotin R® 3% v/v plus Silo 111® (T4); 3 tests areas were treated with
Algophase® 5% v/v plus Hydrophase superfici® (T5); 3 tests areas were treated with
Algophase® 3% v/v plus Hydrophase superfici ® (T6); 3 tests areas were treated with Biotin
R® 4% v/v plus Silo 11®1 (T7); 3 tests areas were treated with Biotin R ® 3% v/v plus Silo
111® (T8); 3 tests areas were treated Silo 111® ready to use 10% (T9); 3 tests areas were
treated Hydrophase superfici® ready to use 40% (T10); and 4 were left untreated as control
areas (C).
2.4. Field analysis
The treated areas test and the untreated control areas were analysed using microphotos and
colour measurements. The first measurements were taken one month after the application of
the treatments, in April 2014, after which measurements were taken once every two months
until February 2015. Re-colonization was evaluated using a photomicrograph coverage
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analysis using through Image J software, and with a colorimetric analysis performed in situ
during one year of observations comparing treated and untreated areas.
2.4.1. Stereomicroscope observations
In order to detect on site the biological re-colonization, a selection of treated and untreated
areas selected were observed with a portable stereomicroscope (PCE-MM200 Microscope)
using ×20 and ×60 magnifications. Micro-photos were taken at three separate points for
each test due to the heterogeneity of travertine. The images obtained were then processed
with ImageJ 3.0 software (Collins, 2007). This software allows for measuring the
abundance of pixels pertaining to each colour class, quantifying the biological growth on
the stone (as a percentage).
2.4.2. Colour measurements
Colour measurements were performed using a by Konica Chroma Meter CR 200 in
accordance with the procedure described in European Standard EN15886:2010. Ten
measurements were carried out for each test areas; results obtained on the test area with the
same treatment have been averaged to obtain one single data point. Colour variation values
are given using the CIE-L*a*b* system (Uni EN15886:2010) and colour coordinates L*, a*
and b* determine the colour location in colour space: L* indicates lightness; a* (redness–
greenness), and b* (yellowness–blueness). The values of L*, a* and b* were measured in
selected treated areas, and in 4 untreated control tests. Total color variation (ΔE) was
calculated from three colour parameters with the formula:
ΔE= [(ΔL*)2 + (Δa*)2 + (Δb*)2] 1/2
(Eq. 1)
In this study, colour differences were measured between the data point on each treated tests
areas and on the untreated areas “control test” areas obtained in April 2014, date of the first
measurements (i.e. L* = L* treated) − ΔL*(untreated)).
3. Results and discussions
For the tests subjected to pre-treatment with the Preventol R80® (T1, T2, T3 and T4),
values of ΔE (see Fig. 3) show only minor colour changes (ΔE ~ 4). In detail, a year after
the application of the products, the treatments T1 and T2 did not significantly modify the
colour of the surface, with a ΔE value of ~ 2 and therefore not detectable by the naked eye.
The other 4 treatments (T5, T6, T7 and T8) with the sole application of biocides in mixture
with water repellents caused significant colour variations with a value of ΔE of ~ 12. The
variations appear unvaried in time. On the other hand, a very strong variation was observed
after the application with water repellents alone (T9, T10) characterised by a high ΔE value
of ~ 18. The variations of the parameters a and b are all close to zero, therefore the
variation seems to be related mainly to a change in brightness (L*) than to a change in the
colour (a* and b*) of the surface. In detail, after one month from the application of all
treatments the variation of brightness values (ΔL*) shows a surface characterized by a
general darkening (see Fig. 4). In the following months, tests with pre-treatment by
Preventol R80® cause a surface whitening up to a value of ΔL ~ 3 (February 2015, in
test 3). In correspondence to these tests areas, the on-site observation and the biological
coverage analysis by ImageJ software underline a reduction in the biological coverage,
especially in test 3 (Preventol R80® and Biotin R® 4% v/v plus Silo 111®). In 4 tests
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
without Preventol R80® the surface became darker over time reaching values of ΔL ~ -11,
(February 2015). A re-colonisation of the surface could be the main factor responsible for
the colour changes. Image analysis obtained in these tests confirms that, in the course of
one year, there was an increase in colonization of almost 5%. In tests with the two waterrepellents alone the colour of the surface changed markedly during the monitoring period,
showing a clear decrease of ΔL with value of ~ -18. It is interesting to note that the values
of re-colonization in these tests are higher compared to the untreated area test. In
accordance with previous study (Charola et al., 2007) Preventol® shows to be more
effective regarding the rate of re-colonization.
Our findings have shown that biological growth causes also colour changes in the untreated
areas due to the re-colonization. The data obtained over time for the control test show a
variation for ΔL of ~ -4, detectable by the naked eye. The biological coverage analysis
emphasizes an increase in the re-colonization of almost 8%.
Fig. 3: Colour differences over time between treated and untreated area. The differences
are reported as ΔE values.
Fig. 4: Colour differences over time between treated and untreated area. The differences
are reported as ΔL* values.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
4. Conclusion
Our results showed that tests with the preventive treatment with Preventol R80 ® followed
by application of a mixture of biocides and water repellents were effective in preventing or
delaying the biological growth. The colour measurements comparing treated tests area and
the untreated control tests showed lower colour changes in the four tests characterised by
the pre-treatment with Preventol R80®. In detail, test 3 (Preventol R80® and Biotin R® 4%
v/v plus Silo 111®) gave the best results for the prevention of re-colonization, with a
smaller biological coverage. This study provides an important contribution on effectiveness
of biocide water-repellent mixtures for outdoor stone monuments, especially with regard to
travertine stone, and in evaluating the dynamic of re-colonization processes. Future studies
should therefore include follow-up work designed to continue performing tests over time
and to identify the kind of re-colonization present on the stone.
References
Bartolini, M., Pietrini, A.M., Ricci, S., 2007, Valutazione dell’efficacia di alcuni nuovi
biocidi per il trattamento di microflora foto sintetica e di briofite su materiali
lapidei. Bollettino ICR, 14, 101-111.
Bellinzoni, A.M., Caneva, G., Ricci, S., 2003, Ecological trends in travertine colonisation
by pioneer algae and plant communities, International Biodeterioration &
Biodegradation, 51, 203-210.
Caneva, G., Nugari, M.P., Salvadori, O. (Eds.), Plant Biology for Cultural Heritage,
Biodeterioration and Conservation, The Getty Conservation Institute, Los Angeles, 2008.
Charola, A.E., Anjos, M.V., Rodrigues, J.D., Barreiro, A., 2007, Developing a Maintenance
Plan for the Stone Sculptures and Decorative Elements in the Gardens of the
National Palace of Queluz, Portugal”. Restoration of Buildings and Monuments,
13 (6), 377-387.
Collins, T. J., 2007, ImageJ for microscopy, BioTechniques, 43, 25-30.
Delgado, R., Charola, A.E., 2011, Conservation approach diversity to address the
decorative elements in the Gardens of the National Palace of Queluz, Lisbon,
Portugal. In: “Conservation of stone in Parks, Gardens and Cemeteries,
International Conference”, Paris pp. 22-24.
Kumbaric, A., Ceschin, S., Zuccarello, V., Caneva, G., 2012, Main ecological parameters
affecting the colonization of higher plants in the biodeterioration of stone
embankments of Lungotevere (Rome), International Biodeterioration &
Biodegradation, 72, 31-41.
Moreau, C, Vergès-Belmin, V, Leroux, L, Orial, G, Fronteau, G, Barbin, V., 2008, Waterrepellent and biocide treatments: Assessment of the potential combinations. J Cult
Herit. 9(4), 394-400.
Nugari, M.P., Pallecchi, P., Pinna, D., 1993, Methodological evaluation of biocidal
interference with stone materials –preliminary laboratory test. In: “Congress on
Conservation of Stones and Other Materials”. Proceedings of International
UNESCO/RILEM, Paris E & FN Spon, London, pp. 295-302.
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Pinna, D., Salvadori, B., Galeotti, M., 2012, Monitoring the performance of innovative and
traditional biocides mixed with consolidants and water-repellents for the
prevention of biological growth on stone. Science of the Total Environment, 423,
132-141.
Tiano, P., Accolla, P., Tomaselli, L., 1994, Biocidal treatments on algal biocoenosis control
of lasting activity, Science and Technology for Cultural Heritage, 3, 89-94.
Tomaselli, L., Pietrini, A.M., 2008, In: Plant biology for cultural heritage: biodeterioration
and conservation. Caneva G., Nugari M.P., Salvadori O., (eds.), The Getty
Conservation Institute, Los Ange- les. 71-77.
UNI-EN-15886:2010. Misura del colore delle superfici ICS: 97.195. Conservazione dei
Beni Culturali, 2010.
Urzì, C., De Leo, F., 2007, Evaluation of the efficiency of water-repellent and biocide
compounds against microbial colonization of mortars. International
Biodeterioration & Biodegradation, 60, 25-34.
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STATISTICAL ANALYSIS AT THE SERVICE OF
CONSERVATION PRACTICE: DOE FOR THE OPTIMISATION OF
STONE CONSOLIDATION PROCEDURES
Y. Praticò1*, F. Caruso1, T. Wangler1 and R.J. Flatt1
Abstract
Ethyl silicates are extensively used in the field of conservation to treat various types of
stones. It is common belief that the different conditions of temperature, humidity and
techniques of application influence the resulting consolidation. In this study, a statistical
Design of Experiments (DOE), that allows the exploration of the simultaneous effect of
different factors in a limited number of experiments, is used to study this. It is applied to
analyse the possible crossed effect of temperature, relative humidity, application procedure,
concentration and pre-treatment with a swelling inhibitor on the consolidation of a swelling
clay-bearing sandstone. The purpose is to obtain an optimization of the consolidation
treatment under conditions that are both reliable in the laboratory and on site. The results
obtained with our approach show that the consolidation is not affected by temperature,
humidity or the application method. On the other hand, the curing time is strongly
influenced by the above-mentioned factors. In particular, it is shown that higher initial
moisture content is beneficial to the consolidation treatment as it significantly shortens the
curing time.
Keywords: swelling clay-bearing sandstones, ethyl silicate, design of experiment (DoE),
swelling inhibitor, consolidation
1. Introduction
The use of ethyl silicates as consolidants for the conservation of various types of stones is
well established since the early 20th century (Wheeler, 2005a). The effectiveness and
durability of such consolidation treatments is thought to be affected by factors such as
temperature, humidity and technique of application, as well as by the chemistry of the
product (Zha and Roggendorf, 1991). Most of these aspects are difficult to control on-site
and, at the same time, their combined effect on the treatment cannot be characterised
through standard laboratory tests, performed at fixed conditions.
As an example, some studies have explored the role of different application procedures on
the effectiveness of consolidation treatments (Ferreira Pinto and Delgado Rodrigues, 2012;
Franzoni et al., 2014; Moropoulou et al., 2003; Pinto and Rodrigues, 2008), yet without
taking into consideration the potential concurrent influence of the environmental
1
Y. Praticò*, F. Caruso, T. Wangler and R.J. Flatt
Physical Chemistry of Building Materials, Institute for Building Materials, ETH Zürich,
Stefano-Franscini-Platz 3, Zürich 8093, Switzerland
flattr@ethz.ch
*corresponding author
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conditions. As a consequence, the information obtained through laboratory studies is not
easily transferrable to application in the field.
From a more general point of view, the analysis of processes influenced simultaneously by
many different parameters – as in the case of the consolidation with ethyl silicates –
represents a challenge in many fields of science. The effort to isolate the effect of each
variable makes these kinds of studies very time consuming, as the number of the
experiments required increases exponentially with the number of factors involved. For this
reason, systematic studies on the coupled effect of several parameters are rather uncommon
in the field of conservation, where the time and resources available for research are often
very limited.
The Design of Experiment (DOE) is a statistical method that allows for an efficient analysis
of multiple factors, requiring only a limited number of experiments (Hoboken, 2008;
Weissman and Anderson, 2015).
In this work, we use this methodology to optimize the consolidation strategy for a specific
swelling clay-bearing sandstone, which was selected for its homogeneity and
representativity of the Swiss molasses that we are studying for the restoration of the
Cathedral of Lausanne. Based on preliminary experiments, discussion with conservators
and literature review, we decided to examine the combined effects of temperature,
humidity, application procedure, concentration and pre-treatment with a swelling inhibitor
(Caruso et al., 2012). The effect of the swelling inhibitor is studied only in relation to the
initial consolidation. In further work, its influence on the durability of the treatment
subjected to wetting/drying cycles in combination with the other factors will be explored.
The efficiency of the treatment is assessed through the measurement of the final increase in
dynamic elastic modulus (so called “total consolidation”) and the time necessary to reach
this final value (“curing time”).
A sketch of the considered factors and responses is shown in Fig. 1:
Fig. 1: Scheme of factors and responses in a consolidation treatment
with ethyl silicate.
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Dynamic elastic modulus measurements have the advantage of being non-destructive and
therefore very useful for testing property evolution over time. While more extensive
characterization would provide additional insights into differences of consolidation, the
measured responses are sufficient to compare the efficiency of the application method as
well as the other factors considered.
2. Experimental
2.1. Materials
The stone used is a Molasse Blue from Villarlod (Molasse de Villarlod.ch SA, Farvagny,
FR, Switzerland). Stone samples were cut in cylinders of 5 cm of diameter and 5 cm of
length from three different blocks, and randomized among the runs. The samples were cut
so as to keep the bedding direction perpendicular to the cylinder axis. The consolidant used
is SILRES® BS OH 100 (Wacker Chemie AG, Burghausen, Germany). This is a solventfree, ready-to-use product of tetraethyl silicates (40-50%). Absolute ethyl alcohol (≥
99.8%) purchased from Sigma Aldrich (Sigma-Aldrich Chemie GmbH, Steinheim,
Germany) was used for diluting the consolidant. The swelling inhibitor was 1,4diaminobutane dihydrochloride (≥ 99.0%), also purchased from Sigma Aldrich.
2.2. Methods
2.2.1. Design of Experiment (DOE)
The DOE was run on JMP 11.0 (SAS Institute Inc., Cary, NC, USA). The type of design
employed was a fractional factorial with 2 replicates, and 5 two-level factors for a total
number of 48 runs. The factors and their levels are shown in Tab. 1.
Tab. 1: Factors and levels chosen for the DOE study. Factors marked with a single asterisk
(*) are continuous; factors marked with two asterisks (**) are categorical.
Factor
Low level
High level
Temperature *
10°C
30°C
Relative humidity *
50%
85%
Dilution *
Pure
1:3 (v/v) in ethanol
Wet-on-wet
Sorptivity
No
Yes
Application method **
Pre-treatment with swelling inhibitor**
The levels of temperature and relative humidity (RH) were chosen to maximize the
difference between the levels, yet remaining in the range of plausible conditions for an onsite consolidation campaign (Wheeler, 2005b). Climate analysis was performed on local
weather data (provided by IDAWEB Meteo Suisse) and by means of on-site measurements
in the Swiss region.
The analysed responses were total consolidation and curing time.The curing time was
estimated in terms of change in dynamic Young’s modulus (Edyn) computed from ultrasonic
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
pulse velocity (UPV) measurements. The curing time was defined as the necessary time for
the ∆Edyn to become lower than the uncertainty of the measurement (± 10%).
The total consolidation was expressed in the form of final percentage increase of Edyn. Since
the dynamic elastic modulus depends on the RH at which the UPV measurment is
performed, the initial and final Edyn were recorded at the same conditions for every sample
to obtain comparable results. More in detail, the initial Edyn was measured on oven-dried,
untreated stones; the final Edyn was measured on fully consolidated samples, after
equilibration at 20°C and 50% RH.
The UPV was measured with a Pundit Lab by Proceq SA (Schwarzenbach, Switzerland)
with standard 54 kHz transducers mounted on a custom-modified optical rail by GeotronElektronik (Pirna, Germany). The customization of the device was developed to ensure a
constant pressure between the transducers and the samples, by means of an air cylinder
actuated by compressed air at 4 bars. Effective contact between the transducers and the
specimens is achieved by means of a dry couplant of 2 mm thickness (Aqualene dry
couplant, Olympus Scientific Solutions Americas Inc., MA, USA). A Mettler-Toledo
PM4000 technical balance (Mettler-Toledo GmbH, Greifensee, Switzerland) was used to
record the mass changes of the samples.
2.2.2. Pre-treatment with swelling inhibitor
Prior to the pre-treatment, all the samples were oven-dried for 72 hours at 105°C and then
equilibrated at 20°C and 50% RH for one week. The samples were then immersed in a 0.3
mol/L aqueous solution of 1,4-diaminobutane dihydrochloride for 20 hours.
2.2.3. Consolidant application
All samples were pre-equilibrated at the target curing conditions before the consolidation
treatment. Stable climatic conditions (maximum oscillations: ± 2°C for the temperature and
± 8% for the RH) were obtained in a Vötsch VC 4060 (Vötsch Industrietechnik GmbH,
Balingen-Frommern, Germany) and in a Feutron KPK600 (Feutron Klimasimulation
GmbH, Langenwetzendorf, Germany) climatic chambers.
Two different methods of application were used during this study: an application by
sorptivity, and a cyclic “wet-on-wet” application. Both methods reproduce the effect of a
consolidation treatment applied only on one side of a stone surface.
2.2.3.1.
Sorptivity
The cylindrical samples were hung below a technical balance to monitor the mass increase,
with one of the faces in contact with the consolidant. All the other surfaces of the sample
were sealed with Parafilm to avoid evaporation. The treatment was stopped when the
samples reached saturation.
2.2.3.2.
Wet-on-wet applications
A cyclic wet-on-wet application was used to simulate on-site practice, such as the cyclic
application with a brush. To control the quantity applied for each application, a pipette was
used to spread the consolidant over the surface. The mass of consolidant absorbed at each
application was measured with a technical balance. The procedure (quantity per application,
as well as frequency of the applications) was designed according to the recommendations of
the producers and case studies reports (Commission technique de la cathédrale de
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Lausanne, 2012).The penetration of the consolidant (assessed by visual observation and
mass uptake measurements) was always at least 4 cm. This depth of treatment would allow
for the consolidation of severely damaged stones (swelling clay-bearing stones typically
show scaling at up to a depth of 3 cm (Furlan and Girardet, 1996).
The application procedure was as follows: two cycles of applications were performed with
an interval of 3 hours. Each cycle consisted of 3 applications of 0.4 g of consolidant every 5
minutes. Every 3 applications, an interval of 15 minutes was taken.
3. Results and discussion
Values of curing time across different combinations of factors varied from 7 to 98 days,
whereas values of total consolidation varied from 0% to over 150%. The DOE analysis of
the influence of the factors on total consolidation and curing time is presented in Fig. 2.
Fig. 2: t-Ratio plot 5 of the factors influence on the total consolidation (left) and on curing
time (right). The t-Ratio is the ratio of the parameter estimated to its standard error and
quantifies the influence of a factor. The effect of a factor is considered significant with a
95% confidence when the t-Ratio is higher than the critical value at 0.05 significance level
(horizontal dashed line in Fig. 2). Positive numbers indicate a proportional influence of the
factor on the response (i.e. higher concentration leads to a higher total consolidation),
whereas negative numbers indicate a negatively proportional effect (i.e. high relative
humidity decreases the curing time).
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Fig. 2 (left) shows that the total consolidation is not affected by differences in the
environmental condition or in the application procedure. On the contrary, the concentration
of the consolidant seems to play a substantial role. In fact, despite what has been suggested
in the literature (Scherer and Wheeler, 2009), under the conditions of our experiments, the
dilution of the product leads to a dramatic decrease in the effectiveness of the consolidation
(in some cases not showing any significant Edyn increase), and – at the same time – does not
show any positive effect on the penetration of the product (sorptivity data not shown).
The pre-treatment with the swelling inhibitor also causes an increase in the elastic modulus
of the stone. This effect is known for this type of stone (Gonzalez and Scherer, 2004), and
has been suggested to result from the ability of the swelling inhibitor to prevent the
separation of the clay layers, but does not appear to be related to the consolidation process.
In fact, the final positive effect recorded is equivalent to the initial Edyn increase obtained on
the unconsolidated stone.
On the other hand, most of the above mentioned factors show a significant effect on the
curing time (Fig. 2, right). In particular, temperature and humidity have the strongest
influence, drastically decreasing the time necessary for the curing when set on higher
values. This is shown in Fig. 3, where the curves of samples treated with the same
procedure but cured at different temperature and RH are compared.
Fig. 3: Curing of samples consolidated with pure Wacker OH 100 by wet-on-wet
applications, not pre-treated with swelling inhibitor. The curves are normalized to the
highest total consolidation reached.
In this specific case, the samples treated at T=30°C and RH=85% showed a curing time as
low as 14 days, whereas samples treated at T=10°C and RH=50% needed up to 85 days to
reach a stable elastic modulus. With samples pre-treated with swelling inhibitor, this effect
becomes even more evident, showing values of curing time of 7 days for samples cured at
T=30°C and RH=85%, and 98 days for samples cured at T=10°C and RH=50%.
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This seems to indicate that the consolidation depends on both the initial moisture content
during a first phase and on the vapour pressure of water in the surrounding environment in
a second phase, as suggested by the evolution of modulus in Fig. 3.
This can be explained assuming that the consolidation kinetics of the sample in the second
phase is limited by the vapour diffusion and progressive uptake of water by the unreacted
consolidant in the porous network. This must also be at stake in presence of the swelling
inhibitor. However, the reason why this compound would accelerate the consolidation at
high temperature and slow it down a lower temperature is not obvious. Various processes,
including a basic catalysis of the condensation may be involved, but we presently cannot
advance a solid explanation for it.
4. Conclusions
This paper presents a study of the factors affecting the success of a stone consolidation
treatment with ethyl silicates. The efficiency of the treatment on a clay-bearing sandstone
was assessed by varying temperature, relative humidity, application procedure,
concentration of the consolidant, and pre-treatment with a swelling inhibitor and by
measuring the total consolidation and the time necessary to reach this final value.
One of the original aspects of this work was the use of the Design of Experiment for
exploring the above factors and the way they dictate the effectiveness of the consolidation
process. The results show that this kind of approach enables the study of such a multivariable problem and for the extrapolation, from a relatively small number of experiments,
of general principles useful for on-site practice.
The total consolidation (increase in dynamic modulus) only depends on the product used
and remains the same regardless of the climatic conditions or the chosen procedure of
application. This also implies that experimental results obtained through a controlled
sorptivity procedure can be transferred to on-site “wet-on-wet” application.
Swelling inhibitors slightly increase the total consolidation, but in the same relative way
they increase the elastic modulus of the untreated stone. This suggests that they do not
directly interact with the consolidation process. On the other hand, a pre-treatment with
swelling inhibitors decreases the curing time.
Finally, temperature and relative humidity strongly influence the curing time. In particular,
curing time decreases drastically when the humidity “available” in the stone increases. This
provides a completely new perspective with respect to what field experience claims about
the factors affecting consolidation. Indeed, most of these reports probably refer to a fixed
time period that can be expected to be shorter than what is needed to reach ultimate
consolidation under detrimental conditions. Certainly this is relevant to practitioners, but
not in terms of the monument being consolidated. We hope that this observation will
stimulate critical thoughts on this important subject.
Acknowledgements
The authors would like to thank Mr Fred Girardet (Rino S.A.R.L.) for very useful
discussions and Mr Christophe Amsler and Ms Olga Kirikova for their openness and
support in discussing conservation issues in relation to the Cathedral of Lausanne.
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References
Caruso, F., Wangler, T.P., Aguilar Sanchez, A.M., Richner, H., Melchior, J., Flatt, R.J.,
2012. Effect of swelling inhibitors and self restraint on the durability of ethylsilicates consolidants applied to clay-bearing stones, in: 12th International
Congress on the Deterioration and Conservation of Stone Columbia University.
New York.
Commission technique de la cathédrale de Lausanne, 2012. Déontologie de la pierre.
Stratégies d’intervention pour la cathédrale de Lausanne. Actes Colloq.
Pluridiscip. 14 15 Juin 2012 hors-série 1.
Ferreira Pinto, A.P., Delgado Rodrigues, J., 2012. Consolidation of carbonate stones:
Influence of treatment procedures on the strengthening action of consolidants. J.
Cult. Herit. 13, 154–166.
Franzoni, E., Graziani, G., Sassoni, E., Bacilieri, G., Griffa, M., Lura, P., 2014. Solventbased ethyl silicate for stone consolidation: influence of the application technique
on penetration depth, efficacy and pore occlusion. Mater. Struct. 1–13.
Furlan, V., Girardet, F., 1996. Pollution atmosphérique et dégradation de la molasse, in:
Matériaux de construction. Pierre. Pollution atmosphérique. Peinture murale.
Laboratoire de Conservation de la Pierre. Département des Matériaux., Lausanne.
Gonzalez, I.J., Scherer, G.W., 2004. Effect of swelling inhibitors on the swelling and stress
relaxation of clay bearing stones. Environ. Geol. 46, 364–377. Hoboken, N., 2008.
Design and Analysis of Experiments, 7 edition. ed. Wiley.
Moropoulou, A., Kouloumbi, N., Haralampopoulos, G., Konstanti, A., Michailidis, P.,
2003. Criteria and methodology for the evaluation of conservation interventions on
treated porous stone susceptible to salt decay. Prog. Org. Coat., Athens 2002 48,
259–270.
Pinto, A.P.F., Rodrigues, J.D., 2008. Stone consolidation: The role of treatment procedures.
J. Cult. Herit. 9, 38–53.
Scherer, G.W., Wheeler, G.S., 2009. Silicate Consolidants for Stone. Key Eng. Mater. 391,
1–25.
Weissman, S.A., Anderson, N.G., 2015. Design of Experiments (DoE) and Process
Optimization. A Review of Recent Publications. Org. Process Res. Dev. 19, 1605–
1Wheeler, G., 2005a. Historical overview, in: Alkoxysilanes and the
Consolidation of Stone. Getty Publications, pp. 1–11.
Wheeler, G., 2005b. Practice, in: Alkoxysilanes and the Consolidation of Stone. Getty
Publications, pp. 69–88.
Zha, J., Roggendorf, H., 1991. Sol–gel science, the physics and chemistry of sol–gel
processing, Ed. by C. J. Brinker and G. W. Scherer, Academic Press, Boston 1990,
xiv, 908 pp.,. Adv. Mater. 3, 522–522.
930
VACUUM-CIRCLING PROCESS:
A INNOVATIVE STONE CONSERVATION METHOD
E. Pummer1*
Abstract
The vacuum-circling process (VCP) has been developed to minimise and avoid
disadvantages associated with common surface treatments with silica acid ester (ESE).
Shallow treatments with ESE using the “run-over application”, “brushing application” and
“pad application” have been not able to achieve a profound penetration. The possible
outcomes are the shedding of a few millimetres’ thickness, and spalling, which irretrievably
destroys the original surface within a few years of treatment. The main problem of
consolidation by plunging is that non-accelerated ESE may be leaking or sinking after
treatment. Even objects with a highly damaged structure are often able to be treated with
ESE using VCP because of the possibility of deep penetration when common ESE
treatments fail. The method is also suitable for the consolidation of stone objects with
surfaces showing varied or reduced permeability. The use of various strengthening agents is
possible, and it is also possible to treat other materials, such as wood or concrete.
Contamination of the environment, adjacent areas and users are eliminated using the
process. Following restoration, intervals between treatments are increased due to the longlasting conservation effects achieved by VCP treatment. The method of vacuum-circling
has been successfully applied to a wide range of international monuments of various stone
types. The effectiveness has been proven and documented by scientific methods via
acknowledged institutes and also as part of promoted research projects by the EU and
Deutsche Bundesstiftung Umwelt.
Keywords: vacuum, strengthening, consolidation, stone conservation, demineralisation
1. Vacuum-Circling Process (VCP) application
VCP (European patent No. 1 295 859/Austrian patent No. E 366.232, patents owned by
Erich Pummer GmbH) offers a possibility for restoring monuments, stone sculptures,
façades and other freestanding and weathered objects. A key advantage of applying the
VCP is the high-level reliability observed due to the optimal penetration properties of the
various strengthening agents in porous stone or other materials. This is an existentially
important requirement, since a large number of listed monuments have suffered serious
consequential damage in the last few decades as a result of pure surface treatment. This
vacuum technology-based method is reliable and economic to apply in situ or in
workshops. There are no superfluous chemicals that could build up or leak out, making this
a user- and environment-friendly work method. With easy technical adaptations it is also
1
E. Pummer*
Atelier Erich Pummer GmbH, Austria
office@atelier-pummer.at
*corresponding author
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possible to use the treatment for demineralisation and drying. To create an airtight
environment, the object in question—there are no limits to the size or form of the objects—
is shrink-wrapped in solvent-resistant plastic film. A vacuum pump is used to draw the air
out from the plastic film bag and also from the stone object’s pore volume. Once a relative
vacuum has been achieved, a precise dosing system allows the injection of an appropriate
strengthening agent which immediately distributes itself evenly in the vacuum and deep
into the stone, even when the surface is predominantly covered with impenetrable coatings,
as investigations have shown. The whole process is completely odourless, without any
overspill.
The equipment is easily moveable and offers the possibility to conserve objects in any
position or situation, on buildings or freestanding (Fig. 1 and Fig. 2). The principle of VCP
is shown in Fig. 2.
Fig. 1: Mobile VCP equipment, vacuum pump (in the back of the van), balance tank
(middle), tank A&B combination (left; see Fig. 2 for further details).
Fig. 2: Principle of the vacuum circling process.
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2. Operation, utilisation and results by object examples
2.1. Demounted Madonna by Austrian sculptor Joseph Käßmann (1845)
2.1.1. Processing
The sculpture was situated on a façade in the 7th district of Vienna. It is sculptured in a very
porous calcareous Arenite with an original polychromic executed using an oil technique.
The sculpture was demounted and was transported to the restoration laboratory of the
University of Applied Art. The conservation and restoration of this statue are the subject of
a diploma thesis with the task of strengthening the inner structure of the Madonna, which is
covered by several layers of oil paint (2, see Paper for the 13 th International Congress on the
deterioration and Conservation of Stone 2016; M. Milchin et al. 2015). As a first step, the
whole statue was wrapped in polypropylene fleece material (Fig. 3). This material had the
function of protecting the surface of the statue but also to avoid leaking of the polyethylene
foil used to create the airtight environment. On the highest points of the statue, purging
valves were fixed with the foil. At the lowest position, inflow valves were mounted. A
manometer for controlling the negative pressure inside the foil was also connected (Fig. 3).
Fig. 3: VCP treatment of the 160-cm-high statue.
After evacuating the air, the inflow of the strengthened medium silica acid ester (ESE)
300E/accelerated began. The negative pressure inside the foil went up to 800 mb and lasted
for the whole process of 6 hours. When no more medium was absorbed by the stone the
degree of saturation was reached, controlled by measuring the backflow in the circular
flow. As a result, 61 kg ESE was absorbed, despite the fact that the surface of the stone was
covered by oil paint up to nearly 95 percent. The deep penetration took place through the
cracks and small defects in the coating and also through the uncoated base. At the end of
the treatment the excess medium was extracted by the lowest inflow valve. The surface was
not left with any oversaturation because the fleece had the function of blotting paper and
absorbed all surplus liquid. The reaction of the accelerated ESE usually requires a
temperature-dependent time of 4–6 weeks. Because of the prompt start of the reaction, the
ESE neither drained out nor sunk inside the stone.
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2.1.2. Results by drilling resistance
Drilling resistance profiles report the solidity in the different steps of depths. Figures 4 and
5 show examples for drilling resistance profiles. The analysis was done in steps of 1 mm;
blue curve – before strengthening, red curve – after strengthening. The results report the
successful VCP treatment with ESE 300E. The increase in solidity has been achieved
uniformly from the surface right into the depths.
Drilling depth, mm
Drilling 1
Drilling 2
Drilling resistance, s/mm
Time, s
Fig. 4: Profile 1 - Garment fold right, thigh height, covered by several layers of oil paint.
Drilling depth, mm
Drilling 1
Drilling 2
Drilling resistance, s/mm
Time, s
Fig. 5: Profile 2 - Garment fold right, elbow height, covered by several layers of oil paint.
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2.1.3. Principle of drilling resistance measurements
The following figures (Fig. 6 and Fig. 7) show the working principle of the device used for
measuring the drilling resistance prior and after the treatment by VCP.
Fig. 6: Principle drilling resistance.
Fig. 7: Device for measuring the drilling resistance device, developed by
Dr Günther Fleischer, OFI Technologie & Innovation GmbH,
Vienna, Austria.
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2.2. In-situ treatment: Saint Michael’s Church in Munich, Germany
VCP conservation was implemented on four sovereign statues made of Euville limestone.
These were: Theovalda, Duke Albrecht V, Duke Wilhelm V and Imperator Maximilian I.
The conservation was carried out in situ without any movement of the statues, which had a
height of 250 cm. The strengthened media were ESE 300E accelerated and 500E
accelerated, applied in succession.
Fig. 8: VCP conservation of four sovereign statues.
Fig. 9: In situ VCP conservation of Duke Albrecht V; Duration of treatment: 10 hours;
Absorption of ESE: 50 kg.
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Fig. 10: Ultrasonic measurement report
(grey – not consolidated, red – consolidated, blue – difference)
by Dr Eberhard Wendler, Munich (Germany).
3. Result of a surface treatment from 20 years ago
VCP conservation was implemented on four sovereign statues made of Euville limestone.
These were: Theovalda, Duke Albrecht V, Duke Wilhelm V and Imperator Maximilian I.
The conservation was carried out in situ without any movement of the statues, which had a
height of 250 cm. The strengthened media were ESE 300E (accelerated) and
500E (accelerated), applied in succession. Up to a depth of 10 mm the outside section is
still conserved, but because of the different physical characteristics of treated and untreated
stone, the outside section has lost coherence to the inner structure. Therefore the harder
outside section shows spalling.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 11: Photograph of a limestone statue surface-treated with ESE 300 20 years ago.
4. Conclusion
New conservation methods are existentially important, as a large number of listed
monuments have suffered serious consequential damage in the last few decades because of
pure surface treatment. Most negative effects have been identified on fine-grained
limestones and sandstones. Treatments with ESE are having different effects on different
types of stone. The common surface treatments use methods including run-over application,
brushing application and pad application. By using these treatments, more often than not,
the natural capillary absorption is not sufficient to penetrate deep enough inside the stone to
permeate the corroded zone to the inner, healthy core of a stone object. Using negative
pressure to apply ESE enables the medium to penetrate very deep inside the stone. It is even
possible to penetrate the entire already-strengthened outside zone to reach the weak inside
zones below. The VCP application is also suitable for the consolidation of stone objects
with surfaces demonstrating varied or reduced permeability (M. Milchin et al., 2015).
Contamination of the environment, adjacent areas and of users is avoided due to the
process.
References
Milchin, M., Weber, J, Krist, G., Ghaffari, and S. Karacsonyi E., 2015, 2, Ethyl-silicate
consolidation for porous limestone coated with oil paint – a comparison of
application methods / 2016 paper for the 13th International Congress on the
Deterioration and Conservation of Stone.
938
SUSTAINABLE CONSERVATION
IN A MONUMENTAL CEMETERY
S. Salvini1*
Abstract
The 'Foce' monumental cemetery in Sanremo (Ligury, Italy), founded in 1838 and used
until 1948, was central in a study that the Author carried out since January 2013: it is a site
rich in stone artefacts and seriously deteriorated due to the absence of a plan for weed
control and conservation, the lack of heirs and the marine environment. In this study, the
attention is especially focused on sustainable conservation: the paper describes the specificdrawn maintenance plan for the conservation of the site, it also underlines the importance of
using products and techniques with a low environmental impact and finally, it briefly
presents the possibilities of socio-economic sustainability of valorisation and management
considering the cemetery characteristics. The design of maintenance plan is a key step in
modern conservation that is more and more oriented to preventive restoration and
continuous care techniques in spite of sporadic and extraordinary restoration interventions.
In this work, a lot of effort has been put into the design of an inspection form that needs to
be strongly efficient in saving time and economic resources and in the research of low
impact activities of maintenance.
Keywords: stone conservation, sustainability, cemetery conservation, green conservation.
1. Introduction: sustainability in conservation
Since the meaning had been defined by Gro Harlem Brundtland in the UN report Our
Common Future (1987), the term ‘sustainability’ has been connected with the wish of not to
compromise a common heritage in order to permit the future generations respond to their
needs. This term has soon become a central key – word of the technical debates of the last
decades in many fields, including the Cultural Heritage conservation and management.
Sustainability can be applied at various levels: environmental, social, economic. In this
perspective the goals of the conservation discipline are intrinsically sustainable: from a
socio-cultural point of view, cultural heritage is a common asset, because it is the
inheritance of past generations and a container of the collective identity. The reuse of
existing heritage also avoids the consumption of economic and environmental resources
caused by the activity of rebuilding and moreover the construction bubble had led to more
activities on the BH and there could be still a lot of work (Cinieri and Zamperini 2014)
1
S. Salvini*
Built Heritage & Landscape (SSBAP) in-Genova, Italy and
Department of Geosciences, Via Gradenigo 6, 35131, Padua, Italy
silvia.salvini@gmail.com
*corresponding author
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Unfortunately, in the majority of restoration activities carried out on cultural heritage
chemical products are usually employed. These substances can have harmful effects both
on workers and on environment and so they are unsustainable: moreover, the product
selection is often affected by economic interests or sectorial advertising (Macchia et al,
2014). In addition to the toxicity, in the long run these products can produce unexpected
negative effects (e.g. interactions with atmosphere and pollutants) and so they could cause a
pejorative transformation of the material. Regarding the environmental sustainability there
is more attention on the quality design of interventions and on the choice of products and
techniques safer for the environment and the operators. Renewable and natural resources
are more and more recommended.
Moreover a correct conservation also lead to a conservation of the intangible heritage
constituted by the traditional techniques, which were generally more durable than actual
ones and which unfortunately are put down less and less. In addition, the energy
rehabilitations often do not consider the incorporate energy of a building and constructive
characteristics of a specific climate and territory are destroying our heritage. In the past, the
non-sustainability of the restoration, against the recognized value of a cultural asset, has
often been considered acceptable. While this reasoning may still be acceptable for certain
outstanding heritage property, it cannot be extended to the widespread heritage, sometimes
not declared of cultural interest and rarely object of public funding.
It is evident that the ideal aim is a condition of balance, which minimizes the development
of the decay phenomena. Although it is acknowledged that there is not a ‘perfect recipe’
that could stop perpetually a natural and inevitable phenomenon as the degradation of the
cultural heritage, strategies for slowing deterioration phenomena based on the techniques of
preventive restoration and maintenance plan are widely recognized in academic debates. It
is well established that the successful use of these techniques in spite of isolated emergency
restoration activities leads to definitely lower costs in the long run, a condition extremely
important, especially for the critical case of the immense and widespread Italian Cultural
Heritage, cemetery or not, in need of protection (Salvini and Cinieri, 2014).
2. A monumental cemetery: Issues of conservation
Historic Cemetery Heritage in Europe includes a large number of monuments often dated to
the period between the XIX and the XX century, when the funerary sculpture reach its
climax. Cemetery heritage, mostly marble, has complex issues of conservation.
Actually, in a cemetery a variety of materials can be observed: different types of stone,
metals, Liberty decorations (concrete, glass, ceramic tiles, etc.) and so on. Moreover, in
some sites there are high numbers of monuments and complex artefacts like funerary
chapels. However, the major problems are related to the lack of care. In fact, even if the
uncontrolled presence of heirs could signify wrong procedures in most cases they are
beneficial. A consequence of abandonment is the boost of the weed control related issues
that in some contexts encouraged by particular climatic conditions can became a thorny
question.
2.1. Case study: The ‘Foce’ monumental cemetery
2.1.1. History of the ‘Foce’ monumental cemetery of Sanremo, Italy
The ‘Foce’ monumental cemetery was founded in 1838, soon after a cholera epidemic in
1837, and now counts about 2500 graves, one third of which belongs to foreigners,
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
evidences of the city as outstanding tourist destination of the international upper class
during the Belle Epoque (1880-1915). In fact, thanks to its good climate the city was
renowned for the recovery from the diseases of chest by many people, even by Maria
Alessandrovna, Csarina of Russia. Since the end of XIX century many important people
came to Sanremo from all over the world and sometimes here they passed by and were
buried: people like the painter Edward Lear, the anatomist Arthur Hill Hassal, the lady in
waiting of Victoria Queen Lady Caroline Giffard Phillipson, Prussian nobles, a good
number of Russian aristocrats, and many others...
This cemetery is located near the shore in the Western section of the city of Sanremo
between the Foce and San Bernardo streams because the previous and nearer Vallotto
cemetery, had become insane for the city of Sanremo due to the development of the
hygienist theories which culminated in the Napoleonic edict of Saint Cloud (1806). The
present city cemetery is the “Armea” in the Eastern limit of the city, a new site that has
been inaugurated in 1948 causing the partial abandonment of the ‘Foce’ cemetery. In 1980
the cemetery was declared “Monumental Cemetery” in order to protect the area from
building speculation and now, even if some graves had been moved to the new cemetery
the visit of the Foce cemetery is a true dip in the past, in the golden age of the city of
Sanremo.
2.1.2. Specific site issues
Unfortunately, this cemetery is seriously deteriorated. The causes are numerous, the most
important being the lack of heirs and the absence of a plan for weed control and
conservation. The coastal environment also greatly contributes to the acceleration of the
degradation of the building materials, especially metallic ones.
The major part of the graves date back before 1915 and the lack of heirs and of general care
in the past decades had led to the present critical situation made of statically unstable graves
and arcades, weedy plants and typical local shrubs growing wild. Due to the land
occupation of the surrounding area, the cemetery cannot expand and so there is little space
left for new burials that they would be a convenient economic income for the Municipality.
Finally, economic resources do not exist or they are minimal and it is evident that the site
needs the best resource optimization possible.
3. Methodological approach
The solutions proposed in the following paragraphs are based on the main and established
principles of the academic debates of contemporary restoration, i.e.:
-
Minimal intervention: Elimination of unnecessary jobs directly or un-directly
related to the perpetuation of the good. The creations of pure embellishment or
modernization are severely limited since the sign of the time is an historical and an
aesthetic value, extraordinarily evocative.
-
Reversible and identifiable (to the trained eye) intervention.
-
Compatibility of restoration materials with the original ones.
-
Non-destructive and possible no-invasive diagnostic investigations.
-
Preventive conservation and restoration.
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4. The conservation project: from urgent activities to continuous care
4.1. Urgent conservation activities
It is evident that the site needs urgent conservation activities. In the preliminary research
grave materials and infesting plants have been mapped in order to facilitate the subsequent
inspections and the design of the maintenance plans. It is worth noting a widespread
presence of canker of cypress, a fungal infection pervasive in Mediterranean area.
Treatment of Seiridium cardinal (the pathogenic fungus of cypress canker) with
Pseudomonas (Raio et al. 2011) require a specialized labour and exceptional precautionary
measures for the operator, which are objectively not available in the case study site. The
diseased cypresses must be cut down and then the tools should be disinfected with ethanol
and the cut plants burnt (Giunti and Lorenzini, 2013). In order to avoid damage to the
surrounding graves the activities must be carried out by skilled workers who can install
proper protection for underlying gravestones during the operations; moreover, in order to
optimize the resources, they should also secure the graves with static instability and remove
the other weedy and invasive plants (especially Chamerops sp.).
Another critical situation is represented by the roof coverings of the vaulted arcades where
there is often a discontinuity in the earthenware coverings frequently associated with decay
of woody secondary structures and disconnection of almost all the gutters and drainpipes.
The roofs will be disassembled and cleaned from weeds; the underlying vaults must be
consolidated on the extrados with carbon fibres if they are made of brick or with a fibrereinforced net together with gypsum mortar if they are made of arelle (typical wooden
strips); secondary wooden structures should be replaced or restored according to their
conditions (Musso, 2013). The roof surface seems to rest directly on the rafters and joists so
I recommend the use of a waterproof and transpiring sheath or of a tarred sheet on the
replaced/restored joists (the roof planking is optional since we could not find it). Finally,
the drainage channels of the paths must be rearranged and new gutters and drainpipes made
of copper, a material compatible with the building historic and more durable of the current
aluminium one, should be installed (Salvini, 2014).
The shaft tombs were common in the English colony burials: they often have structural
failure of the inside vault and then instability can be observed on the exterior. Due to the
fact that they are graves with a strong historical value they cannot be re-granted, in some
critical cases the quickest and most sustainable solution (economically and
environmentally) is the complete filling of the burial chamber with gravel and sand in order
to eliminate the instability due to the cavity below.
After these early interventions of paramount importance some restoration work had to be
exceptionally carried off on many artifacts. The choice of the restoration techniques, as well
as that of the maintenance activities, is not immediate. It should be made according to the
material and then the most appropriate methodology is further selected by the state of
conservation of the material, its frailty and its historical and artistic value. Experience from
the past tought us to be careful when choosing product and methodology since it became
clear that there no ‘perfect product’ available yet, probably never will be, which stops the
decay forever. In conclusion this means that conservation is a process of constant care and
attention.
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This study underlines the better sustainability of some conservation methods for the stone
materials (Musso, 2013; Salvini, 2014). For example regarding the cleaning physical
methods, like soft brushing with deionized water and micro sandblasting and Dry-Ice
systems, or natural products, like gel agar-based and xi-xi of the Mexican tradition (Segarra
Lagunes, 2006), should be preferred. For the removal of weeds the methods based on
microwaves or flaming are very promising and minimally invasive (Olmi et al. 2011,
Frasconi et al. 2015). For the stone consolidation a widespread method is the ethyl silicate
but nano-silica based formulations or injections of lime mortar with local hydraulic
aggregates are more sustainable. The re-adhesion must be performed only when necessary
using a resin inside the fracture and micro-stuccoes made of lime and powder of the stone
of interest to its outer. The necessary replacements must be performed with materials
compatible with the originals (similar properties, colour, porosity, grain, …) and also
having similar properties. For the integrations, injections of lime and stone paste are
suggested. Regarding the final protection, the methods are controversial and further studies
are needed: the most used method in conservation is the periodic application of
microcrystalline waxes with high melting point (thanks to stability, minimal color changes
or interactions with the substrate). However, these waxes are not very efficient and they
also have the defect of being soluble only in aromatic compounds at room temperature (this
characteristic makes the periodic replacement difficult and not fully sustainable).
4.2. The maintenance plan: design of the inspection form
It is evident that the site firstly needs emergency restoration but with the goal of never
reach any more a critical situation such as the current, a maintenance plan has also been
drafted. The maintenance programme should provide inspections that, in absence of
specific anomalies or exceptional events (weather events, earthquakes, vandalism, etc.),
must always be done at a fixed time rate, possibly in relation to the critical environmental
issues (present degradation, distance from the sea and from pollution source, estimate of
future degradation, ...) where the artefact is placed. In a cemetery context, it is impossible to
think of an ‘item based’ monitoring (Cecchi and Gasparoli, 2011) since the compilation of
all the reports would require too much time and economic and skilled resources that almost
always could not be found (taking also into account the vastness of the cultural heritage,
cemetery and not, in needs of protection). Moreover, too many reports would distract from
the most important issues if there was a presence of degradation phenomena that affect
more than one grave. So, in this contribution is presented the designed inspection form (or
technical schedule) structured for cemetery areas (see Fig. 1).
The ‘Foce’ cemetery (area: 20000 m2 and about 2500 gravestones) has been divided into 47
monitoring areas. For a quicker scheduling of maintenance, gravestones had been
renumbered in a more logical way than that used in burial records, sometimes missing. The
form has been designed in order to optimize the execution of the monitoring: it presents a
spatial orientation part and another one related to the inspection itself. In the first part the
items constituent the area under investigation are shown as a list of codes together with a
planimetry (of course with indication of codes). In the second part, it has been made a list
of alterations of the lexicon ICOMOS (or UNI EN 1182:2006) to be monitored: the
deterioration patterns that are more unstable or have a tendency to evolve more rapidly than
others have been selected because these alterations are also those that generally require a
timely intervention and/or could lead to a rescheduling of the maintenance plan.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 1: Model of inspection form to be used in cemetery contexts (Salvini, 2014).
4.3. Maintenance activities
The timetable of the maintenance activities have been also divided depending on the
difficulty among different professionalisms: dealer, guardian or gardener, skilled worker,
restorer, specialized technician (Salvini, 2014). Very simple operations could be entrusted
to the dealers or to the caretakers briefly trained with the intention of making them
collaborators in the conservation of a site of great historical and artistic value that is part of
the town's history (see Fig. 2). The periodic inspection could be also scheduled together
with some activities of small maintenance entrusting an optimized inspection team.
4.4. Valorisation and management
The management of the site is difficult because it is considered by some local institutions as
a waste of money due to the fact it is not fully used and the large amount of resources
required for its conservation puts the cemetery area at a constant risk of ‘wild re-granting’.
Actually, some plots can be reused for rotational burials and selected empty gravestones
and arcades could be re-granted by means of competitive auction with specific prescriptions
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
drafted case by case, as it is working in other monumental cemeteries (es. Genova, Paris).
Another source of income can be the cultural activities staged at the cemetery (es. Poblenou
cemetery, Barcelona), given the presence of an area suitable for the purpose.
The cemetery valorisation is required in order to obtain funds for its preservation. The
historical importance of the site, evidence of the importance of the city of Sanremo during
the Belle Epoque, must be preserved: different routes connecting the cemetery with the
artistic surrounding assets were created and in the future they will be enhanced through
Internet and mobile Apps (Salvini, 2014). The site management must consider the
participation of the local workforce like custodians and gardeners and grave caretakers
properly formed (Nagaoka, 2011) and supervised.
Fig. 2: Timetable of the maintenance activities.
5. Conclusions
The 'Foce' cemetery is a hidden pearl of the city of Sanremo that by now has not received
the attention it deserves, but there are the presuppositions to make it a practical example of
sustainable conservation and continuous care. The interest of local associations has enabled
a first small restoration in accord with local institutions: on 9 th July 2015 ended the
restoration of the anatomist A.H. Hassall’s grave (thanks to the sponsor Rotary Club
Sanremo) and in November 2015 have begun sporadic volunteer days where local people
perform routine maintenance activities supervised by experts according to the
Superintendency.
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References
Cecchi, R., Gasparoli, P., 2011, La manutenzione programmata dei beni culturali edificati:
procedimenti scientifici per lo sviluppo di piani programmati di manutenzione,
Alinea, Firenze.
Cinieri, V., Zamperini, E., 2014, Approccio lifecycle alla gestione e conservazione
sostenibile del patrimonio costruito, in Proceedings of XXXth Scienza e Beni
Culturali, Biscontin, G. and Driussi, G. (Eds.), Arcadia R., Venezia, 723-732.
Frasconi, C., Fontanelli, M., Martelloni, L., Pirchio, M., Raffaelli, M. and Peruzzi, A.,
2015, Thermal weed control in archaeological sites as an alternative to herbicides
application, in Book of Abstracts, Green Conservation Workshop, October 27th28th, Roma.
Giunti, M. and Lorenzini, G. (Eds.), 2013, Un archivio di pietra: l’antico cimitero degli
inglesi di Livorno – Note storiche e progetti di restauro, Pacini, Pisa.
Macchia, A., Sacco, F., Morello, S., Prestileo, F., La Russa F.M., Ruffolo, S., Luvidi, L.,
Settimo, G., Rivaroli L., Laurenzi Tabasso, M. and Campanella, L., 2014,
Chemical exposure in Cultural Heritage restoration: questionnarie to define the
state of art, in Proceedings of XXXth Scienza e Beni Culturali, Biscontin, G. and
Driussi, G. (Eds), Arcadia R., Venezia, 723-732.
Musso, S.F., 2013, Tecniche di restauro, UTET, Torino.
Nagaoka M., 2011, Revitalization of Borobudur. Heritage Tourism Promotion and Local
Community Empowerment in Cultural Industries, In AA.VV. Actes du
Symposium scientifique de la 17ème Assemblée générale de l’Icomos. Icomos,
Paris, pg. 658-671.
Olmi, R., Bini, M., Cuzman, O.A., Ignesti, A., Frediani, P., Priori, S., Riminesi, C. and
Tiano, P., 2011, Investigation of the microwave heating method for the control of
biodeteriogens on cultural heritage assets. Proceedings of Art11 - 10th
International Conference on non-destructive investigations and microanalysis for
diagnostic and conservation, Firenze.
Raio, A., Puopolo, G., Cimmino, A., Danti, R., Della Rocca, G. and Evidente, A., 2011
Biocontrol of cypress canker by the Phenazine producer Pseudomonas
Chlororaphis subsp. Aureofaciens strain M71, Biological Control, 58(2), 133-138.
Salvini, S., 2014, Cimitero monumentale della Foce di Sanremo: percorsi di valorizzazione
e linee guida per la conservazione preventiva e la manutenzione programmata,
Final relation of the Post graduate School in Built Heritage and Landscape,
SSBAP-University of Genova, Relator: Musso, Co-relators: Arcolao, De Cupis.
Salvini, S. and Cinieri, V., 2016, La conservazione del patrimonio ecclesiastico diffuso in
Italia, in Proceedings Precomos Conference 2014, Nardini, Firenze, pg.169-178.
Segarra Lagunes, S., 2007, Conservazione e restauro: il caso del cimitero storico del
Tepeyac a Città del Messico, in Proceedings of MO06, Aracne, Roma.
United Nations, 1987, Report of the World Commission on Environment and Development:
Our Common Future.
946
CONSOLIDATION OF SUGARING MARBLE BY
HYDROXYAPATITE: SOME RECENT DEVELOPMENTS IN
PRODUCING AND TREATING DECAYED SAMPLES
E. Sassoni1,2*, G. Graziani1, E. Franzoni1 and G.W. Scherer2
Abstract
Consolidation of sugaring marble (i.e., marble affected by granular disaggregation) still
lacks fully effective solutions. Consequently, the use of an innovative phosphate-based
treatment, aimed at bonding calcite grains by formation of hydroxyapatite at grain
boundaries, has recently been proposed. In this paper, firstly a novel method for producing
artificially decayed marble samples, by contact with a heating plate, is proposed. Then,
some results are presented about the effectiveness and the compatibility of two different
formulations of the phosphate treatment, differing in terms of concentration of the
phosphate precursor (3.0 M or 0.1 M aqueous solutions of diammonium hydrogen
phosphate, DAP), possible ethanol addition to the DAP solution and number of DAP
solution applications (1 or 2). The results of the study point out that the new weathering
method produces specimens with a gradient in microstructural and mechanical properties
with thickness, just like naturally weathered samples. Both phosphate treatments were able
to significantly improve marble cohesion, without causing significant changes in thermal
behaviour and aesthetic appearance after treatment. The addition of small quantities of
ethanol to the DAP solution seems to be a very promising method for favouring HAP
formation and improving the treatment performance.
Keywords: grain loss; thermal ageing; thermal diffusivity; calcium phosphate; ethanol
1. Introduction
The so-called "sugaring" of marble is a degradation phenomenon that consists in grain
detachment and loss, leading to severe alteration of the original morphology of architectural
elements and sculptures. As an example, sugaring affecting carved marble decorations in
the Monumental Cemetery in Bologna (Italy, XIX century) is illustrated in Fig. 1.
Sugaring originates from cyclical thermal excursions that outdoor marble elements
experience. Daily temperature variations cause anisotropic deformation of calcite grains of
which marble is composed, with the result that micro-cracks open at grain boundaries and
grains start to detach (Siegesmund et al., 2000).
1
E. Sassoni*, G. Graziani and E. Franzoni,
Dept. Civil, Chemical, Environmental and Materials Engineering (DICAM), University of Bologna,
Italy
enrico.sassoni2@unibo.it
2
E. Sassoni* and G.W. Scherer
Dept. Civil and Environmental Engineering (CEE), Princeton University, United States of America
esassoni@princeton.edu
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 1: Sugaring marble in the Monumental Cemetery in Bologna, Italy (XIX century).
In spite of the wide diffusion of this weathering phenomenon, no fully satisfactory
treatment for effectively and durably stopping marble sugaring has been developed yet.
Organic polymers exhibit limited compatibility and durability, alkoxysilanes give modest
mechanical improvement and long-term performance, lime-based treatments (also at the
nano-scale) are affected by low penetration depth and effectiveness, ammonium oxalate
provides insufficient consolidation and long-term protection (Sassoni and Franzoni, 2014b).
For this reason, an innovative inorganic phosphate treatment has recently been proposed for
sugaring marble consolidation (Sassoni et al., 2015). The phosphate treatment, originally
proposed for limestone consolidation (Sassoni et al., 2011) and marble protection (Naidu
and Scherer, 2014), is based on the reaction between the calcitic substrate and an aqueous
solution of di-ammonium hydrogen phosphate (DAP) to form hydroxyapatite (HAP).
Results obtained so far on the use of HAP for consolidation of sugaring marble are
extremely promising, in terms of both effectiveness and compatibility of the new treatment
(Sassoni et al., 2015). However, further research is still needed, because:
(i) Experimental tests on the HAP-treatment have been mainly carried out on
marble samples artificially weathered by heating at 400°C for 1 hour in oven,
according to a procedure previously developed by the authors (Sassoni et al.,
2011; Franzoni et al., 2013; Sassoni and Franzoni, 2014). This procedure proved
to be effective in producing samples with characteristics very similar to those of
naturally sugaring samples, namely with increased open porosity and coarsening
of the pore size, with respect to the unweathered condition. However, samples
produced in that way are entirely decayed, whereas naturally weathered samples
exhibit a gradient in microstructural and mechanical properties, the superficial
part being highly damaged and the inner part being basically undamaged. As one
of the goals of consolidation is to restore cohesion in the decayed part of a stone,
so as to bring it back to the condition before weathering, the use of artificially
weathered samples with a gradient in properties is a very important aspect for
studying new consolidants (Lubelli et al., 2015).
(ii) A recent study by the Authors has shown that the addition of ethanol (EtOH) to
the aqueous DAP solution, used to react marble to form HAP, is able to
significantly improve HAP formation (Graziani et al., in press). EtOH addition
resulted in better coverage of marble surface by HAP and a reduction in cracking
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
of the HAP layer, as well as a reduction in the DAP concentration, hence a
beneficial effect is expected also in the case of sugaring marble consolidation.
Therefore, in the present study some preliminary results are presented about:
(i) a new methodology to produce artificially weathered marble samples with a
gradient in microstructural and mechanical properties;
(ii) the effects of adding ethanol to the aqueous DAP solution, in terms of
consolidating efficacy and compatibility with the substrate.
2. Materials and Methods
2.1. Marble
Carrara marble was used for the tests, considering its wide diffusion in historic architecture
and sculpture. For tests on artificial weathering, samples with 2.5×2.5×5 cm3 dimensions
(provided by BasketweaveMosaics.com, USA) were used. For tests on the phosphate
treatments effects, samples with 2×2×3 cm3 dimensions (provided by Imbellone
Michelangelo s.a.s., Italy) were used.
2.2. Artificial weathering of marble samples
For producing a gradient in marble properties, samples were put in contact with a heating
plate already at 350°C, as illustrated in Fig. 2. Four thermocouples, put in contact with
sample surface at various distances from the heating plate (0, 10, 25 and 50 mm) and
connected to a pc, were used to continuously record the temperature reached by the sample
at different heights from the plate. To identify the most suitable time of heating, the method
described in the following was used.
Fig. 2: Experimental set-up for accelerated ageing of marble samples.
Assuming that the heat flow from the heating plate is one-dimensional (which is the case if
sample sides are covered with an insulator, so that heat losses are prevented), the equation
governing the heat flow is:
¶T
¶ æ
¶T ö
=
ç k(x,t)
÷
¶t ¶x è
¶x ø
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(Eq. 1)
13th International Congress on the Deterioration and Conservation of Stone: Conservation
where T is the temperature, t is the time,×is the distance from the heating plate and k is
marble thermal diffusivity. It can be demonstrated, for the case of constant k, that the
sample top at 50 mm from the heating plate is not subject to warming (and hence a gradient
in sample properties can be expected) if the time of heating is limited to:
t
0.1H 2
k
(Eq. 2)
where H is the sample height. To estimate the time of heating, preliminary tests were
carried out to determine the thermal diffusivity of Carrara marble (no reference value was
found in the literature). A 5 cm side cubic sample was placed in contact with the heating
plate (initially cold) and then heated from 24°C to 270°C, heat losses being prevented
insulating sample's lateral sides with a porous stone and top with a glass fibre board.
Temperature variations at different heights from the heating plate (0, 10, 20, 30, 40 and 50
mm) were measured as a function of time, by means of six thermocouples inserted inside
purposely drilled holes. By fitting the T(x,t) curves measured at different heights from the
plate to a numerical solution of Eq. (1), k(x,t) was found to vary parabolically with
temperature, decreasing from 1.6×10-6 m2/s at 24°C to 4.0×10-7 m2/s at 270°C. A very good
fit was obtained to T(x,t) measured at each of the thermocouples, so this model can be used
in the future to simulate arbitrary heating procedures. The details of these calculations will
be presented in a future publication. The decrease in k with T is thought to be a
consequence of microcracks opening as temperature increases. Using Equation (2), with
H=5 cm, the times of heating corresponding to the limiting values of k were calculated and
times of about 2.5 and 10 minutes were obtained.
The effects of heating samples by contact with the heating plate at 350°C for 5 and 10
minutes were evaluated by comparing the two parts of the sample at 0-10 mm and at 40-50
mm from the plate (hence, respectively, directly in contact with the plate and at the opposite
side, Fig. 2). This comparison was performed in terms of ultrasonic pulse velocity (UPV)
and elastic modulus (E) determined by nanoindentation test. UPV was measured, before
and after heating, by transmission method, using a PUNDIT commercial instrument with 54
kHz transducers and a rubber couplant between the sample and the transducers. E was
calculated as the slope of the unloading part of the force-displacement curve obtained by
subjecting the marble sample to the following loading cycle: loading to 400 μN, holding,
unloading. The loading cycle was performed using a Digital Instruments AFM with
integrated nanoindentation capability.
2.3. Consolidation of marble samples
As optimization of the novel weathering procedure is still in progress (cf. § 3.1), samples to
be treated with the phosphate consolidants and untreated references were preliminarily
artificially weathered by heating at 400°C for 1 h in oven, according to a procedure
previously developed by the Authors (Sassoni et al., 2011; Franzoni et al., 2013). Two
treatment conditions were considered:
(i) "3.0 M DAP". These samples were firstly treated with a 3.0 M solution of DAP
(Sigma-Aldrich, reagent grade) and de-ionized water, applied by brushing 15
times. At the end of brushing application, the samples were wrapped in a plastic
film to prevent solution evaporation and left to react for 48 hours. Then, they were
unwrapped, rinsed with water and left to dry. Finally, they were treated with a
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
saturated solution of calcium hydroxide (Sigma-Aldrich, reagent grade) in deionized water (so-called limewater), applied by poultice. The poultice was
prepared using limewater and dry cellulose pulp (MH300 Phase, Italy) with a
weight ratio 6:1. After wrapping in a plastic film for 24 hours and then drying,
samples were ready for characterization tests.
(ii) "0.1 M DAP with 0.5 wt% EtOH + 0.1 M DAP". These samples were treated
according to the method recently proposed by Graziani et al., in press. As a first
step, samples were treated by immersion in a 0.1 M DAP solution with addition of
0.5 wt% EtOH for 24 hours. After rinsing with water and drying, samples were
then subjected to a second treatment with a 0.1 M DAP solution, again applied by
immersion. After drying, samples were ready for tests.
The consolidating efficacy of the two treatments was evaluated in terms of increase in UPV,
with respect to the untreated references. UPV was selected as it is very sensitive to healing
of microcracks and is hence frequently adopted to assess the efficacy of stone consolidants
(Weiss et al., 2002). UPV was measured with a Matest commercial instrument with 55 kHz
transducers, using a rubber couplant between the samples and the transducers.
The compatibility of the two treatments was evaluated in terms of alterations in thermal
behaviour and aesthetic appearance. As marble decay is mainly induced by thermal
excursions, the evaluation of the thermal behaviour of consolidated marble is very
important (Ruedrich et al., 2002). Untreated and treated samples (30×9×7 mm3) were
subjected to the following thermal cycle, using a push-rod dilatometer Netzsch mod. 402 E
(Netzsch-Geratebäu GmbH, Selb, Germany): (i) heating from room temperature to 80°C at
1°C/min, (ii) isothermal dwell for 1 hour at 80°C, (iii) cooling to room temperature at
1°C/min. The maximum heating temperature was chosen to simulate environmental
conditions experienced in the field (Siegesmund et al., 2000). The residual strain after
cooling to room temperature (εr) was considered. The aesthetic alteration was evaluated in
terms of colour change, defined as ΔE = (ΔL*2 + Δa*2 + Δb*2)1/2. The colour parameters
L*a*b* (L* = black÷white, a* = red÷green, b* yellow÷blue) were measured using a
Spectrophotometer cm-2600d, Konica Minolta Sensing.Inc.
3. Results and Discussion
3.1. Artificial weathering
For marble samples put in contact with the heating plate initially at 350°C for 5 and 10
minutes, a remarkable temperature gradient is present inside the samples, as illustrated in
Fig. 3 (left). The thermocouple in contact with the sample and the plate registers a
temperature of 312-335°C after 5 and 10 minutes, respectively (both temperatures being
lower than the initial one because contact with the sample lowers the plate temperature). At
a height of 10 mm from the plate the temperature is sensibly lower (106-117°C,
respectively). At the top of the sample (50 mm height) the temperature is still quite close to
ambient temperature after 5 minutes (42°C) and a little higher after 10 minutes (53°C).
Correspondingly to this temperature gradient, a significant gradient in mechanical
properties was registered. In terms of UPV, decreases with respect to the initial condition
are reported in Fig. 3 (right). In the sample part close to the plate (0-10 mm), a strong UPV
decrease is registered after 5 minutes (-58%). When contact with the plate is increased up to
10 minutes, a similar UPV decrease is recorded in this sample part (-56%). However, the
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
situation is quite different at the top of the sample (40-50 mm from the plate). While after 5
minutes only a minor UPV decrease is registered (-5%), in agreement with the limited
temperature reached in this layer (42°C), after 10 minutes a non-negligible UPV decrease
(-21%) is registered also in this layer, in agreement with the higher temperature reached
(53°C).
Fig. 3: Effects of accelerated ageing: temperature (left) and UPV variation (right) at
different heights from the heating plate after 5 and 10 minutes.
Based on these results, a time of heating of 5 minutes seems to be the most suitable, as it
allows to obtain a marked gradient in UPV across sample thickness, without significantly
altering properties at the extremity of the sample far from the plate. Accordingly, in the
sample heated for 5 minutes a marked difference (-75%) was registered also in terms of
elastic modulus, E, determined by nanoindentation, between parts at 0-10 mm and 40-50
mm from the heating plate.
However, results reported above were obtained for a sample that had been heated over the
plate without insulating the sides and the top, so that some heat loss was experienced.
Consequently, conditions for calculating the time of heating using Equations (1) and (2)
were not strictly respected. For samples subjected to artificial weathering with thermal
insulation, an even more pronounced gradient in temperature and hence in microstructuralmechanical properties is expected. Tests involving insulated samples are currently in
progress. On these samples, a systematic evaluation of mechanical property alteration as a
function of the distance from the heating plate will be carried out by nanoindentation. Being
a non-destructive technique (causing only nanometric damage to calcite grains), it will be
possible to derive profiles of sample elastic modulus E after artificial weathering and after
consolidation by the phosphate treatment.
3.2. Consolidation
The effects of the two consolidating treatments are summarized in Tab. 1. Both treatments
proved to be highly effective in restoring marble mechanical cohesion, being able to bring
UPV almost back to the value before artificial weathering (3.2 km/s). Between the two
treatments, that involving a higher DAP concentration allowed to achieve a higher UPV
increase. However, it is remarkable that the treatment involving EtOH addition allowed to
achieve a comparable increase in UPV, notwithstanding the much lower (30 times)
concentration of DAP used. This can be ascribed to the beneficial effect of: (i) adding
EtOH, that according to some studies favours HAP formation (Lerner et al., 1989); (ii)
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
applying double treatments, that allow to achieve a better coverage of calcite grains,
without causing excessive growth of the HAP film (Graziani et al., in press).
In terms of thermal behaviour after consolidation, both treatments gave good results,
causing a residual strain after the heating-cooling cycle less than or equal to that of the
untreated reference (Tab. 1). This is very important, because if an increase in residual strain
were found, an increase in sensitivity to thermal cycles should be expected (Ruedrich et al.,
2002). Notably, the residual strain of the sample treated with EtOH addition is very close to
the value exhibited by marble before artificial weathering (0.15 mm/m). This is a positive
feature, as stone consolidants should ideally modify the properties of decayed stone so as to
bring them back to the condition before decay.
In terms of aesthetic appearance, the two consolidating treatments exhibited a good
compatibility (Tab. 1), in both cases leading to a colour change ΔE* lower than the
threshold commonly accepted for stone consolidants (ΔE* = 5) and even lower than the
human eye detection limit (ΔE* = 3). The ΔE* caused by the treatment with EtOH addition
was actually lower than the other treatment, which can be ascribed to the lower DAP
concentration involved by this treatment condition.
Tab. 1: Effects of the two consolidating treatments.
UPV
εr
(km/s)
(mm/m)
Untreated
0.6
0.24
-
3.0 M DAP
2.9
0.23
1.5
0.1 M DAP with 5 wt% EtOH + 0.1 M DAP
2.2
0.16
1.1
Specimen
ΔE*
4. Conclusions
In the present paper, some recent developments were reported on the production of
artificially weathered samples for testing of consolidants and on the effects of two different
formulations of the hydroxyapatite-based treatment for consolidation of sugaring marble.
Heating marble samples by contact with a heating plate at 350°C for 5 minutes proved to be
an effective way to produce samples with a marked gradient in mechanical properties (just
like naturally weathered marble), namely an UPV decrease of -58% at a distance f 10-20
mm from the plate and basically no damage at a distance of 40-50 mm. As for
consolidation, the double treatment involving the addition of a very small quantity of
ethanol to a DAP solution with low concentration (0.1 M DAP) produced a significant
mechanical improvement, with only minor alterations in thermal behaviour and aesthetic
appearance. This suggests that ethanol additions to the DAP solution are a very promising
method for favouring HAP formation and improving the treatment performance.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Acknowledgments
This project has received funding from the European Union’s Horizon 2020 research and
innovation programme under the Marie Sklodowska-Curie grant agreement No 655239
(HAP4MARBLE project, "Multi-functionalization of hydroxyapatite for restoration and
preventive conservation of marble artworks"). Prof. Winston Soboyejo and M.Eng. Emre
Turkoz (Dept. Mechanical and Aerospace Engineering, Princeton University, USA) are
gratefully acknowledged for collaboration on nano-indentation tests. Prof. Maria Chiara
Bignozzi and Dr. Giovanni Ridolfi (Centro Ceramico Bologna, Italy) are gratefully
acknowledged for collaboration on thermal behaviour tests.
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marbles caused by anisotropic thermal expansion, Int J Earth Sci, 89, 170-182.
Weiss, T., Rasolofosaon, P.N.J., Siegesmund, S., 2002, Ultrasonic wave velocities as a
diagnostic tool for the quality assessment of marble, in Natural stone, weathering
phenomena, conservation strategies and case studies, Siegesmund, S., Weiss, T.,
Vollbrecht, A. (Eds), Geological Society, London, Special Publications, 205, 149164.
954
APPLICATION OF ETHYL SILICATE BASED CONSOLIDANTS
ON SANDSTONE WITH PARTIAL VACUUM:
A LABORATORY STUDY
H. Siedel1*, J. Wichert2 and T. Frühwirt2
Abstract
To improve the penetration depth of a TEOS consolidant on Cotta sandstone with high
amount of small voids and clay mineral content, the so-called “Vacuum Circulation
Process” (VCP) was applied to test cubes of fresh sandstone. Changes of mechanical and
hydric properties were determined on drill core profiles across the test cubes after a 4
month reaction time. Especially for Remmers Funcosil 300E, the results show a
significantly higher penetration depth compared to a reference cube brushed by hand with
the same agent. Moreover, biaxial flexural strength and Young’s modulus profiles for
Funcosil 300E / VCP are acceptable in terms of the relation of both properties and their
change along the profile line from surface to the interior. Hydric properties show a still
slightly hydrophobic reaction of the penetrated outermost zone. Although these results
encourage the use of VCP also for building stones with a high amount of smaller voids, the
role of the partial vacuum during the process remains unclear, since similar penetration
depths were reached by total immersion of a sandstone cube under atmospheric pressure.
Keywords: consolidation, hydric and mechanical properties, sandstone, penetration depth,
vacuum circulation process
1. Introduction
Inappropriate penetration depths of stone consolidants are a common problem especially for
the treatment of building sandstones with a higher amount of smaller voids and clay
mineral contents. In restoration practice, the so-called “vacuum circulation process” (VCP,
Pummer 2008) has been occasionally used for consolidation treatments of small objects like
sculptures to reach better penetration of the consolidant. For this treatment, the entire stone
object is sealed in a tight plastic foil bag which is “evacuated” by partial vacuum down to 900 mbar (g). Maintaining the partial vacuum, fluid tetra ethyl ester of the orthosilicic acid
(TEOS) is subsequently sucked in the bag with the object via valves in the foil skin.
Although there are only few systematic investigations on the change of physical properties
after VCP treatment, it seems to work well in practice with respect to the penetration depth
especially for stone varieties with coarse voids. However, conservation issues often concern
sandstones with higher amounts of smaller voids and clay contents which are on one hand
1
H. Siedel*
Institute of Geotechnical Engineering, Chair of Applied Geology, TU Dresden, Germany
Heiner.Siedel@tu-dresden.de
2
J. Wichert and T. Frühwirt
Geotechnical Institute, Chair of Rock Mechanics, TU Bergakademie Freiberg, Germany
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
susceptible to weathering and on the other hand hard to penetrate for liquids. The study
aimed at testing the VCP treatment for clay mineral bearing building sandstone with low
average pore diameter. For the tests Elbe Sandstone (Cotta type) from the region of Saxony
(Germany) with median pore diameter D50 of 1.4 µm was chosen (see Fig. 1 and Fig. 2).
The problem of low penetration depths of consolidants is well known from several
conservation measures on this material.
2. Materials and methods
2.1. Cotta sandstone
Cotta sandstone is a building stone from the Upper Cretaceous (Turonian) quarried in the
Elbe Valley some 20 km south of the city of Dresden since the 15 th century. The fine to
medium grained quartz arenite (Fig. 1) contains clay minerals like kaolinite and illite and
has a broad pore size distribution shown in Fig. 2.
3,5
pore volume [%]
3
2,5
2
1,5
1
749,89
421,70
74,99
237,14
42,17
133,35
7,50
23,71
4,22
13,34
2,37
1,33
0,75
0,42
0,24
0,13
0,08
0,04
0,02
0,01
0,008
0,004
0,002
0
0,001
0,5
pore diameter [µm]
Fig. 1: Thin section image of Cotta
sandstone (Nicols II) with light quartz
grains and dark clay mineral layers
Fig. 2: Pore size distribution of Cotta
sandstone used for the tests (U), according to
MIP. Total porosity of this sample is 20.6 %.
2.2. Samples and treatment with VCP
Test cubes of 20×20×20 cm were cut from Cotta type sandstone from the quarry
Lohmgrund II, Sächsische Sandsteinwerke GmbH. The chosen format represents the
thickness of smaller objects such as tombstones or parts of sculptures. In the restorer’s
workshop (Erich Pummer, Rossatz / Wachau, Austria) the cubes were air dried, sealed in
foil bags and treated with TEOS systems with “soft segments” (polyether chains, Snethlage
2014) and different SiO2 gel “content” (Remmers Funcosil 300E, pre-condensed Remmers
Funcosil 500E) applying the VCP. The TEOS systems contained an (unknown) reaction
accelerator designed by Remmers for the use in VCP. Treatment duration was 6-7 hours for
Funcosil 500E and 8 hours for Funcosil 300E; with a TEOS consumption of 5.2 and 3.4-5.2
litres, respectively. As reference additional test cubes were treated in a conventional way by
brushing the liquid (Funcosil 300E without reaction accelerator) several times “wet-in-wet”
on the surface until the stone surface was visibly saturated. To compare the penetration
depth reached by applying partial vacuum to that reached by embedding the same stone in
the liquid under atmospheric pressure, another cube was stored in Funcosil 300E for 6
hours (TEOS consumption 2.7 litres) and cut immediately afterwards.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
After the treatment, all sample cubes were stored 4 months at 65 % RH / 21°C.
Subsequently, 8 drill cores were taken from every cube normal and parallel to bedding
planes of the sandstone, respectively.
2.3. Investigation of physical properties
Drill cores taken from the test cubes were cut into 5 mm thick discs normal to the cylinder
axis to obtain profiles from the surface to the depth. Before cutting the cores, measurements
of the ultrasonic wave velocity (UWV, air-dried condition) had been performed stepwise, in
two orthogonal directions normal to the cylinder axis, with a GEOTRON system. In a first
step, hydric properties (total water uptake, hydric swelling, and water vapour diffusion) of
the discs were determined by non-destructive measurements, followed by destructive
measurements in order to obtain mechanical properties (Siedel and Siegesmund 2014).
2.3.1. Hydric swelling and total water uptake
The air dry samples were fixed in a sample holder (Invar) combined with dilatometer
(precision 0.01 mm) and immersed in demineralised water for 96 h. The maximum swelling
value [mm/m] was registered. Before immersion and after water storing, the samples were
weighed and the mass difference was compared with the dry sample mass [wt.-%].
2.3.2. Water vapour diffusion resistance
Water vapour diffusion was measured following EN-ISO 12572 in the “wet cup”
conditioning (96 vs. 50 % RH, 21°C). From the mass difference over time, the water vapour
resistance value (µ) was calculated. This parameter indicates how many times the resistance
of a material against streaming water vapour is higher compared to a layer of pure air of the
same thickness.
2.3.3. Biaxial flexural strength and Young’s modulus
Biaxial flexural strength (BFS) and Young’s modulus (YM) were determined on each disc,
with the circular disc resting upon a larger ring while pressure is being applied centrically
by a second smaller ring, according to the method described by Kozub (2008).
3. Results and discussion
3.1. Penetration depth
The penetration depth of the liquid consolidant was assessed by cutting two control cubes
immediately after treatment with VCP and Funcosil 300E. Moreover, another test cube was
cut after full immersion in Funcosil 300E under atmospheric pressure. The results are
displayed in Fig. 3 and Fig. 4. They show, that the maximum penetration depths vary
between 2.5 and 5 cm for two different cubes of Cotta sandstone treated with VCP under
the same conditions (-200 to -500 mbar (g)) and do not differ significantly from those
observed on the cube immersed in Funcosil 300E under atmospheric pressure (maximum
3 cm). As can be seen in Fig. 4 (below), penetration depth along bedding planes of the
sandstone is slightly higher than normal to bedding.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 3: Test cubes penetrated by
Funcosil 300E with VCP and cut
parallel to bedding immediately after
the procedure (photos: E. Pummer).
Fig. 4: Test cube penetrated by
Funcosil 300E with total
immersion under atmospheric
pressure and cut parallel (above)
and normal to bedding (below)
immediately after the procedure
(photos: M. Eilenberger).
3.2. Ultrasonic wave velocity
Fig. 5 displays the average values of all UWV profiles measured for the differently treated
samples as well as for the untreated cube after 4 month of storage. The differences of UWV
in the cores of the different sample cubes (deeper than 50-60 mm from surface) give the
range of natural scattering in Cotta sandstone. As can be seen from the graphs, the hand-
Fig. 5: Ultrasonic wave velocity profiles across the test cubes
(average values for all measurements on drill cores).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
treated cube (E) shows the lowest change of UWV of all samples with effects limited to the
first 10 mm from surface. Samples treated with VCP clearly show deeper and stronger
effects (up to about 50 mm in case of Funcosil 300E (P) and about 30 mm in case of
Funcosil 500E (K)). In contrast to the steep slope of the profiles of E and K in the
outermost zone, the cube P treated with VCP and Funcosil 300E shows a more smooth
profile. The profiles obtained from measurements in two different directions, both normal
to the axis of the cores, are highly consistent.
3.3. Biaxial flexural strength and Young’s modulus
Changes in BFS and YM profiles for all samples after the treatment displayed in Fig. 6 and
Fig. 7 reflect the changes in UWV (cf. Fig. 5).
Fig. 6: Biaxial flexural strength profiles across the test cubes
(average values for all measurements on 5 mm discs cut from drill cores).
Fig. 7: Young’s modulus profiles across the test cubes
(average values for all measurements on 5 mm slices cut from drill cores).
The profiles show steep slopes of BFS and YM from the surface to the interior in case of
the hand-treated cube E and the cube K treated with VCP and the pre-condensed
consolidant Funcosil 500E, respectively, whereas cube P treated with Remmers 300E and
VCP shows a more gradual decrease of the values for both parameters. According to
Snethlage (2014), the evolution of YM and BFS values per distance from the surface in a
profile, the relative increase in YM and BFS achieved through treatment as well as the
relation between YM and BFS are crucial criteria to avoid delamination of the stone surface
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
by “over-strengthening” the surface layer. Regarding the change of YM (≤ 1 GPa/mm) and
BFS (≤ 0.2 MPa/mm) from surface to the interior, the changes observed in the profile after
treatment with Funcosil 300E and VCP are within the limits established by Snethlage 2014
(cf. Fig. 6 and Fig. 7). Although the changes in YM and BFS for cube P, compared to YM
and BFS of its untreated inner core, are slightly over the limit in the outermost zone
(changes must be ≤ 50% according to Snethlage 2015), the results are generally satisfying
with that respect. Discussing these parameters, one has to keep in mind that, in contrast to
the hand-treated cube E, the impregnation depth reached by VCP in case of cube P is much
higher. Mechanical stresses affecting the stone material e.g. due to moisture load from the
surface will not reach deeper than a few millimetres, as indicated by the relatively low
capillary water uptake coefficient of fresh Cotta sandstone (1.5-2 kg/m2h0.5). The relation
between YM and BFS displayed in Fig. 8 shows a slight increase towards the surface
penetrated by the consolidant for the VCP-treated samples. Due to the strong scattering of
this coefficient even in untreated stone material this has to be discussed with some care. All
in all, however, the results obtained for mechanical parameters are acceptable in case of
VCP with Funcosil 300E.
Fig. 8: Relation between Young’s modulus and biaxial flexural strength along profiles
across the test cubes (average values for all measurements
on 5 mm discs cut from drill cores).
3.4. Hydric properties
The results obtained for total water uptake and hydric swelling are displayed in Fig. 9 and
Fig. 10. The results for water vapour diffusion resistance can be found in Fig. 11. As can be
seen from Fig. 9 and Fig. 11, water uptake is reduced in the impregnated zones, whereas
diffusion resistance has increased. The investigation of the pore size distribution of the
impregnated and the non-impregnated zones by mercury intrusion porosimetry
(Wichert et al. 2015) has shown that there is no significant change in pore volumes in the
diameter range between 0.1 and 100 µm, which is responsible for capillary transport. Thus,
the decreased water uptake and the increased diffusion resistance might be explained by a
slightly hydrophobic state of the outermost impregnated zones (i.e. the reaction of TEOS to
silica gel is still incomplete after 4 months because the humidity during setting the gel
obviously was too low). Testing with water droplets on the surface of the cubes confirmed
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
this assumption. Although changes are higher than demanded by Snethlage 2014 (≤ 20 %),
they should be reduced in future with further reaction of the consolidant. Measurements of
hydric dilatation (Fig. 10) did not show significant changes due to the impregnation.
Fig. 9: Total water uptake profiles
across the test cubes (measurements on 5
mm discs cut from drill cores; the discs
from the inner core were not measured
for cubes E and K).
Fig. 10: Hydric dilatation profiles across
the test cubes P and K (measure-ments
on 5 mm discs cut from drill cores; 1
parallel, 5 normal to bedding). Discs
from the inner core were not measured
for cube K.
Fig. 11: Water vapour diffusion resistance profiles across the test cubes
(measurements on 5 mm discs cut from drill cores; 1 normal, 5 parallel to bedding).
The discs from the inner core were not measured for cubes E and K.
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4. Conclusions
Treatments of test cubes made of Cotta sandstone with TEOS Funcosil 300E by hand and
with Funcosil 300E and 500E by VCP showed significantly higher penetration depths for
the VCP impregnated cubes. According to measurements of mechanical and hydric
properties on drill core profiles taken from the test cubes, the obtained spatial distribution
of BFS and YM are satisfying in case of Funcosil 300E and VCP, whereas the cubes treated
with Funcosil 500E (VCP) and 300E (by hand) show steep decreases of both values from
surface to the interior, which might be harmful with respect to delamination due to overstrengthening. However, the impregnated zones of all cubes are slightly hydrophobic,
indicating a still incomplete reaction of TEOS after more than 4 months. Although these
results in principle encourage the use of VCP in practice also for building stones with a
high amount of smaller voids, the role of partial vacuum during the process still remains
unclear, since similar penetration depths were reached by total immersion of a sandstone
cube under atmospheric pressure only by capillary suction. Due to the expectable wide
range of physical properties in geologically different stones, the results obtained cannot be
easily applied to similar sandstones. The decision for appropriate conservation techniques
needs detailed investigations of the stone properties and the weathering state in every case.
Acknowledgements
Thanks to Erich Pummer for the good cooperation within the common project and to K.
Bretschneider, W. Lange and M. Eilenberger for technical help. The project funding by the
German Federal Foundation for the Environment (Az 30408) is gratefully acknowledged.
References
Kozub, P., 2008, To the determination of the Young’s modulus from the biaxial flexural
strength, Proceedings of the 11th Int. Congress on Deterioration and Conservation
of Stone, Lukaszewicz, J.W. and Niemcewicz, P, (eds.), Torun, University of
Torun, 407-413.
Pummer, E., 2008, Vacuum circulation process, innovative stone conservation, in
Proceedings of the 11th Int. Congress on Deterioration and Conservation of Stone,
Lukaszewicz, J.W. and Niemcewicz, P, (eds.), Torun, University of Torun, 481488.
Snethlage, R., 2014: Stone conservation, in Siegesmund, S. and Snethlage, R. (eds.), Stone
in Architecture, Springer, Heidelberg, New York, Dordrecht, London, ISBN 9783-642-45154-6, 415-550.
Siedel, H. and Siegesmund, S., 2014, Characterization of Stone Deterioration on Buildings,
in Siegesmund, S. and Snethlage, R. (eds.), Stone in Architecture, Springer,
Heidelberg, New York, Dordrecht, London, ISBN 978-3-642-45154-6, 349-414.
Wichert, J., Siedel, H. Frühwirt, T. and Konietzky, H., 2015, Innovatives Verfahren zur
Festigung von schwer konservierbaren umweltgeschädigten Sandsteindenkmalen
und numerische geomechanische Simulation der Risiken, Report for the German
Federal Foundation for the Environment, TU Bergakademie Freiberg and TU
Dresden, 117 pp (in German).
962
MOULD ATTACKS!
A PRACTICAL AND EFFECTIVE METHOD
OF TREATING MOULD CONTAMINATED STONEWORK
B. Stanley1*, N. Luxford1 and S. Downes2
Abstract
Almost one third of English Heritage’s archaeological collections are stored in several areas
of Fort Brockhurst, Gosport. For the last decade an adequate environment was maintained
in these areas but during the summer of 2014 a combination of extreme moisture ingress
from heavy rainfall patterns, coupled with the catastrophic failure of the industrial
dehumidification units resulted in a widespread mould outbreak in one of these spaces. This
paper will discuss certain assumptions; including the ‘safe’ environmental range of below
65% relative humidity (not applicable to this Aspergillus strain) and suitable treatment
methods, following research carried out at Birkbeck College indicating alcohol based
treatment was also ineffective against Aspergillus. With relatively little literature available
regarding the efficacy and risks of alternative methods we will discuss several treatments
considered and the UVC method trialled and approved in more detail. Finally it will discuss
certain logistical and practical considerations relating to a large scale treatment of
approximately 36 metric tons of stonework.
Keywords: limestone, mould, hydrogen peroxide, ultra-violet, smart ventilation
1. Introduction
A large proportion of English Heritage’s reserve archaeological collections have been
stored at Fort Brockhurst, Gosport for the last decade. The spaces are turf-roof, brick-built
casemates, which although not typical storage spaces have maintained adequate
environmental conditions for robust collections, including stonework. During summer
2014, a combination of extreme moisture ingress from heavy rainfall and catastrophic
failure of the industrial dehumidification units resulted in a mould outbreak at Fort
Brockhurst. The rapid speed of events led to the contamination of a large number of stone
items; approximately 1,400 items, which were stored on wooden pallets but not crated due
to their size. The majority of the stonework was limestone, although sandstone and granite
were also present.
The risk of damage to collections from mould, including stonework is well documented,
with staining of stone commonly reported, Rodrigues & Valero (2003). Literature also
1
B. Stanley* and N. Luxford
English Heritage Trust, United Kingdom
bethan.stanley@english-heritage.org.uk
2
S. Downes
University of London, United Kingdom
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
describes how hyphal penetration of the porous spaces within stone, leads to bio-pitting,
particularly on marble and limestone, Warscheid et al (2000). In addition there are a wide
range of MVOCs that could also cause damage produced during the metabolic process of
fungi that may cause damage in high concentrations, Korpi et al. (2009). The risks from
damage due to germination in an environment with high RH levels meant the necessity to
remove the spores was paramount.
The most prevalent species were isolated from the environmental swabs and
morphologically sorted. Aspergillus was found to be the primary species and those with
varying colony morphologies were genetically analysed using the internal transcribed
spacer regions of the fungal rDNA. This was achieved by DNA extraction, PCR using the
primer pair of ITS4 and ITS5. The resulting products were screened for purity by gel
electrophoresis and then column cleaned and sent for Sanger sequencing. The sequences
produced were then base called, aligned and compared against published fungal sequenced
held by GenBank. Readings indicated a CFU count of over 10 times the recommended
limit. This posed a particular concern as this Aspergillus strain can have severe health risks,
Englehart et al (2002). As xerophilic fungi, this strain can grow at a reduced rate, below
65% RH, the ‘safe’ figure often quoted for environmental control. In-vitro, this species also
germinated within 24 hours of inoculation at 20°C so is incredibly fast growing.
Fig. 1: Air test results, October 2014.
2. Previous Research
Knowledge that the mould strain present at Fort Brockhurst would need considerably lower
RH levels than previously anticipated, highlighted that it might not be possible, or practical,
to achieve this throughout the year. This was of particular concern as analysis of weather
patterns indicated that 2104 was the fourth wettest year in the UK rainfall series from 1910,
behind 2012, 2000 and 1954, Kendon, McCarthy & Jevrejava (2015). The rainfall amount
in SE England during 2014 was 135% of the 1981-2010 average rainfall. This follows
approximately 30 years (1961-1990) of lower than the 1981-2010 average rainfall. Should
the increased rainfall seen during the last decade continue, it may be possible that previous
environmental control methods would be inadequate to maintain the environment
conditions in this store.
It was also important to know that should any collections be moved to another location and
stored with other objects no cross contamination might occur. Research carried out at
Birkbeck indicated alcohol based treatment was ineffective against this strain of Aspergillus
and there was little literature on the efficacy and risks of alternative methods. In-vivo,
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
although alcohols can have an inhibitory effect (70% methanol and ethanol) after two
weeks of incubation at 20°C, the effect on the growth of the fungi was no longer evident.
The ethanol was however more effective than the methanol. Other solvent treatments have
been trialled by this lab in the past (on organic materials) which resulted in both propan-2ol and IMS increasing the rate and intensity of re-colonisation after cleaning.
Sterflinger and Piñar (2013) have described the limited number of biocides tested for
cultural heritage use and outlined some of the risks, such as treatment with quaternary
ammonium compounds leading to a more resistant community, including melanised fungi.
Their work also describes the use of gamma radiation, which has both PPE and object risks
associated with it. Shirakawa et al (2004) described the disinfection followed by repainting
with or without a biocide included, whilst the biocide reduced the recolonization up to 10
months after treatment, after 12 months there was no statistical difference.
A common problem found was that papers either focussed on identifying the species
present without commenting on their removal (Ciferri (1999), Jurado et al (2008),
Montanari et al (2012)), or on possible treatments (Rodrigues and Valero (2003) Gatenby
(1990) Severson (2010)) without having identified the species. Little information was
available on successful treatment methods for specific species. Only recently have
assessments of the efficacy of a treatment started to appear in the conservation literature
(Mason and Scheerer 2014).
3. Treatment Criteria
The resilience of the mould species and quantity of collection needing treatment meant that
clearly any system had to be effective. Due to the scale of collection requiring treatment it
would also need to be practical to administer so therefore as quick and efficient as possible.
This would include the drying time necessary with wet treatments; a particular concern as
alcohol treatments had been discounted. The spaces available for storage and treatment
were unheated and therefore evaporation rate was likely to be slow. From Florian’s (2002)
paper it was clear a thorough misting was necessary to ensure the effectiveness of the
surface treatment but from tests this would result in a saturated surface.
With the quantity of stonework needing to be treated, cost was also a consideration. The
industrial treatment used for all non-collection items could be bought in bulk as a powder
and mixed as required, with minimal PPE. The grade of hydrogen peroxide required for
stonework treatment (silver filtered, rather than the commercial grade hydrogen peroxide,
which has acid added and therefore a lower pH, posing a risk to limestone) gave a cost of
over £200 per 5 litres. From spray tests, this would only be sufficient for several pallets
worth of stonework, so to treat approximately 450 pallets could potentially cost £20-30,000.
From the swab results, it was apparent that although the culture rate on the underside was
lower, it was still significant. Therefore all sides of the stonework would need to be treated,
in some instances the stone items weighed in excess of 200kg with an average weight of at
least 80kg. As we would need to buy in expertise to enable this work, the project was
treated as an opportunity to undertake any other outstanding issues at the time such as
weighing pallets and dealing with outstanding documentation or labelling of items.
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4. Analysis and Trialled Treatments
Smaller items such as bulk pottery, tiles and stone fragments are stored in plastic crates or
boxes. The contents were checked and the majority of objects were not found to have
mould growth. Surface swabs were randomly taken on a number of items and the results
confirmed that the spore count was low for these items. In the small number or instances
where active mould was observed, these crates were labelled and separated and all contents
were dry dusted and repacked (this work is on-going).
The exterior of all crates were sterilised, regardless of the visual or swab results of the
contents. Diluted hydrogen peroxide was suggested as a safer alternative to domestic
chloride bleach and this was tested at a concentration of 1.3% and 2.5% (to avoid lowering
the pH ). A concentration of 4% was also trialled on the plastics. Commercial treatments
Steri7™, Steri7 plus™ and Virkon™, which had previously been used at other properties
were also tested for effectiveness. The solutions were tested ‘in situ’ on a variety of plastic
crates and boxes and also in-vitro testing was conducted using an Aspergillus biofilm on
PDA plates. Results from both swab and culture tests indicated that the Virkon™ was the
most effective treatment, although Steri7™ products also performed well. Hydrogen
peroxide, even at 4% concentration was not effective without multiple applications,
hindered by the drying time needed between each cleaning and spraying application.
The Virkon™ and Steri7™, although very effective on the plastic containers, would not be
suitable for treating stonework. As well as the pink colouration from the Virkon™, both
solutions contain ammonium salts which would have the potential to cause harmful salts in
the structure of limestone, calcareous sandstones and marble stonework. Similarly diluted
domestic bleach could cause chloride salts to form. Hydrogen peroxide was initially
trialled, but at safe concentrations for limestone (1.2%) was found to ineffective without
multiple applications and long drying times. The solution would potentially fizz when in
the presence of biological factors (mould) but also if the limestone was reacting with the
solution. This made it very difficult to visually check for signs of damage whilst carrying
out the treatment.
Thorough cleaning using natural bristle brushes into a HEPA filter vacuum without further
surface treatment was also trialled. This is used extensively as a treatment for localised
mould, such as on a small area on the underside of a piece of furniture for example. It was
also considered that dry dusting might be the most practical treatment for collections that
were not robust enough to be treated by any of the systems tested and particularly where the
display or storage environment is likely to be more controlled. Interestingly it was found
that this method showed a significant improvement, with a 50-60% reduction of spore
germination on the lab cultures. Regular cleaning would also help to reduce the likelihood
of dust or organic matter depositing on the surface of collections on open display (including
stonework), which might encourage mould growth.
Previous work on UVC treatment had noted the appearance of a salt bloom due to salt
efflorescence as a result of heating and drying, Stewart et al (2008) and there was sparse
information regarding light sources, methodology and treatment times. Product literature
for UVC lights (Phillips UV Disinfection) gave values of the rate constant and required
dose for different bacteria, yeasts, mould spores, viruses, protozoa and algae, along with
calculations to determine the required dose for different UVC lights and treatment
parameters. Variables include the effective irradiance (lamp dependent) and the survival
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
rate. Calculations during the UVC trial demonstrated that reducing the survival rate for
Aspergillus niger from 10% to 1% required a doubling of the treatment time (from 57 min
to 114 min for the selected lights). As stonework would need to be treated and then turned
to treat the other side, the length of treatment time to be effective had a significant effect on
the schedule. For example a treatment time of 24 hours, Stewart et al (2008) would
effectively require a treatment schedule of 2.5 days per batch whereas a treatment time of 2
hours (calculated from the UVC lights selected) could potentially allow a batch of
stonework to be treated each day.
Fig. 2: Table of results for cleaning methods.
To test the UVC treatment a pallet of stonework with mould contamination was identified
to give a spread of differing stone types (limestone, chalky limestone, limestone with
extensive pitting and moss and lichen growth, sandstone, granite). Each item of stonework
was thoroughly dry dusted and placed on a plastic pallet. The test area was set up using
existing pallet racking shelving to support the light source, a metre above the pallet
containing the stonework. Three light fittings with Osram UVC 51V, 15W, G13 (T8) light
bulbs were selected and attached to the underside of the pallet racking shelf and the whole
area tented around with aluminium film to reflect the light inside the tent and black stage
curtain fabric to prevent possible light leakage. The lights were left on for 24 hours and
then the stonework was turned over and the process repeated. This was repeated with a
second pallet with a 2 hour UVC light exposure (calculations had indicated this would be
sufficient time to be effective). The difference in performance between treatment times
was negligible, with preliminary tests on individual pieces of stone showing 94% to 100%
effectiveness for both timescales.
5. Practical Treatments
With a suitable treatment tested and showing good results it was agreed to set up a room
space for large scale treatments to optimise the process. A sturdy garden marquee frame
measuring four metres square was purchased and lengths of battening cut to size to affix
florescent light fixings with Osram UVC 51V, 15W, G13 (T8) bulbs fitted. A total of 35
lights were dispersed around the frame. The windows were all covered with black stage
curtain fabric to prevent any light bleed and signage displayed on all doors leading to the
space. A risk assessment was prepared and shared with all staff, to prevent accidental
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exposure; including PPE, locking up procedure and operational safety. This space allowed
an optimum average of 25 Pallets to be treated each time. It would be possible to fit more
into the space but this then made the process of turning the stonework on pallets very
difficult and time consuming.
All stonework has now been treated; a total of 486 pallets, at just under 36 metric tonnes of
stonework. Swabs were taken at different points during the treatment, on different
collections and types of stone and other than one sample (which has been retreated and it is
assumed that human error was to blame, with the failure to turn the piece over) all readings
give a reassuringly low result. This is particularly relevant, as, in hindsight, the increased
distance between the pallets and the gazebo versus the trial racking increased from
approximately one to two meters should have merited a recalculation of treatment times.
6. Smart Ventilation and Environmental Improvements
With the removal of all objects from the storage spaces, all organic storage materials were
removed from the space (including shelving inserts). The area was completely cleaned and
decontaminated by a professional company (Rentokil) and the results were checked using
air samples gathered before and after cleaning. Once the spore levels were reduced to an
acceptable level consideration was given to the most effective way to control the
environment. Dehumidifiers were initially installed into the affected spaces to help reduce
high RH levels. Calculations had shown that for the volume of spaces, the number and
capacity of the dehumidifiers, should reduce the RH levels within a few hours. However the
environment failed to improve. This highlighted that water ingress was a current rather than
a historic problem resulting from heavy rainfall in 2014.
In some spaces there were fans built into the external wall of the casemate. These were
utilised to provide ventilation, however there were concerns that these would bring in damp
air from outside, exacerbating the problem. As a result a trial of smart ventilation was set
up. One of the key controls is to calculate the absolute humidity internally and externally
and switch on the fan when it is drier outside and turn it off when outside is damper. The
trial is continuing in one space, however the high moisture level inside means it is rarely
wetter outside and as a result other internal fans now run continuously. Additional internal
fans provide further air movement around the spaces to prevent the formation of damp
microclimates. The project has highlighted possible building failures leading to the ongoing water ingress. As a result investigations will shortly begin to determine the causes of
water ingress and identify possible solutions. This work will determine whether the spaces
are reused in the future or if alternative storage spaces will be required in the long term.
7. Conclusions
The treatment of such a quantity of collection has been a logistical challenge and has taken
substantial resources. It has also challenged the perceived wisdoms regarding mould,
without identifying the mould species it might have been assumed that maintaining an
environment of around 65% RH for robust stonework would be suitable for long term
storage. Similarly, many existing treatment methods in the available literature are not as
effective as initially thought and has challenged us to re-examine our methods.
Many positives have come from such an unfortunate situation. It has created an
opportunity to investigate more effective ways to deal with mould on robust collections and
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to quantify their effectiveness on real objects as well as in the lab. A more effective
solution has also been trialled and identified for non-collection materials such as crates and
boxes. It is also reassuring to know that good housekeeping can add reducing the potential
of mould germination, to its list of virtues. This information will be used to formulate
guidance on mould treatment and form the basis for any further research on treatments.
Discussion has begun about the merits of using this system on robust fired items such as
pottery and tiles, although further investigation will be required to confirm any glazes or
colorants will not be damaged and that thermal response will not cause an adverse reaction.
The existing equipment is still available and discussion has begun regarding setting up a
‘quick response’ system that could be used at different sites when appropriate. It has also
give an opportunity to reassess other protocols, for instance the collections team will revise
storage procedures to avoid substrates attractive to mould whenever possible, such as
wooden pallets in aggressive environments, and include mould outbreaks in Integrated
Emergency Planning. The stonework which has been treated has improved storage as it has
all now been thoroughly cleaned and treated and repacked. All documentation has been
checked and the new barcoding system used on all pallets to improve the tracking and
identification of objects. Although this not how we would wish to begin a storage project,
the works undertaken have resulted in improved conditions for all the objects involved.
Acknowledgments
A number of individuals have assisted during this project to bring the treatments to a
successful conclusion, but particular thanks must go to Timothy Hill and Adrian Braddock
who carried out the works on site. Also to the following English Heritage Trust staff;
Andrew More, Paul Lankester, Dave Thickett, Amber Xavier-Rowe, Kirsty Huggett,
Emma Hallums, Ann Katrin Koester, Pam Braddock, Cameron Moffett and Martin Allfrey.
Thanks also to Jane Nicklin and Krystina Merka-Richards from Birkbeck College.
References
Stavroudis, C., (compiled by), 2012, Superstorm Sandy: Frontline Advice for Dealing with
Mold and Salvaging Electronic Devices, WAAC Newsletter 34 (3)
Ciferri, O., 1999, Microbial Degradation of Paintings, Applied and Environmental
Microbiology, 65, 879-885
Engelhart et al., 2002, Occurrence of Toxigenic Aspergillus versicolor Isolates and
Sterigmatocystin in Carpet Dust from Damp Indoor Environments, Applied and
Environmental Microbiology, 3886–3890
Florian, M.L., 2002, Fungal Facts: Solving fungal problems in heritage. London, Archetype
Publications
Gatenby, S., 1990, An Investigation into Cleaning Procedures for Mould Stained Australian
Aboriginal Objects Painted with Modern Media, in 9 th ICOM-CC Triennial
Meeting, Dresden (26-31 August 1990), Grimstad, K. (ed.), Los Angeles, ICOM
Committee for Conservation, 157-162
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Gadd, G. M., 2007, Geomycology: Biogeochemical Transformations of Rocks, Minerals,
Metal and Radionuclides by Fungi, Bioweathering and Bioremediation,
Mycological Research, 111, 3-49
Jurado, V., Sanchez-Moral, S. and Saiz-Jimenez, C., 2008, Entomogenous Fungi and the
Conservation of the Cultural Heritage: A Review, International Biodeterioration
and Biodegradation, 62, 325-330
Kendon, M., McCarthy, M., and S. Jevrejeva (2015): State of the UK Climate 2014, Met
Office, Exeter, UK http://www.metoffice.gov.uk/media/pdf/0/a/State_of_the_UK_
climate_2014.pdf
Korpi et al., 2009, Microbial Volatile Organic Compounds, Critical Reviews in
Toxicology, 39, 139–193
Mason, L. and Scheerer, S. 2014, Mould Attack! – Assessment of Dry-Cleaning Methods
for the Decontamination of Leather, In ICOM-CC 17th Triennial Conference
Preprints, Melbourne, 15-19 September 2014, Bridgland, J. (ed.), Paris,
International Council of Museums, flash drive 0702_259
Montanari, M., Melloni, V., Pinzari, F. and Innocenti, G., 2012, Fungal Biodeterioration of
Historical Library Materials Stored in Compactus Movable Shelves, International
Biodeterioration and Biodegradation, 75, 83-88
Philips, n.d., UV Disinfection – Application Information: Perfection Preserved by the
purest of light
Rodrigues, J. D. and Valero, J., 2003, A Brief Note on the Elimination of Dark Stains of
Biological Origin, Studies in Conservation, 48 (1), 17-22
Severson, K., 2010, Formulating Programs for Long-Term Care of Excavated Marble:
Removing & Suppressing Biological Growth, in Proceedings of Conservation and
the Eastern Mediterranean: Contributions to 2010 IIC Congress, Istanbul, Rozeik,
C., Roy, A. & Saunders, D. (eds.), London, Archetype Publications, 172-177
Shirakawa, M. A., John, V. M., Gaylarde, C. C., Gaylarde, P. and Gambale, W. 2004.
Mould and Phototroph Growth on Masonry Facades After Repainting, Materials
and Structures, 37, 472-479
Sterflinger, K., 2000, Fungi as Geologic Agents, Geomicrobiology Journal, 17, 97-124
Sterflinger, K. and Piñar, G., 2013, Microbial Deterioration of Cultural Heritage and Works
of Art – Tilting at Windmills?, Applied Microbiology and Biotechnology, 97,
9637-9646
Stewart, J., More, A. and Simpson, P., 2008, The Use of Ultraviolet Irradiation to Control
Microbiological Growth on Mosaic Pavements: A Preliminary Assessment at
Newport Roman Villa, in Conservation: An Act of Discovery, 10 th Conference of
the International Committee for the Conservation of Mosaics, Palermo, October
20-26 2008, Michaelides, D. (ed.), Palermo, Centro Regionale per la Progettazione
e il Restauro, 296-305
Warscheid, Th. and Braams, J., 2000, Biodeterioration of Stone: A Review, International
Biodeterioration and Biodegradation, 46, 343-368.
970
INJECTION GROUTS BASED ON LITHIUM SLICATE BINDER: A
RVIEW OF INJECTABILITY AND COHESIVE INTEGRITY
A. Thorn1
Abstract
The bonding of detached sandstone in outdoor exposure remains a challenge where long
term stability must combine with sufficient durability to withstand exposure to severe
environmental stresses. Grouts that form or are comprised of minerals not identical to the
original surface run the risk of creating hydrothermal differentiation, altered permeability,
or chemical incompatibility that may lead to rapid future decohesion or the enhanced
growth of micro-flora that become more disfiguring than a poorly matched initial grout.
Following successful development of lithium silicate bound mortars, this paper focusses on
the development and performance of injectable grades that can be applied to closed voids
through 2-3 millimetre openings that set to form a substantial bond between detachment
and parent stone. Following these evaluations the best performing formulation has been
applied to a test site with satisfactory initial results. The visualization provided by the test
method allows the application to be far better informed about the need for consolidation
and injection grouting as symbiotic procedures.
Keywords: lithium silicate injectable grout, ethyl silicate, sandstone
1. Introduction
Previous studies have evaluated the potential for lithium silicate to consolidate sandstone
and calcitic stones (Thorn 2011a) including in wet conditions (Thorn 2011b) and to act as a
binder for bulk mortars (Thorn 2010) the final chapter in developing an all-round repair
material is in the capacity of lithium silicate as an injectable grout, applied by syringe to
closed spaces where it will provide adhesive reattachment of detaching stone. Ethyl silicate
has been trialled as a mortar (Leissen 2004, Thorn 2010) but found to be too weak and
lacking in both cohesion and adhesion when injected through a small opening. Ethyl silicate
rapidly loses strength when grain size is reduced to catheter dimensions and excess silicate
becomes a negative factor. Overall ethyl silicate is unsuited to the high adhesion demands
of an injectable grout. Lithium silicate by contrast has very high bond strength and is
capable, for example, of binding individual sand grains to a glass substrate at high strength.
This paper considers whether lithium silicate can be successfully formulated, pass through a
2 mm opening into a larger cavity, and form a cohesive and adhesive cured mass capable of
securing a detachment to its parent stone. The test methods have been influenced by the
very useful GCI manual - Evaluation of Lime-Based Hydraulic Injection Grouts for the
Conservation of Architectural Surfaces: A Manual of Laboratory and Field Test Methods
1
A. Thorn
Fine art and heritage site conservator, PO Box 333, Carlton North, Victoria 3054, Australia
Andrew.Thorn@artcare.cc
*corresponding author
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(Bicer Simsir B. and Rainer L. 2011). While this manual (referred to henceforth as the GCI
methodology) is focussed on the evaluation of grouts appropriate for calcitic plaster
attachment, its framework provides a useful starting point for the assessment of all
injectable grouts.
The focus on injectable lithium silicate has resulted in a stable material that can be injected
though a catheter or 2 mm opening to completely fill an enclosed void and secure a 10 mm
thick detachment to its matching parent stone. There are separation and shrinkage issues
that remain concerns but the testing has shown how these are not such an issue in real world
application or not as damaging as some test methods might indicate.
2. Grout formulation
The aim of this paper is not to give batching formulations, for which the research is not
complete enough, but to outline the parameters by which a successful injectable grout can
be designed. The limiting factors are that the material must be able to enter an enclosed
void through a two millimetre opening, flow to completely fill all parts of the void below
the hole and to set in a reasonable time to hold the outer detached surface in place with
sufficient adhesive strength. The applied grout must be absorbed into the cavity walls in
such a manner that both initial lubrication and final bond is achieved. The final set grout
should allow moisture to pass through at levels relevant to its location within the stone, as
opposed to how it might respond to direct surface flooding, and ensure that no staining of
the surface will develop through nutrient minerals migrating to the surface and thus
supporting differential bio-colonies. This latter condition is considered critical as mortars
and grouts of both lime and Portland cement have been observed to induce substantial dark
bio-staining on the surface even when placed at depth.
In earlier studies using ethyl silicate as binder, it was found that once the grain size was
reduced below 500 microns the cohesion strength reduced dramatically. Even with grain
size greater than this the strength of non-injectable ethyl silicate mortars was barely
satisfactory in terms of cohesive and adhesive strength. Lithium silicate mortars have much
higher adhesive and cohesive properties to the extent that where they were used to fill
surface cavities in a polished marble sculpture isolated sand grains from the mortar became
strongly attached to the polished surface surrounding the cavity.
Early experimental formulations reduced the lithium silicate content from its original 22%
solids content to as low as 2%. It has been found over the course of several years that
undiluted product will produce a readily water absorbent cured mortar and this is equally
the case with finer grained grouts. One of the advantages over ethyl silicate mortars is that
the material is water absorbent from the outset whereas ethyl silicate passes through a
strongly hydrophobic gel phase, remaining water repellent for several weeks. The downside
of water permeability is that the lithium grout or mortar is readily disturbed by rain and
must remain covered until complete set, as discussed further on.
Lithium silicate binder can be added in its supplied form or diluted 1:1 with water to make
a more porous grout with lower strength. Dilution with solvents is very limited with no
more than 20% ethanol being compatible in the liquid phase. Lime grouts contain large
quantities of free water and this has been considered deleterious. To minimize this,
conservators have for many years reduced the water content while maintaining fluidity by
substituting solvents such as isopropanol. This is only possible to a limited extent with
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
lithium silicate and the current testing has shown that this is not an essential requirement of
the grout.
The addition of phosphoric acid has been discussed elsewhere (Thorn 2012) as a means of
converting the bi-product lithium carbonate into the less soluble and more usefully binding
lithium phosphate. This reduces the pH of the applied liquid, producing a more durable
cured mortar. For this study the modification of the end product has not been addressed in
detail but phosphoric acid additions certainly produce a more durable material, especially in
wet conditions. This paper is focussed exclusively on the mechanics of injection, cure and
bond rather than the formulation of the optimal product, which will be discussed in time.
In preliminary trials mortar shrinkage was assessed by placing a coarse mix containing river
sand and gravel up to 5 mm into a straight sided glass culture dish. The curing mortar
expanded progressively over several weeks to finally shatter the dish. By contrast the finest
filler used in the mortar formulation was a trass (pozzolanic ash) incorporated solely for
colour matching purposes. The trass ranges up to 50 microns in size and when placed in the
same dish displayed extensive shrinkage cracking. Fig. 1 shows both results side by side.
Fig. 1: Two preliminary studies of the interaction between lithium silicate and silicate
fillers. On the left a coarse river sand expanded to the point where the glass container was
cracked. On the right a very fine Trass (pozzolana) shrank excessively.
Quartz flour sieved to 100 microns showed no internal shrinkage cracks but some
peripheral shrinkage. Increasing the grain size to 300 microns did not alter the shrinkage
pattern to any substantial degree. Fig. 2 gives the particle size distribution of the chosen
quartz flour (Sibelco 100WQ) in comparison with other grades.
Grouts applied to enclosed cavities do not need to match surface colour and those applied to
open pockets can be capped with an appropriately matched mortar optimized for exposure.
Hence the current trials have focussed only on granulometry and not aesthetic
considerations. It is important to note however that injectable lithium grouts will, like other
materials, adhere to the opening, which itself needs to be capped to complete the treatment.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 2: Particle size distribution of the selected filler 100WQ compared to two other grades
of Sibelco quartz flour.
3. Test methods
3.1. Shrinkage
The GCI methodology measures shrinkage by placing a quantity of fresh grout into an open
cup made from either an impervious material or, in another method, from a plaster cup,
which better emulates the natural placement conditions, particularly with reference to
absorption during set. In the current development lithium silicate at 20% and 10% solids
(the latter diluted with water 1:1) were mixed with quartz flour 100 WQ to a viscosity that
could be drawn into a 1 mm diameter catheter. The quartz to lithium silicate ratio was
established intuitively to give the desired pick up viscosity than confirmed as 100:55 filler
to binder ratio.
Adopting the GCI methodology created a difficult result. The upper surface shrank
dramatically after about 2 weeks (Fig. 3), but exposed a very stable cured grout beneath.
This anisotropic cure was clearly the result of surface effects of evaporation and reverse
migration depositing excess lithium silicate in the outer crust. A similar crust had been seen
on some of the previous test mortars prepared in glass dishes, although this has never been
an issue with many site trials where the cured mortar remains very close to the texture of
the surrounding stone, largely due to the constant working of the surface to achieve a level
and suitably textured finish.
Under the GCI methodology the grout would not pass the shrinkage test, however it was
recognized that an open cup does not represent the true placement conditions. An enclosed
cavity does not have a broad surface exposed to the atmosphere but rather two broad
surfaces in contact with the stone, a lower depth of ever decreasing dimensions to a point
where an homogenous grout will cease to flow, and an upper thin surface exposed to a wide
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opening or small drill hole of no more than 4 mm. A series of modified test procedures
were adopted to better reflect the real life dimensional configuration that could also observe
the flow and cure behaviour over time. Time lapse photography was employed to record the
behaviour of each test.
Fig. 3: Excessive shrinkage from the 100:55 quartz flour : lithium silicate formulation
when poured into an open impervious cup. This result led to the alternative test methods
relying on more replicative applications to vertically oriented cavities.
The series consisted of combinations of stone surfaces and 1.5 mm thick transparent plastic
sheet (polyethylene phthalate glycol - PETG). The configurations were as follows and as
illustrated in Fig. 4:
Two sheets held vertically and spaced 2 mm apart. All edges were sealed except the
top access surface. The top surface could be temporarily sealed to emulate the access
hole dimensions and natural evaporation conditions.
Two sheets, as above but clamped along the bottom edge to provide a wedge shaped
cavity of decreasing width down to less than 0.1 mm.
One PETG sheet spaced 2mm off a sawn sandstone surface and sealed as above
A 10 mm thick sawn sheet of stone spaced with 2mm wooden spacers off a larger
sawn parent stone, the detachment held against the spacers and removed at timed
intervals. The 10 mm detachment was considered to be heavier than most detachments
that are more typically no more than 3 mm in thickness with proportionally less mass.
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Fig. 4: The four cavity configurations. From the left; two PETG sheets spaced 2mm apart
(top view), the same sheets formed into a tapered cavity closed but not sealed at the bottom
(side view), a PETG sheet spaced off a sawn sandstone block, and a 10 mm thick block
pressed dry onto spacers and then filled with grout. The 10 mm detachment fell after 2
hours but remained firmly in place after 14 hours.
Applying grout to the spaced parallel sheets resulted in an homogenous gout showing initial
shrinkage but eventually, bleed liquid above the initial settlement mark. There was an initial
shrinkage of 10.5%, but upon release of the bleed liquid the final level showed a net
expansion of 6.7%, all of which was lithium silicate solids with no quartz flour filler
(Fig. 5). Further grout applied to the system, emulating a sequential application such as
those necessary to fill large voids, settled onto the top of what had seemed to be bleed
liquid but was in fact solidified lithium silicate. This was undesirable to have a thin band of
solid lithium silicate creating a differential band in the void but also most likely continuing
to a point where it became a brittle non-adhesive rubble in the fill. The final product
showed no signs of cracking, with the shrinkage along the top edge being the only defect.
Expansion of more than 6% may present issues in a closed system, however this only
occurred in the wholly PETG wall scenario. Once stone surfaces were introduced into the
system all bleed liquid was absorbed and no expansion was noted. The PETG on stone
configuration produced an almost perfectly stable dimensional material.
Two sheets of plastic are far from an accurate model for a detachment void in stone. The
next test applied the grout between a plastic sheet spaced off a sawn stone surface. In this
case there was no bleed liquid as it was absorbed into the stone surface as it formed, or was
sufficiently absorbed not to form at the upper surface of the grout. In all tests involving
stone surfaces the stone was saturated with lithium silicate to emulate a normal treatment
protocol. The cured grout appeared stable and in this case did not develop a transparent
lithium silicate upper edge.
The same 100:55 grout was applied to the two stone surfaces following saturation with
liquid lithium silicate. The 10 mm detachment was considered far heavier than a typical
delamination but an appropriate measure of the ability of the grout to form bonds
sufficiently strong to hold such weight. Stone detachments were spaced 2 mm from the
surface and held in place by a single telescopic prop typically used in practice. Once the dry
system was secured in position the internal stone walls were pre-wet with lithium silicate
and the void filled with grout. No topping up was attempted but any leakage through the
spacers was plugged and the void filled to near the top. The prop was removed after 2 hours
with immediate failure. The prop from the second sample was removed after 14 hours
(replicating overnight curing) and in this case the 10mm thick detachment remained
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
perfectly positioned and secured to the parent rock. At this stage no intermediate setting
times have been established and it is reasonable to propose a 24 hour propping period for
normal field practice.
Fig. 5: Grout applied to parallel PETG sheets shrank initially by 10.5% but the bleed
liquid formed a transparent solid block that showed a final expansion of 6.7%. A further
grout application has been applied over the first to indicate the final level of the lower
application. Expansion and bleed liquid were only apparent where two plastic sheets
formed the walls of the cavity. Once sandstone walls were introduced they absorbed all
bleed liquid and showed shrinkage only.
The stone on stone sample was further exposed to outdoor conditions for 45 days where it
received rain, incidental watering and ambient temperatures of up to 40°C. After the 45
days the detachment was separated from the parent rock to empirically assess its bond
strength and, more importantly, the consistency of the cured grout. It was seen that the
grout displayed a network of shrinkage cracks not seen in the test configurations involving
plastic sheet (see figure 6). There was no evidence of bleed water related transparent
lithium silicate but some evidence of shrinkage to the open top surface but not away from
the three enclosed sides. The test, as with all those previously described, relied on the bond
strength of pure lithium silicate without the additions, previously indicated, that improve
the strength and rheological properties of cured product. At this stage the research is
concentrating on the performance of pure lithium silicate knowing that it can be
strengthened with proven additions.
Fig. 6: Grout applied to two sandstone surfaces remained secure for 45 days at which point
it was separated. The bond was adequate but lower than ideal. The inner surface showed a
network of cracks that no doubt contributed to this. The shrinkage is considered to be the
result of the stone sucking liquid from the grout too quickly, emphasizing the need for
adequate pre-wetting of the inner surfaces.
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The final grout was adequate for reattachment of a heavy detachment but less than achieved
with the plastic sheet trials containing all of the grout with no absorption into adjacent
porous material. The grout formed between two stone surfaces was also substantially
weaker than lithium silicate mortars applied directly to stone surfaces. From this a couple of
points of consideration emerge. The first is that wetting of the inner stone surfaces must be
thorough; a critical consideration when applying gouts to closed voids. The second is that
further improvement is desirable. While the lithium silicate was adequate it was not ideal.
Both the addition of silica sol and especially phosphoric acid has shown a marked
improvement in cohesive strength of lithium silicate mortars and these refinements will be
evaluated in ongoing trials. The additive performance is already well understood from
previous mortar trials and thus the transfer of knowledge presents reasonably well defined
parameters.
3.2. Bleed liquid
Bleed water has been discussed already but it is worth highlighting the issues specific to
lithium silicate grout. The GCI methodology for lime grouts defines limits of 0.4% bleed
water. This may be significant for lime gouts as the excess water contributes little to the
final product but substantially to shrinkage cracking and other defects. Recent field research
on the stabilisation of clay renders for Himalayan mural paintings by Nicolaescu (2016), in
which this author assisted, it was found that the bleed water content of the ideal clay based
grout was almost 9%. In that research the amount of water required to pre-wet the clay
walls, using industry standard pre-wetting procedures, exceeded the bleed water content of
the clay based grouts. Hence bleed water was considered less threatening to the stability of
the mural than the accepted pre-wetting regime. The 9% bleed water is that achieved in a
glass cylinder and, as in the lithium silicate experiments described above, does not translate
to conditions encountered inside a clay void where suction into the render on one side and
the mass of adobe blocks on the other determines that no amount of bleed water will
neutralize suction.
Bleed liquid measured in a sealed container reached approximately 10% after 24 hours.
This was less than the solid transparent lithium silicate zone formed in the vertical cavity
trials (figure5), which indicated a 16% expansion from the maximum shrinkage to final
expansion states.
The current view of bleeding, both in clay stabilisation and the current research, is that its
contribution to the grouting process needs to be clearly understood and not assumed to be
negative without firm evidence. In the current research bleed liquid is considered positive,
as illustrated by grouts flowing into the plastic sheet wedge aimed at measuring unimpeded
flow properties. In this test the standard 100:55 grout was deposited into a plastic wedge
with both sides sealed, the bottom clamped tightly together and the top open to a width of
approximately 5mm. The side view of this configuration, any point of which could be
precisely measured from photographs, can be seen second from the left in figure 4. The
grout flowed quickly initially to where it stopped flowing at around 0.9mm width. Over the
following 24 hours the grout continued to flow into finer voids, eventually arriving at the
bottom of the wedge where the width was less than 0.2 mm. During this delayed flow, and
perhaps because of it, bleed liquid emerged at the bottom of the void rather than at the top
of the grout. Two phases developed, one a transparent phase of presumably pure lithium
silicate and a second milky phase that contained some quartz flour. Fig. 7 shows after 5
days that the grout has separated into three phases. The bulk of the grout remains in the
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
zone 0.2-0.9 mm with a milky phase flowing into available spaces. The clear areas in the
lower section are all solid lithium silicate, indicating that the grout is self-filling through the
release of bleed liquid. While the intended 100 micron grout formulation does not flow
much below 200 microns the subsequent bleed phases do allow further penetration. Torraca
(1981) has articulated the importance of securing a detachment at its crack propagation
point and the bleed liquid can achieve this better than the bulk grout alone. It has to be
borne in mind however that lithium silicate bleed liquid is not observed once a porous wall
is introduced into the system. Lithium silicate will be deposited into the finest pore spacings
through the pre-wetting treatment and the treatment does not rely on bleed liquid
performing this function.
Where the 100:55 grout was applied to two stones surfaces the pull-off resistance was
lower than desired. This combined with the crazed inner surface (Fig. 6) suggests that
rather than excessive bleed liquid, the system suffers too much from suction into the stone
surfaces, leaving the grout depleted of binder. This means that no further reduction of
lithium silicate is currently contemplated and that a more thorough pre-wetting regime is
necessary.
Fig. 7: Lithium silicate grout applied to a tapered cavity ranging from 5 mm at the top to
less than 0.2 mm at the bottom. The grout sat initially at cavities greater than 0.9 mm then
in time began to flow into the finer dimensions down to 0.2 mm. This only began once the
bleed liquid provided addition lubrication and some separation of the particles began. The
clear areas at the bottom are transparent lithium silicate solids while a zone of milky grout
can be seen along the left edge in two places.
3.3. Flow
The GCI protocol describes two means of assessing flow. The first is flow down an open
grooved tile where 10mL of an ideal grout should travel at least 200 mm, and the second is
a rubble filled syringe through which the grout should flow and depart through the open
hole at the bottom.
These tests were performed using the lithium silicate grouts. The open tile test achieved a
high score and the rubble filled flow test showed gout flowing through the rubble
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adequately, provided it was sufficiently wet prior to grout application. The grout, due to its
broad viscosity tolerance (pure lithium silicate Li 22 will set into a solid transparent film
that maintains structural stability for years) can have controlled flow depending on the
application. What would be considered too wet in a lime based grout will form a solid
stable lithium silicate grout. Films of lithium silicate and quartz flour that formed on the
sides of the plastic sheet could be removed as thin sheets of less than 50 microns and retain
their cohesive structure and yet these would have been very liquid films when applied.
4. Conclusion
While the work described here remains experimental the final grout, using several
modifications not yet discussed, will be applied to a controlled field trial at a site that has
received extensive ethyl silicate grouts over 20 years. It has been established that the
lithium silicate mortar variant is far superior to those achieved with ethyl silicate. Injection
grouts were not possible using ethyl silicate with the injected product lacking cohesive and
adhesive properties when applied to porous surfaces.
The lithium silicate grouts described here have proven themselves capable of attaching an
oversized delamination to parent rock with minimal pre-wetting and preparation. Earlier
mortar development with modifications of silica sol and phosphoric acid, while not
complete enough when incorporated into injectable grouts to describe here, increase the
cohesive strength. This combined with a more thorough pre-wetting regime should ensure
that a lithium silicate based injectable grout is capable of reattaching stone in the short
term. Controlled trials will establish the longevity of such treatments.
References
Leisen, H., von Plehwe-Leisen, E., Warrak, S. 2004. Success and limits for stone repair
mortars based on tetra ethyl silicate-conservation of the reliefs at Angkor Wat
Temple, Cambodia. In Proceedings of the 10th International congress on
Deterioration and Conservation of Stone; ICOMOS Sweden, Stockholm. 331-338.
Nicolaescu, A.C. 2016. Conservation of Buddhist wall paintings with traditional materials.
In XII World Congress on Earthen Architecture, Lyon. In press.
Thorn, A. 2010. Two siliceous grouts for the preservation of stone. In Proceedings of the
2nd conference and of the Final Workshop of RILEM TC203-RHM: Pro 78;
Historic Mortars. 1199-1208.
Thorn, A. 2011a The consolidation and bonding of water-saturated siliceous stone with
lithium silicate —A preliminary evaluation. In Proceedings of the Canadian
Conservation Institute Symposium 2011: Adhesives and Consolidants for
Conservation. Accessed on 05/02/16 at https://www.cci-icc.gc.ca/discoverccidecouvriricc/PDFs/Paper%2028%20-%20Thorn%20-%20English.pdf.
Thorn, A. 2011b. Preliminary evaluation of lithium silicate for consolidation and grouting
of stone in wet locations. In Wall Paintings in Crypts, Grottoes and Catacombs.
Strategies for the Conservation of Coated Surfaces in Damp Environments.
ICOMOS Germany.
Torraca, G., 1981, Porous Building Materials: Materials Science for Architectural
Conservation. ICCROM Rome.
980
INNOVATIVE TREATMENTS AND MATERIALS FOR THE
CONSERVATION OF THE STRONGLY SALT- CONTAMINATED
MICHAELIS CHURCH IN ZEITZ, GERMANY
W. Wedekind1*, R.A. López-Doncel2, J. Rüdrich3 and Y. Rieffel4
Abstract
The sandstone of the Michaelis Church in Zeitz shows a strong decay in form of relief and
alveolar weathering. The main cause for the deterioration is an extreme salt attack by
magnesium sulfate. The stone as well as the weathering forms were investigated. The
alveoles were desalinated by using a sprinkling method and filled by a developed hot-lime
mortar. Consequently, a concept of conservation could be formulated from all the
investigations and the results obtained from the treatments that could be successfully
applied in a test case.
Keywords: alveolar weathering, salt, desalination, conservation
1. Introduction
The Michaelis Church in Zeitz represents a 10th century building, which has consistently
undergone modifications to its façade over time. The church was constructed out of
dolomite cemented sandstone that often shows alveolar weathering as a result of salt
weathering (Ruedrich et al. 2006).
2. Preliminary investigations
2.1. Geological setting, rock material and weathering agents
2.1.1. Geological setting and rock material
The walls are constructed from the regional sandstone (Buntsandstein Formation).
Hirschwald (1910) mentions quarries near Kretschau and Kuhndorf. Other large rock
formations are located in the north-eastern region around the Zeitz as is shown in (Fig. 1b).
1
W. Wedekind*
Geoscience Centre of the University Göttingen and
Applied conservation Science (ACS), Göttingen, Germany
wwedekind@gmx.de
2
R.A. López-Doncel
Geological Institute, Autonomous University of San Luis Potosi, Mexico
3
J. Rüdrich
Geoscience Centre of the University Göttingen, Germany
4
Y. Rieffel
Berlin Monument Authority, Berlin, Germany
*corresponding author
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Fig. 1: a) The main wind and rain directions in percent (www.windfinder.com). b) Zeitz
and its environs around 1912 with location of quarries and industrial areas. c) Lithograph
of the medieval city of Zeitz from the “Topographia Germaniae” by Matthäus Merian
(1593-1650), showing the outstanding historical buildings and topography. d) The western
façade of the church in 2005.
2.1.2. Environmental impacts and geographical setting
During the industrial revolution Zeitz became one of the main centers for charcoal
extraction and coal briquette production, starting in 1800 and continuing up into the 1990s.
The briquette production factories, that produce a high content of sulfur from industrial
pollution, were located near the mining areas west of the town. The church is located on a
hill at the southwest of the historical city. The main wind and rain direction is from the
southwest with 13.4 %, followed by a west-southwest direction with 11.6 %, and the southsouthwest with 10.9 % (Fig 1a). Consequently, sulfur pollutants were transported
continuously in the direction of the historical city over a period of nearly two hundred
years. The impact can be seen today on the Michaelis Church, which exhibits dramatic
forms of alveolar weathering on the western and southwestern side of the building (Fig. 1d,
Fig. 2b).
2.1.3. Salt and weathering forms
In the case of historical buildings in Zeitz, industrial pollution in combination with the
binding material of the sandstone creates a salt with a high potential for damage:
magnesium sulfate. This salt results in extensive salt weathering in historical monuments as
well, if dolomite-cemented stone or mortar and gypsum mortars are present (Siedel 2003,
2013, Wedekind 2014). The system of magnesium sulfate consists of three stable
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
crystalline phases in the atmosphere with a different number of water molecules bound
within the crystalline structure: epsomite (MgSO4 · 7H2O), hexahydrate (MgSO4 · 6H2O)
and kieserite (MgSO4 · H2O). The damage potential of magnesium sulfate can be traced
back to the stress generated by crystallization and hydration (Steiger et al. 2008). The main
stress is induced by salt crystallization (Balboni et al. 2011). Salt weathering in Zeitz is
characterized by contour scaling associated with alveolar weathering (Fig. 2).
2.2. Methods of Investigations and applied conservation
2.2.1. Petrographic and petrophysical properties of the rock
Porosity and the matrix- and bulk density were measured using hydrostatic weighting (DIN
52 102). The capillary water absorption or water uptake was measured on cubes (65 mm)
with respect to the X, Y and Z directions. For the compressive strength tests, standard
cylindrical specimens of 50 mm in diameter and 50 mm in length with co-planar end-faces
were used and tested by a servo-hydraulic testing machine. To assess the salt weathering
sensitivity of the investigated sandstone in this study, a salt-weathering test according to the
standard DIN EN 12370 was performed. Polarisation and cathodoluminescence microscopy
on standard thin sections were used for the petrographic analyses (e.g. mineralogical
composition, grain boundary geometry, average grain size and sorting).
2.2.2. Onsite investigations
To register and evaluate the weathering damages, mappings of intensity and forms were
done for selected sub-areas at the main façade of the building. Samples were taken by drill
cores (Fig. 5 b). The amount of soluble salts was measured by ion chromatography and
photo-spectrometry. In order to identify the crystalline salt phases, x-ray diffraction was
carried out.
2.2.3. Desalination and evaluation
Salt reduction is a basic prerequisite for a sustainable restoration. The most suitable
desalination method is dependent on a number of factors. Factors that need to be taken into
account are the rock material, the degree of contamination and depth and type of salt
responsible for the damage. It becomes clear that the contamination detected at depth can
not be reached by the poultice method (Fig. 4b) and the drying rate of the material is quite
small. In general, immobilization of the salt by chemical ionic exchange and subsequent
precipitation would be possible but in this case difficult to control. For this reason the
sprinkling method was chosen as the most effective technique in terms of function, time
and costs. To evaluate a suitable conservation treatment a strongly weathered pillar was
chosen as a test case. The surface of the pillar was divided into different treatment sections
(Fig. 2). The development of weathering was documented by using historical photos
(Fig. 2a to 2c).
The sprinkling method was developed for the desalination of salt contaminated tafoni of the
rock cut façade in Petra/Jordan (Wedekind, Rüdrich 2006). The method was already used
successfully for the desalination of architectural elements at the Franciscan Church in Zeitz
(Wedekind, Rieffel 2014). Through spray nozzles, connected within a raster-like pipe
system, water was sprayed on the different sections. The water running down the pillar was
collected and measured by electrical conductivity. At the beginning of the procedure the
water is predominantly absorbed by the porous stone surface through capillary forces.
Water absorption is dependent upon the transport properties of the material. These are
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
controlled by the pore space properties, such as porosity and pore radii distribution, and are
a time-dependent process (Wittmann 1996).
At the lower end of the treated area a drain gutter was constructed from clay, so that the
eluate can be funneled into a sample container. Excess water not absorbed by the stone was
collected in five liter amounts and measured for electrical conductivity (mS/cm). Fifty liters
of eluate were collected and tested in five liter amounts per cycle. The sprinkling was
terminated after a treatment of about 10 minutes. After every sprinkling cycle, a break of
one week was observed in order to initiate the drying procedure, which leads to the
concentration of salts in the near-surface area of the stone.
Five cycles were done over a period of three months. The correlation between the electrical
conductivity and the real content of soluble substances within the eluate was calculated by
evaporation of different samples consisting of one liter eluate in a drying oven and
weighing. Consolidation was not necessary because all the unstable material was removed
by the smooth washing process of desalination.
Fig. 2: a-c) The chosen pillar during different years. d) Architectural drawing with
weathering conditions and treatment areas and e-g) alveolar weathering forms in detail.
2.2.4. Material physics of the restoration mortar
As a finishing mortar for restoration a modified hot-lime mortar was configured. To reduce
and to control the speed of thermal reaction as well as to enhance the workability, an
additive of a hydraulic binder was added to the dry mortar mix. The change in reaction
could by measured by thermal expansion and temperature. Crushed and sieved sand made
from the local sandstone with a grain size distribution ranging 0.1-0.5 mm was used as
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
aggregate to create compatibility with the stone material. Specimens after DIN EN 196-1
(4×4×16 cm) of different mortar mixes were made: The binder/aggregate composition of
the hot lime mortar was 1:3. Main binding material of the specimens for the hot lime mortar
was unhydrated lime Cl 80 Q modified with white Portland cement (WC) in different ratios.
During the process of hardening, the surface temperature as well as the dilatation was
measured on the specimen top to evaluate the intensity of the exothermic reaction and the
process of expansion and shrinking. After 28 days of drying under the same conditions,
porosity, density and flexural (FS) and uniaxial compressive strength (UCS) were
measured.
3. Results
3.1. The sandstone
3.1.1. Petrography
The sandstone of Zeitz mostly has a yellow color. Besides these varieties, which clearly
dominate the stone architecture of the town, grayish to greenish types are also present. The
medium sandstones show a good parallel or obliquely layered structure. Many sedimentary
structures like cross bedding and wavy lamination, mudcracks and ripple marks are
observable. The sandstones show grain sizes ranging 0.2 to 0.5 mm, are poorly rounded to
angular, well-sorted grains of polycrystalline and monocrystalline quartz (50 - 60% vol.),
feldspars (35 - 40%) and lithoclasts (<10%) and are embedded in dolomitic cement. The
rather coarse cement proportion (40%) is dolomitic and shows a clearly oolithic texture
(Fig. 3 a), causing a very strong reduction in porosity. The secondary porosity is caused by
a local, minor dissolution of the cement and its values range 1 - 3% of the whole rock (very
poor porosity) (López-Doncel et al, 2002).
Fig. 3: a) Thin section of the Zeitz sandstone Rounded oolithes are visible in grains of
mono- and polycrystalline quartz) and feldspars, which are embedded in a dolomitic
matrix. b) Thin section under cathodoluminescence. c) Salt bursting test and d) weathering
related to the bedding.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
The color of the stone is due to high concentrations of feldspar, mica and clayish substances
clearly identified by CL-microscopy (Fig. 3b). The dolomite cement could be determined
by cathodoluminescence microscopy (red), clay is blue and feldspar shows a light blue
color (Fig. 3b).
3.1.2. Petrophysics
The rock material has a low porosity that varies between 3 and 15 % with a dominance of
macropores, and contains a homogeneous fine to medium grain size with a clearly visible
layered structure. The dolomite cementation varies between 13 and 76 % by volume, and
therefore reaches a density of 2.72 g/cm3. The stone has a low water uptake rate (averaged
0.8 kg/m2 that varies as much as 46 % with the bedding direction. Compressive strength
with 100 N/cm2 is quite high as compared to other sandstones. This may be the reason why
the stone shows a good resistance to salt bursting, which was performed on cubic samples
6.5 by 6.5 cm in size and submersed in a 10 % NaSO4 solution (DIN EN 12370). A material
loss of 30 % after 30 cycles could be determined (Fig. 3c). After discoloration due to iron
oxidation, a massive contour scaling starts at the 20 th cycle and continues with further
material loss (Fig. 3c). In the last stage a weathering related to the bedding is observable,
which can also be found at the church building (Fig. 3d).
3.2. Weathering forms and agents
3.2.1. Weathering forms
The sandstone blocks show severe deterioration with weathering depths up to 30 cm
(Fig. 4a to Fig. 4c). The main decay phenomena are two different types of weathering,
relief and alveolar (Fig. 4a). Dark crusts and discolorations are of only subordinate
importance. Weathering is characterized by heterogeneous back-weathering, which depends
on the bedding of the sandstone. The relief "weathering type I" represents a modified
alveolar weathering, which is characterized by deep gouges. The material loss is dominated
by granular disintegration. For "relief weathering type II" the weathering intensity is slight
with up to 3 cm. Strong back-weathering also follows the bedding of the sandstone. This
weathering form achieves back-weathering rates up to 30 cm. The material loss in the
gouges is dominated by flaking and contour scaling. Relief weathering type II is located at
areas of direct water action, whereas relief weathering type I and strong back-weathering
occurs in expositions protected by water run-off but effected by moisture penetration.
3.2.2. Salt-weathering
The x-ray diffraction shows that different magnesium sulphate hydrate phases are
detectable. Next to epsomite (MgSO · 7H2O) and hexahydrate (MgSO · 6H2O) kieserite
(MgSO · H2O) also occurs (Fig. 5a). The quantitative salt analyses show that the salt
content of magnesium sulphate from samples of relief type II is much higher than those of
relief type I (Fig. 5b). Some samples taken out of the alveolar weathered areas show a
contamination that reaches a profile depth of more than 10 cm (Fig. 4b and Fig. 5).
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 4: a) Weathering forms, b) damage intensity and
c) reasons for material loss at the testing area.
Fig. 5: a) X-ray diffraction of the salt efflorescences shows different MgSO-phases. b)
Quantitative salt analyses in the depth profile taken from different weathering zones.
3.3. Conservation/restoration
3.3.1. Desalination
Around 1100 g of soluble material could be extracted, while the desalination rate of the
different sections differs between 21 g/m2 and 71 g/m2 according to the intensity of
weathering (Tab. 1). The effect of desalination was also tested by drill dust samples that
show a significant decrease of salt load after treatment.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Tab. 1: Summary of results from the desalination.
Sprinkling
area
Sum of electrical
conductivity
Total salt content
Rate of desalination
[mS/cm]
[g]
[g/m2]
I
61.68
88
22
II
121.32
173.3
69.3
III
187.66
286
67
IV
86.91
124
31
V
201.46
288
71
VI
97.76
140
21
Total /
757.78
1099
44
3.3.2. Restoration
During the hardening of the pure hot lime mortar (Cl 80 Q), the temperature rose from
21°C to 45.7°C in a period of 10 minutes (Fig. 6a). The expansion reached 0.8 mm, a
percentage of 2 % and exhibits a low shrinking tendency (Fig. 5b). The specimens modified
with the white cement (WC) attained temperatures of 29.6°C/8min to 37.3°C/18min
(Fig. 7a). No shrinking took place but a moderate expansion ranged between 0.1 mm and
0.5 mm (Fig. 6b). The mortars modified with white cement reach up to two times higher
values of compressive strength (USC) and flexural strength (FS) than the pure hot lime
mortar (Fig. 6c). The different amounts of the hydraulic additive result in an increase from
1.42 MPa to 2.05 MPa in the case of USC and from 0.58 MPa to 0.98 MPa for FC as shown
in Fig. 6c.
Fig. 6: a) Exothermic reaction of the different mortar mixes and b) expansion/shrinking of
the different mortar mixes. c) Compressive and flexural strength of the different mortars.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
4. Final Conclusions
The results of these investigations lead to an understanding of the weathering process and
the development of a suitable conservation strategy. By using the described sprinkling
technique for desalination, a control of the process was immediately possible by electric
conductivity measurements. This allows a calculation of the contamination as well as the
planning and application of the whole desalination process. The hot lime mortars show
interesting properties for stone conservation and restoration. According to the results, a
fractional amount of white-cement improves the mechanical properties as well as the
workability of the material. For restoration the variety with a CaO:WC ratio of 3:1 was
chosen. Structural interventions can be prevented in the historical building by the
desalination and mortar filling method, thus costs can be reduced by around 30%.
Furthermore, by conservation instead of traditional restoration the church can be restored
close to the international regulations of conservation as defined in the "Charta of Venice"
and other regulations of ICOMOS (International Council on Monuments and Sites).
Acknowledgments
We would like to thank master sculptor Christian Spaete and architect Regina Hartkopf for
their friendly cooperation.
References
Balboni, E., Espinosa-Marzal, R.M., Doehne, E., Scherer, G.W., 2011, Can drying and rewetting of magnesium sulfate salts lead damage of stone?, Environ Earth Sci, (63,
Issue 7-8), 1463-1473.
Hirschwald, J., 1910, Die bautechnisch verwertbaren Gesteins-Vorkommnisse des
Preussischen Staates und einiger Nachbargebiete. Bornträger, Berlin.
Ruedrich, J., Seidel, M., Wedekind, W., Siegesmund, S., 2006 Damage Phenomenon and
Salt Deterioration at the Michaelis Church in Zeitz (Germany). Poster-presentation
at the EGU General Assembly 2006 Vienna, Austria.
López-Doncel, R.A., Heise, G., Kulke H., 2002, Kirche Breunsdorf - Charakterisierung und
Kartierung der Bausteinarten in den Bauphasen von der Romanik bis zur
Neugotik, Untersuchungen zu ihrer Herkunft. In: OEXLE, J. (Ed): Kirche und
Friedhof von Breunsdorf - Beiträge zu Sakralarchitektur und Totenbrauchtum in
einer ländlichen Siedlung südlich von Leipzig. Band 35: 125-146.
Siedel, H., 2003, Dolomitkalkmörtel und Salzbildung an historischer Bausubstanz, in
Mauersalze und Architekturoberfläche in proceedings Salze im Mauerwerk,
Leitner H., Laue S., Siedel H. (eds.), Hochschule für bildende Künste, Dresden,
57-64.
Siedel, H, 2013, Magnesium sulphate salts on monuments in Saxony (Germany): regional
geological and environmental causes. Environmental Earth Sciences, Vol. 69,
Issue 4, 1249-1261.
Steiger, M., Linnow, K., Juling, H., Gülke,r G., El Jarad, A. Brüggerhoff, S., Kirchner, D.,
2008, Hydration of MgSO4·H2O and Generation of Stress in Porous Materials,
Crystal Growth and Design 1 (8), 336-343.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Wedekind W., 2014, Schwierige Ruinen - Zur Erhaltung der Ruinen an der Unstrut, in
Natur - Stein - Kultur - Wein - zwischen Saale und Unstrut, Siegesmund S.,
Hoppert M., Epperlein K. (eds.), Leipzig, Mitteldeutscher Verlag, 289-316.
Wedekind W., Rüdrich, J., 2006 Salt-weathering, conservation techniques and strategies to
protect the rock cut facades in Petra/Jordan, proceedings of Heritage, Weathering
and Conservation, Fort R., Álvarez de Buergo M., Gomez-Heras M. and VazquezCalvo C. eds., London, Taylor & Francis, 261-268.
Wedekind, W., Rieffel, Y. 2014, Desalination of the painted vault ribs of the Franciscan
monastery Church of Zeitz. In proceedings SWBSS 2014 Third International
Conference on Salt Weathering of Buildings and Stone Sculptures Brussels, De
Clercq, H. (ed.) Royal Institute for Cultural Heritage (KIK/IRPA): 469-480.
Wittmann, F.H., 1996, Feuchtigkeitstransport in porösen Werkstoffen des Bauwesens, in
Verfahren zum Entsalzen von Naturstein, Mauerwerk und Putz, Goretzki, L. (ed.),
Freiburg, Aedificatio-Verlag, 6-16.
990
FIELD TRIALS OF DESALINATION BY
CAPTIVE-HEAD WASHING
D. Young1
Abstract
Captive-head washing is a system designed for cleaning dirt and grime from building
façades in which the dirty wash water is retained within a close-fitting head and captured by
a wet vacuum cleaner, thus minimising clean-up and waste disposal issues. The system’s
potential for reducing excessive salt loads in masonry has been recognised for some years
and anecdotal evidence suggests that it works well enough to justify its on-going use, yet
there is little data to support this. Trials were conducted in 2014 on an internal face of an
exterior wall of an 1820s brick blacksmith’s shop at the World Heritage listed Woolmers
Estate in Tasmania, Australia. The 350 mm thick brickwork suffers from rising and
penetrating dampness carrying salts through the wall to the interior surface where the lowfired bricks are severely decayed by salt attack. Samples of the wash water from two cycles
of captive-head washing were analysed for soluble salts (total dissolved solids) by electrical
conductivity. The results show that a significant quantity of salt was removed from the
wall: depending on assumptions made about the depth of penetration/extraction and the
density of the brickwork, salt extraction was in the range 0.2–0.6% by weight (for the two
cycles combined). The second cycle removed about one third the amount of salt of the first
cycle, which raised the question of whether additional cycles may be beneficial. Further
trials were conducted in 2015 with four cycles of captive-head washing. Although these
were simple field trials, they confirm that the technique has considerable potential for use in
desalinating masonry walls.
Keywords: desalination, captive-head washing, salt attack, salt weathering
1. Introduction
Captive-head washing is a system designed for cleaning dirt and grime from building
façades in which the dirty wash water is captured by a wet vacuum cleaner, thus
minimising clean-up and waste disposal issues. Figure 1 shows the head in use, cleaning
dust and dirt from a brick wall prior to render repairs. The head contains a low-pressure
spray nozzle which is connected to a water supply at normal pressures. A flexible rubber
‘skirt’ encloses the head and seals the unit against the wall surface so that the attached wet
vacuum-cleaner recovers almost all of the wash water. The system’s potential for reducing
salt loads has been recognised for some years (Young, 2008) and anecdotal evidence
suggests that it works well enough to justify its on-going use, yet there is little data to
supports this. Trials were conducted during the 2014 and 2015 sessions of the Longford
1
D. Young*
Heritage Consultant, Melbourne, Australia
david.young@netspeed.com.au
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Academy, a combined training and fieldwork program organised by the Australasian
Chapter of the Association for Preservation Technology International (APTI) and located at
the Brickendon and Woolmers World Heritage properties at Longford, Tasmania, Australia.
Fig. 1: Captive-head washing system being used by Walter Heim to remove dust and dirt
from brickwork prior to render repairs at Brickendon, Longford, Tasmania.
2. Woolmers Blacksmith’s Shop
The 1820s blacksmith’s shop on the Woolmers estate (Fig. 2) is a brick building with a
harled or roughcast-rendered exterior and limewash finishes on the interior. The 350 mm
thick brickwork suffers from rising and penetrating dampness which carry salts through the
walls to the interior surfaces. The northwest wall is the worst-effected, the low-fired bricks
are severely decayed by salt attack (salt weathering) across much of the interior surface
(Fig. 3). Moisture transport through the walls towards the interior would have been
increased when the smithy was in operation, producing warm evaporative conditions inside
the building.
The weak, powdery surface of the decaying brickwork was consolidated by multiple
applications of limewater in May 2013. The surface hardening was sufficient to allow
desalination treatment without significant further loss of material. The 2014 and 2015
campaigns included trials of the captive-head washing system, which was kindly supplied
and operated by Walter Heim of Heim Surface Technologies, Sydney.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
Fig. 2: Woolmers Estate blacksmith’s shop from the north. Failed rendering (harling) on
the northwest wall (to the right) is allowing penetrating dampness to carry salts through
the 350 mm brickwork to the interior (see Figure 3).
Figure 3: Interior of northwest wall showing extensive decay of low-fired bricks due to salt
attack. Early limewash finishes remain on undamaged parts of the wall.
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13th International Congress on the Deterioration and Conservation of Stone: Conservation
3. 2014 trials
In 2014 trials were conducted on the interior of the northwest wall (Fig. 3) and covered an
area of 8.8 square metres. The captive-head unit was drawn slowly across the surface to
allow time for the wash water to dissolve readily-soluble salt lying on and in the surface of
the brickwork. Two separate passes were made across the whole surface of the wall.
The amount of wash water retained by the vacuum system was recorded and samples of
each batch were collected and analyses for soluble salts (total dissolved solids) by electrical
conductivity. This technique uses a portable conductivity meter and is a quick and simple
way of determining the total concentration of salt present, though it cannot distinguish
between different types of salt. The salt concentrations are multiplied by the volume of
wash water to obtain the total amount of salt extracted.
4. 2014 results
The first pass extracted 81.6 g, the second 27.8 g making a total of 109.4 g of salt extracted
from a wall area of 8.8 m2, at an average of 12.4 g/m2.
Deriving a weight per cent salt extraction depends on two assumptions:
Depth of effective extraction in mm;
Density of the brickwork, which, for this purpose,
is assumed to be 2.0 g/cm3 (kg/L) though given the very porous bricks,
it could be much lower.
Assuming that the depth of effective extraction is one mm into the brickwork, the average
salt extraction is around 0.6% by weight. This is a high figure; it is more than the
commonly used 0.5% threshold above which salt extraction is warranted. Alternatively, if
the effective depth of extraction is two mm, then the salt extracted is 0.3% by weight, and if
the extraction depth is three mm, the figure becomes 0.2% by weight of the brickwork. Any
of these results is a good outcome; substantial salt has been removed from the wall.
The amount of salt extracted in the second pass was about one third that of the first pass.
However, less water was used in the second pass (15 L instead of 25 L in the first pass),
which indicates that the second pass was faster (assuming the water supply rate remains
constant). Ignoring the differences in the amount of water used, and considering only the
concentration of the salty wash water, the second pass extracted about 60% of the salt
extracted in the first pass. These results suggest that a third, or even fourth, pass should be
effective at salt extraction, and that slower passes extract more salt.
5. 2015 trials and results
In 2015 an additional area of 1.2 m2 was treated, but this time using four passes of captivehead washing, with the aim of testing the observations from the previous year’s work. The
four passes extracted a total of 22.7 g salt at an average of 18.9 g/m2. Significantly, the third
and fourth passes continued to extract salt, as shown in Tab. 1.
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Table 1: Results of 2015 trials
Passes
Concentration
Water used
Salt extracted
ppm
L
g
1 & 2 (combined)
512
25
12.8
3
320
15
4.8
4
512
10
5.1
These results show a decline in salt concentration from the first and second to the third
pass, which is expected as the salt load in the wall is reduced. However, the concentration
of the fourth pass increases to the previous level, which may suggest that salts deeper in the
wall are being mobilised and brought to the surface. In turn, this suggests that additional
passes are warranted to maximise salt extraction.
6. Discussion
There are a range of variables and factors that should be considered in designing future
trials. These include the solubility of the various salts and whether pre-wetting of the wall is
warranted to initiate dissolution of the salts. The walls should not dry out between passes,
and between any pre-wetting and the first pass. This is to ensure that the salts remain in
solution so that (a) they can be removed in subsequent passes, and importantly, (b) that they
do not recrystallize and cause more damage to the masonry. This is particularly important
in hot dry places like Australia. In turn this means arranging the work flow so that, once
commenced, the treatment of a section of wall can be completed without it drying out. This
does not necessarily mean passing the captive head at a fast rate over the wall surface, nor
that the interval between passes should be as short as possible. Rather, a slower rate of
passing across the surface should extract more salt (per pass) and maximising the total time
of wetting (i.e. passes plus the intervals between them) should maximise the chances of (a)
less-soluble salts dissolving, and (b) deeper salts migrating towards the surface.
7. Conclusions
Field trials have demonstrated that captive-head washing is effective at desalinating porous
masonry walls with high salt loads. Multiple passes may be required to reduce salt loads to
acceptable levels. Slower passes across the wall surface will extract more salt per pass. A
combination of multiple passes and adjusting the rate of passing across the surface should
be trialled in order to optimise the technique. Other factors which should be considered
include pre-wetting to initiate dissolution, and the effect of different nozzle flow rates.
Future trials should test:
Pre-wetting to initiate dissolution;
Multiple passes across the surface;
Varying speeds of passing across the surface;
Different substrates and salt loads, and
Different nozzle flow rates, in order to optimise the technique.
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Reference
Young, D., 2008, Salt attack and rising damp: a guide to salt damp in historic and older
buildings. Heritage Council of NSW, South Australian Department for
Environment and Heritage, Adelaide City Council, Heritage Victoria, Melbourne,
Australia, ISBN 978-0-9805126-5-6, 80pp.
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DIGITISATION
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998
DIGITAL MAPPING AS A TOOL FOR ASSESSING THE
CONSERVATION STATE OF THE ROMANESQUE PORTALS OF
THE CATHEDRAL OF OUR LADY IN TOURNAI, BELGIUM
J. De Roy1*, S. Huysmans1, L. Hoornaert1, L. Fontaine2 and N. Verhulst1
Abstract
In the framework of the conservation of the Cathedral of Our Lady in Tournai (Belgium),
the Royal Institute for Cultural Heritage (KIK-IRPA, Brussels) was called upon in 2012 to
carry out a preliminary study of two Romanesque portals called the Mantile and Capitole
portals. The aim of this study was to understand the deterioration mechanisms of the stone
and to propose a conservation strategy. Both portals are constructed from the local black
Tournai stone, with the exception of the 19th century restoration in Belgian bluestone. Due
to the strongly deteriorated state and the large size of the portals, a detailed visual
inspection survey of each stone block was necessary to obtain an overview of the actual
state of conservation and to develop an adapted conservation strategy. The deterioration
patterns were digitally mapped with the Metigo MAP software (fokus GmbH), using
rectified photographs as a template. These mappings present a visual clarification of the
location, extent and degree of the different deterioration patterns. They also enable us to
evaluate and compare the deterioration patterns of both portals and can be linked to the
results of the laboratory analyses.
Keywords: Tournai stone, deterioration mapping, Tournai cathedral, Romanesque portals,
Metigo MAP, delamination, black crust
1. Introduction
Construction of the Cathedral of Our Lady in Tournai (Belgium) started in the first half of
the 12th century. The nave and transept date back to the Romanesque period and are topped
with five towers, all predating the Gothic choir. Its important artistic and historical value
was recognised by UNESCO in 2000 with their acknowledgement of the Cathedral as a
World Heritage Site. Despite successive architectural changes to the Romanesque
construction, two original side portals dating from around 1125 (Deléhouzée 2013) have
been spared: the Mantile and Capitole portals, located respectively at the northeast and
southwest side of the nave. In spite of their strongly deteriorated state, these finely sculpted
portals in Tournai limestone are unique examples of Romanesque monumental sculpture in
Western Europe (Fig. 1). Both portals consist of multiple round arches embodied in a trefoil
arch with a drip moulding. The arches are supported by jambs and jamb columns. Each
1
J. De Roy*, S. Huysmans, L. Hoornaert, L. Fontaine and N. Verhulst
Stone sculpture studio, Royal Institute for Cultural Heritage, KIK-IRPA, Brussels, Belgium
judy.de.roy@kikirpa.be
2
L. Fontaine
Monuments and monumental decoration lab, KIK-IRPA, Brussels, Belgium
*corresponding author
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block is decorated with a Romanesque sculpted relief and the entire surface was probably
polychromed (for further details see De Roy J. et al., in press).
In 1999, a new restoration campaign of the Cathedral was considered crucial. In this
framework, a preliminary study of the Romanesque side portals was commissioned to the
KIK-IRPA in 2012. The aim was to understand the deterioration mechanisms of the black
Tournai stone in an urban environment and to work out a conservation strategy for these
portals.
Fig. 1: Mantile portal Mantile portal (left), picture dating from 1899 © KIK-IRPA,
Brussels, B3188. Capitole portal (centre) © KIK-IRPA, Brussels, A126815. Relief of inner
arch of Mantile portal (upper-right) © KIK-IRPA, Brussels, X049701. Relief of trefoil arch
of Capitole portal (bottom-right) © KIK-IRPA, Brussels, X057496.
2. Characterization of the stone
Both the architecture and the sculptures of the Mantile and Capitole portals were executed
in black Tournai stone, a local “black marble” (sedimentary limestone that allows for fine
polishing) also known as Noir de Tournai, which was widely used in the Low Countries
from the 11th to the 15th century (Groessens 2008). Tournai stone is a local stone exploited
on the right bank of the Scheldt river near the city of Tournai. Geologically, the black
Tournai stone is a compact, fine-grained, silicified and clay-bearing limestone from the
Lower Carboniferous (Tournaisian) age (Camerman 1944; Hennebert and Doremus 1997).
The stone can be described as a bioclastic wackestone according to Dunham’s classification
(Dunham 1962) and as a biomicrite according to Folk’s classification (Folk 1965).
Petrographic analysis of loose samples from the portals revealed that the silicified matrix of
the stone mainly consists of calcite, sometimes with grains of dolomite. While the compact
stone core has coarser bioclasts (≤ 250 μm) than the outer edges (≤ 100 μm), careful
examination reveals a more prominent presence of small clay laminae in the outer edges
which are almost absent in the stone core. The clay laminae form a laminated structure on
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the outer edges of the stone. As further research revealed, this distribution of clay minerals
in the stone, in combination with extrinsic factors, is the most important reason for the
deteriorated state of the portals (for further details see Fontaine et al., 2015).
3. Material history
Already in the mid-18th century the ruinous state of the portals was mentioned (Van Den
Noortgaete, 1995) and in the second quarter of the 19 th century it was argued that there
would soon be nothing left of the original sculptures (Scaff, 1971). This poor condition led
to the restoration of the two Romanesque portals by architect Bruyenne between 1848 and
1871. The restoration mainly consisted of replacing strongly degraded stone volumes by
Belgian bluestone or Petit Granit. The fact that the Capitole portal contains far more
replaced stone volumes than the Mantile portal suggests that the former was much more
deteriorated in the 19th century. Since the replacement stone is still in good condition, it
was not included in this preliminary study.
Despite this restoration, the poor condition of the remaining original Tournai stone was still
mentioned throughout the 20th century (Van Den Noortgaete, 1995). Photographs from
different archives confirm this ruinous state, but a detailed inventory of the condition has
never been made.
A precious source of information for evaluating the progression of the degradation are the
photographs from 1943 made by the KIK-IRPA in the context of a major inventory
campaign during the Second World War. Comparison with the current state of conservation
leads to conclude that the general condition of the portals did not undergo major changes.
Large lacunae did not expand and the current deterioration patterns were already present.
4. Digital mappings
To obtain an overview of the state of conservation two kind of mappings were carried out
by visual inspection from scaffoldings:
Detailed mappings of each different deterioration pattern of each single block of
Tournai stone: 78 blocks for the Mantile portal and 57 for the Capitole portal
(Fig. 2)
General mappings for each portal with the main deterioration patterns, the
positioning of the stone blocks, the readability of the sculpted reliefs and an
inventory of the 19th-century restoration
Rectified, accurate photographs on true scale were used as templates for these mappings,
carried out using the Metigo MAP software by Fokus GmbH. The true scale gave us the
opportunity to document each deterioration pattern in detail but also to calculate very
precisely the damage of each deterioration pattern. Nevertheless it has to be taken into
account that it concerns reliefs mapped in two dimensions and thus sculptural undercuts are
not included. The mappings of the portals are a combination of line- and area-mappings.
The mapping terminology and colour scheme of the weathering phenomena was based on
the classification of the ICOMOS-ISCS Illustrated glossary on stone deterioration patterns
(ICOMOS-ISCS, 2008).
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The following deterioration patterns were observed on both portals:
detachment/delamination, cracks, black crusts in various thicknesses, soiling, biological
colonization, blistering and efflorescence.
For quantitatively important deterioration patterns, namely black crusts and delamination,
sub-categories were made to indicate the degree of the deterioration.
Fig. 2: Detailed mapping of block BC2 (Bandeau Cintré 2) of the Mantile portal.© KIKIRPA, Brussels.
The mapping of the bedding planes of the Tournai stone proves that the construction of
both portals is similar. Although the positioning of each block was not random (Fig. 3), the
bedding planes were not taken into account during the construction of the portals. The
blocks were positioned in three different directions, namely natural-bedded, edge-bedded
and face-bedded. The latter blocks suffer from material loss due to their weaker and
fragmented schist-like outer edge positioned parallel to the surface. This loss continues to a
few centimeters depth, making a lot of sculpted reliefs hardly readable or even leading to
their total loss.
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From the identical positioning of the stone blocks in both portals we can derive that the
lower part of the Capitole portal was very likely face-bedded. This would explain why that
part would have suffered substantial material loss and was replaced with Belgian bluestone
in the 19th century.
Fig. 3: Mapping of the bedding planes of the original stone blocks in the Mantile (left) and
Capitole portal (right). Hatchings underlines the bedding planes, while crosshatching is
used for face-bedded blocks. Blue-coloured zones correspond to the 19th century
restoration with Belgian bluestone ©KIK-IRPA, Brussels.
5. Results
From the detailed mappings an overview can be deducted of the different degradation
phenomena and their distribution on the portals (Fig. 4). Detachment is a common
phenomenon of the original Tournai stone and was found on 51% of the original surface of
the Mantile portal and on 39% of the Capitole portal. Black crusts were omnipresent as
well: on 62% of the Mantile portal and on 79% of the Capitole portal. These phenomena
are divided in different subcategories according to their degree of degradation. Other
deterioration patterns such as biological colonisation, blistering and efflorescence were less
common and will thus have less impact on the conservation treatment.
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Fig. 4: Mappings and diagrams of the delamination and black crusts on the Mantile (left)
and Capitole portal (right) © KIK-IRPA, Brussels.
A general mapping describing the state of the sculpted surface comprises four different
categories: first of all sculptures with an original surface in good condition, secondly stone
blocks with an original surface that is hardly readable, thirdly original stone surfaces that
have completely disappeared and lastly 19th-century replacements (Fig. 5).
Fig. 5: General mapping and diagrams of the state of conservation of the sculpted surface.
Mantile portal (left) and Capitole portal (right) © KIK-IRPA, Brussels.
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Unfortunately hardly 5% of the finely detailed Romanesque sculptures remains for the
Capitole portal and 21% for the Mantile portal. In total 66% of the Capitole portal and 15%
of the Mantile portal was replaced by Belgian bluestone in the 19th century, leaving only
around a third of the original stone of the Capitole portal while the Mantile portal still
contains 85% of its original stone volumes.
From the mappings it became furthermore clear that orientation of a portal has an influence
on its conservation state. Due to its southwest orientation, corresponding to the direction of
prevailing winds and ample exposure to the sun, the Capitole portal is more deteriorated
than the Mantile portal, as we can read out of the mappings.
Stone volumes in the deeper parts of the archivolts of both portals are better protected from
meteorological phenomena such as rain and direct sunlight and are thus better preserved.
These sheltered areas, however, contain more black crusts.
6. Practical use of the mappings for the conservation treatment.
The detailed mappings were used as a guideline for further scientific research in order to
understand the mechanisms of the deterioration. Furthermore they were used to select
representative locations for sampling and allow an informed choice of on site test-areas for
micro-drilling resistance, ultrasonic pulse velocity and water absorption measurements (for
further details see Fontaine L. et al., 2015).
The results of these measurements in combination with additional scientific research and
the data from the mappings revealed that the specific degradation of the Tournai stone is
caused by intrinsic as well as extrinsic factors. These were studied by the monuments and
monumental decoration lab of the KIK-IRPA. The presence of numerous clay laminae in
the schist-like outer edges of each stone block constitutes an intrinsic factor for the
degradation of the stone. This schist-like ‘crust’ makes the stone unsuitable for use as a
building stone and must ideally be removed before use in an outdoor context. The core of
these blocks is, however, in good condition. The cracks in the outer edges follow the
bedding plane of the stone block. This leads to a high amount of material loss by
detachment when the blocks are face-bedded.
Furthermore also extrinsic factors such as climatic conditions (temperature, humidity,
precipitation) and a malfunctioning of the rainwater drainage system are significant for the
degradation of the portals. Hydric dilatation is the main driving force of this degradation
but hygric and thermic dilatation also play an important role (for further details see
Fontaine L. et al., 2015).
The principal aim of the study of the two Romanesque portals was to develop a
conservation treatment based on a representative test area. The area chosen for this pilot
conservation had to include all the different deterioration phenomena. A representative area
was selected on the basis of the mappings. Furthermore the main focus of the conservation,
namely the stabilization of the detachment, could be deduced from the mappings. With this
in mind, an injection mortar was designed and tested in the lab. During the pilot
conservation all the different steps of the treatment were executed onsite, starting with
injecting an ethyl silicate-based mortar and followed by the removal of the soiling and the
black crusts. The latter was carried out with compresses in combination with microabrasion for the crusts with a thickness of more than 2 mm and by a mechanical elimination
followed by a soft micro-abrasion cleaning for the thinner films (for further details see De
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Roy J. et al., in press). During the removal of the crusts thicker than 2 mm, additional
injections turned out to be necessary due to the thicker transition zone of the outer stone
layer with very limited cohesion (Fontaine L. et al., 2015). This is in contrast with the thin
film-like crusts where the underlying stone support appears in relatively good condition.
The mappings were also used to estimate the cost and time required for the future
conservation project as all the deterioration patterns had been linked to a specific
conservation method.
7. Conclusion
The digital mappings proved to be extremely useful for this complex case of the Mantile
and Capital portals in Tournai stone. Apart from the general mappings, a total of 135
blocks of stone were individually mapped on site using the Metigo MAP software. These
information confirmed the need for a conservation treatment, revealing that most attention
should be paid to stabilizing the delamination. This deterioration pattern is caused by a
combination of both intrinsic and extrinsic factors and led to a study of suitable
conservation methods. The different orientation of both portals is clearly visible in the state
of conservation. Besides a conservation treatment, preventive measures should be taken
into account. The digital mappings can be reused and completed as at the time of our
inspection some cracks and losses were still covered by thick black crusts. We conclude
that such digital mappings are also the perfect tool for monitoring the condition of the
portals in the future.
Aknowledgments
This research is part of the preliminary study of the Romanesque side portals,
commissioned in 2012 by the Walloon cultural heritage agency (DGO4/Département du
Patrimoine), the Province of Hainaut and the City of Tournai. The study has been carried
out in collaboration with the monuments and monumental decoration lab of the Royal
Institute for Cultural Heritage (KIK-IRPA, Brussels). The authors would like to thank the
following colleagues at the KIK-IRPA for their contribution to the preliminary study: R.
Hendrickx, C. De Clercq and H. De Clercq.
References
Camerman, C., 1944, La pierre de Tournai : son gisement, sa structure et ses propriétés, son
emploi actuel, Mémoires de la Société belge de Géologie, de Paléontologie et
d’Hydrologie, Nouvelle série in-4°, 1-86.
Deléhouzée L., 2013, La place des portails dans la chronologie du chantier roman, Book of
abstracts Les portails romans de la Cathédrale Notre-Dame de Tournai:
Contextualisation et restauration (international conference), Tournai (Belgium),
January 31-February 1, p 1.
De Roy J., Fontaine L., Hoornaert L., Hendrickx R., De Clercq C., Huysmans S., De Clercq
H., in press, Les portails romans de la cathédrale Notre-Dame de Tournai
(Belgique). Résultats de l’étude matérielle et technique en vue de la conservation,
Archéovision .
Ecclesiology Today 29:3-11 (www.ecclsoc.org/ET.29.pdf)
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Dunham R.J., 1962, Classification of carbonate rocks according to depositional texture. In:
Ham WE (ed) Classification of carbonate rocks, Am Assoc Pet Geol Mem 1, 108121.
Folk R.L,1965,Petrology of Sedimentary Rocks. Hemphill Publishing Company, Austin
(USA), 182.
Fontaine, L., Hendrickx R. et De Clercq H., 2015, Deterioration mechanisms of the
compact clay-bearing limestone of Tournai used in the Romanesque portals of
theTournai Cathedral, Environmental Earth Sciences,74, 3207-3221.
Groessens, E., 2008, La pierre de Tournai, un matériau de choix depuis la période romaine
et un des fleurons parmi les autres marbres belges, Revue trimestrielle de la
Société tournaisienne de géologie, préhistoire et archéologie, X (7), 197-216.
Hennebert M, Doremus P., 1997, Notice explicative de la carte géologique Hertain-Tournai
37/5-6 à l’échelle 1:25000. Direction Générale des Ressources Naturelles et de
l’Environnement, Ministère de la Région Wallonne, Jambes, Belgium, 66.
ICOMOS-ISCS, 2008. Illustrated glossary on stone deterioration patterns – Glossaire
illustré sur les formes d’altération de la pierre. Monuments and Sites XV, 78 p.
Scaff, V., 1971, La sculpture romane de la cathédrale Notre-Dame de Tournai, Tournai,
Casterman.
Van Den Noortgaete, T., 1995, Étude préliminaire à la restauration de la cathédrale de
Tournai. Porte Mantile et Porte du Capitole. Rapport archéologique préalable à la
restauration des sculptures romanes, 2 vol., rapport inédit.
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1008
DIGITAL FIELD DOCUMENTATION: THE CENTRAL PARK
OBELISK
C. Gembinski 1*
Abstract
The digital field documentation of the existing conditions and application of the
conservation treatments at the Central Park Obelisk performed in 2014 created challenges
for conservators, historians and those studying or working on the monument in the field.
New and constantly changing technologies can make gathering and sharing information, as
well as planning interventions, faster and easier. Today, we anticipate increasingly more
applications that will allow the opportunity to explore, discuss, and fine-tune options for
digitally generating and storing information suggesting that our documentation efforts no
longer desire the creation of static models; rather we seek an interactive solution. Our
experience to date translating hand-drawn field notes into digital formats has shown a
potential for the loss of information, or the inclusion of incorrect data. While digital
documentation in the field cannot replace the artistry of hand-draw sketches, it can reduce,
if not eliminate potential transcription errors. The digital application ultimately selected for
the documentation of the work at the Obelisk came after researching and testing three
applications on several conservation projects. This paper illustrates discussions specific to
the Obelisk project, including how users favoured the methods they knew, and how
conservators entering information on handheld devices often returned to paper and pencil,
thereby adding to the continuing discussion of how field documentation for conservation
can advance together with technology and our ever changing expectations.
Keywords: digital documentation, mobile applications, field recording, existing conditions,
conservation treatment, Central Park Obelisk
1. Introduction
Two goals were identified for the conservation work at the Central Park Obelisk: 1)
Archival information, and 2) Data Analysis. The need for accurate archival information was
important in order to create a baseline document for use in analysing the patterns and
factors involved in the development of the existing conditions, and develop a proposed
treatment campaign. Documentation of the treatment applications was desired to provide
future conservators with the locations of previous conditions and applied treatments, and to
help them monitor the success of the treatments as well as predict potential future
deterioration. With on-going observation, the documentation should also assist in the
identification of a rate of change.
1
C. Gembinski*
Building Conservation Associates, Inc., United States of America
cgembinski@bcausa.com
*corresponding author
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An iterative documentation process utilized multiple digital applications to collect and
record the data in multiple formats, analyse the efficiency and effectiveness of the
recording methods, and modify the approach and/or application to meet the requirements of
the Project.
2. Examination of the Obelisk
The Central Park Obelisk is a solid pink granite shaft approximately 21 meters high and
tapered 2 ¼ meters to 1 ¼ meters, set on a base of the same stone, originally quarried in
Aswan and erected in Heliopolis to honour Pharaoh Thutmose III and later Ramses II
(Central Park Conservancy 2016). It is thought to have been originally erected
approximately 3,500 years ago and was brought to New York City and erected in its present
location on Greywacke Knoll, behind the Metropolitan Museum of Art in 1881.
The project team: The Central Park Conservancy (CPC), a Conservancy Consulting
Scientist (CCS), Building Conservation Associates, Inc. (BCA), and SAT, Inc. (SAT) 1
completed conservation work on October 31, 2014. The work addressed the previously
untreated weathered conditions on the granite obelisk shaft and its supporting plinth. Using
existing Computer Aided Design (CAD) survey documents provided by the CPC, the team
also examined the monument to confirm locations of previously documented conditions of
deterioration and previously applied temporary stabilization treatments. The conservators
performed and documented conservation work on over 6,000 conditions, thus proving the
need for a documentation method that could record and deliver a large amount of
information.
Using the International Council on Monuments and Sites “Glossary of Stone Deterioration
Patterns” as the basis for identifying the conditions, the team recorded locations of
atmospheric soiling, biological growth, cracks, disaggregation, and spalls. The conservators
implemented and documented treatments developed by the team onsite. Areas of granular
disintegration were treated with a polymer consolidant (Paraloid B-48N in solution with
acetone). Some very isolated areas of disintegration warranted a treatment with an ethyl
silicate consolidant (Conservare OH100). An adhesive injection repair for the treatment of
cracks and microfissures included the application of a chemical adhesive (Paraloid B-48N
in solution with acetone, ethanol and xylene and the addition of Cab-o-sil M5 fumed silica).
Isolated spalls required the application of an injectable proprietary mortar grout (Edison
X53i grout) where injection of adhesive could not adequately fill cracks or allow water to
shed from treated areas. All locations exhibiting obvious biological growth were treated
with a proprietary biocide before the application of any adhesive repairs (D/2 Biological
Solution).
3. Documentation
3.1. Previous Documentation
A previous project in 2013 included cleaning and stabilising the Obelisk surface. At that
time, the CPC took advantage of the opportunity to thoroughly document the monument
and create a reference point for future study and conservation. That pprevious
documentation included the use of laser scanning, photography, and hands-on surveys.
1
Maria Warsh, Matthew Rielly, and John Harrigan, CPC; Dr. George Wheeler, CSS; Raymond Pepi,
Christopher Gembinski, John Glavan, Zach Tatti and Steve Johnson, BCA; Steve Tatti, SAT.
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A High Definition Survey phased-based 3D Laser Scan of the Obelisk was created in
March 2013, which provided the team with a data point cloud that could be used in
conjunction with other imaging applications. However, it did not provide a consistent and
suitably detailed level of data to be useful to the conservators (Central Park Conservancy
2016). The 3D laser scan did not provide sufficient detail to comprehensively document the
condition of the surface therefore high-resolution digital photographs were taken by the
Metropolitan Museum of Art for this purpose in August 2013. Each face of the Obelisk was
divided into 63 rectified digital images, which were tiled together to create a composite
Portable Document File (PDF) of each elevation of the monument. Conditions were
recorded as overlays on these images in a CAD program (Central Park Conservancy 2014).
The photographs proved useful in two ways. First, they assisted in documenting a baseline
condition of the monument. Second, they provided the graphic documents on which new
information could be traced during subsequent surveys and treatment campaigns.
3.2. Goals of the Present Documentation
CPC required that the documentation for the treatments applied to the Obelisk “be recorded
in detail on the survey documentation provided, and this documentation of treatments
incorporated into a final report on the conservation, ” (Central Park Conservancy 2014). In
addition to creating a record of the work performed in 2014, it was the conservators’ desire
to provide new documentation that, among other goals, could be digitally archived, used as
an analysis tool and be updated in the future. Other goals included the elimination of the
need to print and transport physical drawings between the site and office; the elimination of
potential for transcription errors; and the creation of readily available information in a
flexible format. Ultimately, the best solution would consider the project budget, along with
the accuracy and detail of the documentation.
3.3. Field Documentation Application Comparison
This study looks at three digital applications for collecting data in the field to document the
as-applied treatments at the Obelisk. Note that none of these programs were evaluated for
the collection of data into a database management program for this project.
3.4. Computer Aided Design (CAD) Computer Program
Initially, the conservators found that using a CAD program (AutoCAD 2013 by AutoDesk,
Inc.) to record the as-applied treatments on site on a laptop computer proved cumbersome
and the equipment required a portable power source due to the limitation of the batteries in
the device at the time. The laptop did provide a touch screen function with stylus feature.
Although this feature allowed the conservators to document the applied treatments directly
into the CPC CAD file, it proved to have limited accuracy in sketching actual conditions
and the documentation progress was slow. At the time, files were stored directly on the
laptop hard drive, requiring hard wired transfers to a server at a different time and location.
In addition, multiple expensive devices, as well as users with proficient knowledge of the
programs, were required. If the team had chosen to continue with this method it also would
have required additional time to train the hands-on conservators who did not know the
program, or it would have required additional CAD trained staff. Therefore, the first
alternate digital solution was considered for efficiency.
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3.5. 2D PDF Mark Up Application
The second digital documentation application used was a proprietary tablet application
ReVu 2014 by Bluebeam Software, Inc. using a mark up overlay system layered on the
PDF files of the existing documentation. This application was considered and tested for its
ability to mark up 2D PDF documents with customisable tools such as text, lines,
highlighting, and hatch patterns. The expectations were that this application would help
annotate the existing project documentation files and illustrate the new as-built conditions.
The digitisation of the information was intended to save time, and the application purported
to improve the sharing of information as well as keep the information organised and
conveniently stored in a central location.
Using a stylus in the field, the conservators could mark up PDF files on user defined layers
with components such as lines or polygons, and highlight selected areas. An icon-based
toolbar could be customised to create an efficient workflow by making “rubber stamps” for
specific treatments. The application allowed for the manipulation of components using a
“one-click” process for changing the appearance (colour, fill, line type, etc.). A calibrated
scale feature could resize the components automatically with different scales within zoom
viewports during the recording process. The components included customisable attributes
that could record the date, conservator, application issues, measurements, quantities, etc.
The information contained within the components was stored in a database within the
digital file in customisable cells and columns, containing formulae and other information
accessible from dropdown menus or manually entered. The information could be managed
in a list format within the application, filtered, or searched, and exported to CSV, XML or
PDF formats.
The project files could be stored and accessed from either the local tablet drive on site or a
cloud based storage system from both the field tablets via Wi-Fi, or an office desktop
computer connected to the Internet. Information stored directly on a tablet required
uploading to a server for access by others. Real time editing and multi-users in one file was
not available for this application at the time of the project. At times the upload/download
process resulted in the loss of information due to the overwriting of data stored in one or
more devices during offline editing. Reportedly, the newest version of the software allows
for real time collaboration of mark ups and comments with shared users. This feature, not
available at the time of the Obelisk project, was available in the third solution considered.
3.6. CAD File Reader and Editor Tablet Application for Files in DWG Format
As third solution AutoCAD 360 2014 by Autodesk, Inc. a proprietary portable CAD file
reader and editor for files in DWG format was investigated. It was considered because it
could connect directly to the existing project CAD files via Wi-Fi access if available. If
Internet connectivity was not possible, the files could be stored locally on mobile devices
and the information uploaded/downloaded when Internet access became available. The
extent of the real-time link to the files between desktop, web and mobile device
applications surpassed the other applications tried.
Although advertised as simple and easy to use, the program required some knowledge of
the features available in the proprietary desktop program. The drafting of lines, polygons
and other components was similar to the first program considered. However, it was limited
to the tools available within the application. The CAD application, at the time of the
project, allowed for very little customisation, particularly in the field. The creation of
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components with customisable attributes did exist, but it was only a feature available on the
desktop version of the program.
The real-time cloud collaboration sharing tools allowing work with other users in multiple
locations, albeit remarkable at first, did not end up being utilised in the actual
documentation process. The ability of the application to use password protection of files
and set user permissions could be set up to prevent the overwriting of data thereby reducing
the risk of lost or incorrect records. Files used and shared in this application were stored on
a third-party web-based server and accessible on both portable devices and desktops with
Internet connectivity. Files created in this application could be exported to other DWG file
compatible programs. However the information contained in attributes of the components
drafted in the application could not be accessed fro the tablet.
3.7. Observations and Comparison
The assessment of the digital documentation solutions evaluated for the Obelisk project
considered, among the features available: the level of accuracy and detail; the level of
efficiency; and the risk of recording inaccurate data and the potential for lost data. The
features for all digital solutions continue to develop and increase. All of the applications
evaluated maintained a similar amount of customisation at the time. All provided the ability
to sketch onto the two types of digital files using a stylus. The tablet applications offered
Wi-Fi connectivity to a remote server.
The level of accuracy of the information recorded tended to be more detailed in the CAD
program and CAD application. The PDF application consisted of documentation that
appeared more “cartoonish” and relied more on notes and comments. The rubber-stamp
feature was a quick method of documentation, although it recorded generic information that
required edits. Not surprisingly, the conservators were able to document a higher level of
detail by hand with pencil on paper.
The efficiency of all three programs was disputable. While the field collection of data in
digital format appeared to be faster, this was not always the case. What was gained in
efficiency in the field tended to be balanced by the amount of work interpreting the data in
the office. For all applications evaluated the documentation on digital devices removed the
conservators from the hands on conservation work to perform the digital documentation. In
the case of the PDF application, the time saved by the effective functions of the application
in the field required additional time in the office to transfer the information into the CAD
files as required by the Project. Sketching directly in the CAD files in the field proved more
time consuming for the conservators, albeit this process eliminated the potential for
transcription errors, which was one of the Project goals. Again, sketching with pencil on
paper was the fastest method of documenting the locations of the applied treatments at the
Obelisk.
The CAD program and application required the conservators in the field either to already
know the program or take time to learn it. When the conservators applying the treatments
did not know the CAD application, additional staff required to perform the documentation
increased the number of field personnel and the cost.
All digital hand held devices collecting data in the field over a Wi-Fi Internet connection
have an increased risk of data loss. The connectivity of the CAD editing program was
attractive, but proved to be more of an amusement (watching people on a desktop computer
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sketch in the field miles from the office) and was not used to any further possibility.
However, the information was directly linked to a remote server, which reduced the
potential for the loss of data once it was input into the file.
The volume of the data files was limited to that of the hand held device in the case of the
tablet applications or laptop computer when connection to a remote server was not possible.
In the case of the PDF application, this was an issue because the PDF files were too large to
store more than a few at a time on the tablets. Therefore, the information needed regular
transfer between the field devices and the office computers. The PDF application performed
with undesirable results and after several events when data was lost, the CAD tablet
application became the preferred tool. Working on a laptop computer increased the amount
of storage available.
4. Conclusions
For the documentation at the Obelisk, the conservators began using one program and, based
on their experience in the field continued to seek either customisation of that program or an
alternate application, changed to another application, and ultimately, to a more traditional
method of hand drawing with the expectation of digitising the information off-site at a later
time. Our experience showed that a few factors continually lead us back to the use of paper
and pencil. First, the conservators found it distracting to document the treatments as they
were applying them. It distracted them from the execution of the repairs in that once a
repair was complete, the documentation process obliged them to look away from the repair
site potentially missing for example the migration of excess materials requiring clean up.
Using digital media continued to be slow and the conservators reported that at times, it was
difficult to record multiple treatment locations as applied since the treatments used at the
Obelisk were by design virtually invisible. However, this situation is not solely a problem
of the digital solutions.
The sequencing of the documentation was considered. Documentation of the treatments
before application did not prove useful nor was it an efficient procedure because the
treatments when applied did not always conform to the graphic recorded before application.
This was the case for both digital applications and hand drawn documentation.
Documentation immediately after the application of treatments proved to be the most
efficient recording method and the most accurate in identifying the repair locations.
Ultimately, the conservators chose to trace the applied treatments by hand on the printed
photographs to save time and to provide more accurate records of the applied repairs. This
highly accurate documentation, however, left open the possibility for transcription errors
when entering the data at a later time.
The potential for transcription errors was discussed after the conservators decided that
using paper and pencil was the most efficient and accurate recording method for them. It
was determined that since a record hard copy of the documentation existed, any future
discrepancies in the digital files could be checked against the original documentation.
Essentially, this process created a redundancy in the data that could prove valuable.
Additionally, the loss of data recorded on paper was a concern. Digital technology does not
alleviate this fear; in fact one could suggest that it increases it. When using pencil and
paper, one could argue that a torn or water damaged piece of paper or smeared ink still can
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convey information, even if partial, potentially triggering the memory of a detail or
condition. The lost of digital data presents no peripheral opportunities.
Why do we keep going back to paper and pencil? Does the existence of technology create
anticipation that there will be a paradigm shift to all digital solutions? Why do we continue
to pursue digital solutions for traditional methods of documentation? We do learn
something, however esoterically or intrinsically defined, when measuring by hand and
drawing details with pencil on paper. What is lost when the process is digitised? Sketching
on a tablet is still sketching by hand. The options for hundreds of colour and textures in a
digital sketch are attractive, but not necessary. A pencil has comparatively limited options,
however, it still gets the job done, inexpensively and so far comparably quickly. Digital
technology has the ability to transform the way we work, and hand held device applications
can replace paper, but there should be an effort to continue to keep the tactile form of
documentation among the tools used for collecting data. That documentation is important in
the conservation process is not a question. Proper and accurate documentation can assess
value, inform the efforts of conservators, and manage risk.
David Woodcock, guest editor of the APT Bulletin listed several concerns regarding digital
documentation in 2010: transferability, the size of files, the lack of standards for collection,
transmission and integration, as well as the demand of clients to provide greater access to
information (Woodcock 2010). Today, in 2016, these same issues remain in the forefront of
our discussions regarding the use of digital technology for the recoding of heritage assets.
The goals of digital documentation vary widely, whether it is, as in the case of the Obelisk,
the recording of existing conditions and applied treatments, the gathering of a large volume
of data related to heritage assets, or the development of public access to previously
unavailable information on art and archives. The complexity of each of these goals requires
different approaches to the collection and management of the data. The solutions available
need to be specifically tailored to each project. A single digital solution is not possible,
however the view of digital documentation as a tool that can assist in the management of
data is correct, but only so far as it is designed on a case-by-case basis, making the linking
of application and data between disparate projects difficult. The expectation that one
solution can be used across many projects becomes difficult as technology continues to
rapidly develop; they become obsolete or are replaced with new versions with enhanced
features.
Acknowledgements
The author would like to thank Maria Warsh, Matthew Rielly, and John Harrigan of The
Central Park Conservancy, and Dr. George Wheeler, the Conservancy Consulting Scientist,
their extensive time and generous support during this Project.
References
Building Conservation Associates, Inc., 2014, “Central Park Conservancy Central Park
Obelisk, New York, NY: Conservation treatment Report”, Building Conservation
Associates, Inc., 1-6.
Central Park Conservancy, 2014, “Request for Proposals: The Conservation of the Obelisk
in Central Park, New York, New York”, Central Park Conservancy, 3-4.
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13th International Congress on the Deterioration and Conservation of Stone: Digitisation
Central Park Conservancy, 2014, “Conservation Treatment Proposal: The Obelisk, Near
80th Street and the East Drive in Central Park, New York, New York”, Central
Park Conservancy 1, 3, 7, 10.
Central Park Conservancy, 2016, “Final Report of the Conservation of The Obelisk, Near
80th Street and the East Drive in Central Park, New York, New York”, Central
Park Conservancy, 11.
Clark, Kate, 2010, “Informed Conservation The Place of Research and Documentation in
Preservation”, APT Bulletin, 41 (4), 5-10.
Letellier, Robin, and Rand Eppich, eds., 2015, “Recording, documentation and information
management for the conservation of heritage places”.
Roy,
Ashok, Foister, Susan, and Rudenstine, Angelica., 2007, “Conservation
Documentation in Digital Form: A continuing Dialogue About the Issues”, Studies
in Conservation, 52 (4), 315-317.
Woodcock, David, G., 2010, “Guest Editor’s Note”, APT Bulletin, 41 (4), 3.
1016
COMPUTATIONAL IMAGING TECHNIQUES FOR
DOCUMENTATION AND CONSERVATION OF GRAVESTONES
AT JEWISH CEMETERIES IN GERMANY
C.A. Graham1* and S. Simon1
Abstract
The following study focuses on the application of computational imaging techniques to
enhance legibility, enable dissemination and aid conservation of eroding gravestone
inscriptions. This methodology comprises the use of reflectance transformation imaging
(RTI) in order to create dynamic visualizations and 3D models. RTI is an extremely
powerful method of digitization that brings specific analytical attributes to a project as the
generation of digital surrogates and their realization in visualization software allow for an
unprecedented degree of user interaction and investigation.
Keywords: gravestones, RTI, interactive re-lighting, 3D surface geometry,
conservation practice
1. Introduction
1.1. Aim
A major aim of this project is to use computational imaging techniques and new viewing
tools to create and disseminate digital documentation of gravestones that are susceptible to
deterioration and weathering in Jewish cemeteries. This on-going and evolving endeavor
seeks to bring together students and specialists alike to advance didactic and conservation
objectives associated with these gravestones in order to shine a light on the once vibrant
Jewish communities of Lower Franconia in the German state of Bavaria.
1.2. Cultural relevance
Vanishing inscriptions on undocumented gravestones tell the stories of Jewish communities
that resided in the Bavarian countryside before the Second World War. These communities
were disturbed greatly by the war as Jewish families were uprooted and expelled from their
villages. Funerary symbols and inscriptions hold some of the last remaining information
after the holocaust pertaining to the social structure of these communities, rich with
demographic details about vocation, gender, kinship, and interconnectedness of village
inhabitants. As time passes, agents of erosion render these engravings more difficult to
decipher and, as such, the history they hold falls in greater peril of being lost forever.
1.3. Previous work
In recent years, vulnerable Jewish cemeteries in Lower Franconia have served as the focus
of a documentation enterprise carried out by two high schools: Rhön Gymnasium (Bad
1 C.A. Graham* and S. Simon
Institute for the Preservation of Cultural Heritage, Yale University, United States of America
c.graham@yale.edu
*corresponding author
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Neustadt an der Saale, Germany) and Mikve Israel (Holon, Israel). This project, comprising
fieldwork and classroom seminars, is carried out under the auspices of their long-standing
partnership. Since 1992, the schools have hosted cultural exchanges in their home country
every second year. In 2013 and 2015, German and Israeli students worked together closely
to map Jewish cemeteries in Lower Franconia and record information about past
inhabitants. From the onset, their work fostered a real sense of collaboration, as they drew
from multiple sources in order to form a complete picture of the lost Jewish communities.
The students’ efforts have been complimented by technical support in the form of
documentarians, historians, archivists, conservators and imaging specialists, who help to
give context to their work. The project unites people from different countries, backgrounds,
religions and ages to explore a joint or intersecting past. Documentarians provide the
framework for the students’ work, which extends beyond documentation in the cemetery to
historical societies, archives and the homes of local villagers and ex-pat survivors. When
possible, students collect oral histories in person and via electronic correspondence. As
gravestone inscriptions are connected with historical records and first-hand accounts, the
character and dynamics of the community emerge.
As a major consideration for this project is to provide universal access to and promote
preservation of eroding gravestones, a project website was established (Caine 2014). This
site presents the results of the work carried out in the Jewish cemetery in Bad Neustadt an
der Saale during the 2013 exchange. The newly established record of the cemetery is
publically available in English and German to visitors from around the world. The
collaborative efforts and outstanding dedication that were necessary to achieve these results
were acknowledged when the project received the second honor in the prestigious SimonSnopkowski award ceremony held in Munich in 2014. This prize, awarded by the Bavarian
State Ministry of Education and Culture, was established to recognize research projects that
study Jewish history and culture in Bavaria and the holocaust.
1.4. Current focus
In the autumn of 2015, the documentation project was continued with a renewed focus on a
cemetery in the nearby village of Unsleben. This cemetery is located atop a steep hill about
a kilometer outside of heart of the village, where a Jewish community originally began to
burgeon under the patronage of a nobleman in the mid 1500s. In this cemetery stand the
gravestones of locals of Jewish faith, 229 of whom were interred from 1856 through 1942
(Hesselbach nd, Main Post 2008). The mostly sandstone memorials are currently badly
weathered and were desecrated during the Second World War. After the war, dedicated
villagers attempted to restore the cemetery as best they could, but many ambiguities remain
as to the gravestone inscriptions and identities of those buried (Hesselbach pers. comm.).
This project strives to resolve some of those uncertainties. While the fieldwork in the
cemetery focused on student-driven transcription of symbols and inscriptions, it also
featured the application of computational photography techniques.
2. Digitization
2.1. Methodology
The primary form of digitization employed, reflectance transformation imaging (RTI), is a
non-contact method of capturing how the surface of an object interacts with light. RTI has
long been lauded for its ability to aid in visualization and inspection of cultural heritage
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13th International Congress on the Deterioration and Conservation of Stone: Digitisation
objects (Malzbender et al., 2001). The acquisition process encompasses the capture of a
sequence of images of an object illuminated by a light source set at different positions.
Standard field documentation is traditionally photography with uniform lighting and static
shadows, which poses problems for legibility and enquiry, especially for researchers at a
distance. RTI differs in that the change in the angle of illumination between each capture is
visible in the varying highlights and shadows that are present in images. Data captured
during an RTI acquisition can be post-processed into visualizations that convey the detail
and dimension of the surface of an object. These visualizations allow for examination of the
surface morphology by allowing a user to manipulate the direction of light sources and
promote the virtual investigation of the geometry of surface in three dimensions.
2.2. Applications
Through RTI, reflectance values for the surface of the object are captured per pixel, as a
stationary camera takes a series of images of an object under changing light conditions.
Since the camera and the object remain stationary, each pixel corresponds to the same
feature on the surface of an object in each image in the series. This pixel-specific
information is processed through a mathematical algorithm, which renders a texture map
that allows for dynamic simulation of how each pixel will interact with light under varying
conditions.
This technique yields visualizations that allow users to interactively manipulate the
direction of virtual light sources in real time. In doing so, users may illuminate an object
and change the appearance of highlights and shadows. Software for viewing RTI
visualization files is free, intuitive and embeddable on the web (Palma et al., 2012). This
software allows for user interaction with the manner in which light falls across the surface
of an object, thus accentuating the fine-grained geometry of low relief surface features,
such as inscriptions, tool marks, veins and fracture lines.
The reflectance values captured corresponding to the surface of an object further allow for a
per-pixel approximation of the direction of normals on the surface of an object
(Malzbender et al., 2006; Palma et al., 2010). Surface normals are the directional vectors
perpendicular to the surface plane of an object at specific points. Since RTI data contains
detailed information about surface normals, it can be used to generate fine-grained 3D
information for surface geometry of an object. The scale of this data can exceed the detail
yielded through laser scanning and does not require any additional acquisition time.
It is of great interest to generate 3D data for individual features from RTI, especially in the
context of this project, where more importance is placed on surface morphology and
geometric detail of the inscriptions than the holistic geometry of the gravestone. The
rapidity of acquisition and post-processing for 3D data generated from RTI far surpasses
laser scanning. 3D models have significant applications in research, dissemination and
educational outreach (Dellepiane et al., 2012).
3. Reflectance transformation imaging of gravestones in Unsleben
3.1. Data acquisition
During the first week of October 2015, RTI capture was carried out for 13 gravestones in
the Jewish cemetery in Unsleben. The acquisition campaign was led by a digital imaging
specialist from the Institute for the Preservation of Cultural Heritage at Yale University and
performed by German and Israeli students who worked together in mixed groups of three.
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13th International Congress on the Deterioration and Conservation of Stone: Digitisation
Before the start of this project, in-situ RTI acquisition strategies for gravestone inscriptions
were established and refined during a project in the historic crypt of the Center Church on
the Green in New Haven, Connecticut. Development of this local pilot project enabled an
optimized approach to student training and allowed for an organized focus on gravestone
selection in Unsleben.
Criteria for selection of gravestones for imaging were guided by three main factors –
legibility of inscription, degree of deterioration of inscription and stability of stone
structure. Illegible, visibly eroded and particularly unstable gravestones were given priority
for RTI. Imaging was also impacted by other factors, however, including student schedules,
additional documentation activities in the cemetery and position of sun in the sky. The
cemetery is located atop a hill with the inscribed faces of gravestones facing westward with
little cover from the sun. During the project, the cemetery was abuzz with activity, as
approximately 40 students carried out documentation work.
These factors allowed for creativity in problem solving during RTI acquisitions using the
highlight method (Duffy 2013). For this method of imaging, the team used a standard
DSLR camera and synched flash. The flash was manually situated at equidistant locations
and moved between shots in an arc around the surface of the inscription, creating a virtual
umbrella of light around the face of the gravestone. A string was affixed to the flash to
ensure the distance of the flash to the center of the inscription remained consistent for all
images. Team members were assigned distinctive responsibilities – orientation of flash,
maintenance of consistent distance, and remote camera control via computer (Fig. 1).
Fig. 1: A group prepares to capture a photograph of a gravestone in the Jewish cemetery in
Unsleben in an RTI sequence using the highlight method.
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A color checker and two reflective spheres were set in the frame of each image for the
purpose of reliability in future data generation. The purpose of the reflective spheres is to
capture the flash location in each image. Since they remain immobile throughout the
capture sequence, they may be individually isolated during post-processing and sampled in
order to create a comprehensive map of the coordinates of all light directions captured
during the acquisition.
3.2. Data processing
Thirteen unique sets of captures were taken of gravestones at the Jewish cemetery in
Unsleben in order to support an RTI workflow. For each gravestone, between 30 and 60
images were processed in order to yield RTI visualization files and 3D models. Due to time
constraints, data was solely collected and assessed in the cemetery and then post-processed
after fieldwork.
The first step in processing the data was to thoroughly examine the data sets to validate the
quality and consistency of images. Corrupted images, due to human or mechanical error
were rejected. Coordinates of reference spheres were closely analyzed and compared. Two
reference spheres were placed in the composition of each frame in case one was
unintentionally moved. This happened often due to the high volume of activity in the
cemetery. Moving forward with the approved image set, processing commenced.
For the purposes of creation of high fidelity data, minimal image editing and no image
enhancement took place. Lens and color corrections were carried out consistently to all of
the images in a sequence from the capture of an individual gravestone. Free and opensource software, RTIBuilder, was used to process images into RTI visualization files.
In order to extract the 3D data from the image sets, masks were produced. A mask is a
black and white image created in order to guide the software. First, the gravestone was
outlined, and then erased so that white substitutes the silhouette. Next, the background was
deleted and filled in with black. The creation of this high contrast image focuses the
software for creation of 3D geometry from surface normals corresponding to the pixels in
the white region. Software created by Yale University’s Department of Computer Science,
RTI23D, was used to generate this data. These 3D models may be viewed and manipulated
in free, open-source software, MeshLab (Cignoni 2008).
3.3. Interpretation and dissemination
RTI allows for visualization and interaction with the manner in which light falls across the
surface of an object, opening new possibilities for examination (Fig. 2). Visualization of
low-relief geometry has benefitted greatly from RTI, with results that address the needs of
historians, scientists and conservators alike (Fig. 3). Conservators have added RTI to their
arsenal of diagnostic and documentary tools. Historians and researchers are able to view
and accentuate surface properties to enhance the appearance of features of interest.
Interactive visualizations can be enhanced to bring crumbling inscriptions into focus.
These visualizations can lead to important discoveries, guide practices and allow access and
collaboration across the distances.
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13th International Congress on the Deterioration and Conservation of Stone: Digitisation
Fig. 2: Snapshots of an RTI visualization of an inscription on a gravestone in the Jewish
cemetery in Unsleben with lighting from different directions.
Fig. 3: A side-by-side comparison of a standard image (left) and a snapshot of an enhanced
RTI visualization (right) of an inscription on a gravestone in the Jewish cemetery in
Unsleben.
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The by-products of the RTI campaign in Unsleben will be applied to meet different goals,
including research, preservation and public education. Interactive visualizations of
inscriptions from the gravestones in Unsleben cemetery will be featured on a website
sponsored by the town council. This form of exhibition can be used to engage viewers and
garner public interest and support for the care of cemeteries.
While RTI is an effective way to connect an audience with the past, it is also a powerful
way to ensure the trajectory of the gravestones in an endangered cemetery into the future.
RTI is a diagnostic tool, which can help to guide both assessment and preservation. 3D data
can be applied in stress modelling for evaluation of structural integrity and formation of a
conservation plan for gravestones at risk.
RTI also has quantitative applications in conservation and conditions monitoring
(Manfredi et al., 2013, 2014). Imaging can be used as a benchmark of the current state of an
object. The data can then be compared to future conditions via deviation analysis. This is a
way to track the effect of weathering and erosion. The clear, customizable visualizations
that RTI generates give an enhanced perception of surface morphology and have the ability
to inform and extend research and conservation methods.
4. Conclusion
Digitization allows for enhanced perception of the inscriptions on the surface of
gravestones that agents of erosion and damage have garnered less prominent over the years.
Through computational imaging, inscriptions that have long eluded visitors may be
digitally illuminated, accentuated and disseminated to allow for interaction and
interpretation by a wide audience in a manner that has previously been impossible. This
kind of access aims to bring viewers closer to the identities of those interred, despite long
distances or the passing of time, to reveal relatable stories that are rooted in the rich culture
of the past Jewish communities of Bavaria.
This digitization project serves as a manner of applying computer vision to quickly eroding
historical records. It offers a means to document, preserve and make accessible culturally
rich funerary engravings. This has proven essential in that through digitization, enduring
intangible, yet interactive results have been yielded. These kinds of digital visualizations
serve a didactic purpose as active agents of public education. The results, which are still
very much in development, will be incorporated into an accessible website for virtual
investigation well into the future.
Acknowledgements
Many thanks to the teachers and students of Rhön Gymnasium and Mikve Israel, the
exchange leaders: Günter Henneberger, David Avshalom and Judith Tal, the documentation
team: Eyal Tagar and Nadav Madanes, and Unsleben town council. Much appreciation and
admiration are also due Prof. Dr. Josef Hesselbach.
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reflectance transformation imaging, in the proceedings of Digital Heritage
International Congress, Volume 1, 189 - 192.
Manfredi, M., Bearman, G., Williamson, G., Kronkright, D., Doehne, E., Jacobs, M. and
Marengo, E., 2014, A new quantitative method for the non-invasive
documentation of morphological damage in paintings using RTI surface normals,
Sensors, 14 (7), 12271 - 12284.
Palma, G., Corsini, M., Cignoni, P., Scopigno, R. and Mudge, M., 2010, Dynamic shading
enhancement for reflectance transformation imaging, Journal on Computing and
Cultural Heritage, 3 (2), 6:1 - 20.
Palma, G., Siotto, E., Proesmans, M., Baldassarri, M., Baracchini, C., Batino, S., Scopigno,
R., 2012, in the proceedings of the 40 th Computer Applications and Quantitative
Methods in Archaeology (CAA) Conference, 177-185.
1024
A METADATA-SUPPORTED DATABASE SCHEMA FOR STONE
CONSERVATION PROJECTS
E. Kardara1* and T. Pomonis1
Abstract
The aim of this work is to help stone conservators benefit from the ease of use of modern
cultural databases. We introduce an approach for a database schema that not only
constitutes a complete, typical digital cataloguing system for monuments and artefacts, but
is also used to log and provide additional conservation-oriented information for each one of
them. The whole database schema is focused on the process of stone conservation and
contains all the information needed by conservators during the treatment of a monument or
artefact. In addition, the whole data structure is supported by a custom metadata schema,
originating from the Dublin Core Metadata Initiative. Stone conservators can exploit this
information architecture to manage and support all of their activities while facing a
monument.
Keywords: database schema, metadata, stone conservation, projects
1. Introduction
Nowadays we witness a really broad use of computer technology and software products in
all aspects of cultural information management, especially in terms of digital archiving of
cultural heritage and culture-specific databases. The main incentive behind this broad
spreading of cultural databases came from museums and cultural institutions all over the
world, as there was a great need for cataloguing and supporting the documentation of its
collections, in an efficient and cost effective way. That's why they started developing their
own in-house solutions in order to support their specific needs. All this effort led to really
interesting and innovative implementations, but also to a complex and greatly fragmented
reality of DBMS solutions and usage. In museums and conservation centres, as well as in
conservation and restoration sites, the need for a Database Management System arises for
the purpose of efficient object-related information storage and retrieval. The use of such a
DBMS for archiving is a reasonable choice. With the aid of an ordinary DBMS it is
possible to store, modify, display specific records as well as find records that satisfy certain
search criteria. Although there are several database products that offer this level of
functionality, either they are not specialized to cultural heritage objects archiving, or they
lack seriously in conservation specific functionality.
1
E. Kardara* and T. Pomonis
Conservation of Cultural Heritage Department, Technological Educational Institution of Ionian
Islands, Greece
kardaraeva@gmail.com
*corresponding author
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2. A conservation-oriented database
2.1. Background
There are many such DBMS implementations all over the word, from institution-oriented
databases as CDS/ISIS1 and Museum Plus2, to more complete and solid solutions like the
European Union research project NARCISSE, which provided a solid framework for the
digital representation of art-related information (European Commission, 1993). The thing is
that all these DBMS solutions were developed to support cataloguing of collections and,
more or less, lack in describing the aspect of conservation and restoration process in an
efficient and thorough way. The need for conservation-specific solutions led to the
development of such databases and modules that could support the required processes.
Because of the complexity of this issue, most of them are limited in certain aspects of the
conservation process (Basir et al., 2014), (Pedeli, 2013) or stay focused on a single domain
(Pappas et al., 1999), (Velios and Pickwoad, 2005). There are also more complete and solid
approaches that vary from holistic management ideas (Yen et al., 2011) and
documentation-oriented systems (Naoumidou et al., 2008), to even more complex and
powerful solutions like the EROS database (Aitken et al., 2005). Although the latter are
potent and sufficient in covering the conservation process, they lack greatly in simplicity,
mainly because they are mostly based in CIDOC-CRM (Doerr, 2002) which sacrifices ease
of use to provide greater completeness.
2.2. Our approach
To overcome the above handicaps we decided to design a custom database for stone
conservation cataloguing, utilised in stone conservation projects, but also for in-house use
in stone conservation courses at Conservation of Cultural Heritage Department
(http://conservation.teiion.gr) of Technological Educational Institute of Ionian Islands.
2.2.1. Design
During the design process the desired characteristics were:
I.
II.
III.
IV.
Our database would be operated mainly by conservators so its metadata schema
has to be focused on conservation processes.
It had to be easy to operate as it will be used by conservation students during
their lessons and practice, and visited by inexperienced users.
It had to be as object-agnostic as possible, meaning that it had to be able to
handle any kind and size of stone artefacts under conservation.
If possible, it had to interoperate with other pre-existing artefact cataloguing
systems and cultural databases.
2.2.2. Structure
To make our database able to interoperate with pre-existing cataloguing schemas, we
decided to divide it in two discrete modules, an Object Description Module and a
Conservation Module. The first one contains only the cataloguing information about an
object, while the latter comprises all the conservation specific data and documentation.
These two modules are interconnected only on foreign key basis, so it is possible to put
1
http://portal.unesco.org/ci/en/ev.phpURL_ID=2071&URL_DO=DO_TOPIC&URL_SECTION=201.html
2
http://www.zetcom.com/en/products/museumplus/
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aside the Object Description one and use the Conservation Module with any convenient
cataloguing schema.
3. Metadata schema
As we decided to divide our database into two modules, we had to provide a suitable
metadata schema for each one. For the Object Description Module we decided to keep in
line with all the current cultural database trends, and design a trivial schema mainly based
on Dublin Core metadata standard (France and Toth, 2006) while also incorporating the
Object ID guidelines (Thornes, 1999). The result was a typical cultural documenting
schema that can be used even as a separate solution (Fig. 2). The really challenging part
was to design a suitable schema for the Conservation Module. For this we had to track the
exact process used on stone conservation tasks and try to deduce the discrete steps and their
requirements. The result was a highly abstractive schema that can be used on almost all
cases of stone conservation and restoration (Fig. 1).
Fig. 1: Conservation Metadata Schema.
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Fig. 2: Object Description Metadata Schema.
The fundamental entities in this schema are Conservation Process, Conservation Task and
Condition, which are used to describe the main steps and instances of conserving an
artefact.
3.1. Main entities
Their main entities are:
Conservation Process
Supervisor: The conservator responsible for the whole conservation process.
Category: Preventive or Interventive conservation.
Start: Date and time that the process started.
End: Date and time that the process ended.
Tasks: The sub-tasks of this process.
Starting Condition: The object’s condition at the beginning of the
conservation.
Final Condition: The object’s condition at the end of the conservation.
Mid-Conditions: Object’s condition instances during the conservation.
Previous Interventions: Everything that happened due to human interference.
Conservation Task
Conservators: All the persons involved in this task.
Kind: What kind of conservation act is performed, e.g. cleaning, fill etc.
Location: Where it is taking place, e.g. dig site, laboratory etc.
Tools: Which tools were used.
Materials: Which materials were used.
Methods: Which methods were used.
Infrastructure: Any required conservation infrastructure, e.g. scaffolding.
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Condition
Date: Date and time of the object’s condition instance.
Required Interventions: What has to be done.
Environmental Factors: Environmental conditions in this instance.
Damages: e.g. cracks, deformation, etc.
Erosion: e.g. loss, rounding, etc.
Deposits: e.g. dust, biological, etc.
Protection: Temporal protection in this instance.
Storage: Temporal storage in this instance.
Photographs: Photographic material of this instance.
Designs: Designs of this instance.
3.2. Secondary entities
In addition, there are some secondary entities that conclude the above ones:
o
o
o
o
o
o
Damage: Kind, Expansion.
Erosion: Kind, Expansion, Analyses.
Deposit: Kind, Expansion, Analyses.
Environmental Factor: Kind, Value, Unit, Instrument.
Photograph: Kind, Actor, Camera, Light, File.
Design: Kind, Actor, Software, File.
3.3. Thesaurus
To support the above metadata fields, we had to create a corresponding Greek thesaurus of
conservation terms, which conservators keep in mind while filling the respective fields.
This thesaurus was based on ICOMOS-ISCS: Illustrated glossary on stone deterioration
pattern
(http://www.icomos.org/publications/monuments_and_sites/15/pdf/Monuments_
and_Sites_15_ISCS_Glossary_Stone.pdf) and A Glossary of Historic Masonry
Deterioration Problems and Preservation Treatments (Grimmer, 1984).
4. Conclusions
In this paper we presented a proposed metadata schema for a conservation-oriented
database that can be used during stone conservation projects, while being as simple and
easy to operate as possible. The specific schema was used in developing a primary version
of an in-house database solution for the Conservation of Cultural Heritage Department of
Technological Education Institution of Ionian Islands. This database was then utilized by
students of stone conservation lessons in their laboratory practice, where they handled
objects of various complexity and materials. In addition our database was used in
cataloguing the real-time conservation process of several stone parts and also of some midscale monuments in Zakynthos island. All these examples resulted in a really useful stress
test for our database and proved its usefulness in supporting the conservation process. From
now on we intend to continue developing and testing our database in ever more
complicated and different conservation cases, to fine-tune it where needed, while trying to
extend it towards supporting the conservation process of artefacts made of different
materials other than stone. Finally, we aim in developing an international (English) version
of our implementation and have it open-accessed in order to be used by other conservators.
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References
Aitken G., Lahanier C., Pillay R. and Pitzalis D., 2005, EROS: An Open Source Database
For Museum Conservation Restoration. In Preprints de la 14eme reunion triennale
du Comite International pour la Conservation ICOM-CC, pp. 15–23.
Basir W.N.F.W.A., Setan H., Majid Z. and Chong A., 2014, Geospatial database for
heritage building conservation. ISDE, International Symposium of the Digital
Earth, 8 - IOP Conference Series: Earth and Environmental Science (Online).
Doerr M., 2002, "The CIDOC CRM - an Ontological Approach to Semantic
Interoperability of Metadata". AI Magazine - Special Issue on Ontologies, March.
European Commission, 1993, NARCISSE: Network of Art Research Computer Images
Systems in Europe, Arquivos Nacionais/Torre Do Tombo, Lisbonne.
France F.G. and Toth M.B., 2006, Developing cultural heritage preservation databases
based on Dublin Core data elements. In Proceedings of the 2006 international
conference on Dublin Core and Metadata Applications: metadata for knowledge
and learning (DCMI '06). Dublin Core Metadata Initiative 233-243.
Grimmer E.A., 1984, A Glossary of Historic Masonry Deterioration Problems and
Preservation Treatments, Department of the Interior National Park Service
Preservation Assistance Division.
Naoumidou N., Chatzidaki M. and Alexopoulou A., 2008, "ARIADNE" Conservation
Documentation System: Conceptual design and projection on the CIDOC CRM
framework and limits, 2008 Annual Conference of CIDOC Athens.
Pappas M., Angelopoulos G., Kadoglou A. and Pitas I., 1999, “A Database management
System for Digital Archiving of Paintings and Works of Art”, The Gordon and
Breach Publishing Group, (15-35).
Pedeli C., 2013, An Interdisciplinary Conservation Module for Condition Survey on
Cultural Heritages with a 3D Information System In: Recording, Documentation
and Cooperation for Cultural heritage, XXIV International CIPA 2013
Symposium, Strasbourg.
Thornes R., 1999, Introduction to Object ID: Guidelines for Making Records that Describe
Art, Antiques and Antiquities. Getty Information Institute.
Velios A. and Pickwoad N., 2005, Current use and future development of the database of
the St. Catherine’s Library conservation project. The Paper Conservator, 29. pp.
39-53.
Yen Yaning, Weng Kuo Hua, Cheng Hung Ming and Hsu Wei Shan, 2011, The standard of
management and application of cultural heritage documentation. Proceeding of
CIPA 23rd symposium.
1030
3D PHOTO MONITORING AS A LONG-TERM MONUMENT
MAPPING METHOD FOR STONE SCULPTURES
B. Kozub 1 and P. Kozub1*
Abstract
This 3D monument mapping method is a non-destructive procedure which allows scientists
to see even the smallest changes on the stone sculpture. Until now it has been common
method to use 2D- mapping. The biggest problem is, the information must be transferred
from the 3D- dimensional object to a two dimensional image. This paper describes
preliminary results from a novel optical-based system for three-dimensional damage
mapping used on different stone sculptures, the Moai of Easter Island and a late baroque
tombstone and shows the advantages of 3D photo monitoring as a non-destructive
documentation tool.
Keywords: cultural heritage, 3D photo monitoring, monument mapping, point cloud
The results, which are presented here, pertain to the appraisal of climate-induced deterioration of
the stone sculpture Moai of Ahu Hanua Nua Mea on the Easter Island. The appraisal was done as
part of the expert activity of Prof. Dr. Peter Kozub during the German Archaeological (DAI)
project. Another object is a late baroque tombstone (ca.1725 AD, Wolkenburger quarry) which is
now located in the restoration atelier of the University of Applied Sciences in Cologne.
1
B. Kozub and P. Kozub*
TH Köln - University of Applied Sciences, Cologne Institute for Conservation Sciences (CICS),
Ubierring 40, 50678 Köln, Germany
peter.kozub@th-koeln.de
*corresponding author
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1. Stone sculptures on Easter Island
Easter Island lies in the Southeast Pacific, approximately 3800 km off the Chilean coast and
is known for its stone sculptures, the so-called Moai. There are about 900 Moai on the
island, most of which are made of lapilli tuff. They were sculpted in the period between the
10th and the 16th century and, since 1995, are enlisted as a UNESCO World Heritage Site.
Their cultish significance has faded from collective memory. However, scientific research
leads to the conclusion that they formed an integral part of the cult of ancestors. They were
most likely knocked over in the 18th century, when rivaling tribes on the island engaged in
altercations. Many of the stone sculptures are damaged and lie facedown.
Fig. 1: Monumental stone sculpture: Moai on the Easter Island, Rano Raraku quarry.
2. Object of research
The volcanic island is made up entirely of volcanic rocks. It comprises three principal
volcanoes and over 70 subsidiary eruptive centers. Each of the main volcanoes has a
different structure - Poike, to the east, is a simple strato-volcano; Rano Kau, to the
southwest, has a well-developed central caldera; Terevaka, to the north, is a complex
fissure volcano. The volcanic rocks on Easter Island belong to the alkaline suite and have a
wide petrographical and geochemical range, from basalt to trachyte and tuff.
Almost all of the Moai stone sculpture which are presently found on the Island were carved
from the Rano Raraku lapilli tuff. Most of them were built by using a Tuff outcropping in
the southern part of the Rano Raraku volcano, where ancient quarries are still visible. From
the volcano, hundreds of Moai were obtained and erected on the Island. Also, the object of
this research: Moai of Ahu Hanua Nua Mea was carved quite likely from Rano Raraku
lapilli tuff.
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Fig. 2: 3D point cloud: Moai of Ahu Hanua Nua Mea lies facedown, with surroundings.
2.1. Material used for the Moai
The material used for the Moai may be described as a stratified tuff, with very frequent
variations in grain size within the single layers. It is made up of a yellowish-brownish
pumiceous and ashy matrix with embedded lapilli, scoriae, pumices and black lava
fragments of a size ranging from a few mm to several cm. The tuff coherence varies from
level to level, but generally it is not very strong: frequently, just by manual pressure,
pulverisation or fragment detachment occurs on the surfaces. Weakness is particularly
evident on the junction plane of different-grain-sized levels. The overall colours varies from
light brown to yellowish with greenish shades.
2.1.1. Stone deterioration
Since 1956, several Moai have been re-erected and detailed research has been done by
specialists as pertains to morphology and deterioration mechanisms. The first research
concerning the morphology and the nature of the damage of the rocks, was done at the
request of UNESCO in 1973 by Hyvert and in 1981 by Domasłowski.
The main damage phenomenon was rainfall followed by wind erosion, biological growth
mainly due to lichens and algae and salt decay connected with marine spray. These
deterioration mechanisms were confirmed in 1988 by Charola and Lazzarini, adding a
further factor: the effects of temperature changes on the surface of tuff. When the surface of
the Moai is overheated by the sun, and then cooled down by a sudden shower, the rock
undergoes thermal fatigue, which produces superficial scaling and exfoliation over time.
They are all influenced by the mode of cutting of the Moai from the tuff beds. Those cut
along the strata are better preserved than those cut at an angle or perpendicularly.The Moai
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carved out of finer-grained pyroclastics are generally better preserved than those with
coarse to medium grain size lapilli and other components.
As pertains to the Moai of Ahu Hanua Nua Mea which is the object of this research, its
scaling is neither vertical nor horizontal but rather diagonal through the stone sculpture.
The grain size varies widely, ranging from coarse to fine.
Fig. 3: Differences in the composition of the individual layers
2.1.2. Stone deterioration of Moai from Ahu Hanua Nua Mea
The weathering of stone sculptures means the long-term loss of cultural heritage. When
mapping the damage, the terminology from the ICOMOS (International Scientific
Committee for Stone) - ISCS glossary was used in order to prevent misunderstandings
concerning the interpretation of damage and to build the basis for a scientific discussion.
The visible main damage of the stone sculpture Moai of Ahu Hanua Nua Mea:
Differential erosion. As a result, the stone deteriorates irregularly. This feature is
found on heterogeneous stones containing harder and less porous zones.
Detachment – Bursting. Local loss of the stone surface from internal pressure
usually manifesting in the form of an irregularly sided crater.
Encrustation. Compact, hard, mineral outer layer adhering to the stone.
Encrustations are frequently depositions of materials mobilized by water percolation
and thus coming from the object itself. Carbonates, sulphates, metallic oxides and
silica are frequently found.
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Crack. Individual fissure, clearly visible by the naked eye, resulting from separation
of one part from another. Fracturing of a stone along planes of weakness.
Biological colonization – Lichen. Colonization of the stone by micro-organisms.
Lichen is a common feature on outdoor stone and is generally best developed under
clean air.
Soiling. Deposit of a very thin layer of exogenous particles giving a dirty appearance
to the stone surface. With increasing adhesion and cohesion, soiling can transform
into a crust.
2.2. Non-destructive method for damage diagnosis
Stone sculptures, like the Moai, are an important part of our cultural heritage. While doing
research on the Easter Island, it was important to choose a method of diagnosing the
damage of the sculptures that would not, itself, damage the sculptures further. As is widely
known, the damage mapping method is a good method for documenting the current
condition of the stone and to thus make later changes visible. In this case, the acquisition of
the data concerning the weathering damage to the lapilli tuffs was a suitable possibility to
do long-term research and to control the change processes of the stone sculpture.
2.2.1. Non-destructive damage documentation on the Moai stone sculpture
The damage mapping of this particular Moai statue lasted from 2012 until 2015. This long
term method allows scientists to see even the changes on the skulpture. Until now it has
been common method use 2D mapping. Using this method, damages of the object are
entered into the image processing software manually. The biggest problem is that
information has to be transferred from a 3D object onto a 2D image.
Fig. 4: 3D monument damage mapping. Surface of object is rendered shaded.
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2.2.2. 3D model of the Moai of Ahu Hanua Nua
In 2015 we decided to create a 3D model of the Moai of Ahu Hanua Nua Mea and to map
damage on this model.We used the software aSPECT3D. With this program it is possible to
generate 3D models from digital image sequences, which can be recorded using
commercially available digital cameras. We used Olympus OM-D E-M1. The model was
very precise and of high graphic quality so that it was possible to transfer the damage
directly onto the model.
Fig. 5: 3D monument damage mapping detail: Differential erosion and cracks.
2.2.3. 3D model of a late baroque tombstone
The advantage of 3D-mapping are now going to be presented by example of another object.
The object is a late baroque tombstone (ca. 1725 AD, Wolkenburger quarry) which is now
located in the restoration atelier of the University of Applied Sciences in Cologne.
Despite the relatively flat, relief-like nature of the tombstone, using the classical 2Dmapping would render difficult any precise damage mapping. Especially the location of the
damage on the Christ figure and on the sides are often not accurately definable in 2Dmapping. In most cases it is the appraisal of the different recorded damage from all angles
that allows for a correct interpretation.
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Fig. 6: 3D monument damage mapping of late baroque tombstone:
All recorded damage.
Fig. 7: 3D monument damage mapping of late baroque tombstone: Detail.
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2.3. Advantage of 3D-damage mapping
Fig. 8: 3D monument damage mapping: differences in the composition
of the individual layers
The advantages of this new system for 3D-damage mapping are:
The entire surface of the sculpture is visible. With 2D mapping, certain zones can
be distorted.
In the case of the Moai of Ahu Hanua Nua Mea:
one can see the course of the water damage very clearly.
The damage mechanism such as differential erosion can be precisely documented.
Damage on the surface of the Moai can be calculated. The differential erosion
affected area is 2-5 square meters, which accounts for about 25% of the total
registered area.
The exact dimensions of the object can be registered without distortion. The exact
height of the Moai is 3.34 m.
The different layers with the varying composition of rocks can be easily discerned.
The inclination of the base of the stone sculpture is visible.
3D monument damage mapping has the advantage that damage can be traced a lot more
precisely than with conventional 2D mapping, especially as pertains to 3D objects. Hence, a
diagnosis that rests upon 3D damage mapping is of much higher quality. Another
recommendation for damage free long-term documentation in the case of the Moai is 3D
photo monitoring.
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References
Domasłowski, W., 1981, Les statues en pierre de l'Ile de Pâques. UNESCO, Paris, 54pp.
Fitzner, B., Heinrichs, K., 2005, Kartierung und Bewertung von Verwitterungsschäden an
Natursteinbauwerken. [Mapping and evaluation of weathering damage on stone
monuments] – Z. dt. Ges. Geowiss., Schweizerbart´sche Verlagsbuchhandlung,
Stuttgart, 7-24.
Internationalen Rat für Denkmalpflege (ICOMOS) (eds.), 2011, Illustrated glossary on
Stone deterioration patterns /Illustriertes Glossar der Verwitterungsformen von
Naturstein, Imhof, Petersberg, ISBN: 978-3-86568-667-1, 80pp.
Kersten, Th., Lindstaedt, M., Vogt, B., 2009, Preserve the Past for the Future - Terrestrial
Laser Scanning for the Documentation and Deformation Analysis of Easter
Island's Moai, Proceedings of the International Archives of the Photogrammetry,
Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5.
Beijing, 271-277.
Kozub, B., Kozub, P., 2015, 3D photo monitoring of tuff surface alterations of the moai of
Ahu Hanua Nua Mea, 9th International Conference on Easter Island and the Pacific
(EIPC 2015) CULTURAL AND ENVIRONMENTAL DYNAMICS. Ethnological
Museum Dahlem, Berlin, article in press.
Kozub, B., 2014, Konservatorische Erhaltung von Objekten mit Mahnfunktion. Über ein
internationales Online-Projekt, in International Council of Museums (ICOM,
Internationaler Museumsrat Deutschland) (eds.), Zur Ethik des Bewahrens:
Konzepte, Praxis, Perspektiven, Tagungsband zur Jahrestagung von ICOM
Deutschland 2013, ICOM Deutschland – Beiträge zur Museologie 4, Berlin, ISBN
978-3-00-045736-4. 69-74.
Kozub, B., 2011, Konservierung und Restaurierung von „negativem Kulturgut“, scrîpvazVerlag, Schöneiche bei Berlin, ISBN 978-3-931278-58-8. 167pp.
Kozub,
P., 2006, Anwendung von 3D-Modellen für die Visualisierung der
tomographischen Ultraschallmessungen am Beispiel der Königinnenstatue aus Tell
Basta, in Tell Basta, Archäologie in Ägypten. Ein Forschungsüberblick über die
Grabung bis 2005, Tietze Chr. (eds.), DVD. Potsdam, Universität Potsdam.
Lazzarini, L., Lombardi, G., Marconi, F., Meucci, C.,1996, New data on the
characterization and conservation of the easter island´s pyroclastics used for the
moais, in Proceedings of the 8th International Congress on Deterioration and
Conservation of Stone, Riederer, J. (eds.), Berlin, 1147-1158.
Schaich, M., 2012, Mit digitalen Fotoserien zum 3-D-Modell. Anwendungsmöglichkeiten
einer Software, in RESTAURO / Zeitschrift für Kunsttechniken, Restaurierung
und Museumsfragen 5, Callway, München, 26-30.
Seipt, H., Simon, S., Kozub, P., 2008, Ultrasonic Tomography - Correlation of Ultrasonic
Verlocity with Strength Parameters and Exemplary Application on Historical
Stone Objects using Virtual 3D-Models, Proceedings of the 11th International
Congress on Deterioration and Conservation of Stone, Łukaszewicz J.W.,
Niemcewicz P. (eds.), Toruń, Nicolaus Copernicus University Press, 505-512.
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1040
EMERGING DIGITISATION TRENDS IN STONEMASONRY
PRACTICE
S. McGibbon1 and M. Abdel-Wahab1*
Abstract
Stone forms a major component of Scotland's pre-1919 building stock. Current
governmental policy and conservation guidelines stipulate that high quality repair and
maintenance should be carried-out without compromising the building’s historical features
whilst minimising the impact on the natural environment and providing value for money.
Addressing these challenges requires investment in new technologies and calls for
innovative practice. Therefore, this paper examines digitisation trends in the heritage sector,
which includes: Terrestrial Laser Scanning (TLS), Infra-Red Thermography (IRT), and
Historic Building Information Modelling (HBIM). Such trends have the potential to
revolutionise stonemasonry practice of historic buildings by providing accurate sitesurveying and diagnosis of the building condition for informing the development of
appropriate method statements for repairs. Moreover, these technologies can provide
Quality Assurance to ensure that the repairs have been carried-out to the required standards.
Raising awareness of the current digitisation trends is essential for shaping and informing
curriculum development in Further Education (FE) colleges. Demonstration projects thus
become paramount for showcasing the application of digital technologies in a live project
environment along with its accrued benefits.
Keywords: digitisation, laser scanning, stonemasonry, repair, maintenance,
skills development
1. Introduction
Scotland has over 450,000 pre-1919 building stock, and stone is an integral part of the
construction of these buildings. Almost £400 million was estimated to have been spent on
repair and maintenance of these buildings in 2013/14 (Historic Scotland, 2014). Yet,
disrepair levels to the residential and non-residential stock of pre-1919 buildings of 90%,
present a critical period for Scotland’s uniquely diverse stone built heritage; (Scottish
House Condition Survey, 2014; Historic Scotland, 2012). Moreover, a combination of
neglect and poor practice, particularly for stonework repair, further endangers historic
building stability and functionality. Particularly, the methods used for selection and
application of replacement stone and mortar, which have not always resulted in the most
appropriate repair being used resulting in damage to adjacent masonry (Torney et al 2014;
Lott, 2013; Hughes, 2012).This is not solely a common problem for historic buildings;
there is lack of understanding of building physics across the wider R&M sector (The Royal
1
S. McGibbon and M. Abdel-Wahab*
School of Energy, Geoscience, Infrastructure and Society (EGIS), Heriot Watt University,
Edinburgh, United Kingdom
m.abdel- wahab@hw.ac.uk
*corresponding author
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Academy of Engineering, 2010). Yet, the Scottish Historic Environment Policy calls for
appropriate material selection, methods of working and skills to retain historic character
and future performance of older buildings, in line with the British Standard 70913:2013
Guide to the conservation of historic buildings. Furthermore, government legislation
requires that climate change, energy efficiency and sustainability are embedded in the
R&M practice of historic buildings (Scottish Government, 2014).With the move to a low
carbon economy, the up-skilling of the workforce in the use of new technologies and
processes in the repair and maintenance (R&M), of historic buildings becomes essential
(Abdel-Wahab and Bennadji, 2013).
The historic building R&M sector therefore has the dual-challenge of addressing current
performance shortcomings as well as incorporating the sustainability agenda in existing
stonemasonry practice. Research suggests that there is a perennial problem of a
stonemasonry skills shortage and deficiency at both craft and professional level when it
comes to R&M of historic buildings (Pye Tait, 2013). The problem is further complicated
due to the substantial errors in the way that traditional buildings are treated in building
standards, regulations and assessment systems (Sustainable Traditional Buildings Alliance
(STBA), 2012). Recent research found that it is far more likely to observe poor quality
surrounding standards of workmanship and knowledge of masonry practices and that the
number of incidences of previous poor practice and neglect coupled with the challenge of
hidden defects, such as loss of structural integrity had led to an increase in project
budget/planning/programming and difficulty in recruitment (McGibbon and Abdel-Wahab,
2014). This becomes unsurprising when considering that stonemasonry apprenticeship
training and assessment programme (TAP) at Scottish Vocational Qualification (SVQ)
level 3, only covers 13% of R&M industry requirements although 20% is more a realistic
figure now that sustainability has been embedded across the course however it is in generic
form and not directly related to building standards.
Clearly, there is a significant gap between current training provision and industry
requirements. As such, there is a need for the provision of an up to date technical handbook
for the R&M of historic buildings to meet current/future quality and performance standards
and thereby attempting to address the current gaps in training provision (McGibbon and
Abdel-Wahab, 2014). Moreover, adopting new technologies and innovative practice to
historic building R&M throughout a project lifecycle (from planning to completion), will be
fundamental to repair specification to inform practice and generate viable method
statements for on-site operations. Therefore, the aim of this paper is to examine the current
digitisation trends in the R&M of historic buildings by showcasing exemplar projects and
along with its potential impact on the training provision and practice of stonemasonry.
Digitisation refers to the process of converting information into a digital format which
enables capturing an accurate record of the current condition of a historic building. COTAC
(2014) suggested that digitisation could enhance work prioritisation, project
scheduling/programming and monitoring work progress. Digitisation technologies includes:
Terrestrial Laser Scanning (TLS) and Historic Building Information Modelling (HBIM)
(Fig. 1) – which are subsequently discussed.
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Fig. 1: 3D Laser Scanner and Historic Building Information Modelling (HBIM).
2. Exemplars of digitisation in the Heritage sector
2.1. Terrestrial Laser Scanning (TLS)
TLS is increasingly used for surveying and digitally recording historic buildings (Chalal
and Balbo, 2014) as the TLS data capture not only provides accurate representation of
complex buildings and structures containing important yet irregular surfaces both externally
and internally, but also the sculptural features and other intricate architectural elements
which make up these unique buildings (Fig. 2). As such, TLS offers numerous possibilities
such as highly accurate measured surveys, structural and condition monitoring as well as
the production of 2D elevation and plan drawings in AutoCAD (Laing et al., 2014).
Fig. 2: TLS capture of a diverse variety of buildings.
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Although, when collecting survey data, the level of detail of data required will inform the
type of TLS method to be employed, as each technique provides differing levels of
accuracy based on survey requirements (Smits, 2011) (Tab. 1). Yet laser scanning is not
without its limitations as generating and manipulating point clouds, meshes, and models
can be extremely complicated, time consuming, and can be very expensive (Scott, Laing &
Hogg, 2013). Nonetheless with today’s increasing pace in technological change, the use of
3D laser scanners are becoming increasingly more affordable and user-friendly, this in turn
will make 3D-modelling faster, easier, and widely accessible (Sabrina and Wärmländer,
2013). For example, recent research has begun exploring the possibilities of combining a
cheap line laser and a smart-phone into a fully portable laser scanning device (Kolev et al.,
2014) which, as long as it was capable of delivering the required level of accuracy as
outlined in Tab. 1, could provide both professionals and contractors the ability to capture
relevant on-site activity.
Tab. 1: Terrestrial Laser Scanner Types Source: Adapted from Smits (2011).
Laser Scanner
Accuracy @
operating range
Operating Range
Stone Element
Triangulation
0.05mm-1mm @
0.1m - 25m
Close-range
Intricate architectural
details
Terrestrial Phase
Comparison
5mm @ 2-50m Midrange
Mid-range
Façade surveying
Terrestrial Time
of Flight
3-12mm @ 2-100m
Mid to long-range
General surveying
Therefore, for historic building stone conservation and repair work the uptake of this
rapidly developing technology with its non-destructive nature will provide new approaches
to the traditional practices of stonemasonry, particularly stone replacement and stone
carving. For example, the production of highly accurate 2D section drawings of individual
stones from the TLS data will allow the creation of profile templates of the decayed
stonework without the need to cut into the façade. In addition, McGibbon and AbdelWahab, (2014) highlighted that for historic stone re-construction (recording, removing and
re-positioning stones in the exact previous position) laser scanning was instrumental for
visualising the required scale of maintenance (material and skill requirements) but it was
not used for the development of a method statement and Quality Assurance (QA) for onsite operations. Recently, the Glasgow School of Art's Mackintosh building was laser
scanned in the aftermath of a fire outbreak. A 3D plan was created of what survived after
the fire, allowing stones to be marked up corresponding to the data in the plan, and the
damaged wall to be deconstructed and sections of stonework laid aside for conservation. As
such the 3D Models derived from the scan data will allow comparison of project
specifications with as-built data as part of an objective quality assurance approach as
opposed to a subjective quality check, which currently relies on the skill, knowledge and
experience of both the craftsman and the professional (González et al., 2010).
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2.2. Historic Building Information Modelling (HBIM)
BIM is defined by international standards as “shared digital representation of physical and
functional characteristics of any built object, which forms a reliable basis for decisions”
(Volk et al., 2014). In considering the use of BIM for historic buildings, the concept is
absolutely relevant for R&M (Murphy, McGovern and Pavia 2013) (Fig. 3).
Figure3: HBIM including automated documentation (Murphy et al., 2013).
HBIM allows the metric surveying process to produce high resolution reality-based digital
models capable of being linked with different historic building repair documentations
(Cheng et al. 2015); from full engineering drawings and schedules (programme, cost,
inspection, etc) including intelligence to point cloud data, such as detail behind the object’s
surface concerning its methods of construction and material makeup to developing the
HBIM model to simulate structural and energy behaviour for virtual analysis
(Logothetis et al., 2015). CyArk in collaboration with Fresenius University of Applied
Sciences, Cologne and Heriot-Watt University, Edinburgh are currently 3D laser scanning
Cologne Cathedral to develop highly detailed 2D and 3D BIM conservation documents as
well as build a dimensionally accurate photorealistic 3D model for interpretation purposes
(Fig. 4). The data will be used to analyse the structure of the Cathedral, comparing the older
sections of the Cathedral with later construction. For example, the 3D model could be
augmented with any historical drawings/records, if available, to generate a time-lapsed
digital representation of the deterioration of the building. Not only will this provide more
accurate historical record, but also it can inform the development of an effective R&M
programme. While this ability to provide an even more accurate representation of the
original form of the building is essential for historic building conservation work, yet the
current trend in digitisation tends to be focused on documentation with virtually no
application for on-site practice. In fact HBIM like TLS is absolutely relevant for on-site
activity as significantly; the very detailed data collected could act as a benchmark to
precisely monitor the future level of stone erosion of historic buildings elements, in
particular intricate stone carved architectural details such as cornices, statues and pillars,
allowing accurate diagnosis of the building condition for informing the development of
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appropriate method statements, as well as QA key performance indicators such as
conformance to standards, construction time and cost etc. for stonework repairs.
Fig. 4: 3D Laser Scanning of Cologne Cathedral (Zoller + Fröhlich, 2015).
2.3. Piloting a Digital Workflow
Currently there is no defined process available for quality stone replacement in historic
buildings, unsurprising given the majority of techniques and methods used at the
specification and application phases for stonemasonry are still deeply rooted in traditional
practices. Moreover, stone replacement relies on a visual and subjective assessment of the
stonemason resulting in inadequate performance such as inaccuracies in stone replacement
measurements, excessive waste removal, and damage to stones when removing mortar as
well as when on-site variations are required, in part due to inadequate use of modern power
tools. Therefore, developing a holistic process for stone replacement is paramount for
supporting delivering high quality R&M of historic buildings and adopting new
technologies and innovative practice will be fundamental to repair specification to inform
practice. As such, current research by McGibbon and Abdel-Wahab (2016) proposes the
introduction of a digital workflow as a viable framework for on-site operations (Fig. 5).
The project will pilot a new process for stone replacement to historic stonework that
involves the application of laser scanning as well as a demonstration of emerging digital
technology adopted during the surveying, installation and in-use phase, which is low cost,
off-the-shelf and user friendly. The process is disruptively innovative and seeks to change
the landscape of stonework repairs in the historic building R&M sector, shifting the
paradigm for the provision of high quality repair from traditionally subjective appraisals
towards highly objective assessments gained from modern technology application whilst
improving communication both on and off-site, not only between management and
operatives but also improve the flow of information across the supply chain and its
logistics.
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Fig. 5: Innovative Digital Workflow (McGibbon and Abdel-Wahab, 2016).
The aim of the project is to examine how historic building stonework repair can be
enhanced by incorporating innovative/modern technologies (3D laser scanning;
Photogrammetry; Digital documentation) into construction practice by providing an on-site
tool for repair specification in historic stonework. The project will examine current
difficulties in the process for stone replacement surveying, procurement and quality
assurance process through the use of case studies of best practice of natural stone
replacement (indenting) to answer questions such as: What do these difficulties mean for
emerging technologies and processes to aid repair specification and on-site activities? What
does the adoption of emerging technology mean for workforce quality, health and safety,
performance and skills policy development in historic building repair and maintenance
(R&M)? What types of skills development (technical, functional, management) underpin
this proposed innovative process for stonemasonry practice?
It is the belief that this project has the capability to revolutionise the industry and is a
fantastic opportunity for showcasing the latest innovations for stone replacement. It could
lead the way for modernising practice in the R&M of historic buildings by yielding new
empirical data that can contribute to the use of emerging technologies and processes to
improve workforce performance by providing an on-site tool for repair specification in
historic stonework, whilst developing recommendations for addressing the training needs of
the workforce for appropriate use of emerging technologies for historic building R&M. as
well as informing stakeholders (training providers, policy makers, funders, SMEs, etc.) on
areas for skills policy development and implementation, such as quality and standards for
training.
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3. Conclusion
With the increasing demand for delivering high quality R&M, stonemasonry practice still
faces the challenges of: poor skills, skills shortages, application of complex materials and
techniques such as lime mortar, addressing climate change, energy efficiency and
sustainability whilst providing value for money. For practitioners, the embracing of
digitisation trends (3D laser scanning, HBIM, and IRT), and innovative practice
(combining of new technologies tailored to specific project challenges), has the potential to
revolutionise R&M practice of historic buildings by providing accurate site-surveying and
diagnosis of the building condition for informing the development of appropriate method
statements for repairs. Moreover, these technologies can provide Quality Assurance to
ensure that the repairs have been carried-out to the required standards and in turn provide a
level of protection for both the client and contractor vis-à-vis the defects liability period.
With the unprecedented pace of technological change, FE colleges need to keep-up with
modernising their curriculum and demonstrating that digitisation has its place in the
industry which can only attract the digital natives – Generation Y. Digitisation in the R&M
of historic buildings can enhance and promote the image of the heritage sector as being
innovative, high-tech and not for underachievers (Abdel-Wahab, et al., 2012). Therefore,
raising awareness of the current digitisation trends is essential for shaping and informing
curriculum development in FE colleges. Demonstration projects thus become instrumental
for showcasing digitisation technologies in a live project environment, which will require
an in-depth understanding of industry practice as well as a good understanding of the
capabilities and limitations of digitisation technologies.
References
Abdel-Wahab, MS (2012). 'Rethinking apprenticeship training in the British construction
industry' Journal of Vocational Education and Training, vol 64, no. 2, pp. 145154., 10.1080/13636820.2011.622450
Abdel-Wahab, M., & Bennadji, A. (2013). Skills development for retrofitting a historic
listed building in Scotland. International Journal of Low-Carbon Technologies,
ctt043.
Armesto-González, J., Riveiro-Rodríguez, B., González-Aguilera, D., & Rivas-Brea, M. T.
(2010). Terrestrial laser scanning intensity data applied to damage detection for
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Chalal, M. L., and Balbo, R. (2014) Framing Digital Tools and Techniques in Built
Heritage 3D Modelling: The Problem of Level of Detail in a Simplified
Environment. International Journal of the Constructed Environment, 4(2).
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documentation and refurbishing. ISPRS-International Archives of the
Photogrammetry, Remote Sensing and Spatial Information Sciences, 1, 85-90.
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Conference on Training in Architectural Conservation (COTAC) (2014) Integrating Digital
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Conservation(HBIM) http://www.cotac.org.uk/docs/COTAC-HBIM-Report-FinalA-21-April-2014-2-small.pdf
Heritage Innovation Preservation (HIP) Institute (2015) ABOUT“SCANPYRAMIDS”
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Hughes J.J. (2012), RILEM TC 203-RHM: Repair mortars for historic masonry. The role of
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mortars. Materials and Structures, 45, pp.1287–1294.
Kolev, K., Tanskanen, P., Speciale, P., & Pollefeys, M. (2014) Turning mobile phones into
3D scanners. In Computer Vision and Pattern Recognition (CVPR), 2014 IEEE
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Collection Techniques to Support BIM Design Decision Making, Procedia
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Logothetis, S., Delinasiou, A., and Stylianidis, E. (2015). Building Information Modelling
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Sensing and Spatial Information Sciences, 1, 177-183.
Lott, G. (2013) The Sands of Time, Britain’s Building Sandstones, The Building
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McGibbon, S., and Abdel-Wahab, M. (2014) Skills development for stonemasonry: Two
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(18-19th February 2014), Surgeons’ Hall, Edinburgh, UK.
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4–6 June 2012; St. Petersburg, Russia (pp. 170-184).
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Scottish Government (2014) Historic Environment (Amendment) (Scotland) Act 2014
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Scottish House Condition Survey (2013) Key Findings.
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& Fröhlich (2015) How we build reality; Student project “3Dom“
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1050
DIGITALISATION AND DOCUMENTATION OF STONE
DETERIORATION, USING CLOSE-RANGE DIGITAL
PHOTOGRAMMETRY
M.Á. Soto-Zamora1, R.A. López-Doncel2, G. Araiza-Garaygordobil1 and
I.E. Vizcaino-Hernández3
Abstract
The digitalisation of the deterioration in stone elements is a complex problem due mainly to
the difficulty in accurate geometrical definition of the volumetric losses of the studied
element. Despite the existence of methodologies for geometrical documentation and
digitalisation of the deterioration of stone in the market, such as laser scanners, these
methodologies have a limited application, especially in developing countries, where the
cost of the required equipment as well as the training for application, precludes the massive
application of these techniques. Because of this, it was decided to evaluate the application
of a very economical and easy-to-apply technique, close-range digital photogrammetry; this
technique consists in taking photographs from different angles of the object to be modelled,
and by applying photogrammetry software, a model is constructed. This model represents a
good precision in the representation of the geometry, colour and textures of the modelling
object. This paper presents the results of the evaluation of the photogrammetric method in
the geometric modelling of stone specimens damaged artificially. The volumetric loss of
the specimens for each cycle of degradation was evaluated by comparing the results of the
volume calculated with photogrammetric method and the volume of the specimens obtained
through direct measurement in laboratory testing. It has been found that the correlation
between the volumes calculated and measured in the laboratory for these specimens is very
good, which leads us to conclude that close-range digital photogrammetry is a very
inexpensive and easy-to-apply tool for the digitalisation in the documentation of the
deterioration processes in stone elements, allowing for the massification of its application.
Keywords: digitalisation, Close-Range Digital Photogrammetry (CRDP), 3D-modelling,
stone deterioration
1
M.Á. Soto-Zamora*and G. Araiza-Garaygordobil
Universidad Autónoma de Aguascalientes, México
miguelsotoic86@gmail.com
2
R.A. López-Doncel
Universidad Autónoma de San Luis Potosí, México
3
I.E. Vizcaino-Hernández
Instituto Tecnológico del Grullo, México
*corresponding author
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1. Introduction
Close-range digital photogrammetry (CRDP) is a technique that allows one to obtain
information on the geometric properties of any object through obtaining stereoscopic
photographs of the objects by computer processing the characteristics of these images,
minimising physical interaction with the analysed object. This technique has long been used
as a technique for the three-dimensional topographic representation of certain regions of the
Earth's surface and for measuring the elements in the photographs, mainly through the use
of aerial or satellite photographs using stereoscopic pairs of photos by using an optical or
digital stereoscope. In our days, thanks to the power of the existing computer equipment,
and the enormous availability of quality cameras that have appeared, various software have
the ability to overlay hundreds and even thousands of stereoscopic photographs to create
high-resolution three-dimensional models. This is of great importance when very accurate
representations of the dimensions and the geometrical characteristics of objects of complex
geometry are required, as is the case of deterioration in architectural stone by anthropogenic
or natural effects.
The main advantages of CRDP over other remote measurement methods, such as laser
scanners, lie in four fundamental aspects:
a) CRDP is an inexpensive technique since it does not require the use of specialised
equipment, cameras used can be of any kind, including the ones integrated in
mobile phones as long as their resolution is of good quality, preferably over
5MPX.
b) Specialised training is not required for the implementation of the technique.
Anyone who can operate a camera can gather information in the field, which
makes this technique accessible to anyone with minimal training regardless of their
academic or practical background.
c) This technique allows a better control of the density of vectorial meshes, because
the amount of spatial points can be defined during the process step, according to
the needs of the research and computational capacity of equipment employed.
d) The final modelled object, further contains surface colour and texture making it
optimal for carrying out stone mapping, as well as the present pathologies.
The main objective of this study was to verify the applicability of the technique to record
the volumetric deterioration of the stones in architecture, verifying the volume of various
specimens modelled with CRDP; these results were contrasted with the results to
volumetric measurements in laboratory of the same specimens using a digital scale yielding
very encouraging results, for the application of this technique.
2. Methodology
The methodology consisted in obtaining stone specimens, which were subjected to
degradation cycles. In each specimen and for each cycle of degradation a number of
stereoscopic photographs was performed; with these photographs, a photogrammetric
model was generated; also, the volume of the specimen was measured in the laboratory by
implementing a digital balance.
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Fig. 1: Flowchart demonstrating the cycles of deterioration, modelling and measurement.
These flowcharts illustrate the methodological process that is followed in order to evaluate
CRDP to the deterioration of the stone. The first (Fig. 1) represents the general cycle for the
experimental campaign presented in this paper; the second (Fig. 2) one shows the detailed
process for obtaining the relative error in the calculated volumes using both methods.
Fig. 2: Flowchart demonstrating the volumetric measurement processes for each
deteriorating cycle.
2.1. Materials and Equipment
2.1.1. Stone specimens
To perform the experimental campaign, four specimens, including three natural stone
specimens 5cm wide, 5cm long and 15 cm in height, where prepared. For each specimen,
natural stone of a specific colour and texture was used in order to evaluate the effect of
these characteristics on the quality of the generated models with CRDP. Stone ‘A’ - Black
to grayish pyroclastic igneous rock with a porphyritic to serial texture made of non
collapsed black pumice fragments, white pumice fragments, lithics and phenocrystals of
sanidine, quartz and plagioclase. The matrix has a glassy texture. The ratio between
components and matrix is (65%-35%). This rock is locally called Cantera Negra (Black
Tuff) from Escolasticas (Querétaro) and is classified after Fisher (1966) as Lapilli tuff /
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Tuff breccia. Stone ‘B’ - Pink to reddish pyroclastic igneous rock with a porphyritic texture
composed out of lithic fragments, fiammes, collapsed pumice and quartz and sanidine
phenocrystals hosted on a microcrystalline, devitrified reddish matrix with eutaxitic texture.
Contains about 40% of components and 60% matrix. This rock is locally called as Cantera
Melón from Galindo, (Querétaro) and it is classified after Fisher (1966) as Lapilli tuff.
Stone ‘C’ - Gray to pale-gray pyroclastic igneous rock with a porphyritic-seriate texture
composed out of lithic fragments, few fiammes, non-collapsed pumice, quartz, alkali
feldspar and many lithic clasts (phenocrystals) embedded in a glassy / microcrystalline
matrix (hypocrystalline texture). This volcanic tuff rock contains around 40% crystals and
grains and 60% matrix. This tuff rock is locally called as Cantera Blanca de Huichápan
(Hidalgo) and it is classified after Fisher (1966) as Lapilli tuff. The fourth specimen used
was a concrete cylinder 7.5cm in diameter and 15cm in height.
Fig. 3: Stone Specimens used in the experimental campaign.
In order to facilitate the photogrammetric process, photogrammetry markers were placed,
which, thanks to its colour and distinctive patterns, can improve the detection of match
points, increasing the quality of the generated models.
2.1.2. Equipment
In order to obtain the photographs of the models analysed in this investigation, the
following photographic equipment was used:
a) Nikon COOLPIX® L820 Digital Camera 16.0 million Effective pixels Image sensor
1/2.3-in. type CMOS.
An assembled computer was used to perform the process; this computer has the following
hardware:
b) AMD FX 8-Core Black Edition FX-8350, S-AM3+, 4.00GHz, 8MB L2 cache
c) RAM Memory Kingston HyperX Savage DDR3, 2400MHz, 32GB (4 x 8GB)
d) Graphic Nvidia MSI GeForce GTX 970 Gaming 4 GB
e) Motherboard ASUS Crosshair V Formula-Z AM3
f) Ventilation Corsair Cooling Hydro Series H80i + 6 Air Ventilators
For determining the volume of the specimens in laboratory:
g) Digital scale with capacity of 1000 g and precision e= 0.1g
2.1.3. Software
The photogrammetric process was carried out using a Student Version License Software
Agisoft PhotoScan® a stand-alone software product that performs photogrammetric
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processing of digital images and generates 3D spatial data to be used in cultural heritage
documentation as well as for indirect measurements of objects of various scales. The 3D
rendering and volume calculation was performed using SketchUp Pro 2015 Teacher
Version®.
2.2. Techniques and Procedures
2.2.1. Stone Deterioration
In the early stages of this project, we considered using a technique of artificial damage
based on salts, specifically Magnesium Sulphate (MgSO 4); however, once the degradation
cycles were initiated, it became clear that for the stones most resistant to chemical
weathering, the volumetric changes between one cycle and another were less than 0.50%,
making it impossible to determine if the measured volumetric change is significant because
the change is very close to the relative error of the method used. Given this situation, we
decided to use random mechanical wear on the specimens, in order to generate geometries
as complex as possible. Such wear was performed using metal hammers of different
dimensions and progressively removing random sections of material specimens.
2.2.2. Photogrammetric Models
The application of CRDP method requires taking photographs of the object or surface to
model; the number of photographs used depends on the size of the element to model, as
does the distance from the camera to the object, in this case were used between 50 and 60
photographs at an approximate distance of one meter, such photographs must be taken
from different angles to achieve the stereoscopic effect; in addition to this, the photographs
must meet two basic conditions to be aligned in the model:
a) The photographs must have an effective connection between them so the software
can be able to detect the commonalities between these pictures and make a
calculation based on the depth of the gap between them.
b) They should cover the whole object or surface as much as possible to avoid gaps in
the mesh.
After taking the photographic sequences (regardless of the equipment and instruments
used), there are two options for building the model: the first is to conduct a pre-processing
of the pictures by using masks, selecting only the areas of each photo that are required for
the photogrammetric model, which concentrates all the connection points in defined areas,
improving the quality of the generated model thanks to the densification of points made by
the software; however, it is possible to generate models without the use of masks, but this
reduces the quality of the generated model. Once the pre-processing of the information is
done and applying one or more software, a process of four stages, which contribute to the
final integration of photogrammetric model, is performed:
a) Once the photographs of the model are selected and pre-processed, the first phase
involves the orientation of photographs, a process by which the software defines a
number of points (sparse cloud) in common between the photographs, by which it
then calculates the position of each photo and by a digital parallax technique,
calculates the depth of those points in the entire set of the scene. During this
process, it is necessary to define a reference measurement whereby we may scale
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the photogrammetric model; the measure must be easily recognisable between two
points in the mesh, to facilitate the modelling. If during this stage of modelling, the
model has deficiencies, such as discontinuities, incorrect overlaps, or not modelled
faces, the photographic sequence must be repeated to increase the number of
photographs and the overlap between them.
b) The second process consists of densifying the dispersed cloud of points, adding
points interpolated between points already detected in the first procedure; each of
these points possesses information concerning both its spatial position and a
defined colour according to the pictures that have been obtained. After completing
this process, it is quite possible to faithfully observe the model with all of its
elements as a dense cloud of points. During this stage, it is possible to eliminate
the points that should not be interpolated to create the mesh, this in order to clean
the model of all points not required for the modelling.
c) The third stage creates the mesh of the model. At this stage, a series of triangles
defined by the points of the dense or sparse cloud, are generated leading to a
triangle mesh. Usually, as the mesh density is defined by the density of the cloud
of points to be used, it is necessary to limit the number of mesh elements created in
order to avoid creating too heavy a model.
d) Generally, the mesh created by photogrammetry software presents gaps and has no
defined scale, so it is essential to import them into software that repairs the mesh
errors and scales the model according to the reference measurement initially
obtained. After this is done, convert the mesh into a solid bounded by a closed
surface which can be measured in order to obtain the volume. Almost any threedimensional modelling software has these characteristics; however, it is important
to consider that given the number of polygons of the mesh generated by the
photogrammetry process, a computer system with high capacity and speed is
required for the processing.
The laboratory measurement of the volumes of specimens for each cycle of degradation
was performed using a digital scale weighing each of these specimens "in the air", and then
the specimen gained weight while the specimen was immersed in double distilled water.
For each measurement cycle, the water temperature for the determination of density was
recorded; given the purity of the water, no variations were considered in the density of
water due to dissolved solids. The formula used to calculate the volume was as follows:
𝑉𝐿𝑎𝑏 =
𝑊𝑎 − 𝑊𝑠
𝜌𝑤°𝐶
(Eq. 1)
where VLab is the volume of the specimen measured in laboratory, Wa is the weight of the
specimen in the air, Ws is the weight of the specimen submerged in water and ρw°C is the
density of the water for a certain temperature (West 1989).
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3. Results
Tab. 1 shows the results of the volumetric measurements performed in the laboratory and
from the CRDP model, the initial state (Cycle 0) and two cycles of mechanical wear is
shown. The relative error was calculated as follows:
𝐸𝑟 % =
|𝑉𝐿𝑎𝑏 − 𝑉𝐶𝑅𝐷𝑃 |
∗ 100
𝑉𝐿𝑎𝑏
(Eq. 2)
where VLab is the volume of the specimen measured in laboratory and VCRDP is the volume
of the specimen measured in the 3D modelling software.
Tab. 1: Summary of results in measurement of the volumes by both methods.
Specimen
Cycle 0
Degradation Cycle
Cycle 1
Cycle 2
(dm )
0.3784
0.3555
0.2132
𝑉𝐶𝑅𝐷𝑃 (dm )
0.3824
0.3519
0.2177
𝑬𝒓 %
1.0571 %
1.0127%
2.1107%
(dm3)
0.3957
0.2028
0.1666
𝑉𝐶𝑅𝐷𝑃 (dm )
0.3942
0.2011
0.1659
𝑬𝒓 %
0.3791%
0.8383%
0.4202%
(dm3)
0.3968
0.3735
0.3328
𝑉𝐶𝑅𝐷𝑃 (dm )
0.3934
0.3730
0.3339
𝑬𝒓 %
0.8569%
0.1339%
0.3305%
(dm )
0.6510
0.5880
0.5070
𝑉𝐶𝑅𝐷𝑃 (dm )
0.6490
0.5870
0.5020
𝑬𝒓 %
0.3070%
0.1700%
0.9860%
Measurement
Methodology
𝑉𝐿𝑎𝑏
Stone A
3
3
𝑉𝐿𝑎𝑏
Stone B
3
𝑉𝐿𝑎𝑏
Stone C
3
Concrete A
𝑉𝐿𝑎𝑏
3
3
Fig. 4: Models of the stages of deterioration of the stone specimens.
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Fig. 5: Models of the stages of deterioration of the concrete cylinder.
4. Conclusions
The implementation of the CRDP method for the Measuring and registering of the
deterioration of stone and architectural elements built from these is widely recommended,
especially for its low cost, high precision and little training required for its implementation
in the field. This allows almost anyone with minimal training to gather information in the
field, after which the information is properly processed by specialised 3D modelling staff,
allowing one to obtain models of high precision using everyday equipment like common
photo cameras and even those present in modern mobile phones. In most of the cases
analysed, the relative error generated by the modelling was less than 2.2%, which justifies
the conclusion that the method is accurate enough to model the mechanical wear caused by
natural or anthropogenic factors. However, these levels of precision are not sufficient for
the documentation of chemical weathering, as this occurs in a very long time and therefore
the volumetric losses (in most cases) are too small to distinguish from the probable error of
the method. Likewise, there is no evidence that the colour of the specimen material affects
the precision of the CRDP method, but it is preferable to work with objects that have
distinctive elements, which allow the photogrammetry software to align and calculate the
depth of the elements on the scene; however, if the element to model does not possess these
characteristics, one can apply photogrammetric markers that serve as points of alignment
between photographs. The time required for the implementation of this method represents a
significant advance compared to other methods, mainly in the field information recording
and generation of meshes for geometric modelling, but the demands of the software make it
necessary to have a computational equipment with high RAM capacity and processor
speed.
References
Fisher, R.V. 1966, Rocks composed of volcanic fragments. In: Earth Sci. Rev., 1: 287- 298;
Amsterdam.
West, R.C., 1989, CRC Handbook of Chemistry and Physics 69TH Edition, CRC Press, Inc.,
978-0849304699, F4.
1058
RECORDING, MONITORING AND MANAGING
THE CONSERVATION OF HISTORIC SITES:
A NEW APPLICATION FOR BGS SIGMA
E.A. Tracey1*, N. Smith1 and K. Lawrie1
Abstract
Historic Environment Scotland (HES), a non-departmental public body of the Scottish
Government charged with safeguarding the nation’s historic environment, is directly
responsible for 335 sites of national significance, most of which are built from stone.
Similar to other heritage organisations, HES needs a system that can store and present
conservation and maintenance information for historic sites; ideally, the same system could
be used to plan effective programmes of maintenance and repair. To meet this need, the
British Geological Survey (BGS) has worked with HES to develop an integrated digital site
assessment system that provides a refined survey process for stone-built (and other) historic
sites. Based on the BGS System for Integrated Geoscience Mapping (BGS▪SIGMA)—an
integrated workflow underpinned by a geo-spatial platform for data capture and
interpretation—the system is built on top of ESRI’s ArcGIS software, and underpinned by a
relational database. Users can populate custom-built data entry forms to record maintenance
issues and repair specifications for architectural elements ranging from individual blocks of
stone to entire building elevations. Photographs, sketches, and digital documents can be
linked to architectural elements to enhance the usability of the data. Predetermined data
fields and supporting dictionaries constrain the input parameters to ensure a high degree of
consistency and facilitate data extraction and querying. Presenting the data within a GIS
provides a versatile planning tool for scheduling works, specifying materials, identifying
skills needed for repairs, and allocating resources. The overall condition of a site can be
monitored accurately over time by repeating the survey at regular intervals (e.g. every
5 years). Other datasets can be linked to the database and other geospatially referenced
datasets can be superimposed in GIS, adding considerably to the scope and utility of the
system. The system can be applied to any geospatially referenced object in a wide range of
situations thus providing many potential applications in conservation, archaeology and
related fields.
Keywords: heritage management, conservation, maintenance and repair,
geospatial data capture
1. Introduction
Many heritage organisations are responsible for conserving and maintaining historic built
sites. In Scotland, under the “Historic Environment Scotland Act” (2014), Historic
1
E.A. Tracey*, N. Smith and K. Lawrie
British Geological Survey, United Kingdom
emiace@bgs.ac.uk
*corresponding author
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Environment Scotland (HES; a new non-departmental public body) was established to take
over the functions of Historic Scotland and the Royal Commission on the Ancient and
Historic Monuments of Scotland. Under the Act, the new organisation is required to
monitor and report on the condition of properties in the care of Scottish Ministers (referred
to as the ‘HES Estate’ in this paper). The HES Estate comprises 335 sites of national
significance, most of which are built from stone.
Historically, HES architects undertook detailed analogue condition assessments for each
historic site across the HES Estate. The aim of the condition assessment was to inform and
prioritise the conservation work at individual historic sites and across the entire HES Estate.
The output format was typically a Microsoft Word document. This method of data capture
and delivery has made any subsequent interrogation of the data captured for individual or
multiple sites extremely difficult and time consuming, both in terms of condition or
conservation work done and by whom or when. Today, HES needs a system that can store
and present conservation and maintenance information for historic sites; ideally, the same
system could be used to make the process of recording data more efficient and more
consistent, and plan effective programmes of maintenance and repair.
Property asset management systems with monitoring schemes and planning tools have been
in existence for decades. However, these systems are most suitable for the management of
non-historic assets and are generally based on ‘obsolescence’ (i.e. repairs and replacement
based on fashion and usefulness rather than perpetuity (Historic Environment Scotland
2015)). Some heritage asset management systems do exist. For example, ‘The Museum
System’ was designed for museum collections and archives management, but was not
intended for use with built sites; and ‘Tribal’ was recently specified by Historic England for
managing its historic estate. However, none of the available asset management systems (for
heritage assets or otherwise) seem to provide a means of interrogating the data recorded at a
particular site on a particular date, or comparing the data amassed over a period of time. It
is also apparent that it is challenging to keep many asset management systems up to date,
mainly due to complexities of data entry.
To address these issues, the British Geological Survey (BGS) has worked with HES to
research and develop an integrated digital site assessment system that provides a refined
survey process for stone-built (and other) historic sites. Based on the BGS System for
Integrated Geoscience Mapping (BGS▪SIGMA) - an integrated workflow underpinned by a
geo-spatial platform for data capture and interpretation - the system is built on top of
ESRI’s ArcGIS software, and is underpinned by a relational database. The system is
capable of generating indicators of urgency and risk for conservation and maintenance
issues across the HES Estate and is currently assisting with the preparation of a
methodology for monitoring and reporting the condition of the Estate to Scottish Ministers.
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2. Historic Environment Scotland SIGMA application
The System for Integrated Geoscience Mapping (BGS▪SIGMA) is a digital tool that was
initially developed by BGS to facilitate the collection of digital data during geological field
surveys and the interpretation of this data once back in the office. BGS▪SIGMA is a suite of
fully customised ArcGIS tools and data entry forms that store data in a fully relational
geodatabase. Within BGS it is the default toolkit for projects requiring geological data
acquisition in the field. Data are currently captured using ‘ruggedized’ Panasonic
Toughbooks and Toughpads. BGS▪SIGMA is designed to allow a wide range of geological
and other data to be captured quickly and consistently. Separate modules are tailored to
different types of survey (e.g. geological mapping and borehole logging activities).
Building on the existing BGS▪SIGMA toolkit, a prototype field-based site assessment
system has been developed recently by BGS to store and present conservation and
maintenance information for the historic sites within the HES Estate. Data capture modules
specific to HES requirements are included in the prototype, which currently is referred to as
‘HESSIGMA’. HESSIGMA has been developed using ESRI ArcGIS 10.1 software with
an underlying Microsoft Access personal geodatabase.
BGS implemented the following to develop HESSIGMA:
1. Unique GIS layers (feature classes), attributes and dictionaries within the
personal geodatabase.
2. Modifications to existing BGS▪SIGMA forms and modules to facilitate HES data
entry.
3. New custom forms for capturing condition survey items and associated
maintenance actions data which are stored in the personal geodatabase.
4. Report output tool for exporting all recorded data.
The application module consists of a database of hierarchically arranged attribute fields,
many of which are supported by dictionaries of defined terms that guide and constrain the
way they can be populated. A simplified representation of the hierarchical structure of
HESSIGMA is shown in Fig. 1 and screenshots of the HESSIGMA forms with
predetermined data fields and supporting dictionaries are presented in Fig. 2. Further
explanation of these is provided by means of the case study presented in the following
section.
Capturing accurate survey data for historic sites in a concise, consistent way is made
difficult due to the fact that built sites vary enormously in many ways, including their
physical attributes, materials and construction history. For example, an effective data
capture system needs to be able to accommodate any type of built structure (e.g. buildings,
monuments, bridges, paved areas) and, for buildings alone, it needs to be able to deal with
any number of façades, roof pitches and corresponding architectural elements (walling,
dressings, chimneys, carvings, etc.).
The key features of HESSIGMA are:
Individual architectural elements are recorded as separate entities associated to
individual sites (e.g. buildings) and are fully linked to the site which they belong by
means of a unique identifier, GPS location and data fields with supporting ‘site
hierarchy’ dictionaries.
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Predetermined data fields and supporting dictionaries guide and restrict the range of
conservation and maintenance properties that can be recorded, ensuring a high
degree of consistency in the dataset.
Conservation and maintenance properties can be recorded for the different
architectural elements of an individual site.
Once the survey is complete, the recorded data can be interrogated directly in the
database or visualized within a Geographic Information System (GIS).
A report generator tool enables the data to be output in the form of tailored
Microsoft Word documents, thus suiting any project requirement.
Fig. 1: ‘Integrated Logical’ and ‘Work Flow’ diagrams for HES SIGMA. The former
defines the relationship of the data elements in HES SIGMA and their underlying
structures, while the latter sets out the process of population and data delivery.
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The combined database-GIS approach provides a convenient means of systematically
recording, storing, updating, interrogating and displaying a wide range of spatially
referenced data. In its GIS form the dataset can be presented as tabulations, statistical
results, or on a map. Queries can be used to quickly select, organise and view subsets of
data, or to compare and contrast different aspects of the data, thereby providing a powerful
and versatile planning tool.
The digital, hierarchical method of data capture and storage has two important advantages
over traditional ‘analogue’ methods: (i) the predetermined hierarchy of fields and the
supporting dictionaries ensure a high degree of consistency in the dataset; (ii) data recorded
for single attributes or combinations of attributes can be selected and manipulated easily,
allowing statistical and/or geospatial patterns to be drawn from the data.
3. Craigmillar Castle case study
Craigmillar Castle (part of the HES Estate) provides a useful case study to demonstrate the
utility and GIS output of HESSIGMA. The castle, which now lies within the city of
Edinburgh, is an early 15th century L-plan towerhouse with later extensions, curtain walls
and ancillary buildings, and is constructed mainly of local stone from the Carboniferous
Kinnesswood Formation. BGS has hosted workshops with future users of the new system at
Craigmillar Castle to ensure the application modules fulfil the needs of HES. Data captured
as part of a survey must inform and help prioritise conservation work at individual sites,
and also across the whole of the HES Estate. HESSIGMA generates a form for the user to
record the condition and maintenance issues for a historic site and the actions that must be
taken to remedy each issue. Once the survey is complete, it is followed by a process of
interrogation and interpretation from which the user is able to plan effective programmes of
maintenance and repair.
3.1. The survey
The HESSIGMA data capture modules were designed to accommodate a wide range of
historic site types (e.g. roofed and unroofed structures, standing stones, carved stones, field
monuments). Prior to survey, ‘baseline data’ are collated and loaded to a HESSIGMA
project for the site. This includes any 2-dimensional data that can be used in GIS (e.g. site
boundaries, plans, national topographic survey maps (past and present), aerial photographs,
past survey documentation). Incorporation of baseline data allows the user to take any
additional information into the field that may assist them with the survey.
For each site, observations relating to condition and maintenance issues are recorded
against architectural elements and stored in the project database. Prior to recording
observations, the location of the architectural element is identified by clicking on the
desired position within the site polygon (in this case Craigmillar Castle) to create a new
‘field observation point’ (FOP). Once the FOP has been created, the ‘Switchboard’ form
(Fig. 2a) automatically opens allowing the user to enter additional location information
using ‘site hierarchy dictionaries’.
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Fig. 2: HES SIGMA forms (clockwise from left to right): a) ‘Switchboard’ form; b)
‘Condition Survey’ form; c) ‘Condition Actions’ form.
‘Site hierarchy dictionaries’ are prepared for each historic site to ensure consistency across
the dataset and between users, and to provide the ability to monitor maintenance issues on
the same architectural element over a period of time. This also allows for data sorting,
querying and statistical analysis upon survey completion.
The ‘Switchboard’ form (Fig. 2a) is the primary access point for recording detailed data
within the system. On this form location information and architectural element descriptions
are entered; photographs, sketches and samples (e.g. stone, mortar) can be attributed to the
architectural element described; and access to the more detailed data entry forms for
recording condition and maintenance ‘issues’ is provided.
‘Description’, ‘Risk’, ‘Urgency’ and ‘Condition Indicator’ observations on condition and
maintenance issues are attributed to each architectural element in the ‘Condition Survey’
form (Fig. 2b). More than one condition can be captured if necessary.
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‘Actions’ can also be recorded against each observation on the ‘Condition Survey’ form. A
dictionary of pre-defined terms constrains the actions required based on what stage in the
repair process the work is in (i.e. monitor and review, develop proposals, works, obtain
budget costs). The action can be further described, and a date can be assigned upon
completion of the action. Details of who will complete the action, what specialist skills are
required and why the action needs to be completed (e.g. routine conservation, maintenance)
are entered in the ‘Condition Actions’ form (Fig. 2c). A timescale for inspection of works
may also be attributed to the observation in this form. These data can be entered either in
the field or back in the office.
HESSIGMA has no limitation on the number of architectural elements that can be
recorded or observation data that can be attributed to specific architectural elements. All
entered data are displayed in a ‘data grid’ on the bottom of the Condition Survey form and
Condition Actions form for easy viewing.
3.2. Data outputs and uses
Data entered in the field can be immediately viewed in GIS for interpretation. Once field
work is complete, the captured data can be utilised in the office for site-wide interpretation,
then validated and loaded to a corporate database for estate-wide analysis and data delivery.
With data in the corporate database, analysis on one, many, or all historic site(s) can be
undertaken. The conceptual work flow diagram for HESSIGMA is presented in Fig. 1.
If the data are uploaded to a central database it is easy to quantify the number of
observations at any given site, and identify what the risk and urgency associated with any
of these observations are, what actions are required, who needs to complete the actions and
within what time scale. Data gathered using HESSIGMA provide crucial information that
can be used by architects, for example, when planning work on a historic site. The data
allow users to assess and plan programmes of works for a single site and across an entire
estate. In GIS, users are able to use baseline data in conjunction with collected data relevant
to the site to assist in data interrogation and to produce useful datasets for architects and
tradesmen.Another key functionality within HES▪SIGMA is the ‘Report Generator’ tool.
This tool creates a formatted Microsoft Word document containing all entered data for a
single site or multiple sites. The output can be adapted to suit project requirements.
4. Conclusion
A system that can store and present conservation and maintenance information for historic
sites is being developed for Historic Environment Scotland (based on the BGS System for
Integrated GeoScience Mapping [BGS▪SIGMA]). The system, referred to as HES▪SIGMA,
allows for a wide range of attributes describing condition to be linked to individual
architectural elements within single geospatially referenced sites, rapidly and consistently,
in a digital, hierarchical form, in the field. The system is designed to facilitate more
effective planning of programmes of maintenance and repair.
The fully relational capability of HES▪SIGMA, with data fields and predetermined
dictionaries, allows subsets of the data to be queried and analysed. The results can be
presented in either statistical or map form in GIS, thereby providing a powerful and
versatile planning tool.
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This approach provides the flexibility required for surveying historic sites. The resulting
datasets provide crucial information that can be used by architects for planning programmes
of conservation works for single sites or entire estates. A range of expertise is needed to
fully populate the module; however, the data can be presented in a user-friendly visual
manner as a GIS map or in the form of a Microsoft Word document using the built-in
Report Generator tool. Additionally, the spatially referenced digital data can easily be
interrogated through queries and converted into statistical form due to the use of predetermined, hierarchical fields and supporting dictionaries, which ensure a high degree of
accuracy and consistency in the dataset. Other spatially referenced data can be imported
into a GIS for comparison and further analysis.
HES will use this newly developed survey methodology to ensure a consistency of
approach and provide a means to store and present conservation information for historic
sites included in the HES Estate. The system will allow HES to plan effective programmes
of maintenance and repair works, and to monitor the condition of the Estate over an
extended period of time. HES▪SIGMA will provide a means of reporting on the condition
of the Estate to the Scottish Government and to its members. With further development,
HES▪SIGMA could be applied across the heritage sector as a planning and management
tool for the wider historic built environment.
Acknowledgements
This paper is published with the permission of the Executive Director of the British
Geological Survey (NERC).
References
Historic Environment Scotland Act 2014, asp 19 (http://www.legislation.gov.uk/
asp/2014/19 /pdfs/asp_20140019_en.pdf, accessed 1 November 2015).
Historic Environment Scotland, 2015, Condition monitoring system for properties in the
care of Scottish Ministers and associated collections (http://www.historicscotland.gov.uk/hes-condition-monitoring-system.pdf, accessed 1 November
2015).
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CASE STUDIES
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1068
CONDITION SURVEY OF AQUIA CREEK SANDSTONE
COLUMNS FROM THE U.S. CAPITOL RE-ERECTED AT THE
U.S. NATIONAL ARBORETUM
E. Aloiz1*, C. Grissom2, R.A. Livingston3 and A.E. Charola2
Abstract
Aquia Creek sandstone was the preeminent stone used in the architecture of early federal
buildings in Washington, D.C., including the U.S. Capitol and White House. In 1826, a
portico with 10-meter-high monolithic columns made of the sandstone was completed on
the east front of the Capitol. In 1958, columns from the portico were put into outdoor
storage and replaced with marble replicas. Thirty years later, 22 of the 24 original columns
were re-erected free-standing as a “ruined classical temple” at the U.S. National Arboretum.
Since then this site has become the Arboretum’s most prominent visitor attraction. Visible
evidence of stone deterioration by delamination and concern about falling pieces from the
columns’ Corinthian capitals led to a systematic survey of damage. Each of the columns
was documented visually by a series of photographs that were stitched together. Different
types of damage and past repairs were defined and mapped digitally. Nondestructive
methods included sounding with a handheld tool to detect delaminations or voids. Limited
areas were also scanned for delamination using passive thermal IR imaging. A major type
of distress is the loss of the original smooth surface layer on the column shafts. This layer is
indurated, apparently by evaporation of quarry sap, and it tends to spall, mostly from the
bottom of column shafts upwards. Another type of damage is associated with the corrosion
of wrought-iron rings, which were embedded into the tops of column shafts. Corrosion of
the rings has led to cracking and loss of stone from astragals at the top of the column shafts.
Evidence of human intervention is also apparent, including original patches, paint traces,
dutchmen, and eight broken shafts that were reconstructed. Treatments to retard
deterioration were tested, and consolidation was undertaken on one astragal.
Recommendations were made for future stabilization.
Keywords: sandstone, delamination
1. Introduction
Many of the earliest buildings in Washington, D.C., made use of Aquia Creek sandstone,
including the Bullfinch Gateposts and Gatehouses, U.S. Patent Office (now the
1
E. Aloiz*
John Milner Associates Preservation, United States of America
emilya@jmapreservation.com
2
C. Grissom and A.E. Charola
Museum Conservation Institute (MCI), Smithsonian Institution, United States of America
3
R.A. Livingston
Materials Science and Engineering Department, University of Maryland, United States of America
*corresponding author
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Smithsonian Museum of American Art/National Portrait Gallery), White House and the
U.S. Capitol. Twenty-two of the 24 Aquia Creek sandstone columns from the east central
portico of the U.S. Capitol currently stand in the Ellipse Meadow of the U.S. National
Arboretum in Washington, D.C. (Fig. 1), where the ensemble is known as the Capitol
Columns. Each column is 10 meters high and composed of five blocks. A Corinthian
capital was modeled after a design in Sir William Chambers’ Treatise (1791), carved in two
parts, and placed above an un-fluted, monolithic shaft finished with an astragal at top and
fillet at bottom. Below the shaft is a single block composed of a circular base and
rectangular plinth. A square pedestal supports each column.
Since the Capitol Columns are the Arboretum’s most prominent visitor attraction, concern
about falling pieces and other deterioration prompted this study of the columns, carried out
on site and at the Smithsonian Museum Conservation Institute from March through
September 2013. For a systematic survey of damage, each column was inspected and
photographed; using AutoCAD software, conditions were mapped on photographs, which
had been stitched together. To assess surface detachments and voids behind them, a
combination of sounding and thermal imaging was used. Sounding was conducted on all of
the lowest portions of column shafts, as well as many upper portions reachable from a lift.
A large flat-head screw driver was gently glided over the surface of the stone; a tone
change identified the presence of voids. Thermal imaging, conducted by Gary Johanssen of
the Smithsonian’s National Museum of Natural History, confirmed the location of voids
using a FLIR T640 Thermal Imaging Camera. Air heats at a different rate than stone, and
distinct infrared radiation of voids was revealed as columns began to heat in the morning.
2. The journey of the columns
The columns are in remarkably good condition considering their nearly 200-year exposure
since quarrying on an island in Virginia and placement on the east portico of the U.S.
Capitol (1826 to 1958), storage at two locations for 27 years and re-erection at the
Arboretum in 1988. Evidence of repairs from their initial carving and their time on the
Capitol Building can still be found on the columns. Examples include patching material
found to contain white lead and paint remnants in the decorative crevices of the capitals.
The columns were regularly painted white, and in 2001 a study by Blythe McCarthy and
William Ginell identified 16 layers of paint on them. Gouges also remain where a railing
was attached between pedestals on the Capitol building.
In 1958, the columns were removed in separate pieces from the Capitol along with the rest
of the portico for replacement there with marble replicas. The shafts were lifted using two
bands around their girth, revealing circular lead sheets that were installed beneath them
while they were on the Capitol. Once removed, each shaft was covered with slats and stored
horizontally, as documented by photographs in the archives of the Architect of the Capitol.
The capitals were crated, but the pedestals and base/plinths were left exposed. Without a
home or purpose, column pieces were moved multiple times. Eight shafts were broken
during that time, and much of the paint was lost.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 1: Twenty-two Aquia Creek Sandstone columns from the U.S. Capitol are seen here at
their present location in the National Arboretum in Washington D.C.
After many false starts, the columns were physically transferred to the Arboretum in 1984
to be erected in a classical temple plan with central fountain as envisioned by the noted
English landscape architect, Russell Page (1906–1985). The installation process at the
Arboretum, which required moving the columns a seventh time, involved considerable
planning and diverse voices, including landscape architects, the Friends of the Arboretum
non-profit organization, structural engineers, mechanical and electrical engineers, architects
and multiple contractors (EDAWinc. et al. 1987). A concrete foundation and footer were
created for each column, and all column parts were connected with stainless steel dowels
epoxied into newly drilled holes. The capital tops, which had never been directly exposed
to rain before, were covered with flashing, and a damp-proof metal course was installed
beneath the pedestals. In addition, the columns were stripped of remaining paint, and a
consolidant with a water repellent, Conservare H (comparable to Wacker H), was applied to
two columns.
3. Ongoing deterioration
Aquia Creek sandstone itself has inherent vice: it is not optimal as a building stone in terms
of durability, as was already recognized at the time of its selection; rather, it was chosen
because it was locally available and easily worked. Aquia Creek is an arkosic sandstone
formed by deposition of sediments during the Lower Cretaceous period over 100 million
years ago, part of the Potomac Group (Nelson 1992, McGee and Woodruff 1992). The
sediments were compacted along the Potomac River near Aquia, Virginia (Fig. 2). Major
components of the sandstone include quartz, which gives the stone strength and acid
resistance, and smaller amount of feldspars, which give the stone warm coloration. Small
amounts of iron averaging about 1% according to XRF and ICP analyses (McCarthy and
Ginell 2001, p 27) provide red coloration to the stone, appearing in the form of uniform
“stains,” lines or dots. Grains are bound with secondary amorphous silica (Hockman and
Kessler 1957), but the stone is considered weakly cemented.
Pervasive surface delamination was identified during the condition survey. Contour loss,
where the delaminated surface has completely detached, was found on 18 of the 22 shafts
during this study, mostly around the bases of the shafts, but also around shaft repairs and
isolated areas higher up on the shafts. Fig. 3 shows an area of detachment, and Fig. 4
shows an example of contour loss at the base of a shaft. The detached crusts range up to 13
mm in thickness. The same type of deterioration was found on many of the pedestals,
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
although the thickness of the crusts (1-2 mm) was much less than the surface crusts on the
shafts. The crusts are well cemented on their surfaces, where McCarthy and Ginell (2001)
found a higher quartz to feldspar ratio based on X-ray diffraction intensities and lower
porosity by both image analysis and mercury porosimetry.
Fig. 2: Quarry face on Government Island, a state park where Aquia Creek sandstone was
once quarried, with horizontal voids indicating stone unsuitable for buildings (2013).
Hardening of column surfaces apparently first occurred from quarry sap as the columns
dried out. Calculations made by Livingston indicate that induration of Arboretum shaft
surfaces can be accounted for mainly by deposition of dissolved silica from feldspars
attacked by carbonic acid in groundwater at the quarry. The carbon dioxide (CO2) level in
groundwater can be significantly elevated above atmospheric concentrations because of
biological activity in the soil. Pore water contains dissolved silica along with other ions
produced by the breakdown of feldspars according to the following reaction given by
Stumm and Morgan (1981):
KAlSi3 O8 +CO2 +5.5H2 O = K + + HCO3- + 2H 4SiOo4 + 0.5Al2Si 2 O5 (OH)4
Orthoclase
Silicic Acid
Kaolinite
When the quarry sap evaporates, its dissolved silica content is left behind in pore spaces at
or just below the surface of stone, where it acts as a cement, thus producing the case
hardening effect observed by McCarthy and Ginell (2001). Once the case-hardened surface
layer (or, when they were on the Capitol, the many layers of paint on the surface) is
breached, moisture has likely continued to attack the bulk stone by the feldspar dissolution
process described above, eventually causing voids to form behind the surface. This creates
a zone of weakness at the transition between the case hardened surface layer and the
underlying stone.
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Fig. 3: A detachment on the shaft
of column L20, which is has not
progressed to contour loss.
Fig. 4: The lower shaft of column L20 has the
highest contour loss, extending more than six
feet; a detached area reaches even higher.
The area of detachment can be seen
on the left.
Washington D.C. has a humid, subtropical climate with multiple wet/dry and freeze/thaw
cycles that would continually stress weaker areas, eventually leading to contour loss,
although the exact driving mechanism remains a matter of discussion. Detachment was
likely occurring early in the columns' existence while still on the U.S. Capitol or in
subsequent storage, since significant contour losses were documented by the architectural
firm Oehrlein and Associates just before the columns were erected in the Arboretum
(EDAWinc. et al. 1987, A2-A7). The earliest photographs that could be obtained showing
contour losses were taken by the second author in 1988: comparison to current condition
suggests about 10-15% additional loss over the 25 years since then (Fig. 5 and Fig. 6).
Wrought-iron rings set in lead at the top of each shaft present a second instance of inherent
vice. Since the rings are covered by the capitals, it is almost certain that they were installed
at the time of original construction, although their purpose remains unclear. Corrosion of
the iron has resulted in cracking or loss at 13 of the 22 astragals, as seen in Fig. 7.
Deterioration at the tops of the shafts is particularly concerning because of their height from
the ground, which could harm visitors when pieces fall. Loose pieces of one astragal were
removed from column L7 during the survey to prevent this from occurring. The area from
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which they were taken was disaggregating; in order to strengthen the newly exposed
surface, Prosoco's Conservare OH 100 was applied according to the manufacturer's
specifications. The same treatment was also applied to the pieces removed from the
deteriorated astragal. Comparison of thin sections made before and after treatment showed
that the consolidant provides reinforcement along the tangential surfaces of the grains
without substantially filling the pores.
Multiple repairs to the columns, including various patches, reattachment of broken pieces
with adhesives and dutchmen, appear to have occurred through multiple phases of the
columns' existence. The majority of old repairs are in stable condition. Additional
deterioration can be linked to joints made during installation of the shafts at the Arboretum;
the joins appear stable, but impermeable epoxy adhesive is likely causing stone at exterior
edges to deteriorate and shallow mortar applied to the outside of the epoxy joint to detach.
Fig. 5: Contour losses on column L5 in
1988.
Fig. 6: Same location as the previous
in 2013, showing an estimated 10-15%
additional contour losses after 25 years.
4. Recommended treatments
Not all damage to the columns requires immediate or any treatment. Many alterations are
evidence of the long history of the columns. However, maintenance of old patches is
required to prevent moisture from pooling in vulnerable areas, such as where mortar repairs
are detaching at the bases of the shafts. Use of epoxy adhesive and a polyester adhesive
previously employed to reattach broken fragments is not recommended, because their
strength and porosity are not compatible with the stone, and durability is limited in UV
light. However, where old repairs are stable and not causing damage to the surrounding
stone, it is recommended that they be left in place instead of risking further damage in their
removal.
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Fig. 7: Detail of stone loss from L13’s astragal, revealing its iron ring directly below the
bottom edge of the capital.
The astragals present the most complex and difficult problems for the columns, since the
lead-bedded iron rings set into the top of column shafts are covered by the capitals. The
only means of completely halting deterioration would be to remove the rings. This would
be nearly impossible to do without harming the stone, since the capitals are fixed to the
shafts with epoxied steel dowels and mortar. In lieu of removal, a method to slow water
entry is required such as flashing to top surface of the astragals.
The breakdown and redeposition of minerals on the surface of Aquia Creek sandstone is
inevitable outdoors, but loss of surface crusts may be hindered. Grouting is recommended
in voids behind detached crusts to reestablish adhesion and stop water from pooling.
Where the crusts have already been lost, consolidation can strengthen the fragile surface.
Voids were filled on two columns behind detached surface layers. Use of a pozzolanic
lime-based grout is recommended as it sets with moisture and chemical reactions to form
vapor-permeable solids that have properties similar to Aquia Creek sandstone. Voidspan's
CG-70 was tested in four areas of detachment; a year and a half later the surfaces are still
intact. Monitoring will determine the long-term effectiveness of the treatment. Applying a
surface coating such as paint would not stop void formation and might even encourage it by
making the surface layer less permeable. Furthermore, the application of Conservare H in
1988 does not appear to have stopped contour loss on the two columns to which it was
applied, but left visible glossy streaking that is still visible today.
5. Conclusions
The case study of the twenty-two Aquia Creek sandstone columns at the National
Arboretum demonstrates the complexity of stone heritage preservation. To understand the
condition of the stone, its geology is an essential factor, and indeed the inherent vice of the
Aquia Creek sandstone has led to delamination of indurated surface crusts; however,
additional factors, such as storage, transportation and previous repairs play a role in the
monument's durability. Conservation treatment is recommended on a limited basis to areas
where patches have failed and in areas of water retention such as in voids behind
delaminating surfaces or at top of the shafts where water can reach the iron rings. Where
surface crusts have already been lost, consolidation may be a viable option to protect
weakened areas newly exposed to the weather. As this popular monument adds new layers
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to its already multifaceted history, the condition documentation completed during this study
will be essential in determining the rate and occurrence of change.
Acknowledgements
Funding for this project was made available by the National Arboretum of the U.S.
Department of Agriculture. Additional staff time and research was provided by the
Smithsonian’s Museum Conservation Institute (MCI# 6542). The authors would also like to
thank Ramon Jordan, Nancy Luria, John Blunt and Christine Moore of the Arboretum as
well as MCI staff Robert J. Koestler, Paula DePriest, Harriet F. Beaubien, Mel Wachowiak
and E. Keats Webb. Norman Weiss and Irving Slavid provided valued time, expertise and
their research into hydraulic lime grouts. Finally, Blythe McCarthy was generous in
bringing this project to the attention of the authors as well as providing copies of all
documents related to the Capitol Columns in her possession; this report is indebted to the
report that she and William Ginell completed in 2001.
References
Chambers, W., Gwilt, J., Leeds, W.H., and Hardwick, T., 1791, A Treatise on the
Decorative Part of Civil Architecture, Lockwood, London, 167.
EDAWinc., Cutts and Associates, Glassman LeReche and Associates, and Oehrlein and
Associates, 1987 (September 1), National Capitol Columns at the National
Arboretum, unpublished construction documents, 34 pp.
McCarthy, B.E., and Ginell, W.S., 2001, Deterioration of the U.S. Capitol Building Aquia
Creek sandstone columns at the National Arboretum, Washington D.C.,
unpublished report, The Getty Conservation Institute, Los Angeles, 45 pp.
Nelson, L., 1992, White House Stone Carving: Builders and Restorers, U.S. Government
Printing Office, Washington, D.C., ISBN 9780160380143.
McGee, E.S. and Woodruff, M.E., 1992, Characteristics and weathering features of
sandstone quoins at Fort McHenry, Baltimore Maryland, Department of the
Interior. U.S. Geological Survey, Open-File report 92-541, Washington, D.C., 10
pp.
Hockman, A. and Kessler, D.W., January 8, 1957, A study of the properties of the U.S.
Capitol sandstone, National Bureau of Standards Report 4998, Gaithersburg, MD,
29 pp.
Stumm, W. and Morgan, J.L., 1981, Aquatic Chemistry, Wiley Interscience, New York,
ISBN 9780471048312.
1076
THE BLACK SURFACES OF THE PORTA NIGRA IN TRIER
(GERMANY) AND THE QUESTION OF CLEANING
M. Auras1*, H. Ettl2, W. Hartleitner3 and T. Meier4
Abstract
Many monuments and buildings made of natural stone are or have been covered by black
crusts or - more generally speaking – by black surface alterations. Various detrimental
effects are reported for these black crusts and similar surface alterations and therefore in
most cases the crusts are removed or are at least reduced by various cleaning techniques.
However, in the case of the Porta Nigra at Trier – belonging to the UNESCO world heritage
– the black surface is a characteristic feature of the entire building and thus the decision
about stone cleaning is not trivial. In preparation to future conservation work it was
necessary to distinguish various types of blackened surfaces and to evaluate the role of
different damage processes. Preferentially non-destructive techniques, like ultrasonic
Rayleigh wave propagation, or low-destructive methods such as drilling resistance
measurements and microscopic studies on small samples were applied to quantify stone
properties and alterations by black films and crusts. Various cleaning techniques were
tested and it is shown that laser-induced cleaning of low intensity is sufficient to open the
sealed surface and to allow for the successful application of a consolidant while the dark
colour of the surface is only changed to a minimum extent.
Keywords: conservation of stone, black crust, cleaning, laser cleaning
1. Introduction
The Porta Nigra (Fig. 1, left) is regarded as the largest city gate from Roman times north of
the Alps. It was built at the end of the 2nd century AD. The construction work stopped in the
3rd century. The gate endured for many centuries because it was transformed into a
Christian church in the 11th century. At the beginning of the 19th century it was
retransformed into a Roman gate and only one medieval element of the church, the
Romanesque apsis attached to the eastern tower, was conserved.
The building material of the Porta Nigra is a fine-grained, muscovite-bearing sandstone of a
light grey colour. Today the sandstone is called Kordeler Sandstein and stratigraphically it
1
M. Auras*
Institut für Steinkonservierung e.V., Mainz, Germany
auras@ifs-mainz.de
2
H. Ettl
Labor für Erforschung und Begutachtung umweltbedingter Gebäudeschäden, München, Germany
3
W. Hartleitner
Planungsbüro für Naturstein und Denkmalpflege, Hofheim-Rügheim, Germany
4
T. Meier
Institut für Geowissenschaften, Christian-Albrechts-Universität, Kiel, Germany
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
belongs to the Upper Buntsandstein. The name Porta Nigra, meaning „The Black Gate“, is
known since medieval times. It provides evidence that the darkening of the stone surface
has been characteristic for the monument for very long times.
Scientific investigations on the origin of black crusts and related kinds of darkened surfaces
have been carried out on many historic stone buildings. In many studies the compounds of
those black crusts have been analysed and always the role of air pollution was pointed out
(amongst others Honeybourne 1990, Camuffo 1996, Becker et al. 2005). The most
important factor is the deposition of sulphur dioxide and its secondary products which
finally leads to the formation and enrichment of gypsum on the surface of buildings. Those
gypsum-rich crusts attracted much interest because they are obviously connected to stone
damage. They are confined to building parts sheltered from direct run-off rain water.
Besides gypsum, compounds of iron and other metals have been deposited from air on the
surfaces of buildings. Soot, dust, particulate matter, soluble salts, microorganisms, and their
decomposition products have been identified (Wilimzig et al. 1993, Nijland et al. 2003,
Warscheid 2005, Brimblecombe 2011, Graue et al. 2013).
Besides air pollution the oxidation and mobilization of iron and manganese compounds
from within the stone and their precipitation at the surface can lead to intensive blackening
of sandstones (Nord & Ericson 1993, Neumann 1994, Steger & Mehnert 1998, Thomachot
and Jeannette 2000). This process leads to the formation of thin black films particularly at
building parts exposed to the run-off rain water.
Several detrimental processes and their complex interactions have been discussed as causes
for stone deterioration by black crusts and other kinds of surface alterations. For example,
the delay of drying may lead to higher moisture contents behind the crusts, the increase of
strength and brittleness, the enrichment of gypsum and other soluble salts, the increased
heating by insolation, the enhancement of microbiological growth, and further aspects have
been considered (Camuffo 1996, Thomachot and Jeannette 2000, Charola and Ware 2002,
Warscheid 2005, Snethlage and Sterflinger 2011, Sterflinger 2011).
Therefore, black crusts on stone surfaces are usually seen as detrimental to the stone and as
unaesthetic to the building. In most cases they are removed or at least reduced during
conservation work.
Stone cleaning is problematic in the case of the Porta Nigra because the characteristic
blackening should be conserved. Thus several topics were to be investigated, before a
decision is possible. Within the framework of a research project the following questions
had to be answered:
•
Which processes led to the blackening of the stone’s surface?
•
Is it possible and necessary to distinguish different kinds of black surfaces?
•
Is it possible to identify the various damaging mechanisms suggested in the
literature and to evaluate their damage potential for the Porta Nigra?
•
Should the stones of the Porta Nigra be cleaned for reasons of preservation?
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
2. Methods
A precise survey and mapping of the building materials and their damage forms provided
the base for a detailed classification of surface alterations associated with colour changes.
A light-optical microscope (Zeiss Axioplan) and two scanning electron microscopes (FEI
ESEM Quanta 200 FEG at the Technical University Darmstadt and Zeiss DSM 960 A at the
Ludwig-Maximilians-Universität München) were used for the analysis of the black surfaces
and for the evaluation of cleaning tests.
The chemistry of black surfaces was examined onsite by means of portable XRF (Tracer
IV-SD, Bruker) with friendly assistance by the Römisch-Germanisches Zentralmuseum
Archaeological Research Institute. Based on this survey, 10 samples of black surfaces were
taken and analysed by ICP-OES at Bauhaus-Universität Weimar. Organic compounds were
analysed by GC/MS and HRGC/LRMS by the Gesellschaft für Umweltchemie, Munich.
Ultrasonic measurements were performed in a frequency range between 10 kHz and
300 kHz using piezoelectric broad-band transducers and receivers (Geotron Elektronik,
Pirna). Rayleigh waves were recorded by measuring profiles using a coupling device with a
fixed source and movable receiver. The measurements were performed without any
coupling medium. Details are given by Meier et al. (in press).
The results of additional tests to determine capillary water adsorption, drilling resistance
and thermal properties will be reported elsewhere.
Micro-sandblasting was applied for cleaning tests using slag tap granulate, calcite powder,
and garnet powder as blasting materials. Cleaning tests with laser were carried out with
fiber-coupled laser cleaning devices based on diode pumped solid-state lasers with 20 W or
100 W power and a duration of the laser pulses of about 100 ns (CL 20 and CL 100
devices, Clean-Lasersysteme, Herzogenrath).
3. Results
To ensure the conciseness of this publication, only aspects regarding black surfaces are
reported here. Other topics, such as stone conservation require their own discussion.
3.1. Classification of discolouration, pollution, and crusts
A detailed macroscopic survey of the darkened stone surfaces of the Porta Nigra led to the
following classification:
A) Brownish discolouration due to the enrichment of Fe-(hydr-)oxides
B) Grey pollution due to deposition of dust and soot
C) Black films, thin and strongly adherent to the stone, covering the surface partially or
completely
(“Patina” after ISCS glossary, but here the term “black film” is used, see 3.2)
D) Black crusts, a few millimetres thick, characterized by irregular formed surfaces and
showing a tendency to detach from stone with increasing thickness
E) Microbiological growth, predominately by algae, fungi and moss
F) Colour paint, of dark greyish colour, applied during the restoration work in 1969-1972
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Manifold small-scale transitions and overlaps were observed between these types.
The types A, C, and D are characterized by the enrichment of Fe-(hydr-)oxides on the stone
surface. Drill cores taken from a weathered sandstone block with a slightly discoloured
surface (Type A-B) displayed an intensive brownish discolouration after testing the
capillary water adsorption and subsequent drying (Fig. 1, right). This indicates that the
enrichment is mainly due to the mobilization of some compounds in the interior of stone
and their transport to the surface with pore fluids.
Fig. 1: The Porta Nigra in Trier and drill cores showing brown discolouration after testing
for capillary water absorption.
The deposition of particulate matter is a relevant factor for the formation of types B, C and
D. The occurrence of typical black crusts (D) is confined to narrow zones being
periodically moistened but sheltered from direct wetting by run-off rain water. These are
the undersides of cornices and capitals or areas behind corners where turbulences occur.
Compared to the large areas covered by type C, the type D crusts occur in small and
confined zones only, because they were removed during former conservation work in 19681973 and the formation of new crusts was rather limited. Microbiological growth (E) is
confined to areas of increased moisture content. These are protruding parts, water run-off
zones, and areas exposed to splash water. Dark grey colour paints (F) were applied during
former restoration work on replaced stones and on restoration mortars. In the surrounding
of those newly added parts the colour paint also was applied on historical stone surfaces.
Aesthetically the colour paint tries to imitate black films but it shows differing physical and
chemical properties.
3.2. Properties of the blackened surfaces
Qualitative analysis by mobile XRF, by EDX at SEM investigations and the results of
quantitative analysis by ICP-OES showed enrichments of Ca, S, Fe, P, Ti, Pb, and Sr in
both black films and black crusts (Fig. 2). These results are consistent with the results of
SEM-studies (Fig. 2) and with literature data on the chemistry of black films and black
crusts from other monuments (amongst others Neumann 1994, Thomachot and Jeannette
2000, Nijland et al. 2003, Graue et al. 2013).
Regarding the use of the term black films, it should be pointed out that several previous
studies stated an origin of the black films or black layers on sandstone mainly by
mobilization of iron oxide compounds in the stone, their subsequent transport by pore fluids
and their enrichment at the stone’s surface. (Nord and Ericson 1993, Neumann 1994;
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Steeger and Mehnert 1998; Thomachot and Jeannette 2000). Because this process might be
seen as a “natural” response of the sandstone to the impact of precipitation, sometimes the
term “patina” is used for this type of blackening, e.g. in the ISCS glossary (ISCS 2008).
In the case of the Porta Nigra chemical data and SEM observations (Fig. 2) provide
evidence that the enrichment of iron oxide compounds from the stone’s interior is
superimposed by the deposition of airborne particulate matter. Thus the formation of black
films is not only of intrinsic, but also of environmental origin. Therefore the term “black
film” is preferred in this paper instead of “patina”.
Fig. 2: Polished thin section of a sample with black film under optical and scanning
electron microscope: An interstice between quartz grains (Q) filled with Ti-rich fly ash
(Ti1) and other Ti- (Ti2) and Fe-rich (Fe) particles embedded in gypsum and between clay
minerals(C) and small quartz grains.
Organic compounds were analysed in two steps. Screening tests detected various alkanes
and other substances in two of six samples, that are probably related to diesel and biodiesel
fuel from nearby road traffic. In another sample DEHP, a common plasticizer, and n–
Nonacosan, a long-chain alkane, were detected. Furthermore 23 representative polycyclic
aromatic hydrocarbons (PAH) were analysed. In 5 of 6 samples the PAH concentrations
exceeded the detection threshold. The highest concentrations were found in a sample taken
close to a heavy-trafficked bus stop.
Ultrasonic surface measurements show a broad range of Rayleigh wave velocities between
0.6 and 1.9 km/s. Variations of stone properties and different degrees of deterioration are
the causes of this spread. Rayleigh wave velocities from different measuring profiles show
varying dependencies on frequency. Since the frequency comprises also information about
the depth of the surface wave sensitivity, different forms of damage can be recognized by
the variation of velocity with frequency. Examples are given in Fig. 3, whereupon every
curve represents an average of 10 to 15 measurements at one profile. Results of wave form
inversion showed that in the case of the Porta Nigra sandstone the analysed frequency band
corresponds to depths up to 2 cm (Meier et al. 2014).
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 3 shows curves from thin black films (Fig. 3a) and thick black crusts (Fig. 3c) where
Rayleigh wave velocity increases with frequency, indicating an increase in density at or just
below the stone’s surface. Microscopic studies on a few samples show that this corresponds
to the part of the pore space commonly filled with gypsum, clay minerals and iron oxides
(Fig. 4). Based on waveform inversions, the thickness of the crusts is estimated to vary
between a few millimetres and nearly a centimetre (Meier et al. 2014). However, between
film and crust the stone is characterized by a bright and sanding surface (Fig. 3b) and
accordingly the velocities decrease with frequency. These negative slopes point to a loss of
strength in the outermost millimetres.
a b c
bc
a)
a
b)
c)
Fig. 3: Rayleigh waves showing an increase or decrease of velocity with increasing
frequency (Meier 2016).
Microscopic studies proved the occurrence of gypsum and Fe-(hydr-)oxides in the pore
space below black films and black crusts. The zone of gypsum enrichment underneath
black crusts is about 1–10 mm thick, whereas underneath black films it is confined to a few
grain layers (0.2–2 mm).
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 4: Thin section images showing gypsum (G), and agglomerates of gypsum, clay
minerals and Fe-compounds (GCFe) in the pore space below very thin black films.
3.3. Evaluation of cleaning tests
Cleaning tests were carried out using micro-sandblasting and laser ablation, shifting the
intensities gradationally. The efficiency of the cleaning was evaluated by the optical
appearance and SEM studies, as well as by measurements of capillary water absorption
(Karsten tubes), permeability, and colour changes. In Tab. 1 some results of the Karsten
measurements are compiled. They show a very effective increase of capillary water
adsorption after cleaning at low intensities.
Tab. 1: Coefficient of capillary water adsorption coefficient [in kg/mh0.5] of black films
before and after cleaning
Black Film
On Roman Stone
On Romanesque Stone
Untreated After micro-sandblasting After laser cleaning
0.15
5 - 10
5–8
4
10
13
Applying low-intensity laser cleaning only achieved minor colour changes, but thermal
heating by insolation and capillary water adsorption were restored to values corresponding
approximately to the unspoiled stone. Furthermore air permeability showed a distinct
increase after cleaning. SEM studies verify the partial removal of black films from the
mineral surfaces by laser cleaning, while gypsum remained in the pore space.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
4. Conclusions
The darkened stone surface of the Porta Nigra, the famous Roman city gate in Trier,
Germany, has been the subject of comprehensive scientific research. Various types of
discolouration, pollution and colour paint were classified and analysed. The weathering
forms and intensities of deterioration were mapped and examined. This paper focusses on
the sensitive aspect of stone cleaning and therefore other parts of the research are omitted.
The stone surfaces of the Porta Nigra show different types of discolouration and pollution
related to their exposure to weather and air pollution. The main feature is the coverage by
thin black films adhering firmly to the stone. It could be shown that moisture transport,
strength profiles and thermal properties vary between the different types of surface
alterations. These factors are compiled in Tab. 2, giving a basis for an evaluation of the risk
estimation of each of those alterations.
Tab. 2: Changes of physical and chemical properties due to the different type of surface
alteration
Type
A
B
C1
C2
D
E
F
Enrichment of soluble salts
–
–
+–
+–
++
–
–
Sealed surface, decrease of capillarity and drying
–
–
o
++
?
?
++
Reduction of air permeability
–
–
o
++
+–?
–
++
Hardening of the surface
o
o
+
++
++
?
++
Deterioration of the stone’s surface
o
o
+–
+–
++
+–
o
Increased heating by insolation
–
–
–
++
–
–
++
Increased thermal dilatation
–
–
+
+
–
–
++
Increased hygric dilatation
–
–
–
–
–
–
–
Increased moisture content
–
–
–
–
–
+
–
Risk estimation
–
o
+–
+
++
low low low medium high low high
not determined
no or negligible effect
Effect sometimes verifiably
Effect definitely verifiable
Obviously combined with damage
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
The following recommendations can be deduced from Tab. 2:
- Types A and B: Brownish discoloration and grey staining have a low risk potential
and do not need any treatment.
- Type C: Thin black films require further classification:
o C1: When they cover the surface only partially, their effects on the physical
properties of stone are not detrimental.
o C2a: When they cover the surface completely, their effects are conflicting: capillary
water absorption is reduced, but on the other hand air permeability is also strongly
reduced and heating by insolation is considerably increased. This stage can be
tolerated as long as there is no visible damage or massive enrichment of gypsum
below the black films.
o C2b: At construction parts particularly exposed to rainfall or run-off the black films
and the outermost grain layers often are detached from the stone and the light stone
is visible. In the majority of these cases a strengthening treatment with silicic acid
ester will be necessary and a thinning of the black films in adjacent areas is
recommended.
o C2c: If there is an additional enrichment of gypsum below the surface, it will be
beneficial to reduce the content of gypsum. Otherwise the frequent recrystallization
of gypsum in the pore space will have detrimental effects as it is the case for thick
gypsum crusts. The data of ultrasonic surface wave measurements showed that in
most cases ultrasonic velocities are enhanced below the surface, providing evidence
for a densification in the first 3–10 mm of the surface which is due to the
enrichment of gypsum. Reduction of gypsum in the pore space needs an opening of
the sealed surface, which can be achieved by cleaning.
- Type D: Thick black crusts rich in gypsum have a serious detrimental effect as
reported by Charola and Ware (2002), Brimblecombe (2011), and others. The
frequent recrystallization of gypsum in response to changing conditions of moisture
and temperature obviously causes alternating stresses to the stone, leading to the
formation of micro-cracks in the stone’s surface and finally to visible damage. These
crusts have to be removed by cleaning in order to prevent further damage.
- Type E: The growth of algae, lichen and moss develop mostly at construction parts
with increased moisture content. Instead of using biocides it is recommended to
check the possibilities of constructive methods to reduce the run-off of rain water in
order to diminish the moisture content in these parts.
- Type F: A removal or at least a thinning of the silicate-bound colour paint is
recommended, because microscopic studies, measurements of capillary water
absorption, Rayleigh waves and air permeability show, that they seal the stone
surface almost completely and strengthen the outermost grain layers of the surface
intensively. Both factors are known to be detrimental on a long term scale.
Besides the question of cleaning several other aspects of conservation work were examined.
But yet the removal of gypsum from the pore space is not yet solved. This issue needs
further tests and examinations of the building.
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Acknowledgements
Thanks to Marion Basten, Ercan Erkul, Moritz Fehr, Lothar Goretzki, Janina Haus, Kalle
Jepsen, Thomas Kessler, Karin Kraus, Esther Klinkner, Daniel Köhn, Klaus Rapp, Helmut
Santl, Dirk Scheuvens, Eric Spangenberg, Florian Ströbele and others for experimental
assistance and organizational support. Funding by the German Federal Environmental
Foundation is gratefully acknowledged.
References
Becker, K.-H., Brüggerhoff, S., Steiger, M., Warscheid, T., 2005, Luftschadstoffe und
Natursteinschäden. In: Siegesmund, S., Auras, M., Snethlage, R. (eds), Stein
Zerfall und Konservierung, Edition Leipzig, 36-45.
Brimblecombe, P., 1987, The Big Smoke. Methuen, London
Brimblecombe, P., 2011, Environment and Architectural Stone. In: Siegesmund, S.,
Snethlage, R. (eds.): Stone in Architecture, Springer-Verlag, Berlin, S. 317-346.
Camuffo, D., 1996,Perspectives on Risks to Architectural Heritage, In: Baer, N.S. and
Snethlage, R., (eds), Saving Our Architectural Heritage, Dahlem Workshop
Report, John Wiley and Sons, New York, S. 63-92.
Charola, A.E., and Ware, R., 2002, Acid deposition and the deterioration of Stone: A brief
review of a broad topic. In: Siegesmund, S., Weiss, T., and Vollbrecht, A. (eds),
Natural stone, weathering phenomena, conservation strategies and case studies.
Geol Soc Spec Publ 205: 393-406.
Graue, B., Siegesmund, S., Oyhantcabal, P., Naumann, R., Licha, T., Simon, K., 2013, The
effect of air pollution on stone decay: the decay of the Drachenfels trachyte in
industrial, urban, and rural environments—a case study of the Cologne, Altenberg
and Xanten cathedrals. Environmental Earth Science, 69, 1095-1124.
Honeybourne, D.B., 1990, Weathering and decay of masonry. In: Ashurst, J. and Dimes,
F.G. (eds.): Conservation of Building and Decorative Stone, BotterworthHeinemann, London, Vol. 1: 153-178.
ISCS, 2008, Illustrated glossary on stone deterioration patterns. ICOMOS International
Scientific Committee for Stone (ISCS), Monuments & Sites XV, 86 pp.
Meier, T., Auras, M., Erkul, E., Fehr, M., Jepsen, K., Milde, C., Schulte-Kortnack, D.,
Spangenberg, E., Steinkraus, T., Wilken, D., 2014, Physikalische Untersuchungen
an der Porta Nigra - Ultraschall-Oberflächen-Messungen und thermische
Untersuchungen, IFS-Bericht Nr. 47, Institut für Steinkonservierung e. V., Mainz,
50-62.
Meier, T., Auras, M., Fehr, M., Köhn, D., Cristiano, L., Sobott, R., Mosca, I., Ettl, H.,
Eckel, F., Steinkraus, T., Erkul, E., Schulte-Kortnack, D., Sigloch, K., Bilgili, F.,
Di Gioia, E., Parisi-Presicce, C., in press, Investigating surficial alterations of
natural stone by ultrasonic surface measurements. In: Masini, N. and Soldovieri, F.
(eds.): Sensing the Past. Springer International Publishing AG.
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Neumann, H.-H., 1994, Aufbau, Ausbildung und Verbreitung schwarzer Gipskrusten,
dünner schwarzer Schichten und Schalen sowie damit zusammenhängender
Gefügeschäden an Bauwerken aus Naturstein. Dissertation, Universität Hamburg.
Nijland, T.G., C.W. Dubelaar, van Hees R.P.J., van der Linden, T.J.M., 2003, Black
weathering of Bentheim and Oberkirchen sandstone. HERON, 48, No. 3 (Special
Issue), 179-195.
Nord, A.-G., Ericson, T., 1993, Chemical analysis of thin black layers on building stone.
Studies in Conservation, 38., 1/1993, S. 25-35.
Snethlage, R., and Sterflinger, K., 2011, Stone conservation. In: Siegesmund, S., Snethlage,
R. (eds.): Stone in Architecture. Springer, Berlin, 411-544.
Steger, W. E., Mehner, H., 1998, The iron in black weathering crusts on saxonian
sandstones investigated by Mössbauer spectroscopy. Studies in Conservation, 43,
Heft 1, S. 49-58.
Sterflinger, K., 2011, Biodeterioration of Stone. In: Siegesmund, S., Snethlage, R. (eds.):
Stone in Architecture. Springer, Berlin, 291-316.
Thomachot, C., Jeannette, D., 2000, Petrophysical properties modifications of Strasbourg’s
Cathedral Sandstone by black crusts. Proceedings of the 9th International
Congress on Deterioration and Conservation of Stone, Venice, 265-273.
Warscheid, T., 2005, Mikrobieller Befall und Schädigung von Natursteinen und
Möglichkeiten einer praxisgerechten Beseitigung. In: Grabsteinerhaltung. Institut
für Steinkonservierung e.V., Mainz, IFS-Bericht Nr. 20: 57-62.
Wilimzig, M., Fahrig, N., Meyer, C., Bock, E., 1993, Biogene Schwarze Krusten auf
Gesteinen. Bautenschutz + Bausanierung, 16, 2/93, S. (22-25).
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1088
THE CONSERVATION OF GIOVANNI LABUS’S SCULPTURE OF
BONAVENTURA BAVALLIERI (1844) AND ANTONIO GALLI’S
SCULPTURE OF CARLO OTTAVIO CASTIGLIONE (1855)
I. Ruiz Bazán1, V. Bresciani2, A. Balloi3, A. Quarto4,
I. Marelli4, M. Colella5*, C. Sotgia6 and F. Arosio7
Abstract
In this project a cleaning intervention of the neoclassical statues in the Brera Academy
courtyard was performed with the use of living microbial cells. These living organisms,
belonging to the species Desulfovibrio vulgaris, were able to remove chemical alterations,
mainly caused by sulfates, from the stone surface of the statues. The method has been
chosen because it is highly efficient, respectful to the original material, the environment and
the restorer operating it. Thanks to the microorganism’s selectiveness, it was possible to
remove only the harmful alteration of the stones, respecting the so-called “noble patina” a
key element in art pieces. Considering the precarious state of conservation of the hands
belonging to the statue of Carlo Ottavio Castiglione, a 3D (Rilievo 3D) survey was taken.
Keywords: 3D survey, convergent photogrammetry, bio-restoration, sculpture, marble,
cleaning
1
I. Ruiz Bazán
Architect, Milan, Italy and Zaragoza, Spain
2
V. Bresciani
Bresciani s.r.l., Milan, Italy
3
A. Balloi
Micro4yoU s.r.l., Milan, Italy
4
A. Quarto and I. Marelli4
Soprintendenza Belle Arti e Paesaggio, Milan (Italy
5
M. Colella*
Servabo Conservation Studio, Milan, Italy
servabo.colella@gmail.com
6
C. Sotgia
C.S.G. Palladio s.r.l., Vicenza, Italy
7
F. Arosio
Amici di Brera, Milan, Italy
*corresponding author
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1. Introduction and historical background
Designed by Francesco Maria Richini (1584-1658) for the Jesuit College, the Brera
Academy courtyard (1615) hosts in its arcades stone busts and statues figuring the most
illustrious Milanese artists, scientists and philosophers. Thanks to the coworking of:
Associazione Amici di Brera, Musei Milanesi, the Milanese superintendence BSAE and the
generous contribution of Pirelli it was possible to restore the statues of Bonaventura
Cavallieri and Carlo Ottavio Castiglione.
Fig. 1: Brera courtyard (Silver Bromide fixed on paper (1920-1940) from: Raccolte
Grafiche e Fotografiche del Castello Sforzesco, Civico Archivio Fotografico, RI 14344).
Of Milanese birth Bonaventura Cavallieri (1598-1647) studied mathematics at the
University of Pisa where he was student of Galileo Galilei. Bonaventura’s fame is due to
his approach to the method of the indivisibles, useful to determine areas and volumes. His
studies were of fundamental importance for the future development of infinitesimal
calculus. The statue representing this great mathematician was created by Giovanni
Antonio Labus (1806-1857) who was a teacher at the Brera Academy and operated in the
most outstanding construction sites of his times like the Duomo of Milan and the Arco della
Pace. This extremely eloquent statue is one of his greatest achievements.
Carlo Ottavio Castiglione (1784-1849) was a numsimatist and a scholar of Semitic and
Indo-European languages. In 1819 he published a detailed description of Kufic coins,
minted by the Normans and kept in the Brera cabinet. His main work regard the study of
oriental languages and researching the origins and history of the city of Barbary (Tripoli)
whose name can still be found on ancient Arab coins. Sculptor Antonio Galli (1812-1862)
studied at the Brera Academy and moved to Rome to work in Thorvaldsen’s studio. After
this Roman stay he returned to Milan to work in the Duomo construction site. Galli presents
Castiglione purposely seen from below with an intense look pointing his finger directly to a
coin held in his hand.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 2: Initial phases of the conservation of Antonio Galli's sculpture of Carlo Ottavio
Castiglione (1855). Height of statue plus the pedestal 503 cm (198 inches), Just the statue
305 cm (120 inches). The original surface appears hidden by a layer of aged protective
varnish.
Fig. 3: Final phase of the conservation - Cleaning by sulphate reducing bacteria has given
back the surface’s original smoothness caused by the use of fine chisel for surface finishin
and revealt a compact saccharoidal white limestone that is very similar in appearance to
Venato Apuano marble.
2. 3D Survey by convergent photogrammetry
Since the hands are probably the most fragile parts on the sculpture a 3D model of the
hands of the statue has been created as a preventive measure before the restoration to allow
for future reproduction of those pieces. Due the difficult morphology of this area of the
statue, we chose the convergent photogrammetry technique, which is one of the most used
methods on sculpture. The basis of this method is the reinterpretation of the conic
perspective through the use of an assemblage of pictures taken of the sculpture. Unlike
lasers, this method does not reflect light back to the camera which makes it very useful for
mapping complex surfaces. Another advantage of this method is that we obtain a map of
the real texture of the surface which can then be incorporated in the 3D model thus
significantly improving the accuracy documentation. With this high degree of accuracy it is
possible to create an exact replica of the object.
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3. Diagnostic phase
Two samples where taken: the first from the sculpture of Carlo Ottavio Castiglione in a
yellowed area, the second from the sculpture of Bonaventura Francesco Cavalieri in a
blackened area. Sample 1 was embedded in polyester resin to prepare a specimen of the
cross section. First the cross section was examined by optical microscopy before
proceeding with investigations including the use of an electron microscope (ESEM) and a
FTIR spectophotometer. Especially, the latter was used to determine inorganic and organic
compounds, for example products due to previous conservation work, which might be
responsible for surface alteration. For the characterization of the composition of sample 2,
which consisted of powder, XRD and EDS analyses was carried out.
a)
b)
Fig. 4: a) Sampling point for sample 1; b) Micrograph of the cross section of sample 1
(magnification: ×240).
In both samples analysed it has been revealed the presence of gypsum and specific air
pollution: this is related to a widespread surface sulfation. In particular in sample 1 the
electron microscope images show an advanced state of decohesion of the stone material.
The spectrophotometric FTIR analysis has revealed calcium carbonate, gypsum and silicate
but also very weak absorptions of probably synthetic resin and/or oxalates. The oxalates are
usually referred to the organic substances degrade. In sample 2 both XRD analysis and EDS
measurements could confirmed the presence of sulfates in the form of gypsum (calcium
sulfate dihydrate) and of bassanite (calcium sulfate hemihydrate). The EDS analysis has
revealed silicates and also fluorine: these can be linked to conservation attempts based on
fluorinated compounds or fluorosilicates undertaken in the 1970s and 1980s.
4. Conservation
The conservation work took place in the months of June, July and August 2015 in the Brera
Academy courtyard. In the case of Antonio Galli's sculpture of Carlo Ottavio Castiglione
Castiglione the cleaning effort has given back the surface’s original smoothness produced
by a fine chisel. The Bonaventura statue surface is rougher, with intentionally visible
circular furrows made by the chisel. The statues in which we intervened are made of white
compact saccharoidal marble, which is thought to be an apuano marble in between the
common white Carrara marble and the so called Venato Apuano marble. It is a white
marble with intense grey veins which the sculptor has let fall obliquely on the drapery.
During these conservation interventions there was no access to first hand data specifying
the quarries from which these marbles came from. Judging by the aesthetic appearance of
these marbles it can be assumed that this type of sculpting stone comes from Tuscany more
specifically from the zones between Minucciano (Lucca), Cantonaccio and Fivizzano
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
(Massa Carrara). The tone is compact and of a medium fine grain, with a light greyish
colour with abundant dark grey veins. These dark grey veins intersect each other, creating
an intense dense superficial weave. There are also rare small (not more than a couple of
millimetres) grey spots on the surface. A large part of the surface is covered by deposits of
atmospheric particles and a conspicuous sulfation. Thin section analysis has revealed
sulfation to measure circa 5 mm deep. In particular the ESEM images have revealed a
remarked decohesion in the intergranular spaces of the calcite crystals (Fig. 5).
Fig. 6: The removal of aged yellowed protective layer and dirt has revealed the original
surface texture the statue of Bonaventura which presents signs of scratches and abrasion
related to the use of a fine but large chisel (circular furrows) for the surface finish.
Fig. 5: SEM-BS image (low vacuum mode) of sample 1 showing the intergranular
decohesion is apparent throughout the thickness of the sample.
Since the statue hands had reached such a critical state it was opted for consolidation by
submerging them in a low viscos acrylic dispersion with either Primal™ B60 or Primal™
WS-24 (by Rohm & Haas) and water (dip coating, Fig. 7). The web of acrylic dispersion
which is generated inside the pores increases the mechanical properties of the treated
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surface, reducing its porosity though not obstructing the pores and respecting the surface’s
qualities. The consolidation resulted in the creation of bridges in the spaces in between the
grains of the degraded stone.
Sulfation caused by smog is a widespread problem in all major urban centres. Sulfur
dioxide in the presence of humidity, is transformed into sulfite ions, these in contact with
oxidants such as oxygen become sulfate ions. Sulfate ions, once in contact with the stone,
cause a consequent chemical transformation of the calcium carbonate (CaCO 3) into calcium
sulfate dihydrate or gypsum (CaSO4·2H2O) During the crystallization of gypsum, airborne
pollutants, such as carbonaceous particles (soot), are embedded in the mineral matrix and
cause the formation of black crusts in sheltered areas. Sulfate-reducing bacteria belonging
to the species Desulfovibrio vulgaris, thanks to their metabolism are able to dissociate
gypsum into Ca2+ and SO42+ ions. SO42+ ions are then reduced by the bacteria into H 2S,
while the Ca2+ ions react with carbon dioxide to form new calcite. The commercial name of
the microbial product used in this work is Micro4Art, made by Micro4yoU Srl and
distributed by Bresciani Srl.
With the help of Dr. Annalisa Balloi sulfate-reducing bacteria through a gelatinous medium
were applied on sulfated areas that appeared altered. The gelatinous medium was left
overnight on the stone surface until the desired result where obtained. The bacteria
contained in the gel attack and eliminate the sulfate. Local interventions of traditional
cleaning were limited to the removal of varnish drops that had fallen from above. These
interventions have been performed by swabbing soluble non-polar solvents. The
conservation intervention was then concluded with a mild application (4% micro-dispersed
acrylic in water) with a protective patina on all the surfaces, to reduce the absorption of
meteoric and condensation water (albeit for a limited time).
a)
b)
Fig. 7: a) Scheme of the consolidation system adopted (dip coating); b): Dr. Annalisa
Balloi during the application of sulfate-reducing bacteria through a gelatinous medium on
the areas that were altered and covered by sulfates.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 8: Signature of Antonio Galli on the statue of Carlo Ottavio Castiglione (1855) before
the application of sulfate-reducing bacteria by a gelatinous medium.
Fig. 9: Signature of Carlo Ottavio Castiglione’s statue (1855) during the cleaning using
sulfate-reducing bacteria applied to the surface with the aid of a gelatinous medium. The
cleaning has brought to light (for example in the right area of the cartouche) some
punctual spots along the surface. FTIR analysis carried out by Palladio Analisi s.r.l.
laboratories identified calcium carbonate, gypsum, silicates, and very feeble traces
fluorosilicate absorptions, which are most probably left by residues of protective and
polishing products used in the past.
5. Conclusion
The use of sulfur-reducing bacteria was found to be much more effective when removing
sulphate from stone surfaces than the traditional solvents, which sometimes can cause harm
to both the art piece and the operator. Other advantages of Bio-Restoration are:
Growing bacteria on large scale does not require great disbursements are easily
applied on surfaces.
Using bacteria does not imply any ethical conflict, since these microbes are not
genetically modified.
Bacteria represent no harm for sculptures and people working with them.
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References:
Bacci M., F. Baldini, R. Carlà, and R. Linari: “A Color Analysis of the Brancacci Chapel
Frescoes. Part I” Applied Spectroscopy 45 (1991), 26-30.
Bacci M., S. Baronti, A. Casini, F. Lotti, M. Picollo and O. Casazza: "Nondestructive
spectroscopic investigations on paintings using optical fibers", Mat. Res. Soc.
Symp. Proc., 267 (1992) pp. 265-283.
Bacci M., M. Picollo, B. Radicati and R. Bellucci: “Spectroscopic Imaging and nondestructive reflectance investigations using fiber optics”, 4 th Intern. Conf. NonDestructive Testing of Works of Art Proc., Berlino (1994), pp. 162-174.
Bacci M. and M. Picollo: “Non-destructive detection of Co(II) in paintings and glasses”,
Studies in Conservation 41 (1996), 136-144.
Chiari R., Picollo M., Porcinai S. and Radicati B.: “Non Destructive Reflectance
Spectroscopy in the discrimination of two authigenic minerals: gypsum and
weddellite” 1996, 2 nd Intern. Symp. The Oxalate films in the conservation of
works of art Proc., Milano (1996), 379-389.
Bacci M., M. Picollo, S. Porcinai and B. Radicati: “Spectrophotometry and colour
measurements” Techne 5 (1997), 28-33.
Cappitelli, F. et al., 2007. Advantages of using microbial technology over traditional
chemical technology in removal of black crust from stone surfaces of historical
monuments. Applied and Environmental Microbiology. 73: 5671-5675.
Polo, A. et al., 2010. Feasibility of removing surface deposits on stone using biological and
chemical remediation methods. Microbial Ecology. 60: 1-14.
Gioventù E. 2010. Comparing the bioremoval of black crusts on colored artistic lithotypes
of the Cathedral of Florence with chemical and laser treatment. International
Biodeterioration & Biodegradation. 65: 832-839
Jazayeri I., Fraser C.S., Cronk S., Automated 3D object reconstruction via multi-image
close-range photogrammetry. International Archives of Photogrammetry, Remote
Sensing and Spatial Information Sciences, Vol. XXXVIII, Part 5 Commission V
Symposium, Newcastle upon Tyne, UK. 2010, 305-310.
Remondino, F. Heritage Recording and 3D Modeling with Photogrammetry and 3D
Scanning. Remote Sens. 2011, 3, 1104-1138.
McCarthy, J. Multi-image photogrammetry as a practical tool for cultural heritage survey
and community engagement. Journal of Archaelogical Science. Volume 43, March
2014, pages 175-185.
1096
RESTORATION OFF-SET BY THE PUBLIC EXHIBITION OF
DECORATED STONE ELEMENTS RESCUED FROM THE
DEMOLISHED VACARESTI MONASTERY, ROMANIA
C. Bîrzu1*
Abstract
The present paper reports a project aiming to recover the image of a now disappeared
monument – the Văcărești Monastery Church. Since the reconstruction of the Văcărești
Monastery Church was not an option, it was decided to conserve the decorated stone parts,
which could be saved during the demolition of the building, and place them in the
"Memorial - Lapidarium". In this cultural space the remaining stone columns are most
spectacularly placed in their vertical orientation to restore, at least partially, the greatness of
the old ecclesiastical edifice of the Văcărești Monastery. Such approach aims to combine
today's cultural act with the Brâncoveanu style and art of the 18 th century.
Keywords: stone conservation, stone restauration, decorated stone elements, exhibition
1. Văcăreşti Monastery - Brief history
An achievement of great value, which falls in the cultural landscape of the time, the
Văcăreşti ensemble benefited from the specific cultural accumulations of the era of Ruler
Constantin Brâncoveanu. Founded by Nicolae Mavrocordat between the years 1716-1722
(1st Phanariot ruler of Wallachia) and continued by his son between the years 1732-1736
the Văcăreşti ensemble represents one of the most important ensembles in the Byzantine
world at its time (Fig. 1a).
a)
b)
Fig. 1: Văcărești Monastery Church before (a) and during the demolition (b).
1
C. Bîrzu
National University of Arts, Bucharest, Romania
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
However, in the 19th century Văcărești Monastery had been abandoned for a long time and
was subsequently turned into a prison for the Romanian revolutionaries of Wallachian
Revolution in 1848. This event probably marks the starting point for the irreversible
deterioration of the Văcăreşti ensemble, which eventually ended with its demolition in
1985-1986 (Fig. 1b).
2. Removal of the decorated stone elements and fresco fragments prior and
during the demolition of the Văcărești Monastery Church
Regarding the removal or saving of the stone elements, the undertaken actions at the time
of the demolition were hasty and as far as known without any intention of preserving
anything for future use in an attempt to rebuilt of the church. For example, cracks in the
preserved columns from both the porch and of the narthex show that these elements were
not carefully removed, but had been simply hit from the side to destroy the structural
integrity of the building. After demolition, the stone blocks were transported to various
locations, with most of them (324 pieces) reaching Mogoșoaia Palace (near Bucharest). In
this case the remaining stone fragments were stored under a covered outdor space at the
eastern edge of lake (Fig. 2). Some other parts arrived at Brâncoveni Monastery, the
National Museum of Art, and the Cotroceni Museum.
Fig. 2: Storage space of the decorated stones.
3. The beginning of the Memorial - Lapidarium project
Ideas for conservation/restoration of these stone elements with their decorations arrived
very soon after the demolition of Văcăreşti Monastery. Some of these ideas included the
rebuilding of the monastery while other only considered a placement of selected stone
pieces in a museum. Fortunately, following the intervention by historian Mrs Doina
Mândru (cultural director of the ensemble Mogoșoaia Palace) a project for a museum,
which combines memorial and cultural purposes, was initiated, thus allowing at least for the
display of the most spectacular stone pieces. At the moment, the project is coming to an end
as the building is approaching its completion. After the completion of a long study plan the
stone pieces have already been installed in the building. Specifically, in the periphery areas
of the Memorial (terrace), 16 assembled stone objects are on display as vertical columns
(similar to their position in the original building).
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 3: Plan of the Memorial - Lapidarium. The red circles or squares mark the future
position of the decorated stones
4. Conservation, restoration and enhancement activities
4.1. Description of the conservation status and decay factors
From the mineralogical analysis it became clear that the rubbles stones of the stone
components of Văcăreşti Architectural Ensemble were carved in biogene limestone with
nummulites from the Eocene age quarried in the area of Albești, Câmpulung MuscelRomânia.
Fig. 4: Structure of the stone at a magnification of ×50.
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Two chronological stages of the damages are observed. The first phase was the period
before the demolition of Văcărești Monastery Church in 1986.
On the inside:
- Considering the church had only been in little use for religious services, the
specific decay and deposits on the stone surface were found to be insignificant.
- Certain repair attempts were undertaken in the past. With respect to the three
layers of paint being found on the stone surface: white, green and ochre (and in
chronological order also cement mortars) it appears as first repair work as dates
probably back to the 19th century. Traces of cement mortar seem to indicate a
repair attempt in the second-half of the 20th century.
On the outside
- Girdle fragments showed deposits/crust probably caused by tars from air pollution.
After a closer examination of the girdle fragments, we could conclude that the
damage level of the girdles was in a 10-15% range. The black crusts were
especially concentrated on the decorated areas of the stone (which are the most
exposed from a geometrical point of view) and areas formerly protected from wind
and rain.
The second phase of damage is the time after the demolition, including transport and
storage in the current shelter.
- Deposition of fine particulate (dust), different plant debris originated from the
storage environment reached a level of 100%.
- Rust stains (small patches of about 10/4 cm) were observable on certain stone
pieces in some areas can be related to the iron support structure of the storage
shelter.
- Biological attack by of several species of lichens was discovered at closer
investigation of the surface crust/biofilm.
4.2. Cleaning and Conservation of the stone fragments
Selection of stone pieces and their future location in the newly build Memorial was done
under the aspect of creating a visual and iconographic spaces within the Memorial. The
narthex columns (large columns and associated bases and capitels) were considered to be
the most spectacular pieces, followed by the porch columns and several other secondary
items (gird, framing of the window, etc.).
In preparation for their future display the selected stone fragments underwent an extended
restoration and conservation process. Surface cleaning started with the removal of the
remainders of soil and of vegetation inflicted by the years of outdoor storage as well as
paint and cementitious repair materials from the previous conservation and repair attempts.
Subsequently, wet removal of the superficially adherent deposits was carried out using
water, sponges, a steamer (steam machine) and different types of brushes, suitable for the
surface geometry of the stone fragments. Additionally, in cases of tougher surface
contaminations paper pulp poultices of ammonium bicarbonate were repeatedly applied at
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different exposure times. In several cases (fragments belonging to the girdle in the torsade
of the church) the removal of deposits (black crusts produced by pollution) from the stone
surface required microsandblasting, using silicate powder (120 or 150 mesh, 1-1.5 bar
pressure). However, only a reduction of the crust was attempted to maintain an appropriate
looking patina on the surface. The occasionally present biofilm was treated with a biocide.
If required a consolidation with ethyl silicate was performed. Epoxy resin was used for the
reattachment of fragments to the fractured stone elements. In order to prevent corrosion
issues after the assembling of the columns at their new location all metal elements were
removed from the stone blocks.
Straight from the beginning it was considered that especially the surviving columns have to
be installed similar to their original constellation within in the ecclesiastical space of
Văcăreşti monastery church to create a place of similar meaningfulness at the new location.
Based on the statically requirements it was concluded that an additional support/
reinforcement system, which consists of 3 epoxy resin embedded fiberglass rods (with a
maximum diameter of 2 cm), has to be installed between the different elements of each
column (Fig. 5d). Depending on the mechanical requirements holes with a depth of 20 or
30 cm were drilled into the stone blocks to accommodate the fibreglass rods. Additionally,
all columns were also anchored in the concrete floor by 4 fiberglass rods (Fig. 5a to 5c)
with each anchor point reaching 22 cm into the floor. Epoxy resin EPO 120 (or EPO 150)
distributed by CTS, Italy was used for the embedding of the fibreglass rod.
a)
b)
d)
e)
c)
f)
Fig. 5: Installation of the columns: a and b) Bottom pin structure, c to e) Assembly of the
decorated stone block to columns in the Royal House; f) Columns of the veranda.
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5. Conclusion
Surviving stone parts of the in 1986 demolished Văcărești Monastery Church were
successfully restored to their old beauty and placed in the newly created Memorial –
Lapidarium. In this cultural space the remaining stone fragments are put on display in a
manner the aims to restore at least partially the greatness of the old ecclesiastical edifice of
the Văcărești Monastery.
References
Dragut, V., 1974, Short historical and architectural documentation of the former monastic
ensemble Vacaresti from Bucharest, BCMI, no. 2 –p1
Ioan, A., What is it and how it looks the architecture with national specific? Conference
NEC –p3
Leahu, G., 1996, Destruction of Văcăreşti Monastery, Publisher Arta Grafică, Bucharest,
1996, 25-27
si Laura Mora, P., Philippot P., 1986, The conservation of the mural paintings, Publisher
Meridiane, Bucharest, 252- p6
Panaitescu, A., 2008, Remember Văcărești Monastery, Publisher Simetria, Bucharest, 44–
p1
1102
ROSSLYN CHAPEL - A REVIEW OF THE CONSERVATION &
ACCESS PROJECT
N. Boyes1*
Abstract
Rosslyn Chapel is a building of exceptional significance, with national and international
architectural and historical importance. Due to the vulnerable condition that the building
was in the 1990’s, an action plan was developed to ensure its long term integrity. The
Chapel was subject to major water ingress problems, combined with poor environmental
conditions, the consequence of which was a cold, damp internal environment within the
building with significant organic growth on the internal roof and wall surfaces. In the late
1990’s a steel canopy was erected over the Chapel to protect it from the worst of the
weather and allow an extended natural drying out process, which significantly changed the
situation. The works on the Chapel commenced in 2005 as part of a conservation,
presentation and accessibility plan. Due to the exposure of the building to the elements, the
masonry suffered from natural physical decay, such as disaggregation, delamination and
contour scaling. Furthermore, one of the most significant decays affecting the building was
the sulphation layer (environmental pollution crust) that was covering the external
stonework. This paper presents a detailed statement of the methodology that was used to
conserve this extraordinary historic building by means of traditional stone masonry skills
and the newest conservation technologies, such as the use of conservation lasers to reduce
the level of environmental pollution products affecting the Rosslyn Chapel stonework.
Keywords: scheduled monument, survey, environmental pollution soiling, laser ablation,
efflorescence
1. Introduction
Rosslyn Chapel is a Category A listed building and Scheduled Ancient Monument located 7
miles South West of Edinburgh in the village of Roslin, Scotland. It is a building of
exceptional national and international significance because of the quality, quantity, and
breadth of the stone carving which covers the building, both internally and externally. The
carvings not only feature traditional Christian iconography but also a variety of plant and animal
life and mythical creatures. The chapel was founded in 1446 by William St. Clair, 3rd Earl of
Orkney, as the Collegiate Church of St. Matthew. The building was originally intended to
be cruciform in plan, featuring a nave, side aisles, transepts, choir and tower. However, the
building was not completed, and only the Lady Chapel, ambulatory, choir and sacristy were
completed before St. Clair’s death in 1484, at which point, work on the building stopped.
The St. Clair family used the completed section of the church until its altars were destroyed
1
N. Boyes*
Nicolas Boyes Stone Conservation, Scotland, United Kingdom
nic@nb-sc.co.uk
*corresponding author
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in 1592 during the Scottish Reformation. No longer a functioning church, the building
gradually fell into disrepair. Conservation efforts have been a part of Rosslyn Chapel’s over
500-year history. The earliest known efforts took place in 1736 when the roof was repaired,
the flagstones in the floor were replaced, and the windows were glazed for the first time.
Architect William Burn conducted remedial works during the first half of the 19th Century.
In 1862, restoration work was undertaken after Queen Victoria visited the chapel and
expressed a desire to see it preserved. These works were completed by Architect David
Bryce and allowed the chapel to once again function as a working church. As a result of
those restorations, the chapel held Sunday services for the first time in 200 years. In 1950,
repair works were carried out by the Ministry of Works, during which a mult-media, multilayered surface treatment was painted onto the interior stone surfaces. Despite these wellintentioned though often misguided, conservation attempts, Rosslyn Chapel was in a
serious state of deterioration by the 1990’s, suffering from damage to the original stone
fabric due to stone decay, previous conservation treatments and other interventions. This
paper will give a brief description of Rosslyn Chapel’s condition when conservation work
began in 2005 and the efforts undertaken by Nicolas Boyes Stone Conservation (NBSC)
that have significantly improved the chapel’s condition since then, including a mixture of
traditional stone masonry skills and new technology such as conservation lasers.
2. Conservation works
2.1. Treatment of stone decay
Rosslyn Chapel is constructed of carboniferous sandstone from two nearby quarries. Over
time, the original stone fabric has suffered from several processes of decay, resulting from
the exposed position of the Chapel, the ingress of water through the roof and the
subsequently high level of moisture throughout the building. Many other factors
contributed, as well, including a range of misguided previous repairs. As a result, Rosslyn
Chapel exhibited several types of stone decay, including cracks, pits, scaling,
disaggregation, delamination, and loose or lost fragments. The first step in addressing these
problems was the erection of a steel canopy over the entire structure in the 1990’s to allow
for the chapel to dry out for an extended period of time. Once the building had sufficiently
dried out, NBSC began careful consolidation works on the deteriorated stone. Areas of
scaling, disaggregation and cracking were treated by first using soft brushes and air
‘puffers’ to remove all loose material from the affected areas. Areas were then treated by
injecting a solution of 10% (w/v) Paraloid B72 acrylic resin in acetone into or over affected
areas, using a syringe and hypodermic needle. Where cracks, pits or areas of scaling were
identified as requiring consolidating fills, an acrylic resin based repair mortar was applied.
Repair mortars were designed, according to each individual fill required, to be sympathetic
to the host stone in terms of colour, texture and durability. In order to do this, aggregates
were selected from a prepared range to closely match the host stone. This was achieved by
collecting a range of sandstones recovered from remedial masonry works to the nearby exvisitor’s reception building. These were crushed and divided into groups according to their
colour. The crushed stone was then sieved to achieve coarse and fine fractions of
aggregates. Subsequently, to avoid any introduction of salts into masonry, aggregates were
desalinated by washing in still water. Aggregates were left in containers filled with
deionised water, and water was changed every day for a week. This caused the water
soluble salts to diffuse out of the aggregates into the water. Finally, all aggregates were
dried properly and stored, ready to mix with Paraloid B72 solution to create repair mortars.
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In addition, if the correct colour could not quite be achieved, some earth pigments were
added to repair mortar to properly match the stone colour. Earth pigments like sienna,
ochre, umber and natural iron oxides were used because of their natural appearance and
their compatibility with mineral composition of sandstones. The ultimate function of these
repair mortars is to be less durable than the host stone and thus work as a renewable
sacrificial element in order to protect the vulnerable host stone against effects of
preferential weathering.
2.1.1. Response to previous treatments
Previous conservation efforts, although well-intentioned, also contributed to the
deterioration of the building over time and needed to be reversed. These included the
application of a layer of asphalt over the roof, use of Ordinary Portland Cement (OPC)
mortar in construction joints and installation of ferrous clamps.
2.1.2. Asphalt roof removal
A thick, hard, brittle layer of asphalt had been applied to the barrel roof, Lady Chapel, and
North and South Aisle Clerestory level roofs as a protective measure during conservation
works in 1954, in line with current thinking at the time. Works were undertaken to carefully
remove this asphalt layer. This was a delicate process and was conducted using hand tools
to minimize any damage to the original stonework beneath, whether through vibration or
direct contact with the tools. A range of sharp tungsten tipped chisels and nylon mallets
were used for this purpose. Similarly the number of conservators conducting these works at
any one time was kept to a minimum; only one worked on the barrel and Lady Chapel roofs
at one time. All construction joints on the external barrel roof pointed with OPC mortar
were carefully raked out and re-pointed in a traditional lime mortar. The asphalt removed
from the North and South Aisle roofs took a slightly different form from the other areas.
They were found to have a similar thick, hard top layer of asphalt, which was carefully
removed using the same methods as in the previous areas. Beneath this top layer, however,
the stone surface was found to be covered with a very sticky and soft asphalt residue, firmly
adhering to the stone surface. This residue was removed from the stone surface by gently
“pecking” with sharp chisels. In this way small parts of asphalt residue were chipped
revealing a striped tooled stone surface. The surface of the stone laying on the north aisle
roof was largely in good condition. The surface of the stone laying on the south aisle roof
was in contrast often quite friable and delaminated. Fragments lost due to such
delamination were re-attached where possible using strategic quantities of thixotropic
polyester resin. Friable areas were consolidated where necessary using acrylic B72 solution
in acetone.
2.1.3. Asphalt run-off cleaning
A number of asphalt runoffs were visible, and it was decided to conduct a series of cleaning
trials to determine the most appropriate and sympathetic method of removing them. These
trials included the use of chemical solvents, laser treatment and mechanical tools.
Ultimately, it was decided that mechanical tools alone (including scalpels and sharp chisels)
were the best method for the removal of asphalt run offs, assuming that the utmost care was
given at all times to ensure no damage to the stone surfaces. This gave the same result as
the chemical method but without any smearing effect caused by the solvents. The
remaining asphalt run offs were removed in this manner.
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2.1.4. Portland cement removal & Lime mortar repointing
Significant portions of the chapel’s construction joints had been repointed with OPC mortar
during an earlier intervention. OPC is harder and less breathable than traditional lime
mortar, causing sacrificial erosion of the surrounding stone as it deteriorates due to the
excess moisture. Because of this, it was important to remove all OPC from the joints at
Rosslyn Chapel and repoint them with traditional lime mortar. All construction joints
identified as requiring re-pointing were carefully raked out using sharp tungsten tipped
chisels and mallets to a sufficient depth to accept lime mortar repair (Fig. 1). Any loose
material within the joint that could decrease the adhesion of the mortar was removed in a
scooping action using a tool of appropriate width to ensure no marking of the dressed stone
surface occurred. The joints were next washed out with water to remove any remaining
debris or dust.
Fig. 1: Raking out vault joints.
Construction joints were then re-pointed using an appropriate lime mortar mix.
Immediately prior to re-pointing, the joints were sprayed with water to prevent the lime
mortar from drying too quickly. This was applied to the joint using hand tools of
appropriate width to prevent marking the dressed surface, pushed deep into the joint and
filled until the mortar was slightly full of the joint. In the cases where the joints were very
deep or wide they were packed also with slate or porous sandstone pieces, terracotta tiles or
oyster shells, all soaked first in water, to prevent shrinkage and improve the setting
characteristics and durability of the lime mortar. The mortar was then pressed back using
steel hand tools, covered with damp hessian and protected from the wind by tarpaulins, so
as to prevent premature drying out and left to carbonate for 2-3 days. During this period of
carbonation the lime mortar pointing and hessian was repeatedly sprayed with water. The
surface of the lime mortar was scraped with a wooden scraper and "stippled" with a fibre
bristle brush as the mortar stiffened. Care was taken to ensure the style of pointing matched
the original as much as possible. A number of small lime mortar repairs were also
conducted at various locations on the Chapel; these were conducted in much the same
manner as the lime mortar pointing. Where necessary, grooves were cut into the stone
surface using tungsten tipped chisels and mallet, to provide a key on to which the mortar
would adhere more easily. Immediately prior to the application of this mortar, the surface
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
was sprayed with water to prevent the lime mortar from drying too quickly. Mortar was
then applied to the surface using spatulas to model the repair into the correct shape. A
conservative approach was adopted to fills so only the necessary repairs were made – no
speculative remodelling was completed. Where repairs were particularly deep, they were
completed in layers, to prevent excessive shrinkage causing cracking and failing of the
repair. Each layer was given a new ‘key’ on to which the next layer might more easily
adhere. The rest of the process was completed in a manner similar to that used in the repointing of construction joint previously described.
2.1.5. Ferrous cramp replacement
Approximately 150 ferrous dog cramps were identified in the ground level plinth course of
each of the Chapel bays, at the North, South and East and West elevations. These were
causing significant damage to stonework as a direct result of their expansion and the
subsequent pressure causing cracking and fragmentation of the stonework. In some areas
the damage had already been done and fragments of stone as well as the original iron
cramps had long since been lost. A trial was conducted to remove one such cramp and
insert a more sympathetic stainless steel replacement. The original ferrous cramp was
removed very easily due to its advanced state of decay, using simple hand tools. The
resulting gap was then measured in order to cut a replacement cramp to the appropriate
size. For this, a 12mm threaded rod stainless steel cramp was used. The resulting gap was
cleaned out thoroughly using soft bristle brushes and the cramp was inserted. This was
adhered into place using strategic quantities of thixotropic polyester resin. The construction
joints directly above and below were pointed using traditional lime mortar as follows, using
the method described in section 2. On the success if the initial trial, works commenced to
replace the remainder of the cramps using the same method as outlined above.
2.2. Rebuilding works and replacements
2.2.1. Pinnacles, finials and ribs
All pinnacles, the East gable finials and a number flying buttresses were identified as
unstable to varying degrees and requiring careful deconstruction or partial deconstruction to
remove all ferrous dowels causing oxide jacking and movement within the structures, as
well as failed bedding mortar, debris and any vegetation/roots growing within joints).
Careful reconstruction could then be conducted. This process was conducted as follows.
Construction joints filled with OPC mortar were raked out using sharp tungsten tipped
chisels and mallets. Any loose material within the joints was removed in a scooping action.
A chain hoist was set up directly above the identified pinnacle, finial or rib and each course
slung with lifting slings one by one and lifted carefully onto nearby softening. Stones were
marked to ensure replacement in the correct order and directions. At this point any
identified ferrous fixings were removed using hand tools and electric drills where required.
The beds of each dismantled stone were cleaned thoroughly of mortar and debris using
chisels and a mallet and brushed clean with soft bristle brushes, prior to inserting new
stainless steel 12mm threaded rod dowels to replace the original fixings or as additional
fixings where required. These were fixed into position using strategic quantities of
thixotropic polyester resin. In some cases further stainless steel or phosphor bronze cramps
were inserted due to cracks or other failures within the stones. Beds were then thoroughly
wetted with clean water to remove any surplus dust/debris, and once again prior to applying
the bedding mortar to prevent it from drying out too quickly. Lime mortar was laid across
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the beds using a hand trowel and the stones lifted back into place, using slings and a chain
hoist. The resulting construction joints were re-pointed using a traditional lime based
mortar.
2.2.2. Indents
Following a detailed survey of the building, a number of items were identified as requiring
new stone indents. These were only specified when deemed absolutely necessary to the
structural integrity of the building. For example, where structural components such as
window arches and tracery were failing and it was no longer possible to simply consolidate
existing stone, new stone indents were specified to prevent the surrounding historic stone
fabric from falling into disrepair (Fig. 2).
Fig. 2: Indent in East window tracery.
It was vital that the stone used for indents matched the original stones in terms of general
appearance, texture, porosity, micro properties and mineral composition. This was to ensure
that the new stone performed in a similar manner to the original stone under the influence
of various conditions and thus ensure long term compatibility. In order to select the most
appropriate stone for indents, two Building Stone Assessments (Geo Reports) were
conducted by British Geological Survey.
2.3. Response to other alterations
2.3.1. Biological growth removal
Due to the exposed location of the Chapel, the external stonework is affected by a range of
biological growth, including lichen, algae and moss. The South elevation suffered to a
lesser degree than the North, but upper exposed features such as the pinnacles, finials and
ribs were still affected. This biological growth was reduced in a number of locations to
improve visibility of the stonework beneath and allow an accurate assessment of the
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condition of the stonework. Lichens and moss were largely removed dry with the aid of
scalpels, dental tools and brushes. Algae and the more stubborn lichen was further reduced
using water from typical hand held sprayers and brushes. The run-off was removed using a
sponge to prevent transportation of spores down the masonry.
2.3.2. Salt efflorescence
Salt efflorescence was identified all over the chapel. This salt efflorescence phenomena is
produced in this area due to an increase of moisture produced by the water dispersal
system, which was designed to shed water from the building at height. This system does not
appear to have functioned successfully due to the exposed position of the chapel, and much
of the dispersed water would have been directed back onto the walls at a lower level. This
increase in water residence on the masonry resulted in an enhanced flux of moisture to the
surface by evaporation resulting in cryptofluorescence and the subsequent blistering. Salt
efflorescence was treated at the most advanced areas where salts were further contributing
to other decay mechanisms. All loose material on the surface was carefully removed using
scalpels, dental tools, soft brushes and a vacuum cleaner to prevent reintegration into the
stone. At this stage any blistering identified in combination with salt efflorescence was also
removed using the same method. Salts were then removed by applying poultice applications
of acid-free tissue paper pulp and clean de-ionised water, in order to draw the identified
salts from the surface of the stone into the poultice. Repeat applications were applied as
necessary.
2.3.3. Desoiling
The Nd:Yag Conservation Laser was employed throughout this project to reduce the level
of environmental pollution products affecting the Rosslyn Chapel stonework (Fig. 3). The
level of soiling to be removed was determined after much discussion and a number of trial
areas. Soiling was initially identified as heavy, medium and light, and a distinction was
made between soiling visibly causing ‘preferential erosion,’ or the visible accelerated decay
of adjacent stonework, and that causing no apparent immediate harm.
Fig. 3: Desoiling using Nd:Yag Conservation Laser System.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
In line with the conservative approach of all conservation works, soiling identified as
requiring removal was restricted to the ‘heavy’ or ‘medium’ soiling (the thickest, most
homogenous) at carved detail that was visually disfiguring or causing accelerated decay to
adjacent or underlying valuable carved stonework. Similarly, the ‘heavy’ or ‘medium’
soiling was not entirely removed but reduced to a ‘medium’ or ‘light’ level where
appropriate. In this way the stonework suffering from decay related to this soiling was
safeguarded against further decay but no unnecessary work was conducted. Aesthetically,
soiling was reduced in a manner to promote a consistent view of the stonework, and
importantly to improve the visibility of carved stonework previous concealed from view.
3. Conclusions
Since 2005, Nicolas Boyes Stone Conservation has conducted a series of conservation
works at Rosslyn Chapel to slow the deterioration of the historic stone fabric caused by
natural stone decay, previous misguided interventions and other transformative alterations.
These works included the use of traditional masonry techniques as well as new technologies
and chemical treatments. The conditions of the chapel have improved significantly thanks
to these efforts. In the future, it is hoped that work will continue with the removal of the
cement layer covering the chapel’s interior surfaces.
References
Cameron, S., et al. (1997). Biological Growths on Sandstone Buildings: Control and
Treatment, Edinburgh, Historic Scotland.
Forbes, R., (1761). An account of the CHAPEL or ROSLIN, &c. Most respectfully
inscribed to WILLIAM ST. CLARE of ROSLIN, Esq; Representative of the
Princely Founder and Endower, The Edinburgh magazine, v-xii.
Historic
Environment
Scotland,
“Roslin,
Roslin
Chapel,”
(https://canmore.org.uk/site/51812/roslin-roslin-chapel, accessed 25th November
2015).
ICOMOS-ISCS, (2008). Illustrated glossary on stone deterioration patterns, Monuments
and Sites, XV, Verges-Belmin V. (ed.), Champigny/Marne, France.
MacGibbon, D. and Ross, T., 1896. The ecclesiastical architecture of Scotland: from the
earliest Christian times to the seventeenth century, Edinburgh, D. Douglas.
Maxwell, I., (2007), Inform Guide: Cleaning Sandstone - Risks and Consequences,
Edinburgh, Historic Scotland.
Parker, J. H., ed., Restoration of Roslin Chapel, The Gentleman's Magazine: and historical
review, July 1856-May 1868, 212 (May 1862), 599.
Urquhart, D., (2007), Stonemasonry Skills and Materials: A methodology to survey
sandstone building facades, Edinburgh, Historic Scotland.
Snow, J. and Torney, C., (2014), Short Guide: Lime Mortars in Traditional Buildings,
Edinburgh. Historic Scotland.
1110
LABORATORY AND IN SITU EVALUATION OF RESTORATION
TREATMENTS IN TWO IMPORTANT MONUMENTS IN PADUA:
“LOGGIA CORNARO” AND “STELE OF MINERVA”
V. Fassina1*, S. Benchiarin2 and G. Molin2
Abstract
In the present study, an evaluation of the durability of consolidation products, commonly
used on historical buildings of Padua in the last four decades, was carried out on two
significant monuments. Non-destructive and micro invasive tests were performed in situ as
well as in the laboratory. In the Loggia Cornaro, in situ water absorption tests (EN 16302)
showed a higher moisture absorption uptake in the lower parts of the monument than those
carried out on the upper parts. This suggests that surfaces close to the basement are more
susceptible to environmental decay than the upper ones. The different deterioration patterns
observable seem to support this suggestion. Stone blocks of the basement and of the lower
parts are characterized by significant amounts of clay minerals as detected by SEM
investigations on cross-sections of the extracted samples. Clay minerals occur near cracks
and microcracks and are also extensively found in the inner parts of the stone far from the
external surface. Surface observations of bulk samples revealed different situations. In the
Loggia Cornaro, some areas show a widespread resin coating, visible on SEM images,
which present a smooth skin with occasional cracks and microcracks. On the contrary, other
areas show coating layers recognisable by the smooth appearance of calcite crystals. The
latter situation also occurs in the Minerva Stele surfaces, although the layer is less evident.
No appreciable traces of resin, except in some isolated cases, were observed on this
monument. The depth of penetration of the resin into the stone and its internal distribution
was investigated by SEM mapping of silicon, which is assumed as a marker of the
consolidant material used. Cross-sections of treated specimens proved to be particularly
good in detecting and discriminating polymer distribution from the inorganic matrix and are
very useful in observing polymer and substrate relationships.
Keywords: deterioration patterns, durability, siloxane polymers, ethyl silicate
1
V. Fassina*
Honorary Inspector of Superintendency to Cultural Heritage of Veneto, Italy,
vasco.fassina@gmail.com
2
S. Benchiarin and G. Molin
Dipartimento dei Beni Culturali, Università degli studi di Padova, Italy
*corresponding author
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1. Introduction
In Padova, between 1975 and today, a lot of restoration interventions have been performed
on external stone surfaces using silicone polymers (Fassina et al, 1985). While there are
many reports on the performance of water repellents and consolidants in laboratory based
situations (Apollonia et al., 2001; Alvarez et al., 2001, D’orazio et al., 2001; Cardianoet al.,
2002; Favaro et al., 2006, 2007), conservation scientists should be aware that results from
stone samples treated in the laboratory are not necessarily representative of those which
would be obtained on real buildings. In the laboratory, samples can be effectively
impregnated. However, on building surfaces it is seldom possible to achieve the same level
of control. Laboratory based applications therefore produce more reproducible results than
the ones that can generally be expected in the field. Despite these difficulties, laboratory
based tests can provide a useful indication of the potential performance of a treatment
where the volume of sample and its situation are a good simulation of the building façade.
More recently, comprehensive studies on chemical deterioration of these synthetic
polymers have been performed with particular emphasis to their behaviour when applied on
stone surfaces, especially taking into consideration the deterioration of building materials
treated with polymers (Fassina et al., 2004, Favaro et al., 2005). To know the condition of
the treated stones it is of great relevance to identify and characterize the polymer applied on
previous treatments and the related decay by-products, in order to understand the
deterioration pathways they undergo after a long term exposure to outside atmospheric
environment. The polymer deterioration in outdoor conditions can modify both their
chemical composition and physical properties: chemical decay leads primarily to the
formation of oxidized species, which quite often produce yellowing of the treated stone
surfaces; on the other side physical changes induce a stiffening and brittleness of polymers
which often result in polymer fissures, detachments from the stone substrate and worsening
of mechanical properties (Melo, 1999).
In the present study the evaluation of the durability of restoration products, commonly used
on historical buildings of Padua in the last four decades, was carried out on two significant
monuments. Loggia Cornaro, made in Nanto stone, is an important example of Renaissance
architectural building, underwent to restoration works in this period (Fig. 1). After twenty
years from the first intervention and four from the latest, a survey on the condition and the
residual efficiency of treatments was carried out by means of in situ tests and analytical
laboratory techniques. Another important artwork restored two decades ago is “The Stele of
Minerva”, made in Yellow San Germano Stone. The presence of significant deterioration
patterns on the monument façade like strong differential decay, white and black features,
surface deposits, etc. were observed (Fig. 2). Two main types of products were used for
restoration. The first is Rhodorsil RC70 (from Rhodia), ethyl silicate, at a concentration of
70% and a density of 0.9 kg/dm3, in the form of a transparent liquid, diluted in white spirit
and designed for pre- and post-consolidation operations. After consolidation, a final
application of methylsiloxane as water repellent was applied to the Minerva Stele. The
second type of restoration product, a methylphenyl-polysiloxane resin, Rhodorsil RC 90,
designed for consolidation and protective operations, was applied to the Loggia Cornaro.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
a)
b)
Fig. 1: a) Loggia Cornaro; b) Minerva stele.
2. Experimental part
The evaluation of treatments was carried out using a non-destructive technique, as well as
laboratory methods that require sampling from treated parts.
a) The in situ water absorption test EN 16302 provides a simple method for
measuring the volume of water absorbed by a material within a specified time
period and represent a measure of the susceptibility of the stone to take up water
through the exposed surface. This test is one of the specific measurements
carried out to evaluate the efficacy of water repellent treatments applied to stone
materials. An effective treatment should substantially reduce permeability of the
stone material to water. By doing so, the treatment will reduce the material’s
vulnerability to water-related deterioration. The field areas to be tested were
selected to ensure that the site equipment can conveniently be used in each
position. Typically, four points along the perpendicular, at different height from
the ground, were selected. For the test to be effective, a relatively smooth
surface, free from dust, debris and organic growth, is required. At least three sets
of readings were taken at each test area.
b) Optical microscopy. Observations by U-polarisation microscope at different
magnification, on thin sections, were carried out to define the textural parameters
and obtain a detailed petrographic characterization of the stones employed. Also
reflected light microscopy observations on cross sections were performed.
c) Scanning Electron Microscope (SEM). Texture, distribution and penetration
depth of the polymer of treated samples have been observed by Camscan
MX2500 scanning electron microscope equipped with an energy dispersive
micro-analyser (SEM-EDS). Both stone surfaces (SE images) and sections
perpendicular to the exposed surface (BS images) were analysed. All specimens
were coated with a graphite film before SEM-EDS investigations.
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3. Discussion of the results
3.1. In field evaluation of consolidation treatments
In situ water absorption tests (EN 16302) for the Loggia Cornaro, showed that moisture
absorption uptake of the lower part of the monument was higher than the one measured on
the upper parts. This suggests that surfaces close to the basement are more susceptible to
environmental decay than the upper ones, and, indeed, different deterioration patterns were
found. The basement and lower parts have a strong marly component ascribed to significant
amounts of clay minerals (Fig. 2). Clay minerals occur near cracks and microcracks and are
also extensively distributed in the internal part far from the façade surface.
The stone of the upper part of the façade belongs to a stratigraphic horizon with lower
contents of clay minerals, thus explaining the good condition and probably lower moisture
uptake. Measurements made vertically at various points showed moisture uptake values
between 0 and 0.04 ml/cm2. In general, these values are still quite low compared with those
of the untreated limestone (110 ml/cm2). The lower values in most of the vertical locations
indicate that, after four years, the treated surfaces are still sufficiently water-repellent.
However, water is clearly able to penetrate into the various parts of the building, albeit
slowly. The build-up of small amounts of water behind some surface areas probably
indicates that the effectiveness of the treatment is deteriorating in these areas, and they may
need attention in the near future. The surfaces of Stele di Minerva could not be examined,
owing to the fact that the pipe tube could not be used on its vertical surfaces.
a)
b)
Fig. 2: a) Typical appearance of stone of lower part of the façade with deep microcracks
parallel to the external surface are visible; b) Microanalysis of clay minerals.
3.2. Evaluation of penetration depth of consolidation treatments
In order to study the stone behaviour, small specimens from the surfaces of the two
monuments were taken and analysed in laboratory. The depth of penetration of the resin
into the stone and its internal distribution were studied by SEM. Cross-sections of treated
specimens proved to be particularly good in detecting polymers and their interaction with
the substrate. The technique was capable of discriminating polymer distribution from the
inorganic matrix.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Surface observations of bulk samples revealed different situations. In the Loggia Cornaro,
some areas show a widespread resin coating, visible in SEM-BS images, which present a
smooth skin with occasional cracks and microcracks. On the contrary, other areas show
coating layers recognisable by the smooth appearance of calcite crystals, visible in SEM-SE
images. The latter situation also occurs in the Minerva Stele surfaces, although in the latter
case the layer is less evident and no appreciable traces of resin were observed, except in
some isolated cases. SEM observations show that ethyl silicate precipitates as an
amorphous SiO2 layer, which covers some portions of the stone surface while in the inner
part of the stone pore and capillary walls were partially coated by amorphous silica, which
does not always seal them. In the Loggia Cornaro, the substrate is covered by a very
compact external layer of silicon-based composition ascribable to polysiloxane polymer
with thickness ranging from 10 to 100 µm. However, this covering layer was not observed
in all samples, and often it is irregular in thickness and continuity on the surface. (Fig. 3).
a)
b)
Fig. 3: Loggia Cornaro, sample LC 18: a) SEM-BS image of mapped area; b) Si-Kα X-ray
map showing the resin distribution and a Si rich layer on the surface.
Evidence of penetration of polymer inside the stone are frequent in several samples, even if
only some cracks are filled with siloxane compared to the totality of fissures. In some
samples penetration path can be visualised by means of X-ray maps on cross sections of
calcium and silicon as markers respectively of calcium carbonate substrate and siliconbased consolidant. These images show a higher content of Si component on the external
layers of stone surface (Fig. 3b). The in depth penetration of polymeric product inside
cracks is clearly visible in Fig. 4.
The situation for the Minerva Stele samples was quite different. Here, only some samples
had external coatings, due to the protective substance being not very adhering to the
substrate thus showing pores and voids between coating and substrate. The presence of this
fill substance, was ascertain for little thickness, in general to a depth of 800 µm. It seems in
general loose from the substrate but incorporate a lot of carbonate particles.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
a)
b)
Fig. 4: Loggia Cornaro, sample LC 24: a) SEM-BS image of mapped area;
b) Si-Kα X-ray map showing the resin distribution.
X-ray maps of calcium (calcium carbonate) and silicon (silicone products) markers made
on cross sections show a certain deposition of silicon polymer inside the pores and a higher
concentration on the surface (Fig. 5).
a)
b)
Fig. 5: Minerva Stele, sample 18: a) SEM-BS image of the cross section of sample SM 18;
b) Si-Kα X-ray map showing the sparse resin distribution and
numerous grains of silica minerals
In the Loggia Cornaro, the samples do not exhibit the typical external deposition layer of
carbonaceous particles and gypsum crystals due to the accumulation of pollutants. In the
Minerva Stele, the extensive presence of gypsum as both lenticular crystals and compact
crusts was evident. The former occur in areas where the polymer has probably disappeared
and consequently the decay process is starting again. X-ray silicon distribution maps
indicate a silicon-based treatment. Silicon distribution is very different in the two
monuments. All samples show that silicon is homogeneously distributed to a depth of
1 mm, but the Loggia Cornaro samples have 5 to 10 times higher amount of silicon than
those ones of the Minerva Stele. In both monuments, however, many cracks in depth (to
3 mm) are empty. In particular, in the Loggia Cornaro, a series of microcracks parallel to
the surface is not filled by the resin, although others at a greater depth are filled. The depth
of penetration of newly formed decay products was also quantitatively studied by means of
a thin drilling core micro-sampling system. Various locations were investigated by
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
considering samples every 2.5 mm of thickness up to a depth of 10 mm. In the Minerva
Stele sulphates amount, representing the gypsum presence, is decreasing from a maximum
of 17% in external layer from 0 to 2.5 to a minimum of 0.5% for the 7.5-10 mm. depth. In
the Loggia Cornaro, the sulphate amount is decreasing from 2% to 0.2% from the external
to the internal layer, probably due to incomplete cleaning operations; in the Minerva Stele
there is evidence of decay ascribable to atmospheric pollutants.
4. Conclusions
Performance evaluation of treatments on two monuments in the city of Padova was
performed, respectively four and twelve years after restoration operations, and it was aimed
at verifying their effectiveness and durability. Cross-sections of treated samples proved to
be particularly useful in detecting synthetic products applied. Distribution and changes in
structure and adherence to the substrate were ascertained with good precision. Applying the
test results, it is possible to make initial evaluation of the effectiveness of a surface
treatment or if a previously treated surface has become ineffective. A shift in pore size
distribution towards smaller pore radii, as well as the percentage reduction of larger pores,
was observed in our treated stone samples, and it is attributed to the deposition mechanism
of the consolidant on the pore surfaces (formation of films or precipitation as amorphous
SiO2).
Penetration depth of the consolidant and new formation of decay products show that silicon
concentration generally decreases from the external surface inwards in both monuments.
SEM-EDS analysis of the cross sections showed large quantities of silcon on the surface
down to a depth of 300 µm.
As regards the new decay formation products, the deposition of sulphur-based compounds
has slightly influenced further gypsum formation in the Loggia Cornaro. In fact, no very
important decay was observed, and cross-section analyses showed the widespread presence
of residual amounts of still active consolidant and protective coating. The salts currently
present were probably insufficiently removed before consolidation. In the Minerva Stele a
significant amount of gypsum was detected thus enhancing more marked decay phenomena
with respect to the Loggia Cornaro. Residual traces of treatments, but not very abundant
were found.
Polymer application has certainly slowed down, but not completed halted, the deterioration
processes of the stone materials examined here. Decay due to atmospheric pollutants has
been greatly reduced, but it has rarely been possible to prevent the penetration of salt
solutions or mitigate the effects of moisture and temperature changes, which undoubtedly
cause disruption within the pore structure as a consequence of mechanical stresses.
These results indicate that certain treatments applied to the monuments have already
deteriorated to such an extent that a re-treatment needs to be considered soon. Data
obtained in the case of Loggia Cornaro are still generally within acceptable values. We
suggest that maintenance should be carried out in the near future by renewing the protective
coating on the whole surface and by consolidating the stone in some areas which are not in
a good state of conservation. In both cases, however, this type of stone may need a
maintenance gentle surface re-treatment approximately every five years.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
References
Alvarez de Buergo Ballester M., Fort Gonzalez R., 2001, Basic methodology for
theassessment and selection of water-repellent treatments applied on carbonatic
materials. Progress in Organic Coatings, 43, 258-266.
Apollonia L., Borgia G.C., Bortolotti V., Brown R.J.S., Fantazzini P., Rezzaro G.,
2001,Effects of hydrophobic treatments of stone in pore water studied by
continuous distribution analysis of NMR relaxation times. Magnetic Resonance
Imaging, 19, 509-512.
Cardiano P., Sergia S., Lazzari M., Piraino P., 2002, Epoxy–silica polymers as restoration
materials. Polymer 43, 6635–6640.
D’Orazio L., Gentile G., Mancarella C., Martuscelli E., Massa V., 2001, Water-dispersed
polymers for the conservation and restoration of Cultural Heritage: A molecular,
thermal, structural and mechanical characterization. Polymer Testing 20, 227-240.
EN 16302, many authors, Conservation of cultural heritage-test methods-Measurement of
water absortion by pipe method. CEN TC 346, Euroepan Committee for
Standardization.
Fassina V. Cherido M., 1985, The Nanto stone deterioration and restoration of Loggia
Cornaro in Padova, Proceedings of 5th Int. Congress Deterioration and
Conservation of Stone, Felix G. (eds.), Lausanne, Polytechniques Romandes, 313324.
Fassina V., Pezzetta E., Cherido M., Naccari A., Melica D., 2004, A survey on the
behaviour of restoration materials of the Loggia Cornaro in Padova after fifteen
years, Proceedings of the 10th Int. Congress on Deterioration and Conservatio of
Stone, Kwiatkowski D., Lovendahl R. (eds.), Stokholm, 415-422.
Favaro M., Mendichi R., Ossola F., Russo U., Simon S., Tomasin P., Vigato P.A., 2006,
Evaluation of polymers for conservation treatments of outdoor exposed stone
monuments. Part I: Photo-oxidative weathering. Polymer Degradation and
Stability, 91, 3083-3096.
Favaro M., Mendichi R., Ossola F., Simon S., Tomasin P., Vigato P.A., 2007, Evaluation of
polymers for conservation treatments of outdoor exposed stone monuments. Part
II: Photo-oxidative and salt-induced weathering of acrylic-silicone mixtures”.
Polymer Degradation and Stability, 92, 335-351.
Favaro M., Simon S., Menichelli C., Fassina V., Vigato P.A., 2005, The four virtues of the
Porta della Carta, Venice-Assessment of the state of preservation and re-evaluation
of the 1979 restoration, Studies in Conservation, London, 50, 109-127.
Melo M.J., Bracci S., Camaiti M., Chiantore O., Piacenti F., Photodegradation of acrylic
resins used in the conservation of stone”, Polymer Degradation and Stability; 66,
23- 30.
1118
INVESTIGATIONS GUIDING THE STONE RESTORATION OF
THE “SCHÖNER ERKER” IN TORGAU, GERMANY
C. Franzen1*, H. Siedel2, S. Pfefferkorn3, A. Kiesewetter4 and S. Weise5
Abstract
As part of the planning for the restoration of the Schöner Erker, a sandstone oriel in Schloss
Hartenfels in Torgau, Germany, extensive preparatory investigations were undertaken.
Several questions about the construction and the material properties had to be addressed.
Investigation techniques included: metal detection, drilling resistance, thermography,
climate measurements, salt and mortar analysis. The results were an important basis for the
restoration work including dismantling, transport, desalination, consolidation, rebuilding
and formulating protective treatment. The now-completed measure makes a striking new
impression in the courtyard of the castle due to the spirited colours of the surface finish.
The paper recounts how the measurement results determined the stone restoration decisions
on the various parts of the oriel.
Keywords: Elbe sandstone, pre-investigation, salt deterioration, stone conservation
1
C. Franzen*
Institut für Diagnostik und Konservierung an Denkmalen in Sachsen und Sachsen-Anhalt e.V.
(IDK), Dresden, Germany
franzen@idk-denkmal.de
2
H. Siedel,
Technische Universität Dresden, Institut für Geotechnik, Dresden, Germany
3
S. Pfefferkorn
HTW Dresden, FB Bauingenieurwesen / Architektur, Dresden, Germany
4
A. Kiesewetter
Landesamt für Denkmalpflege Sachsen, Dresden, Germany
5
S. Weise
Heidelmann&Klingebiel Planungsgesellschaft mbH, Dresden, Germany
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
1. Introduction
The architectural building element "Schöner Erker", which could be translated: the
Beautiful Oriel Window, was built in 1544 in Schloss Hartenfels. It is one of the most
important achievements of sculptural art from the Early Renaissance in Central Germany.
Within the ensemble of the Hartenfels castle in Torgau it is - in its unity of filigree
architecture, ornamentation and figured reliefs - in artistic balance with and complementary
to the Großer Wendelstein (Grand Spiral Staircase) in the courtyard.
The Hartenfels castle in Torgau was founded in the 10th century. Extensive construction
work was started after 1470 when its status was raised to a Saxon Electoral castle. The
central building with the Grand Spiral Staircase was built in 1536. The staircase is one of
the boldest and most important staircase structures of the Renaissance in Central Europe.
The stairs led to the room of the Elector of Saxony. - Building of the castle church started in
1540. It was consecrated by Martin Luther in 1544 as the very first Protestant church. The
“Schöner Erker” (Beautiful Oriel) was built directly beside the castle church in the same
year. Its carved decorations are ascribed to the Leipzig sculptor Stephan Hermsdorf.
Hartenfels Castle developed into one of the most important seats of the Saxon Electors in
the 16th and 17th centuries. The castle came into the possession of Prussia in the middle of
the 18th century and became dilapidated by unsuitable usage. It was used as barracks from
1815 until the end of the 19th century. First restoration work on the Schöner Erker, which
was in danger of collapse, was started in 1836. The whole oriel was pulled down and rebuilt
and clamped together using a great part of the historic stones. The originally three storeys
were reduced by one in order to minimise the load. Moreover, it was completely covered
with oil paint. In 1927/1928 a new roof was added, the oil paint was removed by means of
caustic soda and the stones were partially repaired. In the beginning of the 21 st century
preparation for a sustainable restoration took several years, not only due to financial causes
but also for technical challenges in stone conservation. Finally the restoration was carried
out in 2009-11. Some aspects of the investigations for restoration of the oriel window are
presented in the paper.
2. Methodology
The history of the oriel was compiled based on archive research. One main focus was the
gathering of information about previous damage reports and restoration actions on the oriel.
The existence and distribution of iron anchors in the oriel construction was investigated
with a metal detector, Elcometer Protovale 331 “CoverMaster”. Metal search was
undertaken from outside and inside the rooms of the oriel.
Salt analyses were carried out at several stages of the restoration and in different ways.
During the pre-investigations efflorescences were sampled and subsequently investigated
by XRD, by Siemens D5000, DIFFRAC plus EVA/AUTOQUAN at TU-Dresden. For the
investigation on distribution of soluble salt contents in the sandstone material sampling of
material profiles by drilling was undertaken. Soluble salts were extracted with deionized
water from the drill powder samples and also from poultice material. The total salt content
of the samples was determined by evaporating the solution and weighing the remaining dry
solid matter. Mg, Ca, K, SO4, Cl, and NO3 were quantitatively analysed in the aqueous
solution by means of a HACH spectrophotometer using standardized reagents. Na was
determined with an ion selective electrode. The results were related to the dry sample mass
[wt.-%]. Also poultice application for desalination was analysed. Samples in size of
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
10×10 cm were taken to laboratory. The correct dimensions of the sample is important for
the evaluation of the desalination effectiveness, as this is based on a reference to the area
(Franzen 2006). Results of poultice analysis are expressed in g/m 2 following the
recommendations of WTA (2005). The 100 cm2 samples were diluted in 400 ml H2O and
the filtered eluates were used for further analysis. The electrical conductivity, pH (by
HANNA Hl 991300) and dry residue at 105°C were measured in line with normal practice
in building conservation.
Near-surface weathering profiles were investigated by microdrilling resistance. For the insitu measurement of hardness profiles of historic (building) material like stone, brick and
mortar drilling resistance is a well established technique (Pamplona et al. 2007). The
Durabo drilling systems used here and the procedure are described in Siedel & Siegesmund
(2014). Drill bits (Fa. Porzner) with an aperture of Ø=3 mm came into use. Drill velocity
was stage 2, hammering function, pressure load 1 kg or 2 kg. Due to differences in heat
conduction of building parts the temperature distribution of an object gives insight in the
construction. Infrared thermography measurements were conducted by VARIOSCAN 3021
ST-camera (InfraTec). The camera detects radiation between 8 and 12 µm wavelengths.
Data processing was conducted with IRBIS-professional 2.2.
3. Damage
By the late 1990s the oriel was in a highly problematic state. Irregular visible inspection
from the ground and with telescope or also cumbersome out of the windows indicated
serious damages and an ongoing damage progression on the sandstone parts. Figures 1a and
1b show the significant damage progress within ten years.
a)
b)
Fig. 1: a) Relief of Lucretia at 1991; b) Relief at 2000 (red arrows point out additional
losses compared to 1991).
In 2000 and 2004 more detailed inspection was proceeded by means of a portable hoisting
platform. Serious losses in the artistic highly precious reliefs by sanding, soiling and a
conspicuous peeling (terms as recommended by Vergès-Belmin et al. 2008) was observed
pointing out the alarming state. Looking at the total construction losses of joints in many
positions and several cracks were detected. Due to risks of falling parts the bottom
periphery had to be roped in. A first investigation on the structural conditions raised several
questions about the bonding of the oriel into the building and possible anchoring between
the sandstone parts. Some cracking seemed to originate from corrosive expansion of iron
anchors.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Because many details of the damages and their causes were not clear and the risks of
ongoing damage had to be reduced much more understanding was needed. The main
decision that had to be made was whether the weathered parts of the oriel could be treated
in-situ, or the whole construction dismantled for a more thorough conservation in the
restorer`s workshop. An international expert panel, meeting in 2004 recommended detailed
conservation scientific research on the oriel to address a series of questions.
4. Sandstone
The oriel is built from Cretaceous sandstone quarried about 100 km SE upstream the river
Elbe. All artistic parts are carved in the Cotta type Elbe sandstone which is a fine to
medium grained, clay-bearing quartz sandstone. This relatively weak sandstone has been
widely used for centuries, particularly for sculptures in Saxony (Götze et al. 2007).
Siliceous bonding is dominant and the grainsize lies in the range of 63 to 200 µm. Along
the bedding planes pore filling cements consisting of the clay minerals illite and kaolinite
can be found occasionally. The median pore diameter is approximately 1 µm. Petrophysical
properties of the material, which are strongly dependent on the clay mineral content, are
given in Tab. 1.
Tab. 1: Petrophysical properties of Cotta type Elbe Sandstone.
1
Compressive
strength1
Flexural
strength1
Porosity
Capillary
water uptake
MPa
MPa
vol.-%
kg/m2h0.5
33.5–37.4
4.1–5.4
22.8
1.3–5.5
Water vapour
diffusion, µ
Hydric
dilatation
mm/m
11–21
0.3–0.9
tested by MPA Dresden
5. Construction
To understand the bonding of the oriel into the castle building the interior plaster was
partially removed. Prior to that a conservator inspection of the wall paints made sure that in
and near to the oriel no original plaster and colours could be found. With a metal detector
several anchors clamping oriel parts to the building masonry could be traced. These inner
anchors showed a good state in terms of corrosion. A different picture was gained from the
external inspection. All the reliefs were fixed into the construction by iron anchors (Fig. 2)
which showed serious corrosion in places. Moreover it became obvious, that neither the
cramps nor single reliefs could be taken out of the construction without severe damage to
the sandstone masterpieces.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
iron cramps
lead sheets and other metal parts
uncertain detection
Fig. 2: Distribution of iron cramps and anchors shown on a base plan which identifies all
stone pieces. ”Kopie” indicates pieces replaced in 1928.
6. Salt
6.1. Salt content
Salt content of the sandstone was investigated by sampling of powder from the drilling
profiles. Samples were taken at 5 mm intervals for the first 2 cm, and after that at 1 cm
intervals to a total depth of 5 cm. All profiles showed a similar trend with respect to the salt
concentrations. In the first 5 mm interval, and partially also in the second until 1 cm depth,
soluble salts were present in amounts higher than 2 wt.- %. Sulphate contents were rated as
“extreme” taking into account the scheme of WTA (2005). To the next steps there is a
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
remarkably reduction of soluble salt contents to values lower than 1 wt.-% (Fig. 3a and 3b).
Near the surface sodium, as well as some nitrate was detected, besides abundant calcium.
Those concentrations vanish in greater depth. Sulphate is the dominant anion in all steps,
but in the depth the concentrations are rated as “low” with respect to their damaging
potential (WTA 2005). Also salt efflorescences were sampled and analysed. Those salt
crystals were easily visible on the damaged sandstone surface. Moreover, short time after
undertaking a Karsten tube test a white salt rim generated around the tested area. All XRD
measurements showed thenardite (Na2SO4) and gypsum (CaSO4.·2H2O) as crystallised
soluble salts. The remarkable sodium contents are related referred to the earlier restoration
action when the oil paint was removed by caustic soda (Hoferick & Siedel 1999). Thus,
desalination was needed for all original sandstone pieces, and was undertaken by poultice
desalination of the contaminated surfaces.
b)
salt content [mEq/kg]
salt content [mEq/kg]
a)
1000
NO30 - 0.5 cm
Cl-
800
SO4-Na+
600
K+
0.5 - 1.0 cm
400
Mg++
1.0 - 1.5 cm
Ca++
1000
NO3-
800
SO4--
0.5 - 1.0 cm
Na+
600
K+
1.0 - 1.5 cm
Mg++
400
1.5 - 2.0 cm
1.5 - 2.0 cm
200
Cl0 - 0.5 cm
3.0 - 5.0 cm
2.0 - 3.0 cm
200
Ca++
2.0 - 3.0 cm
3.0 - 5.0 cm
0
0
sample code
sample code
Fig. 3: Salt contents into depth, profile for stone H02 (a) and profile for stone O03(b).
6.2. Poulticing
Desalination proved to be a key step in the conservation action restorative action. In the
workshops the reliefs were treated with wet poultices applications (Vergès-Belmin & Siedel
2005, Heritage et al. 2013) in two cycles. The surface was pre-wetted with deionised water
(electrical conductivity < 10 µS/cm), and the aqueous cellulose poultice was attached to the
stone surface. After the migration of dissolved ions into the drying poultice, the dry, salt
laden poultice was removed. Several poultice samples were analysed for their salt content
to monitor and evaluate the desalination progress (Franzen 2006, WTA 2005). In the
laboratory some of the poultices produced a yellow staining to the eluate, probably caused
by the transport of humic material (Franzen et al. 2015). Most poultices absorbed up to
50 g/m² soluble salts. In one case more than 200 g/m² salts was analysed. Areas which were
identified as highly salt loaded were subsequently treated several times. The ion mixture in
the poultices contained much more sodium, compared to the ionic composition detected in
the material itself. More soluble salts such as thenardite are well extracted by the poultices
while hardly soluble gypsum is not reduced significantly.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
7. Drilling resistance
To gain an insight in the weathering profile of the sandstone, drilling resistance was
measured on damaged and intact surfaces (Fig. 4a and 4b). Fig. 4b compares the profile of a
damaged area (BW1.1) with that of an area, where no damage was observed (BW1.4). The
absolute height of the profiles is not comparable, as the pressure applied to BW1.4 was
double than for BW1.1, but the development with depth is revealing. The damaged area
starts with low strength near the surface, which increases until 2 cm depth. Higher values in
depths > 2 cm can be attributed to increasing side effects by material transport during
drilling (Siedel & Siegesmund 2014). The visibly intact area has a more or less continuous
drilling resistance profile. The damaged area of the surface had to be consolidated, and the
consolidant needed to reach a depth until 2 cm, with decreasing degree of intensity to
replace the lost strength.
b)
drill progress [s/mm]
a)
5
BW1.1 vis damaged
4
BW1.4 vis sound
3
2
1
0
0
5
10
15
20
25
30
35
40
drill depth [mm]
Fig. 4: a) Position of drilling profiles shown in Fig. 4b (left: damaged; right: intact);
b) Drilling profiles of visibly damaged and intact areas.
8. Infrared thermography
Inspection by infrared thermography was intended to locate the iron components in the
construction. Although the measurement circumstances were good (the first storage room
was heated up to 18°C, outer temperature was about -6.5°C) the testing was not successful.
As revealed by the metal detector tests, the metal parts are hidden in geometrically complex
positions, and in those parts they do not significantly contribute to heat transfer. However,
it was observed that very steep temperature profiles occur in winter situations in the thin
sandstone reliefs. While the thicker structural sandstone parts have surface temperatures of
about -4.6°C to -2.1°C, which is close to the outside temperatures, the thin relief panels
show outer surface temperatures of up to 0.9°C.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
a) Front:
b) View from West:
Fig. 5: IR-Thermography ‘Schöner Erker’.
9. Conclusion
The sandstone monument ‘Schöner Erker’ in Torgau, one of the most important
achievements of the art of sculpture from the Early Renaissance in Central Germany, was
rescued by a thorough stone restoration approach including structural and climatic
measures. Extensive investigations were an indispensable basis for sound planning and
realisation of the works. An initially favoured in-situ restoration of all or the most parts of
the oriel window was suspended for several reasons. Due to severe damage, demonstrated
by mapping of weathering forms, salt analyses and measurements of drilling resistance, and
resulting in very fragile stones, all reliefs had to be treated in a workshop. But they could
not be removed without serious damage and risks to the overall structure. Moreover the
corroding iron clamps had to be replaced, which also could not be reached without massive
intervention. Dismantling and reconstruction, which was justified as a last resort decision,
required higher efforts in logistics. The monument had already been dismantled once before
in its lifetime, and so there was neither a concern about originality nor loss of related
decoration like interior wall paintings. The detection of iron parts within the construction
by metal detector and mapping of their positions provided valuable information for the
practical interventions. To further avoid loads on material due to steep temperature profiles
in the thin sandstone panels (as demonstrated by infrared thermography) it was
recommended that the use of the rooms be adapted towards a climatic situation better
coupled to that of the exterior. As could be shown by archive research and salt
investigations, the sandstone had a history of painting, chemical removal of paint and
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
posure to environmental pollution, which lead to serious salt loads and consequent decay.
As desalination is better approached as a reduction of salt contents rather than total
removal, residual contents have to be acknowledged. As demonstrated by chemical
analyses, very large amounts of the active and damaging sodium sulphates were extracted
by poulticing. The deteriorated softened surface parts were consolidated with TEOS and in
parts with Paraloid B72. Its application from the most damaged direction -the outer surfaceenabled reinstatement of a continuous strength profile. For aesthetic reasons related to the
overall concept of renewed coloured surfaces on the Castle of Hartenfels, a decision was
made on a colour finish based on the original colour composition of the oriel. The coating,
based on a silicon resin binder system, should avoid further massive rain and salt attack
This case study demonstrates the essential contribution of scientific investigations to
successful planning and undertaking of restoration measures on high-value architectural
stone objects.
a)
b)
Fig. 10: a) “Schöner Erker” prior its restoration in 2004;
b) Restored “Schöner Erker” in 2011.
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Acknowledgements
The restoration and most parts of the investigative study were made possible due to
cooperative grants of the World Monument Fund (WMF) and the Ostdeutsche
Sparkassenstiftung (OSS). Additional investigation work and publication presentation was
supported by the Ministerium des Innern, Sachsen, Germany.
References
Franzen, C., 2006, Analytische Begleitung von Salzreduzierungsmaßnahmen, in, Praxisorientierte Forschung in der Denkmalpflege –10 Jahre IDK-, Hrsg., Institut für
Diagnostik und Konservierung an Denkmalen in Sachsen und Sachsen-Anhalt e.V.
2006, 31 – 40.
Franzen, C., Kretzschmar, J., Franzen, C. and Weiss, S., 2015, Staining on heritage building
stone identified by NMR spectroscopy, Environmental Earth Science, Volume 74/
6 , 5275-5282, DOI, 10.1007/s12665-015-4538-9.
Götze, J. and Siedel H., 2007, A complex investigation of building sandstones from Saxony
Germany. – Materials Characterization 58 11-12, 1082-1084.
Heritage, A., Heritage, A. and Zezza, F., 2013, Desalination of Historic Structures and
Objects, Archetype Publications, London
Hoferick, F. and Siedel, H., 1999, Die Ablaugung von Ölfarbanstrichen am Dresdner
Zwinger – Geschichte und Folgeschäden. - Mitteilungen des Landesamtes für
Denkmalpflege Sachsen, 80-88. in German
Pamplona M., Kocher M., Snethlage R. and Aires-Barros, L., 2007, Drilling resistance:
overview and outlook. Z. dt. Ges. Geowiss., 158 (3), 665–676.
Siedel, H. and Siegesmund, S., 2014, Characterization of stone deterioration on buildings.
In Siegesmund, S. &Snethlage, R. (eds.) Stone in Architecture, Springer, Berlin
and Heidelberg, 349-414.
Vergès-Belmin V., Anson-Cartwright, T., Bourguignon, E., Bromblet, P., Cassar J.,
Charola, E., DeWitte, E., Delgado-Rodriguez, J., Fassina, V., Fitzner, B., Fortier,
L., Franzen, C., Garcia de Miguel, J.M., Hyslop, E., Klingspor-Rotstein, M.,
Kwiatkowski, D., Krumbein, W.E., Lefèvre, R.A., Maxwell, I., McMillan, A.,
Michoinova, D., Nishiura, T., Queisser, A., Pallot-Frossard, I., Scherrer, G.W.,
Simon, S., Snethlage, R., Tourneur, F., Van Hees, R., Varti-Matarangas, M.,
Warscheid, T., Winterhalter, K., Young, D., 2008, Illustrated glossary on stone
deterioration patterns, ISBN, 978-2-918068-00-0, 78 p.
Vergès-Belmin, V. and Siedel, H., 2005, Desalination of masonries and monumental
sculptures by poulticing, a review. International Journal for Restoration of
Buildings and Monuments, 11 6, 391-407.
WTA Guideline 3-13-01/E, 2005, Non-destructive desalination of natural stones and other
porous materials with poultices. WTA Publications, Munich.
1128
ANANLYSIS AND TREATMENT OF THE
FIRE-DAMAGED MARBLE PLAQUE FROM
THOMAS JEFFERSON’S GRAVE MARKER
C. Grissom1*, E. Vicenzi1, J. Giaccai2, N.C. Little1, C. France1,
A.E. Charola1 and R.A. Livingston3
Abstract
The original grave marker for Thomas Jefferson (1743-1826), third U.S. President, consists
of a granite cube and obelisk, into which was set a white marble plaque inscribed with his
epitaph. After damage led to replacement with a copy in the cemetery at Monticello, the
original grave marker was given to the University of Missouri. Granite portions were
installed in front of the university’s main building, while the plaque was placed inside for
safekeeping. The building burned down in 1892, and the plaque fragmented, portions
disaggregated and were lost, and fire-related materials accreted on its face. Soon afterward,
the plaque was reassembled atop a new marble block with hydraulic lime plaster. When
examined more than a century later, the pieces were found to be misaligned, and areas on
the face had deteriorated, with further loss of lettering and some instability. Instrumental
analyses were done prior to conservation treatment. Stable isotope analysis sourced the
stone to Vermont marble quarries. Other analytical techniques indicated that the marble had
calcined and to some extent recarbonated, and they identified elemental constituents in the
surface accretions deposited during the fire, including copper, tin, lead, and sulfur.
Treatment included disassembly and reassembly of the plaque using Paraloid B48N,
reconstruction of missing areas using a Paraloid B72/ground alabaster mixture for surface
fills and a filled epoxy to support the fill material where there was a large loss, surface
cleaning, and consolidation. Two reproductions were made using photogrammetry, and one
was installed on original granite portions of the grave marker on the University of
Missouri’s David R. Francis Quadrangle.
Keywords: fire, Vermont marble, calcination, recarbonation, photogrammetry
1
C. Grissom*, E. Vicenzi, N.C. Little, C. France and A.E. Charola
Museum Conservation Institute (MCI), Smithsonian Institution, United States of America
grissomc@si.edu.
2
J. Giaccai
Freer/Sackler Galleries, Smithsonian Institution, United States of America
3
R.A. Livingston
Materials Science and Engineering Department, University of Maryland, United States of America
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
1. Introduction
The original grave marker for Thomas Jefferson (1743-1826), third U.S. President, was
made according to his instructions and erected in 1833 in the graveyard at Monticello, his
Virginia home (Peden 1953). It consists of a granite obelisk resting on a granite cube, with
the epitaph carved in a white marble plaque set into the obelisk (Jefferson famously omits
that he had been president in his epitaph). After the grave marker was damaged by souvenir
hunters and replaced by a copy at Monticello in 1883, the original was given to the
University of Missouri. Granite portions were displayed in front of Academic Hall, the
university’s main building, while the plaque was placed inside it for safekeeping. Academic
Hall burned down in 1892, and the “sacred relic ... cracked and burned” (Peden 1953, p 13).
In 2012, the university requested examination and possible treatment of the plaque by the
principal author, and the following year it was sent to the Smithsonian for treatment. At that
time the plaque was enclosed in the same display case and exhibited essentially the same
fragments and fills as in an historic photograph from the 1890s (Fig. 1). Moreover, it was
photographed on the granite structure of the tombstone in front of the ruins of the firedamaged building, suggesting repair soon after the fire. After the display case was removed
in 2013, discarded printed matter from the 1880s and 1890s was found used as shims,
confirming this hypothesis.
Fig. 1: Thomas Jefferson’s grave marker displaying the repaired plaque in a frame
following the 1892 fire, on the grounds of the University of Missouri. Courtesy, University
of Missouri Archives.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
2. Examination and analyses
2.1. The marble
Marble grains on the plaque range from 0.25 to 0.6 mm; accessory feldspar and quartz are
found at grain boundaries. In the absence of documents sourcing the marble, it was
hypothesized that its small grain size limited possibilities to marble imported from Carrara,
Italy, or quarried in Vermont. Carbon and oxygen isotopes for samples from the plaque
were compared to reference isotope datasets from Carrara and quarries in the northeast U.S.
(Dooley and Herz 1995) and found to best match those of Dorset, Proctor, West Rutland, or
Pittsford, Vermont (Fig. 2).
Fig. 2: The stable isotope average for TJ #1 is plotted on a graph showing averages for
marble samples mainly from Vermont and Massachusetts, after Dooley and Herz (1995).
2.2. Condition of the plaque before treatment
Examination of the plaque at the Smithsonian revealed considerable fire-induced damage,
including breakage into five pieces, numbered in Fig. 3. After disassembly, break edges
were found to have the convex shapes characteristic of fire damage, known as conchoidal
fracture (Steiger et al. 2014, p 227-228). Disaggregation along broken edges suggested that
fragmentation occurred from simultaneous expansion and contraction of anisotropic calcite
crystals, which can induce strain in marble at temperatures as low as 60 o C (Siegesmund
and Dürrast 2014, p 149-150). The rate of transmission of heat through the 5-cm-thick
block would have been highest at corners, consistent with detachment of the small
triangular pieces designated 1 and 4, as well as the formation of oblique cracks across the
lower left corner visible in Fig. 4. Losses can also be readily seen in Fig. 4 because of the
irregular surfaces of fills that replaced them. They are significant along broken edges,
particularly at the left edge, where as much as 3 cm of the plaque is missing (apart from
small areas at top and bottom corners) and may indicate the direction of the fire. Adjacent
to this loss, a layer about 1-cm thick is missing on the back face, suggesting that the plaque
may have been in a wooden case that burned in the fire. The plaque is slightly convex on
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
the back, probably from residual expansion caused by greater exposure to the fire;
concomitantly, it is slightly concave on the front. Front surfaces at the left and bottom are
partially calcined, distinguishable by whitening (Fig. 3). Expansion of these areas can be
felt where they intersect sound stone. Partially delaminated areas with voids below were
also found to have expanded, preventing readhesion; during treatment, the voids were filled
instead. Since the historic photograph was taken in the 1890s, lettering has been lost at the
left edge, visible as bright areas, e.g., where the first letter of “AMERICAN” is missing.
Fig. 3: The tombstone plaque before
treatment; fragments are numbered at left.
Height = 74cm. Photo by Don Hurlbert
Fig. 4: RTIViewer screenshot in the
specular enhancement mode shows
surface irregularity of the plaque before
treatment. Photo by E. Keats Webb
2.3. Deterioration of the marble
Decomposition of calcite (CaCO3), or calcination, occurs at temperatures above 700°C;
carbon dioxide (CO2) evolves, leaving calcium oxide (CaO) behind. The CaO can
subsequently recarbonate in air to form poorly cohesive calcite. The calcined upper part of
a marble sample from the plaque appears chalky white to the naked eye (Fig. 5), and a thin
section shows that the marble’s granular texture there has been replaced with an opaque
material (Fig. 6), which is very fine. Micro-X-ray diffraction analysis of samples from such
areas found both calcite and calcium hydroxide [Ca(OH) 2], and preliminary
thermogravime-tric analysis (TGA) indicates about 95% calcite and 5% Ca(OH) 2. In the
intermediate zone between calcined marble and smoke-darkened marble grains below
(Fig. 7), hyperspectral energy dispersive analysis using the SEM indicated that rims of
grains had calcined and recarbonated. Below this zone, smoke-darkened marble retains its
structure but is disaggregating (Fig. 5 and Fig. 6), presuma-bly because of the heat-induced
residual stresses in calcite grains.
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Fig. 5: Damaged sample from the
plaque. The calcined surface is
opaque and white, with a dark blue
spot on top; below, smoke-darkened
marble grains are disaggregating.
The black line marks the plane of
the thin section in the next image.
Fig. 6: Thin section made from the previous
sample in darkfield illumination, with mm scale at
right; stained red for calcite. The calcined upper
surface has lost its marble texture, while grains
and cleavage planes can still be seen in the smokedamaged disaggregating marble below. The
partially calcined zone in between is shown at
higher magnification in the following figure.
Fig. 7: An area in the intermediate
zone of the previous thin section, at
higher magnification in plain
polarized light. Completely
calcined marble (above) is dark.
Calcite grains (below) are bright,
except where calcined at rims and
at cleavage planes. The brightest
particle at center left is quartz. Blue
epoxy medium can be seen in
cracks, which to some extent follow
grain boundaries.
Bar = 500µm.
2.4. Surface accretions
A light cleaning using a surfactant and water revealed several materials disfiguring the front
surface of the plaque. Constituents were analysed to determine which should be removed,
and cleaning tests were done to determine removal feasibi-lity. Micro-scanning X-ray
fluores-cence (XRF) analysis using a Bruker AXS Artax proved valuable for suggesting
extraneous materials related to the fire by identifying elements in them compared to
adjacent stone. Dark veins appeared to follow a diagonal pattern across the plaque from
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
upper right to lower left (Fig. 3) but were sometimes difficult to dif-ferentiate from surfaces
soiled by smoke. Scanning XRF confirmed locations of veins by finding silicon and
potassium in them, consistent with quartz and feld-spars. No elements, other than calcium,
were found in areas that appeared more likely to be darkened by smoke. This finding does
not rule out the presence of carbon deposited from smoke, however, since this element is
not detectable by the XRF instrument. Cleaning tests found reduction but not elimination of
soiling from smoke, apparently because smoke had penetrated the disaggregating stone.
Disfiguring black spots and streaks of a type seen in Fig. 8 were found to contain copper,
tin, lead, and sulfur as the main elements, confirmed by SEM EDS; they are probably metal
sulfides derived from plumbing or other building materials burned in the fire. Microscopic
examination of these accretions indicated that they were so intimately mixed with the stone
that they could not be removed mechanically or by laser ablation without damaging the
stone. Scanning XRF identified mainly
sulfur and calcium in dark blue spots
atop calcined areas (Fig. 5) but also
small amounts of lead, confirmed by Xray micro-analysis of a dark blue spot
on both the thin section (Fig. 6) and a
second fragment; this result suggests
that lead sulphide may have provided
the blue color. A sticky material on the
surface of the plaque was analysed by
Fourier transform infrared spectroscopy
(FTIR) and found to have a spectrum
similar to parchment. This would be
consistent with application of a material
Fig. 8: Copper, tin, lead, and sulfur were the
such as animal glue during the 1890s
main elements found in the black spot using
restoration and its removal with an
scanning XRF and SEM EDS analyses. Bar =
aqueous solution during the 2013
0.5 mm.
treatment.
3. Treatment of the plaque
Treatment included disassembly and reassembly of the plaque, reconstruction of missing
areas, surface cleaning, and consolidation. During the restoration after the fire, the five
fragments had been reassembled on a nearly 3-cm-thick marble block with hydraulic lime
plaster, also used to fill losses. Individual fragments were not in the same plane, the
composite was heavy, and fills were deteriorating and unattractive. It was decided to
remove the original fragments from the newer marble support block, which would reduce
the weight significantly, allow for improved reassembly, and provide an opportunity for
replacing deteriorating fills. Disassembly was time consuming but more easily done than
expected. The plaster was found to be poorly adhered to both the original and new marble,
and it was often cracked, allowing relatively easy separation near edges. Toward the center,
the plaster was sawn through to separate the original and new marble blocks.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 9: Plaque front after treatment.
Lighting is even; hence, lighter areas at left
and bottom reflect calcination. Photo by
Brittany Hance.
Fig. 10 Back of plaque after treatment. At
the right, a structural fill completes the
edge; next to it is an area missing a cmthick layer of stone. In the light-colored
central area, a thick layer on the surface
has been calcined but remains. At the left,
the marble is smoke damaged but more or
less intact. Photo by Brittany Hance.
Fragments were separated from each other mechanically, and old fill material was removed.
The five pieces were reassembled using the acrylic resin Paraloid B48N dissolved in
acetone as adhesive. Small compromises had to be made in joining fragments, attributed to
distortion by the fire. Reattachment of detached surfaces and consolidation of weakened
stone was done with a second acrylic resin, Paraloid B72 in acetone. Fills were also made
with that resin heavily bulked with alabaster ground to pass a sieve with 500 μm openings
(Wolfe 2009). On the front, fills were made smooth and level with the stone (Fig. 9), but on
the back they were recessed slightly and textured (Fig. 10). To begin recreation of the
missing area on the left edge, a structural fill was made on the back using filled epoxy putty
(Aves’ Fixit) isolated from the stone with the acrylic fill material; the latter was also used to
complete the left edge and cover the filled epoxy.
The front surface of the plaque was initially cleaned using mineral spirits, acetone, and an
aqueous solution with a surfactant. Areas in good condition were further cleaned with
methyl cellulose poultices; to prevent detachment of calcite grains, the poultices were
bulked with silica and calcium carbonate powders and removed before dryness. Cleaning
was limited on calcined areas at left and bottom edges because of their fragility. Treatment
was completed with retouching of fills using watercolor and gouache paints to match the
stone on the front (Fig. 9). Fills on the back were left lighter in color than the stone
(Fig. 10).
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Staff at the Smithsonian’s Office of Exhibits Central made two replicas of the plaque using
photogrammetry. Digital photographs of the conserved tombstone were taken, and files
were manipulated using Autodesk’s Recap (freeware) and Geomagic. From those results, a
copy was milled in hard foam using a CNC (computer numerical control) machining center.
After the copy was touched up, a silicone rubber mold was made. One copy was cast in
glass fiber-reinforced gypsum (GFRC) for exterior display and a second in fiberglass. The
replicas were painted with acrylic paints to imitate the plaque when it was new and coated
with a flat automotive polyurethane paint for protection.
The conserved plaque was returned to the University of Missouri, where it is now displayed
in a case indoors. The GFRC copy is displayed outdoors on the original granite portions of
the tombstone, forming a “complete” grave marker for the first time in many years.
4. Conclusions
The study and treatment of the tombstone plaque is a rare contribution to the literature on
burned marble artifacts. In addition, a sacred relic has been preserved representing the
thoughts of a U.S. President as to his important contributions: the Declaration of
Independence, the Virginia statute for religious freedom, and founding of the University of
Virginia – but not his role as president.
Acknowledgements
Staff time for research and treatment of the Jefferson plaque was underwritten by the
Museum Conservation Institute (MCI #6526). Thanks especially to Marianne and Bob
Marti for facilitating the project and Miriam Hiebert for XRD analyses.
References
Dooley, K. and Herz, N., 1995, Provenance determination of early American marbles, in
The Study of Marble and Other Stones Used in Antiquity, Y. Maniatis, N. Herz,
and Y. Basiakos (eds.), Archetype, ISBN 1 873132 0 18, 243-252.
France, C.A.M. and Grissom, C.A., 2015, Carbon and oxygen isotopes as indicators of
provenance in cultural artefacts: A case study of Thomas Jefferson’s tombstone
plaque, Abstract for Seventh MaSC (mass spectrometry and chromatography)
Meeting, Chicago, 17-22 May 2015.
Peden, W., 1953, The Jefferson Monument, University of Missouri Bulletin, 54 (32), 1-18.
Siegesmund, S. and Dürrast, H., 2014, Physical and mechanical properties of rocks, in
Stone in Architecture: Properties, Durability, S. Siegesmund and R. Snethlage
(eds.), Springer, ISBN 9 783642451 5 46, 97-224.
Steiger, M., Charola, A.E., and Sterflinger, K., Weathering and degradation, in Stone in
Architecture: Properties, Durability, S. Siegesmund and R. Snethlage (eds.),
Springer, ISBN 9 783642451 5 46, 225-316.
Wolfe, J., 2009, Effects of bulking Paraloid B-72 for marble fills, Journal of the American
Institute for Conservation, 48, 121-140.
1136
THE DIAGNOSTIC AND MONITORING APPROACH FOR THE
PREVENTIVE CONSERVATION OF THE FAÇADE OF THE
MILAN CATHEDRAL
D. Gulotta1, P. Fermo2, A. Bonazza3 and L. Toniolo1*
Abstract
The importance of preventive conservation strategies for the built heritage has been debated
in the last years, but there still is a limited number of applied research involving complex
architectural sites. The identification and monitoring of the decay processes after the
restoration activities can provide valuable information on the degradation rate and extent,
thus supporting the future planned conservation. In the present work the methodology and
some selected results of the post-treatment diagnostic and monitoring of the façade of the
Milan Cathedral are presented. The main conservation issues have been identified and
studied. A non-invasive colorimetric monitoring of selected areas of the façade has been
carried out during a two-year period in order to evaluate the soiling effect. Fragments of
stone and samples of the particulate matter deposits have been collected and characterized
in laboratory according to a multi-analytical approach. As the early stages of deposition and
erosion at the end of the intervention are particularly relevant for the evaluation of the
degradation rate, several set of stone specimens have been also exposed on the façade in
different conditions. The results of the in situ monitoring, supported by the study of the
specimens, confirmed that soiling is the main and most rapidly-evolving deterioration effect
and it is therefore expected to have a significant impact in the next future. Moreover, beside
the carbonaceous fraction responsible for the surface blackening, the deposits composition
showed high content of potentially harmful soluble compounds which can react with the
stone matrix and therefore needs to be monitored over time.
Keywords: monitoring, marble decay, deposition, surface erosion, stone blackening,
preventive conservation
1. Introduction
The importance of preventive conservation strategies for the built heritage has been debated
in the last years. Despite the theoretical studies available so far (Della Torre 2003), there is
still a limited number of applied researches conducted in the field and involving complex
1
D. Gulotta and L. Toniolo*
Politecnico di Milano, Dipartimento di Chimica,
Materiali e Ingegneria Chimica “Giulio Natta”, Italy
lucia.toniolo@polimi.it
2
P. Fermo
Università degli Studi di Milano, Dipartimento di Chimica, Italy
3
A. Bonazza
Nazionale delle Ricerche - Istituto di Scienze dell’Atmosfera e del Clima, Italy
*corresponding author
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architectural buildings and sites (Brimblecombe & Grossi 2005; Price 2007; Ghedini et al.
2011; Bortolotto et al. 2013). As far as the stone surfaces exposed outdoor are concerned,
the identification and the monitoring of the decay processes after the restoration activities
can provide valuable information on the degradation rate and extent. Indications for
preventive conservation able to delay and possibly reduce the occurrence of the damage can
be provided accordingly. In the present work, the diagnostic and monitoring strategy for the
preventive conservation of the façade of the Milan Cathedral is presented. The Duomo is a
major landmark of the city, a remarkable example of the late gothic architecture and a
primary touristic resource. The continuous exposition to the highly polluted atmosphere of
Milan city centre progressively damaged the Candoglia marble of the façade according to
well-known deterioration mechanisms (Watt et al. 2009), so that extensive conservative
interventions had to be performed during the last century in 1935-39 and 1972-74. More
recently, due to the worrying state of conservation of the surfaces, particularly affected by
soiling and black crust formation (Toniolo et al. 2009), a new and complex restoration
project was carried out in 2003-2009. The post-intervention monitoring and diagnostic
activity started two years later. The main conservation issues to be monitored have been
identified and included: i) soiling and blackening effects due to the deposition of
atmospheric pollutants and soil dust in sheltered areas; ii) surface erosion of the elements
exposed to direct rain-wash. A non-invasive colorimetric monitoring of selected areas of
the façade has been carried out during a 18-month period in order to evaluate the soiling
and blackening effect. Fragments of stone and samples of the particulate matter deposits
have been collected and characterized in laboratory according to a multi-analytical
approach. As the early stages of deposition and erosion at the end of the intervention are
particularly relevant for the evaluation of the degradation rate, several set of Candoglia
marble reference specimens have been exposed on the façade in different conditions
(height, orientation, superficial finishing, sheltered/non-sheltered condition) and monitored
every 6 months.
2. Materials and methods
Colorimetric measurements have been performed by a Konica Minolta CM-600D
instrument equipped with a D65 illuminant at 8° (400-700 nm range). Measurements were
elaborated according to the CIE L*a*b* standard colour system; FTIR analyses were
carried out with a Nicolet 6700 spectrophotometer with a DTGS (4000-400 cm-1 range) on
powder samples in KBr pellets; XRD analyses were performed using a Philips PW1830
diffractometer with Bragg-Brentano geometry using a Cu anticathode and Kα radiation (λ =
1,54058 Ǻ). ESEM-EDX analyses were performed using a Zeiss EVO 50 EP environmental
scanning electron microscope, with an Oxford INCA 200-Pentafet LZ4 spectrometer.
Anions analysis was carried out by means of a Ion Pac AS14A (Dionex) column and a
detection conductivity system equipped with a ASRS-ULTRA suppression mode (Dionex).
Cations determination was performed by means of a CS12A (Dionex) and a detection
conductivity system equipped with a CSRS-ULTRA suppression mode (Dionex). Laser
profilometry was performed by a UBM Microfocus instrument, with a 150 pts/mm density.
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3. Results and discussion
3.1. Soiling and blackening effects
3.1.1. Deposits characterization
After few years from the last cleaning operations most of the marble surface of the basrelief, of the sculptures and of all the areas sheltered from direct rainfall show slight to
significant accumulation of deposit. Samples of the dark deposits have been collected from
seven different locations which varied in height from the ground level to almost 20 meters.
The XRD characterization of the deposit highlighted the presence of quartz, feldspar,
gypsum and calcite as the main mineralogical phases, together with clay minerals in minor
amount. Sodium chloride, as halite, has also been found in some of the samples collected
from the lowest locations. The deposit has also been studied by SEM-EDX (Fig. 1).
Metallic particles containing iron and titanium are the most diffused within the deposited
material, with an average diameter which decreases with height: in the highest sampling
site (almost 20 m), where the prevalent transport mechanism is the wind-driven deposition,
the particles diameter ranges from 2 to 20 µm; in the lowest location (2 m), where
anthropogenic and vehicular re-suspension of soil dust and particulate matter from the
ground is also effective, their diameter rises to a range of 20 to 50 µm. Aluminosilicate
particles have been traced as well, but their size distribution seems to be less effectively
related to height. Only rare carbonaceous particles containing sulphur and vanadium have
been found in the upper sampling sites.
Fig. 1: ESEM micrographs of metallic (a), aluminosilicate (b) and carbonaceous (c)
particles from the façade surface deposits.
The compositional characterization after FTIR analysis (Fig. 2) confirmed the prevailing
presence of gypsum as the major component of the deposit (characteristic absorption
doublets at 3532-3405, 1680-1622, 1140-1116 and 670-600 cm-1). The sharp intense peak
at 1385 cm-1 indicates the presence of high amount of nitrates and the smaller one located at
1323 cm-1 is related to the presence of calcium oxalate (most probably as weddellite). The
calcite contribution is evidenced by the peaks around 1430, 875 and 715 cm -1, present in
minor amount together with silicates (Si-O characteristic peak around 1030 cm-1) and
quartz (779-799 cm-1). The comparison between the deposits formed over the real sculpted
surfaces (Fig. 2, grey line) as a result of the outdoor post-restoration exposition and the
deposited material collected from the Candoglia marble specimens after six months of
sheltered exposing condition on the façade (Fig. 2, black line) shows that no significant
differences in the general composition are present.
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Fig. 2: FTIR spectra of samples of deposit from real façade surfaces (grey line) and
collected from exposed Candoglia marble sample (black line).
The natural deposition over the sculpted surfaces is enriched in soluble compounds due to
the longer exposition to the atmospheric pollutants and, as for gypsum, to the contribution
provided by the partially sulfated substrate. It is worth noting that the overall composition
of the latter deposits shows similar characteristics respect to the results of black layers and
black crust characterization of samples of previous studies of the façade (Toniolo et al.
2009; Barca et al. 2014).
Fig. 3: Anions and cations content of deposit on quartz filter (white bars) and Candoglia
marble specimens (grey bars) after six months of sheltered-condition exposition on the
façade.
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The evaluation of the soluble salts content of deposits collected on stone specimens and
quartz filter after a six-month exposition period is reported in Fig. 3. The main ions
concentrations determined in the two different cases are characterized by a comparable
trend, thus confirming that the quartz filter represents a valid supporting material to collect
the atmospheric particulate matter affecting the surfaces. Marble shows slightly higher
concentrations of sulfate, nitrate and calcium. These differences could be partly due to early
stage of sulfation process of the stone material.
3.1.2. Blackening
Surface blackening has been evaluated by colorimetric monitoring of fifty selected areas of
the façade. The main parameter related to the blackening effect is the variation of L* which
effectively describe the darkening of the surface as a result of the deposit accumulation.
The real façade surfaces have shown a high dispersion of the initial values of this parameter
due to the very different conditions of the substrate respect to: orientation, finishing,
material heterogeneity and, most of all, presence of substituted elements as a result of the
conservative interventions and of the regular maintenance activity of the building. The
initial value of L* of the “original” surfaces (those belonging to elements not recently
substituted) ranges from 50 to 75 units, whereas the values of the substituted elements is
always above 85. A general trend for such diverse situations therefore cannot be traced. In
Fig. 4 is reported, as an example, the evaluation of two surfaces characterized by the same
orientation, location and overall geometry but with significantly different exposition period.
The “original” horizontal sheltered upper surface of the sculpted element shows an initial
L* value of 51, which decrease of about 5 units at the end of the first year of monitoring.
The substituted element shows a similar trend but with a lower variation in the same period
(3 units), which can be related to the different surface condition of the marble characterized
by a less weathered surfaces (as confirmed by on-site qualitative microscopic observation).
Such surface can be considered as less prone to deposit accumulation due to its lower
surface roughness.
Fig. 4: Photographic documentation of two areas of the colorimetric monitoring
characterized by the presence of “original” (a) and more recently substituted (b) marble
elements; b) variation of the L* parameter within the first year of monitoring.
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The generally limited L* variations of the real areas have been compared to those of marble
reference specimens, to properly take into account the non-linear trend of surface
blackening (Brimblecombe & Grossi 2005). The results of the reference specimens exposed
in the central area of the façade indicate a more significant and progressive reduction of the
superficial lightness (Fig. 5, left). After the first exposition interval (6 months), the
variation of L* is around 4 units, thus being already barely detectable by the naked eye, and
it reaches a final decrease of 14 units after 18 months. The b* variations follow an opposite
trend (Fig. 5, right) indicating that the deposit accumulation is characterized by a saturation
of the yellow colorimetric coordinate, even though to a minor extent respect to the most
relevant blackening effect. The final increase of the b* value is limited to almost 4 units.
Fig. 5: variation of the L* (left) and b* (right) parameters of Candoglia marble reference
specimens within 18-month exposition in sheltered condition.
3.2. Surface erosion
The surface erosion of marble due to the effect of direct rain wash and of run-off water
flowing over the flat cladding slabs represents a major conservation issue that all the
previous interventions had to deal with. Such mechanism is particularly efficient on the
elements located on the top of the façade, such as the spires, and on the prominent sculpted
figures of the lower register. The progressive erosive effects on the Candoglia
microstructure are visible in Fig. 6, where the reference non-exposed material (Fig. 6a) is
compared to fragments coming from a recently substituted element (Fig. 6b) and an
“original” one (Fig. 6c). The grain morphology of the freshly sculpted marble is
characterized by a very compact appearance, where the single grains show well defined
regular borders and no discontinuities are present.
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Fig. 6: ESEM documentation of the marble microstructure of a reference non-exposed
material (a), compared to fragments from a recently substituted element (b) and from an
“original” one (c).
As a result of the outdoor exposition, the erosive effect can be identified in the rounding of
the grain edges and in the typical accentuated cleavage planes (Weber et al. 2007), which
can be observed as parallel fissures. The prolonged exposition further enhances this
deterioration pattern, leading to dramatic rounding of the grain and loss of material even on
a macroscopic scale. The erosion extent has been monitored by laser profilometry on
polished marble reference specimen exposed to the most severe non-sheltered façade
condition.
Fig. 7: Average surface roughness (Ra) of marble reference specimens evaluated after
laser profilometry.
The decay effect has been evaluated respect to the variation of the surface roughness, as an
indicator of the state of conservation of the superficial microstructure. The results show an
increment of the average roughness as a result of the exposition, which is more than twice
the initial one after 18 months of exposition (Fig. 7). Moreover, the higher standard
deviation calculated for the final measurements is related to the increased surface
irregularity (loss of material, formation of fissures, rounding effects) which is confirmed by
the ESEM observations.
4. Conclusions
The diagnostic and monitoring approach for the real surfaces, supported by the study of the
marble reference specimens, indicates that soiling is the main and most rapidly-evolving
deterioration effect and is therefore expected to have a significant impact in the next future.
Beside the carbonaceous fraction responsible for the surface soiling and blackening, the
deposits composition showed high content of potentially harmful soluble compounds,
which can react with the stone matrix leading to crystallization damages and crust
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formation. It therefore needs to be monitored over time. The deposition rate is confirmed to
be particularly effective during the first stage of the exposition of the cleaned surfaces and
tend to slow down over time. This suggests the importance of a proper planning of the
monitoring activity, which should start at the very beginning of the post-restoration period.
The enhancement of the surface roughness potentially leading to loss of material at a
macroscopic scale is the main effect of the erosion mechanism in the non-sheltered areas.
With respect to preventive conservation indications, the results point the attention to the
need for further research to set-up sustainable methodologies for the periodic removal of
the deposits and for surface protection to mitigate the marble corrosion effects.
Acknowledgements
Authors wish to acknowledge the “Veneranda Fabbrica del Duomo di Milano” and Ing.
Benigno Mörlin for the assistance and technical support during the project.
References
Barca, D. et al., 2014, Impact of air pollution in deterioration of carbonate building
materials in Italian urban environments, Applied Geochemistry, 48, 122-131
Bortolotto, S., Gulotta, D. and Toniolo, L., 2013, La cultura della manutenzione, in Il
Cortile del Richini. Un monumento da salvare, Negri, A., and Tucci, P. (eds.),
Skira, ISBN 8857222141, 239-259
Brimblecombe, P. and Grossi, C.M., 2005, Aesthetic thresholds and blackening of stone
buildings, Science of The Total Environment, 349 (1–3), 175-189
Ghedini, N. et al., 2011, Atmospheric aerosol monitoring as a strategy for the preventive
conservation of urban monumental heritage: The Florence Baptistery,
Atmospheric Environment, 45 (33), 5979-5987
Price, C., 2007, Predicting environmental conditions to minimise salt damage at the Tower
of London: a comparison of two approaches, Environmental Geology, 52 (2), 369374
Toniolo, L., Zerbi, C. and Bugini, R., 2009, Black layers on historical architecture,
Environmental Science and Pollution Research, 16 (2), 218-226
Della Torre, S., 2003, La conservazione programmata del patrimonio storico architettonico.
Linee guida per il piano di manutenzione e consuntivo scientifico, Guerini e
Associati, ISBN 8883353595
Watt, J. et al., 2009. The Effects of Air Pollution on Cultural Heritage, Springer Science &
Business Media, ISBN 9780387848938
Weber, J., Beseler, S. and Sterflinger, K., 2007, Thin-section microscopy of decayed
crystalline marble from the garden sculptures of Schoenbrunn Palace in Vienna,
Materials Characterization, 58(11-12), 1042-1051
1144
ENVIROMENTAL MONITORING AND SURFACE TREATMENT
TESTS FOR CONSERVATION OF THE ROCK-HEWN CHURCH
OF ÜZÜMLÜ, CAPPADOCIA
C. Iba1*, Y. Taniguchi2, K. Koizumi3, K. Watanabe4, K. Sano5,
C. Piao6 and M. Yoshioka1
Abstract
A project at Üzümlü Church (St. Nichita’s church: the end of the seventh century AD) in
the Red Valley in Cappadocia, Turkey, has been launched to establish a suitable method for
conservation of the extremely soft and fragile tuff structure of the church through geo- and
environmental-engineering techniques. This project aims to find a method for prolonging
the life of the tuff structures of Cappadocia using material that allows retreatment and is
chemically compatible with the original tuff. To understand the cause and factors of rock
weathering, in situ environmental monitoring was conducted, particularly focusing on heat
and moisture flow in the rock structure and underground. From the results, it seemed that
freeze–thaw cycles would not occur frequently and would not severely damage the
structure. Erosion by water infiltration derived from rain or melting snow appeared to be
more harmful to the rock structure; therefore, prevention of infiltration by liquid water is
emphasised in our project. An outdoor exposure test was launched to evaluate the
effectiveness and aging characteristics of a water-repellent consolidant. To quantify the
degree of weathering, stainless steel nails were anchored to the rock surface and their
lengths were measured by local collaborators every few months using a digital calliper. The
water repellents had the effect of at least delaying deterioration. This case in Üzümlü is
certainly a most technically difficult challenge and could serve as a model case for new
approaches to integrating, presenting and advancing ethical conservation in Cappadocia.
Keywords: rock weathering, fragile tuff, environmental monitoring, surface treatment,
water repellent
1
C. Iba* and M. Yoshioka
Department of Architecture and Architectural Engineering, Kyoto University, Japan
iba@archi.kyoto-u.ac.jp
2
Y. Taniguchi
Faculty of Humanities and Social Sciences, University of Tsukuba, Japan
3
K. Koizumi
Department of Global Architecture, Graduate School of Engineering, Osaka University, Japan
4
K. Watanabe
Department of Environmental Science and Technology, Mie University, Japan
5
K. Sano
D&D Corporation, Japan
6
C. Piao
Hytec Inc., Japan
*corresponding author
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1. Introduction
In 1985, Cappadocia was selected as a UNESCO World Natural and Cultural Heritage Site
under the name ‘Göreme Natural and Historical National Park’ (UNESCO 1985). In this
region, there are many rock-hewn churches, which often contain reliefs and wall paintings
dating from Byzantine and later periods that constitute part of their historical value.
However, the fabric of these churches, which acts as bodies and supports of wall paintings,
is severely damaged and collapses occur due to weathering and seismic activity every year.
The unique landscape of Cappadocia is composed of soft, fragile tuff. The structure of this
rock suffers from stone powdering, spalling and other types of deterioration caused or
exacerbated by wind and rain erosion and insolation stresses. Particularly during winter, the
region receives fairly high levels of rainfall and snowfall, which may cause freezing and
thawing and other severe surface problems, resulting in rapid weathering at a rate of 0.4–
2.5 mm/a (Erguler 2009).
Earlier, the problems of acute cracking and erosion were commonly addressed by applying
a lime-cement-based render over the tuff surface as a tentative measure, since no proposed
water repellents seemed to be convincing for realistic application (Idil 1995). Although
trials were conducted using an iron mesh at the capping-tuff rock interface, detachment
between them always occurs because of possible water infiltration and thermal impact by
intense solar radiation (Yorulmaz et.al 1995). None of the surface treatment and capping
have not been effective at reducing the rate of tuff erosion. Often, intense intervention does
not allow future treatments and fails to provide continuous preservation.
This project aims to find a suitable method for prolonging the life of Cappadocia’s fragile
tuff structures to preserve these valuable sites. This method is expected to slow the speed of
erosion by application of material that is chemically compatible with the original tuff and
does not involve covering the tuff with foreign material. We also aim to allow
‘retreatability’ in at least 10-yr intervals.
The Üzümlü Church (Fig. 1) in the Red Valley, a stand-alone rock-hewn church, was
selected for this case study. The church shows deterioration phenomena such as severe
cracking, surface disintegration and exfoliation caused by the environment, rock
composition and tectonic activity as well as biological and human activities including
continuous vandalism. The church structures have not been treated in the past, providing a
unique opportunity for this type of study.
a)
b)
Fig. 1: Üzümlü Church (a) Appearance in winter (b) Environmental monitoring stations.
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To consider the mechanism of rock weathering and preservation of rock structures, water
and heat flows in the rock should be measured. Temperature and moisture behaviour in the
soil and rocks were monitored at the base of Üzümlü Church. The micro-environment of
the church interior and surroundings was also monitored. Based on the monitoring data
obtained over 12 months, some types of alkoxysilane-based water repellents with
consolidation properties (Permeate® HS-360) were selected for in situ tests to evaluate
their effectiveness and aging characteristics.
2. Environmental monitoring
To understand the environment around the church, meteorological data, indoor temperature
and humidity, soil water content, soil water potential and temperature were measured
throughout the year.
2.1. Measurement outline
A set of environmental monitoring stations (Onset HOBO U30-NRC) for monitoring air
temperature (T), relative humidity (RH), rainfall, wind speed/direction and solar radiation
were installed near Üzümlü Church (Fig. 1b). Additionally, two sets of data loggers, HOBO
U23 for RH/T, were placed in the church to monitor the indoor thermal environment. One
logger was placed in the alcove near the entrance (Fig. 2 (Entrance)), and the other was set
in Room 3 (Fig. 2 (Interior)). Two small pits (15 × 15 cm2) were trenched on the south
(sunny) and north (shady) sides of Üzümlü Church. As shown in Fig. 2, soil water (5TE)
and potential (MPS2) sensors were horizontally inserted into the rock wall at three different
depths (50, 100 and 300 mm) in each pit. The pits were refilled with the original soil. All
data were recorded every 10 min.
Fig. 2: Installation of environmental sensors.
2.2. Outdoor/Indoor/Ground temperatures
Fig. 3 shows the outdoor and indoor temperatures and global solar radiation (including
direct and diffuse sky radiation) and the underground temperature (shady side, 300 mm
depth). There are large diurnal temperature variations in the outdoor air. The temperature
fluctuations in the church are smaller than those outside. The temperature near the entrance
is notably affected by the outdoor air due to ventilation, whereas in Room 3, it slightly
fluctuates owing to the heat capacity of the thick rock. Furthermore, the outer wall in Room
1, located on the southwest side of the church, is exposed to more solar radiation than
Room 3, located on the northern side. We considered that the critical temperature
associated with frost damage to soil or rock is approximately -4°C based on previous
studies (Fukuda 1974, 1983). Such situations were observed only four times in the 2014–
2015 season, significantly less often than that assumed.
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Fig. 3: Outdoor/indoor temperatures and solar radiation (September 2014–June 2015).
The underground temperatures on both the sunny and shady sides of the church are shown
in Fig. 4, focusing on the winter season (December–February 2014). On the sunny side,
diurnal temperature fluctuations were observed in the soil near the ground surface (50 and
100 mm depth), which may result from the effect of direct solar radiation. The temperature
at 300 mm depth on the sunny side was on average a few degrees centigrade higher than
that on the shady side. The underground temperature deeper than 50 mm below the ground
surface did not fall below zero even in the coldest season. From these results, freezing
appears to not penetrate the ground.
Fig. 4: Underground temperature during winter (December 2014–February 2015)
(a) Sunny side (b) Shady side.
2.3. Wind speed and direction
The upper part of Fig. 5 shows wind roses, which indicate the wind direction frequency in
each direction in each season (except for summer) for both daytime and night time.
Particularly in autumn and spring, there is a clear difference in the wind rose between
daytime and night time. Interestingly, since its installation, the weather station has
consistently shown the prevailing wind direction to be north–south around Üzümlü Church
(September 2014–May 2015) probably owing to the geological setting of the Red Valley.
One of the reasons for the daily wind direction change might be caused by the surface
temperature change of the slope behind (north of) the church. An updraft can occur near the
back slope, producing a south wind. The lower part of Fig. 5 shows the cumulative
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frequencies of wind speeds for daytime and night time. In this area, moderate wind speeds
were usually recorded, although relatively strong winds blew, mainly in the daytime, from
the south. When there was slightly heavy rain (over 2.0 mm/10 min.), the wind speed was
generally less than 1.5 m/s from autumn to spring. Therefore, apparently, the influence of
wind direction and speed on moisture transfer in the soil or rock can be ignored in the
analysis of erosion and frost damage.
Fig. 5: Wind direction and speed near Üzümlü Church (September 2014–May 2015).
2.4. Soil water content, potential and temperature
Fig. 6a shows the soil water potential (depth: 50 and 300 mm) at the sunny and shady sides
of the church and the precipitation measured at the weather station. When the soil is dry,
the water potential has a large negative value. Soil water flows because of a potential
gradient (Fig. 6b); therefore, the direction of water flow under the ground surface can be
determined from the potential difference between depths of 50 and 300 mm.
Fig. 6: Underground water potential (a) Time profile from September 2014 to July 2015 (b)
Schematic of moisture flow due to water potential gradient.
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Until the end of November 2014, water appeared to flow downward on both the sunny and
shady sides. After heavy rain at the end of November, the water potential at all measured
points rapidly increased. During winter (December–April), the water potential at each depth
remained high due to periodic small precipitation, and the potential gradient became nearly
zero. After April, the potential in the deeper area decreased, leading to downward water
flow. In June, heavy rain appeared to occur and the potential at 50 mm depth steeply
increased, then gradually increased at 300 mm depth. During summer, the moisture in the
area near the ground surface was prone to evaporate and upward water flow was observed.
Similar tendencies were observed in both sunny and shady sides. Based on these conditions,
we can infer that the church structure did not continuously suck up significant amounts of
groundwater in this area regardless of the solar radiation intensity.
In contrast, a few intervals of heavy rainfall were observed in this area, which could cause
severe erosion of the fragile tuff structure. Therefore, coating with a consolidant/water
repellent and reducing water infiltration to the structure are considered to be very effective
for preventing degradation.
3. Rock consolidation/water repellent test on small rock masses
Based on the environmental monitoring results, an outdoor exposure test was launched to
evaluate the effectiveness and durability of consolidation by surface treatment agents for
tuff rocks.
3.1. Characteristics of water repellent/consolidant
In this trial, Permeate® HS-360 (D&D Corp.) was selected as a surface treatment agent
after laboratory tests to identify possible consolidants and protective materials for tuff
substrates (Sano and Mizukoshi 2015).
Permeate® is based on alkoxysilane containing a methyl or phenyl group, and an alkoxy
group is polymerised by hydrolysis with atmospheric moisture. After polymerisation, the
3D Si–O–Si structure improves bulk strength by firmly hardening in the gaps within the
object. Moreover, after polymerisation, a methyl or phenyl group is left. As these groups
are hydrophobic, the substance becomes water-repellent after curing. This alkoxysilanebased consolidant does not form a film on the porous surface but penetrates and hardens at
a few millimetres depth. Vapour can permeate through the consolidant layer although liquid
water cannot infiltrate the layer. In practice, hydrolysis takes over 24 h.
3.2. Test rocks and testing method
Two small-scale tuff masses near Üzümlü Church were chosen for the test. Fig. 7 shows the
one (b) that was splayed with the Permeate® HS-360 and the other (a) that was left
untreated as a control. To quantify the degree of weathering of the tuff masses, stainless
steel nails were anchored to the rock surface (Fig. 8a). Two nails were set in each direction
(upper and lower parts) and on the top; i.e. each test rock contained nine nails. The nail
length appearing outside the rock was measured with a digital calliper (Fig. 8b) on both
right and left sides. After anchoring, the measurement error of four different measurements
was checked because the rock surface was considerably uneven. The relative error for the
average value was mostly within 10%. The nail length was measured by local collaborators
every few months. In the ‘control’ mass, weathered tuff powder accumulated below the
rock, and four out of the nine nails fell off the mass in the four months after anchoring. In
contrast, in the ‘treated’ mass, the weathered deposits were generally small and only one
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nail fell off. As flakes of a particular suitable thickness appeared to exfoliate in some places
in the ‘treated ’mass in winter, deterioration might occur if moisture could accumulate in
local areas of the mass. A follow-up examination will consider the possibility of frost
damage.
Fig. 7: Outdoor exposure test rocks: (a) Control (b) Treated mass.
Fig. 8: Quantification of the degree of weathering
(a) Anchoring of a nail (b) Measurement of nail length.
4. Conclusions
To understand the causes and factors of rapid weathering of extremely friable tuff rock
structures in Cappadocia, in situ environmental monitoring has been ongoing since 2014,
focusing particularly on heat and moisture flow in the rock structure and underground.
Freeze–thaw cycles occur infrequently and do not appear to cause severe damage to the
structure. Furthermore, upward moisture flow from underground to the above-ground rock
structure scarcely appeared in winter, i.e. groundwater would not be sucked up and supplied
to the structure. From the results, we concluded that prevention of rainwater and infiltration
water from melting snow from outside are the most appropriate measures to be taken in the
project.
For that purpose, some outdoor exposure tests were carried out beforehand in Japan to
assess the efficiency of the water repellent/consolidant. The test sample without water
repellent broke in two weeks and collapsed in four weeks, whereas the sample with water
repellent retained its shape for three months (Sano and Mizukoshi 2015). Following the
results, an outdoor exposure test has been started in Cappadocia to evaluate the
effectiveness and aging characteristics of the consolidant. The water repellents had the
effect of at least delaying deterioration. The degree of weathering will be quantitatively
evaluated through the project.
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Both method and materials must be compatible with the original materials and implemented
on a minimal scale to avoid excess and unnecessary treatments. Moreover, it is necessary to
carefully verify whether a surface treatment might cause different damage or exacerbate
deterioration of the rock structure. Although infrequent, frost damage could occur in this
region. Detailed investigation of heat and moisture flow will be performed using
computational analysis in future.
Due to similarities in the original technique and deterioration with other sites in
Cappadocia, this study will have relevance for a wider region. The case in Üzümlü is
certainly a technically difficult challenge and could serve as a model for new approaches to
integrating, presenting and advancing ethical conservation in the Cappadocia region.
Acknowledgements
The authors would like to express their appreciation to MEXT/JSPS KAKENHI
(24101014) and the Kajima Foundation for their financial support on this project. The
Üzümlü project has been supported by numerous individuals in both Turkey and Japan,
especially staff members of the Nevşehir Restoration and Conservation Regional
Laboratory Directorate: Hatice Temur, Ayça Baştürkmen, Uğur Yalçınkaya, Alev Elçin
Cankur, Merve Aziz Işın, Mustafa Toptepe, Tuğba Eryaşar. Director of the Nevşehir
Museum: Murat Ertuğrul Gülyaz. Director of the Niğde Museum: Fazıl Açıkgöz and
Ibrahim Sakınan and family.
References
Erguler, Z.A., 2009, Field-based experimental determination of the weathering rates of the
Cappadocian tuffs, Engineering Geology, 105, 186-199.
Fukuda, M., 1974, Rock weathering by freezing-thawing cycles, low temperature science
(in Japanese), Low temperature science. Series A, Physical Sciences, 32, 243-249.
Fukuda, M. 1983, An experiment of freeze-thaw cycles of rock specimens (in Japanese),
Low temperature science. Series A, Physical Sciences, 42, 163-169.
Sano, K. and Mizukoshi, S., 2015, II-5 Preliminary aging tests (outdoor environment) of
consolidants for tuff rock samples, in Scientific Studies on Conservation for
Üzümlü Church and its Wall Paintings in Cappadocia, Turkey, Taniguchi, (ed.),
Annual report on the activities in 2014, University of Tsukuba, 37-41.
UNESCO, 1985, Structural conservation of Göreme. Göreme, land of fairy chimneys.
Ministry of Culture and Tourism, Turkey. General Directorate of Antiquities and
Museums.
Yorulmaz, M., Ahunbay, Z. 1995, Structural Consolidation of El Nazar Church, In The
Safeguard of the Rock-Hewn Churches of the Göreme Valley (Proceedings of an
International Seminar, Ürgüp, Cappadocia,Turkey, 5–10 September 1993), 135–
142. Rome: ICCROM, 1995.
Idil, A, Ç., 1995, Testing three products in Göreme valley, Cappadocia, In The Safeguard
of the Rock-Hewn Churches of the Göreme Valley (Proceedings of an
International Seminar, Ürgüp, Cappadocia,Turkey, 5–10 September 1993), 143–
149. Rome: ICCROM, 1995.
1152
TIME TESTED REPAIRS: A REVIEW OF 11 YEARS OF
CEMENTERY STONE REPAIR
M. Jablonski1*
Abstract
We have completed the stone repairs. We have finished the job and walked away. However,
how long will our repairs last? Rarely is there an opportunity to answer this question.
Published information on the durability of outdoor stone treatments over time is minimal as
there is little or no monitoring of exterior stone repairs. There is often little chance to
evaluate the work five or ten years later. Stone repairs in cemeteries offer an opportunity
for evaluation if it is known what materials were used and how they were applied. Many
treatments and repairs made to cemetery markers are used on stone buildings and
cemeteries are relatively easy to access. While stone cemetery markers are smaller and
more exposed than many stones on buildings, they still provide insight into the durability of
repairs over time. This paper examines pinning and grouting repairs made in four
cemeteries in the Mid-Atlantic region of the United States.
Keywords: cemetery, pinning repairs, grouting repairs, sandstone, marble
1. Introduction
The idea for this paper evolved out of a project my company; Jablonski Building
Conservation (JBC) has been working on for three years, Prospect Cemetery in Jamaica,
Queens New York City. JBC has repaired 43 markers. As our firm returns each year for
the next phase of work, it is possible to see what repairs are successful and which are
failing. Everyone talks about reviewing their past work but it is difficult to find the time
and permission to do so. I decided it was time to look back at work that I was involved in
over the last 11 years. There are of course lessons to be learned. This paper will examine
two important types of repairs, pinning and grouting as they are repairs that can have the
most impact on historic fabric.
For an architectural conservator, the goal of our work is to stabilize and slow the rate of
deterioration. We follow the ethic of “Do no harm”. Cemetery repairs strive for a
minimalist treatment that will have the least impact on the historic stone of the marker. The
ideal repair is minimally invasive and retreatable. Interventions should be removable if
necessary with the minimal amount of damage should they fail. However, in order to do no
harm, we need to know the efficacy of our treatments and the failures of treatments that
have occurred.
1
M. Jablonski*
Jablonski Building Conservation and Columbia University, United States of America
mjablonski@jbconservation.com
*corresponding author
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The two treatments discussed in this paper were selected for review because they can be
damaging. Mechanical pinning requires drilling holes into the stone to receive the pins.
Even if the pins are later removed, original fabric is still lost. Injecting grout into voids or
cracks does not always allow for the removal of failed grout without seriously damaging
the marker.
2. Cemeteries Included in this Study
2.1. Bottle Hill Cemetery Main Street Madison, NJ
Bottle Hill Cemetery has grave markers dating from the mid-eighteen century to the early
twentieth century. It contains almost 2,000. The cemetery is owned and administered by
the Presbyterian Church of Madison, NJ and is made up of two historically separate
cemeteries, the burial ground of the Presbyterian Church of Madison and the Hillside
Cemetery. Over a three year period, from 2005 to 2007 JBC provided conservation
treatments to 97 markers. The conservation treatments were extensive and included
pinning as well as grout repairs. The markers conserved were a mix of zinc, sandstone and
marble with the majority of them, 67, being sandstone.
2.2. Whippany Burying Ground, Whippany, NJ
The Whippany Burying Ground is located in Hanover Township in New Jersey. It has
graves dating back to at least 1718 making it one of the oldest cemeteries in New Jersey.
There are approximately 450 graves at the site. Jablonski Building Conservation worked
on 25 markers between 2005 and 2008. Most of these markers were sandstone markers and
the treatments included both pinning and grouting repairs.
2.3. Orient Cemetery, Orient, NY
The Orient cemetery, located at the northern tip of Long Island dates to the early nineteenth
century. In August of 2006, a car crashed into an Orient cemetery and mowed a path
through the cemetery damaging 16 markers; 14 marble and 2 sandstone. JBC was retained
in 2007 to conserve and stabilize the damaged markers. Four of the marble markers were
smashed into 20 to 30 pieces each, and the two oldest brownstone markers in the cemetery
were shattered into approximately 10 pieces each. After the cemetery was searched, various
pieces were carefully matched and the markers were pinned together and conserved. The
pinning was extensive and complicated due to the number of fragments.
2.4. Prospect Cemetery, Queens, NY (New York City)
Prospect Cemetery is in the Jamaica section of the borough of Queens in New York City
and was established in 1668. Markers to be conserved were selected by the Prospect
Cemetery Association and repair specifications were completed by another conservator.
Many of the repairs were made to early sandstone markers, particularly those in danger of
losing the face of the marker due to delamination of the sandstone. In addition to grouting,
an alternative treatment to pining, the installation of stainless steel armatures, was
undertaken.
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3. Pinning
3.1. Pinning Criteria
The basic criteria for architectural pinning repairs are: pins should not corrode, the adhesive
should not stain the stone, the repairs should be aesthetically pleasing, and none of the
materials should cause harm.
Conservation pinning repairs must be kept simple. In order to retain as much historic fabric
as possible, the drilling of holes should be kept to a minimum. The size and number of pins
used should be based upon the shear and tensile strength requirements of the stone being
repaired. While it would be ideal to test the materials for each application, this is
frequently not viable so judgements are made by each conservator. Many of the tests
carried out and reported on in the journals and in thesis work have all been performed in the
laboratory (Glavan 2004 and Wheeler et al. 2010).
Stones have been repaired with pins since ancient times. Traditionally, pins were wrought
iron or bronze. In the later part of the 20th century, threaded nylon pins threaded stainless
steel and ceramic pins came into use. A consideration when selecting pins is that cemetery
markers often sustain impact damage. Traditionally lime mortar or lead were used to hold
pins in place. By the end of the twentieth century epoxy resin adhesive was extensively
used for exterior repairs.
3.2. Pinning Methodology
All of the pinning repairs examined for this study are concealed, blind pinning repairs made
using stainless steel threaded pins. The pins are made by cutting stainless steel rods to the
size of pin required. When making a blind pin repair, holes of equal depth are drilled into
each of the two surfaces. Adhesive is placed in each hole, then pins are inserted into the
holes and the two pieces are adhered with an adhesive at the joined surfaces. For the
cemeteries in this study, either Akimi Akepox 2040 or 5000 were used as the adhesive.
Both of Akepox 2040 and Akepox 5000 are designed for use with damp stones. The
Akepox 5000 is designed to be more stable in ultra violet light. Once the adhesive has
cured, the joint at the break is patched to keep the adhesive from contact with ultraviolet
light and to match the stone surface. The pins are threaded to increase the bond between the
pin and the adhesive. The adhesive then holds the pin in place ensuring lateral stability of
the repair. There has also been testing of adhesives in the laboratory but little examination
of exterior stone adhesives in situ over time (Muir 2008).
3.3. Pinning Failures
Pinning treatments generally fail by breakage of the pin, breakage of stone around the pin,
or pullout of the pin. Failure of the pin will depend on the size of the pin and the type of
pin material. Tensile failure is often assumed to be unlikely as the expected stresses
associated with differential movement are far less than the tensile strength of the pins.
However, impact damage can create tensile forces greater than those of low strength pins.
Stone is also susceptible to cracking and breaking from the pins. This can be caused by
placing pins too close to an exterior surface or spacing the pins too close together. This type
of failure can also occur in cases where the properties of the pin, such as modulus of
elasticity and thermal expansion coefficient, are not compatible with the stone. Research
undertaken by George Wheeler (Wheeler 2010) has noted when pins are installed and touch
the marble, micro-cracking at the pin hole can occur.
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Most of the failures found in older repairs occurred in the marble markers. However, due
to what appears to be human interaction with these failures, it is not possible to evaluate
how much the pin itself has impacted the failure in the cemeteries reviewed.
Pinning failures were found in thin marble markers in the Orient cemetery which was the
only cemetery where pinning repairs were made to thin markers. Marble markers are more
likely to have surface disintegration and intergranular disaggregation than granite or
sandstone. This makes drilling the holes more difficult and the adhesion of the broken
sections more challenging as there is little sound surface to adhere the broken components.
Cracking and breakouts are common characteristics found in pinning failures where there
has been impact damage by vehicles, mowers, and vandalism. Thicker sandstone or marble
markers are more durable and able to take impact damage better than the thin stones.
Two of the marble pinned markers in the Orient cemetery failed 8 years after treatment. As
with many failed pinning treatments, these markers were thin marble, one marker was 2
inches in depth and the other 2 ½ inches. When the cemetery was examined two years ago,
both markers were intact. Currently the two markers are lying on the ground, each in a
different direction, and they are broken again along some of the pinned breaks. It is not
clear exactly what happened but it appears some human factor was involved. A pin was
bent on one marker and stone is still attached to top of the pin in a pattern similar to failure
in a pull- out test.
Another mode of failure found during the survey, is failure of the adhesive. The bond
between the adhesive and the stone was either weak to begin with or the bond to the stone
never occurred. An examination of the breaks in the Orient failure may be a failure of the
epoxy adhesive in the repair. Some of the epoxy adhered to the stone and it was well
adhered to one pin in each stone. The epoxy did not adhere to the top hole in one stone and
the bottom hole in another. In addition, the adhesive along the break minimally adhered to
the bottom stone, and not to the top. Also the epoxy had yellowed on all surfaces including
where it nominally adhered to the stone. It is supposed to be colorless. The cross-section
of the epoxy was examined under the microscope and is not yellowed. It was also noted
during the microscopic examination by Helen Thomas, a conservator at Jablonski Building
Conservation, that the surface of the epoxy has the imprint of the stone, even if there was
no adhesion. This is the same epoxy, Akepox 2040, that was used in all other cemeteries
included in this study. However, conservators have recently been discussing the issue of
this epoxy yellowing when used for sculpture repair in New York City. In one example, a
stone patch repair on a fountain yellowed within months of its application.
It would appear that the markers may have been “bumped” and the failure of the epoxy
contributed to the failure of the repair. Luckily the stone was minimally damaged except
where it was pulled apart at the one pin. There was no cracking of the stone and the
adhesive failed before the stone cracked.
3.4. Successful Pinning Repairs in Sandstone and Marble
Stones with a depth of more than three inches have successful pining repairs whether the
stone is marble or brownstone. The 10 year pin repairs to sandstone and marble markers in
Bottle Hill Cemetery, exhibited no failures. Three sandstone and the 7 pinned marble
markers including a large obelisk were in excellent condition. There was one very complex
sandstone repair of a horizontal 4 inch slab in that had been broken into 10 pieces remains
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completely intact 10 years later (Fig. 1). In addition, a pinned brownstone marker that was
found toppled in the cemetery survived intact. All pinning repairs in the Whippany
cemetery are also intact, for the marble and brownstone. The marble markers at Whippany
were all thick marble greater than 3 inches in depth. Eight marble markers were pinned at
the Orient cemetery as part of their treatment and 6 are still in good condition are both of
the sandstone pinning repairs.
Fig. 1: Vault Slab with Pinning Repair 10 years later.
3.5. Alternate Solutions to Pinning Thin Marble Markers
Our firm remains wary of pinning thin marble markers and is trying a new solution: a
stainless steel armature (Fig. 2). Stephanie Hoagland, a conservator at Jablonski Building
Conservation saw a similar armature in a cemetery and modified the design. We have only
been using these armatures for three years but to-date, they appear to be working well. The
armature supports markers externally by holding them intact. There is no drilling or
adhesives used. This type of armature is used for any marker that is less than 2 inches in
depth as these are impossible to pin.
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4. Grouting
4.1. Grouting Criteria
Injection grouting is a typical method for reattaching delaminating stone layers and filing
voids and small cracks in historic masonry. It has been used for cemetery repairs for many
years. The conservation requirements for grout are: it be injectable, stable, able to
mechanically bond with the stone and be chemically compatible with the stone. There must
also be minimal, if any, shrinkage of the grout.
Fig. 2: Armature supporting thin marble marker in Prospect Cemetery.
4.2. Grouting Methodology
Many of the earliest extant markers in the Northeastern United States are a form of brown
sandstone called “brownstone”. The face of the sandstone markers is carved and can be
quite elaborate in their decoration. In addition to giving information about the deceased,
these stones can be masterpieces of folk art with occasionally the name or initials of the
carver. At the Bottle Hill cemetery, there were a number of stones signed by a very
prominent carver in New Jersey, Ebenezer Price and his workshop. Price was born 1728
and was one of the most skilled and prolific gravestone carvers in colonial America, Price's
work began to appear in the burial grounds of northern New Jersey in 1757 (Sarapin 1994).
One of the major deterioration problems with sandstone is delamination or separation along
the bedding plane of the stone. Sandstones are sedimentary stones formed in layers through
deposits of mineral or organic particles. Weakly joined sedimentary planes when exposed
to weather, have a tendency to separate along the planes. If the stones are placed so that
they are faced bedded, the bedding planes are at right angles to the position they had in the
ground. Weathering can deteriorated the less compacted sedimentary layers causing the
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stone to delaminate. Delaminating sandstone markers faces pose serious conservation
challenges. It has even been suggested that the service life for some of these stones is
only100-125 years (McGinley Kalsow 2012).
Removing deteriorated stone from the delaminating layers and voids is the most difficult
process. It must be removed or consolidated in order to ensure proper adhesion with the rest
of the stone. Deteriorated stone is flushed from the voids out through port holes as best
possible. An attempt is made to keep the port holes as small but they have to be large
enough for debris to be flushed out of them. It can be difficult to remove all the
deteriorated stone. Also these holes can be visually intrusive.
After cleaning the void is grouted. The grout needs to be as low viscosity as possible in
order to flow into the void. Too much water though will result in shrinkage of the grout as
it cures. The port holes are made into the stone at the void to clean it are used to grouted it
from the bottom up with syringes. Many of the grouts are difficult to keep at a low
viscosity in the syringe. Where deteriorated stone is left, the bond between the grout and
sound stone is not very good. Where the face of the stone had come off either before or
during the treatment of a marker, and the deteriorated stone can be almost completely
removed, the repairs are quite solid 10 years later.
4.3. Grouting Failures
Bottle Hill Cemetery in New Jersey has 10 year old repairs. Sixty-seven stones were
grouted with Jahn M40 (manufactured by Cathedral Stone Products, Inc.). It is a nonshrinking grout formulated to repair cracks and voids approximately 5 mm to 15mm and is
completely mineral based. In 2015, 35 or 52% have failed where the grout has debonded
from the stone, cracked, crumbled or all three (Fig. 3 is one example). 22 or 33% are
seriously deteriorated where it sounds hollow behind the repairs and the patching over the
grout has failed. 10 repairs or 15% appear to still in good sound condition. It should be
noted that the mortar caps failures over the grout repairs were approximately 90% but these
mortar repairs did not fail when they were used on stone without the grout. The grout
repairs at the Whippany Burying Ground had similar failures and a 90% failure rate.
Because the success of grouting repairs is dependent on the stone, markers with substantial
friable layers of deterioration may not be treatable. Conservators aim for minimal
treatments which limits aggressive treatments. When the faces delaminate, they can be
cleaned and most of the deteriorated stone can be removed and the faces readhered. Where
these treatments were performed in Whippany and Prospect Cemeteries they have so far
been successful. However, it remains exceedingly difficult to predict which stones can be
successfully grouted. The voids vary for each marker in size and location. Each marker
collects debris as well as the grains of disaggregating stone in varying amounts and size.
Flushing this debris out of small openings is not always effective. One stone in Prospect
Cemetery had snails living in a void. They did not wish to remove themselves and it was
not until the grout failure caused the face of the stone to delaminate that they were
removed. There is also the questions of whether washing the voids may also be
contributing to further deterioration of the already disaggregated stone.
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Fig. 3: Grouting Failure at Bottle Hill Cemetery.
Injecting grouts into a hidden void does not allow for control over the flow and location of
flow. It is difficult if not impossible to determine if the entire void has been grouted, if the
void is only in one layer, or if there are more voids behind the one closest to the surface.
There are serious concerns about whether grouting may cause more damage to the stone by
accelerating the delamination rather than leaving them to deteriorate. Mortar caps on the
grout deteriorate at a much quicker rate than the caps over stone. Often the mortar caps are
gone or cracked which raises concerns. Is the grout contributing to further deterioration of
the already deteriorating stone?
Grouting may be the last resort treatment for some stones. Grouting treatments will
continue for delaminating sandstone markers when there is no other solution and only
where the treatments can be monitored over time. Therefore, monitoring will continue for
the Void Span repairs yearly to see if this product lives up to its promise.
4.4. Grouting Successes
In 2013 at Prospect cemetery, 10 stones were grouted. A working sample or mockup was
made using a mix of St. Atier’s natural hydraulic lime (NHL) 3.5, sieved through a #50
mesh and added casein powder as needed. The grout failed as areas that had been filled
sounded hollow several days later. Next, a mocked up was made using a lime sand and
micro-balloon mixture. Again, the grout treatment failed. The following year, a new
commercially available product, Void Span PHLc Grout, produced by VoidSpan
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Technologies, LLC, was tested. This grout is a breathable, ultra- low shrinkage, flowable,
self-consolidating grout for use in filling cracks and voids in older masonry structures.
Based on a pozzolanic hydraulic lime as per ASTM C1707, it is a low- to-moderate
strength adhesive, filler and mortar replacement material. One year later the grout appears
to be working well in the 10 markers grouted with the Void Span PHLc.
Earlier grouting success appeared to occur where there was more control over removal of
deteriorated stone, mainly when the faces or portions of the faces of the stone were
separated from the stone. In addition, there were two stones at Bottle Hill Cemetery that
appeared to have a different minerology and the grouting repairs on these stones is still
solid.
4.5. Alternatives to Grouting
As it is difficult to predict the success of a grout treatment, it is therefore necessary to
examine other solutions to treating delaminating parallel layers of stones. One treatment is
to install a lead cap over the top of the stone. We have been using these for the last two
years and as long as the squirrels do not eat the lead, they work very effectively.
Fig. 4: Lead cap over delaminating sandstone marker.
5. Conclusion
It must be recognized that a repair may eventually fail or be detrimental to the marker. We
should also consider that we might want to wait to treat stones when we are not sure of the
outcome as there is the possibility that future materials, methods, and technologies may
offer better treatment choices. Ultimately, the effectiveness of treatments performed on
cemetery markers relies on quality of the stone, as well as the quality of the work, repair
techniques, and performance of materials used to make the repairs.
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Examining old treatments has shown that pinning repairs do appear to work in many
instances although pining thin marble markers is not necessarily a good idea. Grouting
repairs have not had a very good track record. It may be that new products coming out on
the market will assist in making these more durable repairs. Time and monitoring of
treatments will tell.
When we leave the cemetery, we need to leave a monitoring and a maintenance plan
behind. Too often there is the belief by the owner that the conservation treatments do not
need any further attention. We know products fail; the execution of the repairs can be
faulty; and common techniques may be damaging. It is only through monitoring we will
truly understand what treatments have withstood the test of time.
References
Bradley, Susan. “Strength testing of adhesives and consolidants for conservation purposes.”
Adhesives and consolidants. N.S. Brommelle et al., eds. London: International
Institute for Conservation of Historic and Artistic Works, 1984. 22-25.
Glavan, J. 2004. An evaluation of mechanical pinning treatments for the repair of marble at
the Second Bank of the United States. Master’s Thesis. University of
Pennsylvania, Philadelphia.
Grimmer, Anne E. Glossary of historic masonry deterioration problems and preservation
treatments. Washington, DC: National Park Service, Preservation Assistance
Division, 1984.
McGinley Kalsow & Associates. Brownstone & Masonry Repairs and Exterior Historic
Structures Report: Concord Town House. 22 Monument Square, Concord, MA
01742. November 8, 2012.
Muir, Christina. 2008. Evaluation of Pinning Materials for Marble Repair. Master’s
Thesis. Columbia University, New York, NY.
Riccardelli, Carolyn, George Wheeler, Christina Muir, George Scherer and Joe Vocaturo.
An examination of pinning materials for marble sculpture. Objects Specialty
Group Postprints, Volume Seventeen, 2010. 95-112.
Sarapin, Janice Kohl. Old Burial Grounds of New Jersey: A guide. Rutgers University
Press, 1994. 26.
Wheeler, George “New Insights on Pinning Fractured Marble”. Talk presented at APTI
Conference: Layers Across Time. Denver 2010.
Zinsmeister, H, etal, 'Laboratory Evaluation of Consolidation Treatment of Massillon
(Ohio) Sandstone', Association for Preservation Technology Bulletin, 20:3, 1988
1162
THE CURRENT STATE AND FACTORS OF SALT
DETERIORATION OF THE BUDDHA STATUE CARVED ONTO A
CLIFF AT MOTOMACHI IN OITA PREFECTURE OF JAPAN
K. Kiriyama1*, S. Wakiya2, N. Takatori3, D. Ogura3,
M. Abuku4 and Y. Kohdzuma5
Abstract
The Motomachi stone-cliff Buddha is located in Oita prefecture, Japan. It was engraved
onto a soft-welded tuff cliff around the 11th to 12th centuries. At this site, salt crystallisation
is a major factor causing deterioration of sediments, especially during winter. This paper
attempts to discuss the relationship between the behaviour of salt and environmental factors
at the Motomachi stone-cliff Buddha site. We conducted four seasons of environmental
research, analysis of dissolved ions in the groundwater, and salt analysis. Results suggest
that a drop in temperature and vapour pressure due to the opening of the doors, combined
with water intrusion within the high-water-content stone could be causes for salt
crystallisation at this site.
Keywords: salt deterioration, Sodium sulphate, Calcium sulphate, environmental research,
solubility, shelter
1. Introduction
Salt crystallisation is one of the most common causes for the occurrence of stone
deterioration. Recent studies have investigated the effect of temperature and relative
humidity on in-situ salt crystallisation (Bionda 2004, Zehnder and Schoch 2009). However,
the behaviour of salt, especially in-situ salt crystallisation, remains controversial. In Japan,
major methods to prevent salt crystallisation include using polymers to strengthen the stone
surface and lowering of groundwater levels. However, the issue of an ideal environment to
restrain salt deterioration awaits further investigation. This paper attempts to investigate the
1
K. Kiriyama*
Graduate School of Advanced Integrated Studies in Human Survivability,
Kyoto University, Japan
kiriyama.kyoko.24n@st.kyoto-u.ac.jp
2
S. Wakiya
Nara National Research Institute for Cultural Properties, Japan
3
N. Takatori and D. Ogura
Graduate School of Engineering, Kyoto University, Japan
4
M. Abuku
Faculty of Architecture, Kinki University, Japan
5
Y. Kohdzuma
Nara National Research Institute for Cultural Properties, Japan
*corresponding author
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relationship between salt behaviour and environment at the Motomachi stone-cliff Buddha
and aims to consider measures to prevent salt deterioration.
2. Background of the Motomachi stone-cliff Buddha
The Motomachi stone-cliff Buddha is located in Oita prefecture, Japan. It was engraved
onto a cliff of soft welded tuff around the 11 th to 12th centuries and was covered by a shelter
which was built during later periods (figure 1). The entrance of the shelter faces east. At
this site, salt crystallisation especially in winter (figure 2) is a major factor causing
deterioration. Powdering and scaling occur on the surface of the stone. A previous
investigation identified thenardite and mirabilite by X-ray diffractometry (XRD) (Oita city
board of education 1996). Although a drainage tunnel and drainage well were built in order
to lower the groundwater levels as a conservation measure, an increase in the amount of salt
was reported after this construction.
3. Methods
To investigate the environmental effects on salt crystallisation, environmental research,
analysis of dissolved ions in the groundwater and analysis of the salt deposit were carried
out over several seasons (1 August 2014, 8 November 2014, 8 February 2015, 18 April
2015, 2 August 2015).
3.1. Environmental research
To investigate the interior environment of the shelter, the interior temperature, relative
humidity, and ventilator frequency were measured, in addition to meteorological
observations. Fig. 3 indicates the locations of door-opening/closing sensors, temperature
and relative humidity data loggers, and the weather station. Temperature and relative
humidity were measured inside and outside the shelter from November 2014. The counts of
door-opening/closing were measured from February 2015. Local meteorological data was
measured from February 2015 at the weather station.
Fig. 1: View of the site from distance.
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Photographed: 27-Oct-2011
Photographed: 12-Feb-2014
Fig. 2: Seasonal changes in salt deposit.
Fig. 3: Measurement points.
3.2. Dissolved component analysis of the groundwater
To evaluate the effect of groundwater on salt crystallisation, dissolved ions of groundwater
were analysed quantitatively by ion chromatography during each season as noted above.
Water-sampling was conducted at the drainage well and observation hole (Fig. 4a). The
drainage well is located in front of the shelter and the observation hole is located behind the
stone-cliff Buddha. The sampled water was transported in a cold state and filtered with 0.45
μm nuclepore filters for analysis. Further, data of annual changes in groundwater tables
were provided by Oita City records.
3.3. Salt analysis
Salt was observed during all field surveys. The salts were identified by X-ray diffraction
during each season. The sampling points are shown in Fig. 4b. These points were selected
in order to compare the salts between different horizontal points, where they appeared to be
in different forms, and different vertical points in which the water content ratio appeared
differs.
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a)
b)
Fig. 4: a) Water sampling points (drainage well and observation hole);
b) Salt sampling points.
4. Results and Discussion
4.1. Observation
According to these observations, it appears that salt crystallisation was concentrated in the
lower part of the surface of the stone. The distribution of crystallised salt could be affected
by water movements. The elevation of the bottom of the stone Buddha and the drainage
tunnel is around the same. Therefore, water may have flowed from the ground into the
stone. Since salt crystallisation was observed in areas that have deteriorated on the surface
of the stone (along a joint or on an exposed surface by scaling), it is suggested that salt was
concentrated here owing to high permeability.
4.2. The interior environment of the shelter
Fig. 5 shows the exterior and interior temperature and absolute humidity throughout the
year. The annual and diurnal fluctuations of the interior temperature and absolute humidity
(Fig. 5) reveal that the shelter has a low degree of airtightness. Figures 6 show temperature
and absolute humidity both inside and outside the shelter during summer and winter period.
The door-closing periods are shaded. During summer and winter, when the doors were
opened, the interior absolute humidity exhibited the same behaviour as that noted in the
exterior. On the other hand, when the doors were closed, the interior absolute humidity was
higher than that of the exterior. If absolute humidity decreases the amount of water
evaporation from stone will increase. Water evaporation promotes salt crystallisation.
Therefore, the opening of the doors may be a factor in salt crystallisation.
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Fig. 5: Inside and outside temperature and absolute humidity.
a)
Summer
b)
Winter period
Fig. 6: Absolute humidity and temperature both inside and outside the shelter.
The closed-door periods are shaded in grey.
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4.3. Effect of groundwater
The result of the analysis of the groundwater is given in Figures 7a and 7b. Sulphate,
calcium and sodium ions, that are the origins of gypsum and thenardite, are detected in the
water. The concentration of ions dissolved in the observation hole water is prone to be
higher than that of the drainage well except for sodium and potassium ions. There are few
seasonal changes in the concentration of ions. This means that the inside environment of the
shelter has an effect on salt crystallisation in winter. Fig. 8 shows the groundwater table of
the observation hole and the precipitation in 2014. The water level seems to be constant at
1-2m above the drainage tunnel except for during continuous rain. The fluctuation within
each season cannot be observed. Therefore, the water level may not have an effect on
seasonal changes in salt crystallisation (as mentioned in background).
a)
b)
Fig. 7: a) Results of ion chromatography of the water from the drainage well; b) Results of
ion chromatography of the water from the observation hole.
Fig. 8: Groundwater table of the observation hole and precipitation.
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4.4. Environmental effects on salt crystallization
The results of the XRD are presented in Tab. 1. Thenardite and gypsum were identified. We
could not collect salt at the points where salt crystallisation usually occurs in winter, as
these were protected by a paper pulp to desalinate the surface layer. The solubility of
calcium sulphate has less temperature dependence. Further, the equilibrium relative
humidity of the calcium sulphate saturated solution is around 99% at normal temperatures.
Therefore, once it crystallised, it is likely that calcium sulphate could have remained on the
surface of the stone in a crystallised state all year long. Therefore, the statement that ‘salt
crystallises in winter and disappears in summer’ as stated in a report (Oita city board of
education 1996) implies that the salt is the soluble sodium sulphate.
Sodium sulphate has two stable phases at room temperature: thenardite (an anhydride) and
mirabilite (a decahydrate). Fig. 9 illustrates a phase diagram for sodium sulphate and the
temperature and relative humidity of daily averages inside the shelter. The continuous lines
indicate the boundaries of the stable phases (Flatt 2002). The temperature and humidity
cross the phase boundary due to annual and diurnal changes. This diagram implies that the
inside environment facilitates damage to stone caused by phase changes and crystallisation
of sodium sulphate. However, this does not correspond entirely to the accrual situation,
which is the disappearance of sodium sulphate crystallisation in the rainy season and in
summer. Some reasons to be considered include decreasing solubility with a drop in
temperature and the concentration of soluble salt.
As regards calcium sulphate, it could appear to be ineffective as compared to sodium
sulphate as it may not repeat the process of crystallisation and disappearance. However,
before repairing the shelter, photos show water intrusions from a crack in the roof that wet
the stone surface during rains. In addition, the high water content of the stone in the lower
parts as well as intrusive water could have made it easy for the slightly soluble calcium
sulphate to move to the surface.
Tab. 1: Result of XRD studies.
01-Aug-14
08-Nov-14
08-Feb-15
18-Apr-15
No.1
Thenardite
Thenardite,
Gypsum
Thenardite
Thenardite,
Gypsum
-
-
No.2
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
No.3
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
No.4
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
No.5
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 9: Phase diagram for sodium sulphate and temperature and relative humidity
of daily average inside the shelter, based upon data from Flatt (2002).
5. Conclusion
To investigate the relationship between salt behaviour and the environment, environmental
research, dissolved ions analysis of the groundwater and salt analysis were carried out for
each season. The results suggest that door-opening, a drop in temperature and water leaking
into the high-water-content stone could be the three factors for salt crystallisation to occur
at the Motomachi stone-cliff Buddha. Proposal of an ideal environment for the preservation
of the stone-cliff Buddha is the subject of further study.
Acknowledgements
We are grateful to the Oita-city board of education for the image of stone-cliff Buddha
(Figure5) and the groundwater table of the observation hole. This work was supported by
JSPS KAKENHI Grant Number 26709043[Grant-in-Aid for Young Scientists (A)]
References
Bionda, D., 2004, Methodology for the preventive conservation of sensitive monuments :
microclimate and salt activity in a church, Proceedings of the 10th international
congress on deterioration and conservation of stone, Daniel Kwiatkowski and
Runo Löfvendahl (eds.), Stockholm, ICOMOS, 2, 627–634.
Flatt, R. J., 2002, Salt damage in porous materials: how high supersaturations are generated,
Journal of Crystal Growth, 242, 435-454.
Oita
city board of education, 1996, Kunishiteishiseki Oitamotomachisekibutsu
Hozonsyurijigyo Hokokusho (in Japanese), oita, sohrinsha.
Zehnder, K. and Schoch, O., 2009, Efflorescence of mirabilite, epsomite and gypsum traced
by automated monitoring on-site, Journal of Cultural Heritage, 10, 319–330.
1170
THE DURBAR SQUARE AND THE ROYAL PALACE OF PATAN,
NEPAL – STONE CONSERVATION BEFORE AND AFTER THE
GREAT EARTHQUAKE OF APRIL 2015
G. Krist1, M. Milchin1* and M. Haselberger1
Abstract
The Durbar Square and the Royal Palace of Patan (Nepal) constitute one of the seven
World Heritage Monument Zones of the Kathmandu Valley. In 2010, the Institute of
Conservation, University of Applied Arts Vienna, joined the conservation project of the
Royal Palace, run by the Kathmandu Valley Preservation Trust (KVPT). The subsequent
cooperation between the Institute and the KVPT has over the years resulted in the
conservation of numerous monuments of stone, wood, metal, ivory and other materials.
When dealing with the stone monuments, the greatest problems conservators were faced
with were structural issues resulting from frequent earthquakes and subsequent inadequate
repairs, combined with the extreme climate of the region. Attention was given to the
removal of inappropriate materials. A brick dust lime mortar was used for the pointing of
the joints, instead of the cement rich mortar which was invariably used in repairs executed
in the second half of the 20th century. To improve the resistance to future seismic activities,
stainless steel pins and clamps were used when reassembling. This presented a novelty (in
the way of doing things). During the severe earthquake of 25th April 2015, also known as
the Gorkha earthquake, and the subsequent one of 12th May, many monuments in the
Valley were damaged. The impact on the Patan Durbar Square and the Royal Palace was
equally devastating. A preliminary survey revealed that the monuments which were
recently treated by the Institute, endured without major damage. On the other hand, many
of those still carrying marks of old repairs were now in dire need of a treatment. Given this
scenario, a conservation project, extending up to 2018, was drafted. Works would be
carried out by the Institute together with Nepalese partners, and with the financial support
of the Austrian government.
Keywords: conservation, earthquake, Kathmandu Valley, Patan, stone
1
G. Krist, M. Milchin* and M. Haselberger
Institute of Conservation, University of Applied Arts Vienna, Austria
marija.milcin@uni-ak.ac.at
*corresponding author
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1. Introduction
The bilateral relations between Nepal and Austria, especially in the field of heritage
preservation, have a long tradition. It started when Eduard Sekler (Harvard University) first
visited Kathmandu Valley in 1962. Subsequent trips, in association with UNESCO, resulted
in the ‘Master Plan for the Preservation of Cultural Heritage of the Kathmandu Valley’ and
the inclusion on the World Heritage List. The first visit of Gabriela Krist (University of
Applied Arts Vienna) and Manfred Trummer (Museum of Applied Arts Vienna) in 2010,
kick-started the presently ongoing cooperation between the Institute of Conservation and
the Kathmandu Valley Preservation Trust (KVPT). From 2010 to 2014, thirteen small
monuments from the Patan Durbar (=Royal) Square and the Royal Palace, one of the seven
monument zones of the Valley, were successfully treated and conserved (Krist et al. 20102014). In 2015, two devastating earthquakes hit the Kathmandu Valley. A new outlining of
priorities was required, and a three-year project (2015-2018) to preserve earthquakedamaged cultural heritage was drafted by the Institute of Conservation together with local
partners and is funded by Austria1. The following report discusses the challenges of the
previous conservation campaigns and the solutions which were eventually used, after the
severe earthquakes.
2. Nepal’s Challenges
The extreme climate conditions, heavy biological colonization, and the distortion of the
structures, are among the main problems of the monuments in Patan. The latter is explained
by cycles of demolition (partial or total) through frequent earthquakes and the efforts to
repair, rebuild and/or restore. The high amount of water available during the monsoon
period combined with the stones’ physical properties, not only favour the fast growth of
microbiology, but also higher plants.
2.1. Material and Structure
Two different stone materials were used for the monuments of the Durbar Square and
Palace of Patan. The first one is a very porous and capillary-active siliceous sandstone. The
grain is fine and the colour can vary from whitish to ochre. In general, the stone is very
homogenous, though some of the blocks show distinct bedding. Tooling marks on the
blocks indicate a very fine workmanship which was only possible due to its homogeneity
and softness. Analysis on stone samples2 in Vienna included thin section microscopy, both
in polarized and unpolarized light, SEM investigations, as well as porosity measurements
and petrographic characterization. In addition, prisms were used to measure the water
absorption after a 24 hour immersion, water absorption coefficient, and the drying rate. The
results show water absorption of 10% to 18% and a water absorption coefficient from 5.25
to 30.2 kg/m2h0.5 (Fuchs 2013). Despite the big differences in the water uptake, these high
values show that the stone is very absorptive in all directions. This property can also be
directly related to the usual damage. Decay through microbiological growth and salt
contamination presents the biggest problem. Sanding, scaling and alveolar decomposition
1
Funding partners: Austrian Development Agency (ADA); the Austrian Federal Chancellery (BKA);
the Federal Ministry for Europe, Integration and Foreign Affairs (BMEIA V, North South Embassy
Project - BMEIA VII); Eurasia-Pacific Uninet (EPU).
2
Katharina Fuchs, Institute of Conservation and Prof. Johannes Weber, Section of Conservation
Sciences, Institute of Art and Technology, University of Applied Arts Vienna, 2012-2013.
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are some of the most common manifestations. Monuments built up of the siliceous
sandstone consist mostly of small blocks that can be carried by a single worker. Originally,
no mortar pointing or metal pins were used. The bonding between singular blocks was
established by simple adding an occasional natural resin dash in the joints. The gaps
between the blocks were so small that the carving sometimes continues over more blocks,
regardless of their dimensions.
Fig. 1: Decay patterns and typical construction of monuments
made of the siliceous sandstone.
The other stone material which was employed, is dense, heavy and grey (light grey to
almost black) in colour. It is a weakly metamorphic material containing a high
concentration of silicates in foliations, surrounded by a very fine grained siliceous marble.
Though the water uptake for this kind of stone was not measured, it can safely be assumed
to be very low. All forms of decay that can be traced to the influence of water are very
superficial. The majority of damage patterns were in all probability caused by mechanical
impact (e.g. different cracks and/or missing parts). The structures made from this material
consist of blocks which are much larger in scale and often contain stone dowels in vertical
structures (e.g. columns and pillars). Even in this case, no bedding or pointing mortar was
used. Both construction methods make the monuments extremely vulnerable during
earthquakes. Distortions are caused as horizontal and/or vertical connections between the
single blocks are only partly given.
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Fig. 2: Decay patterns and typical construction of monuments
made of the metamorphic stone.
2.2. Climate
The climate of the Kathmandu Valley is characterized by heavy rainfall in the monsoon
period and no frost in winter; this favours biological growth (Leiner 2011). Stone surfaces
are covered not only with algae and bacteria, but also with moss. Plants grow within joints
and cracks, where earth and dust has accumulated. Due to the high water uptake and slow
drying rate of the porous sandstone, surfaces remain mostly wet during the rainy season
(Fuchs 2013). The microbiological growth is much stronger here than on the very dense
surfaces of the metamorphic stone.
2.3. Introduced Materials and Recent History
Of the frequent, more-or-less intense earthquakes and apart from the recent quakes of 2015,
the one of 1934 was the last disastrous one. It destroyed a large extent of Patan’s historical
centre. Most of the damage we are faced with today is directly related to materials and
methods used in the course of the twenty years it took to rebuild, reconstruct and restore the
structures affected by the earthquake of 1934. Blocks were sometimes swapped or
completely discarded, and pointing mortar containing very little aggregate – instead of the
traditional natural resin mentioned earlier – was introduced in the joints. In all cases, a low
quality Portland cement was used as a binder (Leiner 2011). As happened elsewhere at the
time, this material was seen as a solution for any situation, and as we now come to expect,
the mortars turned out to be too hard, dense and stiff, and over the course of the years,
damaged the surrounding stonework. Moreover, the copious amounts of water in
combination with the capillary-inactive joints, allowed the blocks to remain wet for a
longer period of time, thereby accelerating deterioration through bio-colonization and salts
(Leiner 2011).
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3. Conservation Campaigns 2010 – 2014
The situation of the stone monuments before the treatments carried out between 2010 and
2014 can be summarized as follows: damage as distortion, cracks, breakages and missing
parts are a result of seismic activity. Repair in various phases has caused further decay
since inappropriate materials, particularly pointing mortars were used. Due to the mild
winter climate and excessive rainfall in the monsoon season, bio-colonization plays an
important role in the overall deterioration mechanism. The aim of the conservation
programme considered international standards which were adapted for the Nepalese
context. The preservation of the structures and surfaces is imperative. The concept for the
conservation had to be applicable in the extreme climatic situation of the Kathmandu
Valley and consider the restricted availability of conservation materials. Additionally, the
appearance of the previously treated surfaces and structures (brick and stone walls, wood
constructions and roofing systems) had to be considered and an additional strengthening of
structures envisaged. During the first four years, the following stone monuments were
treated: the Bhandharkhal Tank pavilion; the stone lions at the Tank; two gate-keeper lions;
the Tusha Hiti ritual bath and two stone relief gates. Wherever possible, the treatments were
carried out in cooperation with local craftsmen. As the majority of the objects needed a
dismantling, a very important first step was the graphic documentation - mapping and
labelling of all elements. The dismantled blocks were cleaned with water and brushes;
mortar remnants, paint spots and thick biological films were reduced mechanically. A
biocide treatment (quaternary ammonium salts, 1-3%) was necessary in preparation for
further works. Blocks with obvious salt damage or those with cases of strong salination
were treated in water baths using monsoon rain (Fuchs 2013). Missing parts were
reconstructed/ carved in stone as indents (Dutchmen) by local stone masons (Fuchs 2013).
This proved to be a good solution since a high level of craftsmanship is still widely
practiced in Nepal. This type of collaboration has the added advantage of contributing to
the preservation of skills as intangible heritage. As a final step, the elements were
reassembled. An important aspect of the conservation was to reduce water infiltration and
improve the stability of the structures to withstand future earthquakes. Where possible,
foundations were dried-out (Leiner 2011) and monuments were reassembled with an air
draft separating them from the brick walls behind them (Fuchs 2013). Pins and clamps were
used to additionally strengthen the structures. Anti-seismic rings were introduced by
connecting the blocks of one specific course with stainless-steel-clamps. The rings
themselves were connected to each other at the corners by using pins. For the pointing of
the joints, a lime-brick dust mortar was used. It worked well in the climate of the valley and
performed satisfactorily with the stone used.
4. The Earthquake and the First Response
In April and May 2015, the Kathmandu Valley experienced two devastating earthquakes,
claiming more than nine thousand human lives and injuring over twenty-two thousand
people.1 The 2015 earthquakes can be considered the worst natural disaster in Nepal since
1934. An estimated total of 2,900 structures of cultural and religious value and major
monuments of the UNESCO World Heritage - including the Durbar Squares of Kathmandu,
Bhaktapur and Patan - were severely damaged or collapsed completely. The emergency
1
Nepal Earthquake, Post Disaster Needs Assessment, Executive Summary, published by the
Government of Nepal, National Planning Commission, 2015.
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response, security and clean-up measures in Patan, started immediately after the
earthquake. Valuable objects - such as wood carvings, gilded metal sculptures and stone
reliefs, and remnants of collapsed temples on the Durbar Square - were brought to the Patan
Museum courtyards and documented. With financial support from the Austrian
government, temporary storage could be built to safely store these objects. Damaged
building structures were secured with wooden beams and roofs were covered with
tarpaulins to reduce water infiltration during the coming monsoon. A fact-finding mission
in June 2015 by two conservators from the Institute of Conservation recorded the extent of
the damage and set priorities for the future work of the Institute. The assessment of the
destruction at Patan’s Durbar Square and Palace can be summarized as follows: two
temples and two rest-houses collapsed completely, several other buildings are still
endangered and had to be secured. Additionally, two pillars with important fire-gilded
sculptures (Lion and King Yoganarendra) collapsed. The stone pillars themselves are partly
broken and/or fissured, the metal sculptures deformed and disfigured. Two roof tops of
buildings that are part of the Royal Palace partly collapsed and had to be dismantled.
Exterior walls of the Palace have been damaged and parts collapsed.
5. Conservation after the Earthquake 2015
Within a working campaign in August/September 2015 – being already the sixth of the
Institute – first important measures on selected objects made of stone as well as metal and
ivory could be implemented. Furthermore the seismic performance of the previously treated
monuments was evaluated.
5.1. Evaluation of the Performance of Past Treatments
It could be concluded that the treatments done in the period between 2010 and 2014
performed well. All of the monuments are still standing and no major damage could be
found. Even after a more detailed investigation only one single crack between the pointing
mortar and the stone block on one of the relief gates of the Palace’s façade facing the
Durbar Square can be associated with the earthquakes.
5.1.1. Treatments
After the earthquake predominantly monuments made of the grey dense marble-like stone
required treatment, whereas those made of sandstone represented the problematic cases in
the period before 2015. There are three possible reasons for this: firstly, most of the
monuments1 made of the porous sandstone were treated shortly before the earthquake and
measures were taken to improve the seismic stability of the structures. This however, seems
to have worked quite well. A second reason is due to the nature of the material. While the
sandstone is very porous and cracks easily stop in pores, the metamorphic stone is very
dense and rigid so that the propagation of cracks and fissures occurs rapidly. Thirdly,
blocks of different sizes behave differently during seismic activity. The sandstone
monuments are made of rather small blocks and therefore the number of joints in the
structure is high. This results in a relatively malleable structure which can deform easily
without damage to the single blocks. The structures made of the metamorphic stone contain
much larger blocks, and when this is combined with the rigid and dense material, greater
1
Bhandarkhal Tank pavilion, two lion sculptures in the Palace’s garden, two lion sculptures in front
of the Mul Chowk, two stone relief gates at the Palace’s façade.
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cracking and fragmentation occurs. Two objects made out of the grey dense stone and the
treatments which were adopted will be discussed.
5.1.2. Hari Shankar
The almost one and a half metre sized sculpture of the god Hari Shankar, stood at the heart
of the Harishankar Temple on the Durbar Square. This collapsed completely in the course
of the earthquake. As a result, the sculpture broke in two. A diagonal crack separated the
figure of the god at waist level, and smaller sculptural details broke off. In the campaign of
2015, the two broken parts were glued together with epoxy resin (Akepox 2020, Akemi)
and two stainless steel pins. Layers of dust, dirt and remnants of offering were reduced
mechanically and with the use of different solvents. A missing attribute of the god was
reconstructed using a stone indent (on request of the local authorities) to improve
readability. Joints and gaps were pointed with adequate mortar.
5.1.3. The Pillar of the Lion Statue
The smallest of the three freestanding pillars on the Durbar Square of Patan partially
collapsed during the course of the earthquake(s) and only the lowest part of the shaft
remained standing. The large upper part of the shaft was broken in two. Work on the pillar
started early to avoid further damage, since the bigger fragments were already being used as
an ad hoc bench or market stand on occasions. The smaller upper stone parts as well as the
metal lion sculpture on its top were recovered from the debris soon after the first
earthquake. In the course of the campaign the broken shaft was glued together using the
same epoxy resin and three stainless steel pins. The missing parts of the capital were
reconstructed in the same stone and mounted with stainless steel pins and epoxy resin. The
remaining gaps were pointed with a matching mortar. All surfaces were cleaned with water
and solvents.
Fig. 3: Partly collapsed pillar used as market stand (left), gluing of broken parts (right).
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
During the course of the work, many technological details came to light. For instance, it
became amply clear that the column had already collapsed in part during the last big
earthquake of 1934. Moreover, the cement paste found in the upper joints was corroborated
with the extensive reconstruction phase carried out in the 1950s. It was decided to remove
the cement based mortar and to re-use the original construction method without joint
mortar. This way, the structure will be rendered less rigid – and consequently more resistant
to seismic action. Also, the device used originally to fit the lion sculpture on top of the
column was renewed.
Fig. 4: Concept for the reassembling of the Lion Statue.
It can therefore be concluded that the stone structures treated by the Institute of
Conservation between 2010 and 2014 were hardly damaged by the earthquakes of 2015. In
general however, monuments made of the metamorphic stone were affected more severely
and require more attention than the ones made from the porous sandstone.
6. Outlook
During the campaign of 2015, four metamorphic stone objects damaged during the
earthquake were treated. The pillar of the Lion Statue will be reassembled in 2016.
Particular attention will be given to the second monument on the Patan Durbar Square
which also collapsed - the pillar of King Yoganarendra Malla. Even though the two pillars
are different in size, both situations are similar. With a height of about 8 m, the King’s
pillar is almost double the height of the Lion’s. The extreme weight of the singular pieces is
of great concern. As good fortune would have it, this pillar did not break, and there is very
little mechanical damage to be observed. The greatest issues however, are the numerous
cracks and fissures that can be seen on the individual stone blocks, primarily on the shaft
pieces. Ultra-sound velocity measurements shall be used to assess the cracks and to decide
whether these require treatment before reassembly. In general the treatment should be
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similar to the one of the Lion’s pillar. The close cooperation with local craftsmen and
architects continues to be of great importance after the earthquake, as the understanding of
the original constructions and the reconstruction of missing parts prove to be essential.
However, the lacunae in the field of conservation cannot yet be covered from the Nepalese
side - this gap is presently occupied by the team of the Institute of Conservation from the
University of Applied Arts Vienna.
Acknowledgements
Many thanks are due to our partners: The Kathmandu Valley Preservation Trust and its
staff, particularly Dr Rohit Ranjitkar; the Austrian Development Agency (ADA); the
Austrian Federal Chancellery (BKA); the Federal Ministry for Europe, Integration and
Foreign Affairs (BMEIA); and Eurasia-Pacific Uninet (EPU). Thanks are due to Prof.
Johannes Weber for the microscopic analyses of the different stone materials and mortars.
Heartfelt thanks also go to all individuals involved in the project during the past six years.
References
Fuchs, K., 2013, Bitumen Coating on Stone, a Nepalese Problem? - The Conservation of
Two Stone Relief Gates at the Nasal Chowk, Patan Royal Palace, pre-thesis,
University of Applied Arts Vienna, Austria.
Fuchs, K., 2014, The Royal Place in Patan, Nepal - Evaluation of the conservation
treatments and recommendation for a maintenance program, diploma thesis,
University of Applied Arts Vienna, Austria.
Government of Nepal/National Planning Commission, 2015, ‘Nepal Earthquake, Post
Disaster Needs Assessment, Executive Summary’ and ‘Vol A: Key Findings’,
reports, Nepal.
Henry, A., 2006, ‘Stone Conservation: Principles and Practice’, Donhead Publishing,
Dorset, Great Britain, ISBN 978-1-87339-478-6.
Krist, G., et al., 2014, ‘Patan Royal Palace (Nepal) - Conservation campaigns 2010-2014’,
unpublished reports, University of Applied Arts Vienna, Austria.
Leiner, S., 2011, Der Pavillon am Bhandarkhal-Tank. Palastkomplex Patan, Nepal, prethesis, University of Applied Arts Vienna, Austria.
Sekler, E.F., 2001, Fragen architektonischer Authentie am Fuss des Himalaya, ÖZKD, 4,
389-403.
Sekler, E.F., 1979, Use of collective space in Patan and other historic towns of the
Kathmandu Valley, Nepal, Monumentum, XVIII-XIX, 97-107.
United States Geological Survey (http://www.usgs.gov, accessed 2nd October 2015).
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1180
RESTORING THE PAST EXPERIENCE OF STONE MASONRY IN
BURKINA FASO FOR FOSTERING THE USE OF LOCAL
MATERIALS
A. Lawane1, A. Pantet2*, R. Vinai3 and J.H. Thomassin1
Abstract
A number of associations, companies, and research institutions are currently working
together in Burkina Faso in order to promote the valorisation and the reuse of laterite
dimension stones (LDS). In this study, old masonry constructions such as schools and
churches built during colonisation period in the city of Dano, situated near the borders of
Ivory Coast and Ghana, were examined. This article gives a description of old and often
abandoned constructions, where dimension stones are however generally well conserved.
At first, a specific classification for laterite masonry able to describe the observed
pathologies is presented. Subsequently, possible cultural causes that could explain the
current state of these constructions are derived, through a survey carried out among local
people. Eventually, a classification for LDS, based on geo-mechanical studies carried out
on material from four local quarries of laterite, is proposed. Three quality grades were
defined and agreed according to local technicians and professionals. Therefore, based on
the traditional experience and on results from geo-mechanical studies, a revamp of the use
of local materials for urban and suburban constructions, both for new buildings and for the
restoration of ancient construction in West Africa, should be fostered, in line with general
principles of sustainability in building construction.
Keywords: laterite, index quality, masonry, vernacular architecture, guidelines,
African local houses
1
A. Lawane and J.H. Thomassin
LEMC, International Institute for Water and Environmental Engineering, Rue de la Science, 01 BP
594 Ouagadougou, Burkina Faso
2
A. Pantet*
LOMC, University Le Havre, COREVA Building, 53 Rue de Prony, BP 540, 76058 Le Havre
Cedex, France
anne.pantet@univ-lehavre.fr
3
R. Vinai
School of Planning, Architecture and Civil Engineering, Queen’s Univ. Belfast, David Keir
Building, 39 Stranmillis Rd., Belfast BT9 5AG, United Kindom
*corresponding author
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1. Introduction
Sub-Saharan Africa is undergoing deep demographic changes. People are moving to the
cities and African population will be more urban than rural by 2030. Housing has been
recognised as one of the most important and essential need after food and water. Housing
construction is a major source of employment and can give an economic propulsion with
creation of jobs in Africa, as a significant component of developing countries’ economies.
Building technology is still extremely labour intensive.
The construction of decent housing is a key component of social development and has
major impacts on health conditions in urban areas, coupled with access to safe drinking
water supplies.
The need for locally manufactured building materials has been emphasized in many
countries. Conventional building materials are expensive and have a high environmental
impact (Chevalier 2009). In order to address to this situation, attention has been focused on
alternative local building materials. In subtropical zone of the Earth, laterites are very
common materials. These can be exploited under two forms, as a soft soil or hardened soil
respectively. In this latter case, the hardened laterite can be used for masonry purposes. A
number of sites exist in the World, like Angkor Temples in Cambodia, the Fortress of
Loropéni in Burkina Faso, and the National Monument in Angadipuram in India, which are
famous due to the use of laterite. Many quarries have been exploited since long time,
initially manually and more recently with mechanical equipment, and laterite dimension
stones (LDS) are usually cut for being used as masonry elements (Indian Standard
Specification 3620, 1998).
This study focused on the valorisation of this local material. It was carried out with the
following objectives:
- To determine the physical and mechanical properties of the material, which can
vary in a wide range due to the very complex weathering processes (that have led
to the laterite formation or happened in the laterite after deposition) that can vary
for each laterite layer. A quality index has been defined, and the best use of LDS
was optimised accordingly. Quality control is therefore of primary importance,
also considering that today testing procedures are available and easily performed
in any civil engineering work.
- To examine the structural behaviour of masonry buildings, taking into account the
state of conservation of the materials used for construction. The structural
performance of masonry wall structures can only be understood if the history of
their construction, their geometry, and the characteristics of the masonry material
are known.
This paper provides a relevant case study, demonstrating that laterite stone masonry
construction can be developed in Burkina Faso for simple, one-storey housing or, when
coupled with concrete frames, for more complex building.
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2. Presentation of the site of the study
The investigation focused on a region in the Southwest of Burkina Faso, West Africa. The
site, (see Fig. 1), is located in Dano in the IOBA Province, about 230 km southwest of
Ouagadougou, on the N12 in Gaoua direction and about 50 km from Loropeni site. In the
region, the laterite stone is commonly used for the construction of masonry buildings.
Laterite, which has reddish brown colour, is a residual rock, and it is the product of subtropical weathering on many rocks. The term laterite is restricted to highly weathered
material rich in secondary form of iron, aluminium, poor in organic content. Laterite is
usually found as superficial layers such as thick ferricretes, typically observed in the
landscape. It is commonly found on top of flat hills or as boulders on slope surfaces. The
weathering profiles developing from different parent rocks exhibit the following upward
succession of layers: saprolite, mottled clay and ferricrete.
The region has a tropical humid climate characterised by a dry season (November to April)
and a rainy season (May to October). Monthly average temperatures ranged from a
minimum of 24.7°C in August to maximum values of 31.9°C in May (as measured in
2006). Long term mean annual precipitation is 926 mm. Eighty percent of the annual
rainfall was recorded from June to September. Precipitations during this season are
characterised by strong and short storms mainly occurring during the evening. The
vegetation cover consists of a semi-humid forest and savannah. A hydrographical network
developed on the plateau. Vegetable gardening flourished in the flood plain created by an
earth dam.
Fig. 1: Site location on Burkina Faso map and Google Earth view of the town of Dano.
The town of Dano was selected for this research due to the existence of several quarries of
laterite, either excavated by hand (for local market and simple self-construction housing) or
with semi-industrial techniques, for local residential market or for trading.
3. Production of laterite dimension stones (LDS)
Physical properties of LDS vary considerably from place to place (Kasthurba and
Santhanam 2005 – Lawane et al., 2014). A careful selection of the laterite stone is
necessary in order to ensure its suitability for masonry construction. In order to provide a
guidance, many studies indicated minimum requirements in terms of compressive strength.
Being soft and porous when freshly extracted, laterite usually hardens if adequate
stabilisation is ensured, i.e. under atmospheric conditions but not exposed to rain. The
blocks shall be tested for compressive strength, but also for water adsorption, and specific
gravity should be measured as well. Stone blocks shall present no cracks, cavities, clay
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veins or others imperfections. The shape of the blocks shall be regular and uniform, with
straight and rough edges at right angle.
A classification of LDS, with three quality grades, based on geo-mechanical studies carried
out on four quarries of laterite and agreed among technicians and professionals was
proposed in Tab. 1. The normalised compressive strength is defined by: 𝑓𝑏 = 𝑅𝑚 ∙ 𝛿 ∙
𝜒where: Rm, the compressive strength (MPa) - , shape factor and curing or drying
conditions coefficient, (Eurocode 6, 2013).
During the excavation of laterite stone, a high volume of waste (around 25 to 30 per cent of
the total laterite) is generated as scraps. This leads to operational problems, since such
material needs to be removed for further excavation. An alternative, added-value option for
this waste rock is to use it as aggregate for the manufacture of concrete blocks.
Tab. 1: Quality index for LDS.
fb (MPa)
>4
2-4
1-2
compact
Grade 1
Grade 2
Grade 3
granular
Grade 2
Grade 3
Grade 3
4. Survey on housing typology in the Dano town
4.1. Background
The town is developed along a main street, with densely built houses (in the form of
buildings with a courtyard), distributed on each side. The spatial structure of the old centre
is more or less determined by the related economic life (markets, handicraft, workshops,
and bars). The expansion of the centre developed in many peripheral zones such as the
administration area (new town hall, school, museum, and hotel), two religious institutions
(cathedral and mosque) and many residential areas.
Tab. 2: Summary of results from building survey (for localization see Fig. 1).
Concrete frame
Materials
LDS
Masonry
Sand -concrete
Banco
Mix
LDS
Centre
9%
10%
18%
60%
2%
Dakole
34%
18%
17%
9%
23%
Two zones have been investigated to compare construction materials used for the
households (or “greater family housing” as defined in Africa). Many households from the
extended family (from grandparents to grandchildren) live together in the same courtyard.
Two building modes can be identified: masonry, using earth blocks (banco), LDS or mixed
techniques, or concrete frame with partition walls in concrete blocks (sand concrete). The
distribution and occurrence of each type is reported in Tab. 2. Most houses are built with
self-produced materials. Under the influence of modernisation, straw has been replaced by
galvanized iron roofing sheets (thatched roofing can still be observed in rural areas),
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
whereas traditional bricks, produced with a mix of wet earth, dung and straw or vegetable
fibres, have been replaced by stabilized earth (soil cement) blocks, and most recently by
sand cement blocks.
The majority of housing in the urban centre is composed by buildings partially realised in
earth bricks or adobe with possible addition of straw, connected with mortar made of clay
and sand. The basement and the lower layer of masonry elements are generally built with
LDS. Coating is applied and smoothened to produce a smooth wall surface, which is treated
with plaster (mixture: clay- cement or clay – lime) to achieve some weather protection.
The Dakole sector, more residential, is an area where houses are built in LDS masonry or
with frame structure in concrete, whereas the partition walls are realised with LDS. The
complex of the Drayer Foundationed, a German charity working for children, has been built
in LDS. No coating was applied, because the aesthetic effects and the waterproof qualities
of the laterite were considered satisfactory.
4.2. Construction techniques with laterite dimension stones (LDS)
The construction system with LDS usually follows horizontal and parallel shelves where
medium and large blocks are mainly used. The mortar used to connect the block is either
clay or lime based. Only for the outer walls, the earth is removed on many centimeters and
replaced by cement mortar, to avoid erosion (water or wind) actions (see detailed photo in
Fig. 2). Inner walls are plastered and painted. In the case of building with concrete frame
structure, a floor slab is casted and supported by columns, isolating the roof space.
Ventilation holes are created in the upper layer of the walls.
Fig. 2: Typical houses in LDS, either load bearing masonry or with frame concrete.
5. Diagnosis survey of laterite constructions
5.1. Description of the state of a colonial building
The oldest building realised in LDS that can be found in Dano is a school, built in the
1930’s by the religious Fathers during the last years of colonial period. The building was
left without any maintenance during the post-independence era, leading to severe
deterioration. The building shows a rectangular plan section sized about 40.5×10.5 m, with
a maximum height of 6.25 m. Two corridors, along the northern and southern load-bearing
walls, give access to the aligned classrooms.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
The construction (see Fig. 3) is composed by thick masonry walls (double walls) built with
adobe with lime mortar and coated with plaster (clay and cement), whereas the top layers,
which are exposed to rain and wind, are made with LDS. The load-bearing walls are made
with a mixed masonry of adobe and stone blocks locally quarried. Stone units are connected
together by means of a weak lime and sand mortar. The cohesion between the mortar and
the stone is weak. All different types of masonry in the structure can be defined as solid
masonry.
Fig. 3: Views of the school and CAD representation.
A layer of lime plaster and one of lime wash paint were applied to create smooth surface.
Masonry blocks have small to medium size (L: 20 cm, h: 15 cm, w: 10 cm) with rough
surface, rectangular or square shape. Some of them show a flattened surface. Blocks were
used according to their strength, being the weaker used for filling or for coating, whereas
the stronger were used for structural purposes. A virtual reconstruction view has been
obtained with a CAD application as shown above left in Fig. 3.
A continuous vaulted gallery ran along the two long sides (north and south walls) of the
building. Pupils accessed the gallery from the courtyard. The arches were built with ashlars,
with a stiff structure made up of well carved headers forming a single arch line. The
opening between columns is about 2 m. A wood formwork was presumably used during the
construction. The eastern and western sides show gables, made up of small headers and
long stones on the corners, without openings. The horizontal elements of the flat roof are
made of a mixed construction system with steel profiles for the classrooms and with wood
beams for the corridors. The whole structure was covered with galvanized iron sheets.
On site visual inspection revealed severe damages. The roof structure of the school was
dismantled and partly destroyed. As a result, the vault of the north wall collapsed, and the
building was no longer in an operational state. Bricks from demolition were reused for
foundations, but also as aggregates in concrete. However, the integrity of the existing
arches appears still satisfactory and not affected by the general conditions. No deformation
and collapse of gabble walls was observed, although these were built as a single layer.
There is no evidence that the building collapsed because under dimensioned, or because of
insufficient bearing capacity of the construction material or due to any overload on the
structure.
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5.2. Deterioration processes observed in LDS structures
Masonry defects can be associated with several reasons, from a wrong choice of materials
to an insufficient quality of the workmanship (Bromblet and Association MEDISTONE,
2010). The local climatic impact can also have a role. Main categories of defects and
related causes were defined by direct observations on the surveyed LDS building (the old
school and the houses) in Fig. 4:
- Deterioration of the structure of LDS, by atmospheric agents, such as sandy wind and
rain, affecting surface stone (a). The block can also be damaged by the cracking
associated with the action of water and temperature variation, which facilitates rock
degradation and failure (b),
- Disintegration of lime and sand mortar joints, due to the moisture transfer or water
runoff action and also because the excessive mortar width between the layers and loss
adherence (c),
- Organic deterioration from musk and other plants growth on the lowermost layer of
masonry elements, due lack of drained or ventilated space in the basements (d),
- Cracks due to uneven distribution of the loads.
Fig. 4: Views of the most usual defects observed in LDS structures.
Some of the above mentioned defects can be avoided by controlling the block production.
Good ashlars with rough, parallel surfaces are to be preferred, since these features improve
the joint strength, contribute to an even distribution of the loads and reduce the potential
accumulation of organic material on joints. The quality of the laying of the block is also an
important factor for preventing structure failures. The width of the joints should be kept at a
minimum, and in some cases the laying should be carried out even without joint. The
quality of the LDS is another key point. Top quality LDS seem to be subject to hardening
upon exposure to alternate wetting and drying, but poor to medium quality are not, since
granular morphologies are disintegrated by drying and wetting cycles. Masons must be
careful when choosing the blocks during construction, trying to use them according to their
quality in different places of the structure.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
6. Conclusions
This study aimed at understanding the potentiality of the utilisation of LDS as building
material. The geological study of laterite quarries showed large variability in quality. Such
variability influences the stone availability, and, consequently, has an impact on the
economic viability and safety of the exploitations. All the material extracted from the
quarries (LDS and waste) need to be valorised to their maximum potential.
The fostering of a return of stone masonry constructions poses important challenges
because of the variability of the properties of traditional materials. The assessment of the
structural conditions of old masonry structures, with the definition of damages or defects
categories that can be listed through visual inspections, contribute to indicate the actual
potential of the use of LDS in building, provided that a proper choice of the material is
carried out and proper construction best practises are followed. The quality grade of LDS
must be considered during the construction phase, since higher or lower quality blocks can
be used for different purposes, also depending on the typology of building structure (load
bearing masonry or concrete frame). When both climatic exposure and thermal properties
of the lateritic material are properly considered, masonry structures can provide the
required thermal comfort to dwellers in a sustainable and energy efficient way, provided
that iron sheet roofing is avoided.
Some requirements for improving design guidelines have been proposed. It is however of
utmost importance to increase the knowledge on the building material through laboratory
tests on samples cored on site (for each quarry) and loading tests on buildings at realistic
scale. Systematic analysis of building defects should also be considered as part of a design
approach aimed at overcoming these challenges.
References
P. Bromblet et Association MEDISTONE, 2010 : Guide "Techniques de conservation de la
pierre". Association MEDISTONE.
Chevalier, J, 2009, Analyse du cycle de vie: Utilisation dans le secteur de la construction,
Techniques de l'ingénieur. Environnement, 1 (G5880).
Eurocode 6, 2013, Calcul des ouvrages en maçonnerie - Partie 1-1 : règles générales pour
ouvrages en maçonnerie armée et non armée, NF EN 1996-1-1+A1 Mars 2013.
Indian Standard Specification 3620, 1998, Indian Standard Specification for Laterite Stone
Block for masonry, Bureau of Indian Standards, New Delhi, India, 86, 1-8.
Kasthurba, A. K., and Santhanam, M., 2005, A re-look into the code specifications for the
strength evaluation of laterite stone blocks for masonry purposes, Journal of The
Institution of Engineers (India), 86, 1-6.
Lawane, A., Vinai, R., Pantet, A., Thomassin, J. H., and Messan, A., 2014, Hygrothermal
Features of Laterite Dimension Stones for Sub-Saharan Residential Building
Construction, Journal of Materials in Civil Engineering, 26 (7).
1188
PROTECTION OF MEDIEVAL TOMBSTONES (STEĆCI) WITH
AMMONIUM OXALATE TREATMENT
V. Marinković1* and D. Mudronja2
Abstract
Since 2013 Croatian Conservation Institute has performed research and preliminary
conservation works on medieval tombstones (stećci) on the archaeological site Crljivica
near Cista Velika in Croatia. During the project, tombstones from several sites in the region
of Cista were analysed for provenance study and for protection of stones. Stone
characterisation was performed using mineralogical-petrographical analysis on different
tombstones and surrounding quarries or rock outcrops. Approximately 80% of analysed
stones from tombstones were determined to be biomicritic limestones ranging from
wackestone to floutstone (according to Dunham classification). They were all determined to
be from the upper Cretaceous. Other analysed tombstones were determined to be dolomites.
Some of the surrounding quarries did show the same type of limestones. Concerning the
protection of tombstones, one of the main goals was to create a protective layer of artificial
calcium oxalate on stone surface through the reaction of ammonium oxalate with calcium
carbonate. In order to establish the most effective way of achieving such kind of protection,
research included laboratory testing and in-situ testing. Ammonium oxalate was applied on
the stone by poultice (24 h), brushing method (1, 2 and 3 hours) and total immersion (24 h).
The method of total immersion of stone provided best results, both in laboratory and on
site.
Keywords: medieval tombstones (stećci), stone deterioration, calcium-oxalate,
ammonium oxalate, limestone
1
V. Marinković*
Department of Stone Conservation, Croatian Conservation Institute, Croatia
vmarinkovic@h-r-z.hr
2
D. Mudronja
Natural Science Laboratory, Croatian Conservation Institute, Croatia
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
1. Introduction
Medieval monolithic tombstones called stećci are found on the entire territory of the present
Bosnia and Herzegovina, as well as in parts of Serbia, Montenegro and Croatia. Stećci first
appeared in the second half of the 12th century, but the period of its most intensive
production range from the 14th to the 15th century. One of the most significant sites with
stećci in Croatia is the archaeological site of Velika and Mala Crljivica near village of Cista
Velika in Dalmatian hinterland. Crljivica is located along the road Trilj-Imotski in a length
of 200 meters and contains more than ninety stećci of all types (slabs, chests and ridged
monuments). The entire area is an unique complex of archaeology, history and biodiversity.
Since 2013 Croatian Conservation Institute has performed investigation and preliminary
conservation works on some tombstones on the site Crljivica. Also, some analyses were
done on several other sites with stećci near Crljivica: Lovreć, Zadužbina and Bisko. All the
investigations and some preliminary works were done with the intention to create a
systematic plan for conservation and protection of stećci in the region.
The research was supposed to provide answers to few main questions:
1.) What is the state of preservation of monuments, and is it necessary to start with
conservation works on tombstones?
2.) What is the origin of stones and do all the tombstones have the same stone
provenance?
3.) If tombstones need conservation treatments, what kind of surface protection is the
most compatible with the type of stone, and how to apply it?
After preliminary review of the situation on the site, several types of damage were observed
on the stones. The tombstones on the site are exposed to large temperature changes. In
Dalmatian hinterland winters are wet and cold with large diurnal temperature variation
(from 0 to -13°C during a night). Summer is dray and the temperatures are very high (the
mean is approximately 30°C). Cracks, flanking and lowering of stone surface are mainly
caused by frost, acid rain and extreme temperature changes. These types of damage are
possible to observe by naked eye. The lowering of surface and pitting are caused by
complex mechanisms of biological colonization (lichens, moss and cyanobacteria). This
degradation can be seen only after preliminary cleaning treatment and under magnification.
The presence of harmful salts in the stones was not recorded and it was not proven by
laboratory analysis.
Considering the first analysis it was possible to make plan for materials and methodology
supposed to be used during conservation treatment. After finding natural calcium oxalate
patina on tombstones, it was decided to create artificial layer of calcium oxalate to protect
the stones (Matteini 2008; Doherty et al. 2007). Creation of artificial protective layer was
tried using several methods (Mudronja et al. 2013; Vanmeert et al. 2013). In order to
establish the most effective way of achieving such protection, research included laboratory
testing and in situ testing. Ammonium oxalate was applied on the stone by poultice (24 h),
brushing method (1, 2 and 3 hours) and total immersion (24 h). A method by total
immersion provided best results, both in laboratory and on site.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
2. Materials and methods
From region of Cista, 11 samples of stone from tombstones were taken for mineralogical
and petrographic determination of stone. 7 samples from surrounding quarries and stone
outcrops were also taken for comparison. Samples were taken by small core-drill, 2 cm in
diameter (Tab. 1). After sampling, samples of stone were prepared as thin sections and
analysed by mineralogical-petrographic analysis (MPA) using Olympus BX 51 polarised
microscope.
Tab. 1: Analysed samples.
Sample No.
Place of origin
Analysis type
19163
Lovreć, stećak no.3
MPA
19164
Lovreć, stećak no.4
MPA
19165
Zadužbina, stećak no.3
MPA
19166
Zadužbina, stećak no.4
MPA
19167
Crljivica, stećak no. 70
MPA
19168
Crljivica, stećak no. 691
MPA
19169
Crljivica, stećak no. 182
MPA
19170
Crljivica, stećak no. 11
MPA
19171
Crljivica, stećak no. 12
MPA
19172
Bisko, stećak no. F1
MPA
19173
Crljivica, stećak no. 2
MPA
19516
Crljivica, quarry sample C
MPA
19517
Crljivica, quarry sample D
MPA, XRD
19518
Crljivica, quarry sample E
MPA
19519
Bisko, quarry sample F
MPA, XRD
19520
Bisko, quarry sample G
MPA
19521
Lovreć, quarry sample A
MPA, XRD
19522
Zadužbina, quarry sample B
MPA
20519
Crljivica, stećak no. 62
µFT-IR
20520
Crljivica, stećak no. 62
µFT-IR
20521
Crljivica, stećak no. 62
µFT-IR
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Samples from quarries marked 19517, 19519 and 19521 were determined to be closest
match to tombstones samples. Afterwards, these samples were emerged in solution of 5%
ammonium oxalate (AmOx). 24 hours after, samples were taken out of AmOx solution and
air-dried for 7 days. Subsequently their surface was analysed by phase analysis using XRay diffraction (XRD). Phase analysis was done on flat surface of samples using Philips XPert diffractometer with graded parabolic X-ray mirror using Cu X-ray tube with 45kv and
40 mA.
After laboratory tests, 3 samples (Tab. 1) from tombstone no. 62 were taken by small coredrill 7 days after soaking in 5% AmOx. These samples were then embedded in polyester
resin (Scott Bader A-132 UV), and prepared as cross sections. The cross sections were
analysed from the surface to a depth of 1mm with Ge-ATR using Agilent Carry 660 FT-IR
spectrometer fitted with Carry 610 FT-IR microscope (µFT-IR).
3. Results
Mineralogical-petrographic analysis of stone determined that most of the stećci are made of
limestone. Most of them were determined as biomicritic limestones ranging from
wackestone to floutstone (according to Dunham classification). They were all determined to
be from upper Cretaceous. Other analysed stećci were determined as dolomites dolosparite. Some of the surrounding quarries did show the same type of limestones. They
were closest to tombstones sites. We were not successful in finding dolomite quarry. The
results of mineralogical petrographic analysis are shown in Tab. 2.
Samples 19517 (biopelmicritic packestone), 19519 (bioclastic roudist floatstone) and 19521
(biopelmicritic packestone – wackestone) were selected as closest match to stećak stones.
They were then emerged in 5% AmOx solution for 24 hours. After air drying their surface
was analysed by XRD. XRD spectra of samples showed peaks corresponding to whewellite
and weddelite. All intensities were approximately the same, meaning that a protective
oxalate layer has been probably formed on all the treated samples (Fig. 1, Tab. 3, 4 and 5).
Fig. 1: XRD spectra of treated limestones from quarry.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Tab. 2: Results of mineralogical-petrographic analysis of stone.
Sample No.
Place of origin
Stone type
19163
Lovreć, stećak no.3
Bioclastic packestone
19164
Lovreć, stećak no.4
Biomicritic wackestone
19165
Zadužbina, stećak no.3
Biopelmicritic packestone - wackestone
19166
Zadužbina, stećak no.4
Biopelmicritic packestone - wackestone
19167
Crljivica, stećak no. 70
Dolomitized limestone (mudstone)
19168
Crljivica, stećak no. 691
Oncoidic floatstone
19169
Crljivica, stećak no. 182
Dolosparite
19170
Crljivica, stećak no. 11
Peloidic bindstone
19171
Crljivica, stećak no. 12
Biopelmicritic packestone - wackestone
19172
Bisko, stećak no. F1
Biomicritic wackestone
19173
Crljivica, stećak no. 2
Biomicritic wackestone
19516
Crljivica, quarry sample C
Breccia
19517
Crljivica, quarry sample D
Biopelmicritic packestone
19518
Crljivica, quarry sample E
Dolomitic breccia
19519
Bisko, quarry sample F
Bioclastic roudist floatstone
19520
Bisko, quarry sample G
Bioclastic roudist floatstone
19521
Lovreć, quarry sample A
19522
Zadužbina, quarry sample B
Biopelmicritic packestone –
wackestone
20519
Crljivica, stećak no. 62
Breccia
20520
Crljivica, stećak no. 62
Biopelmicritic packestone –
wackestone
20521
Crljivica, stećak no. 62
Biopelmicritic packestone –
wackestone
Biopelmicritic packestone - wackestone
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Tab. 3: XRD data for sample No. 19517.
°2θ
d-[Å]
Rel. Int.[%]
Mineral
14.00
14.93
15.29
17.22
19.55
20.05
23.08
24.40
26.37
28.25
29.45
30.12
30.82
31.52
32.23
34.64
36.05
37.85
38.23
39.46
40.86
43.22
45.90
47.25
47.58
48.57
52.79
56.64
57.47
58.15
60.77
61.31
6.3226
5.9297
5.7892
5.1455
4.5371
4.4250
3.8499
3.6447
3.3777
3.1565
3.0307
2.9646
2.8991
2.8358
2.7749
2.5871
2.4895
2.3752
2.3521
2.2816
2.2068
2.0914
1.9755
1.9220
1.9095
1.8731
1.7327
1.6238
1.6022
1.5851
1.5229
1.5109
58
10
3
2
1
1
9
8
0
0
100
4
1
3
1
1
13
3
3
19
0
16
1
7
15
18
1
3
8
1
6
3
oksammit
whewellit
whewellit
oksammit
whewellit
weddellit
kalcit
whewellit
whewellit
oksammit
kalcit
whewellit
whewellit
kalcit; whewellit
weddellit
oksammit
kalcit; whewellit
whewellit; oksammit
whewellit
kalcit
whewellit
kalcit
whewellit
kalcit
kalcit
kalcit
whewellit
kalcit
kalcit
kalcit
kalcit
kalcit
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Tab. 4: XRD data for sample No. 19519.
°2θ
d-[Å]
Rel. int. [%]
Mineral
13.99
14.93
15.32
17.24
19.60
23.09
24.41
29.46
30.12
30.79
31.51
32.21
34.43
36.03
36.61
37.30
37.82
38.22
39.48
43.25
45.96
46.57
47.13
47.60
48.59
50.99
52.74
56.65
57.48
58.18
60.79
61.36
6.3255
5.9292
5.7796
5.1448
4.5287
3.8519
3.6444
3.0297
2.9646
2.9043
2.8393
2.7789
2.6029
2.4910
2.4526
2.4089
2.3766
2.3527
2.2807
2.0918
1.9748
1.9502
1.9284
1.9087
1.8724
1.7896
1.7344
1.6234
1.6019
1.5844
1.5224
1.5097
62
14
4
1
0
9
11
100
6
1
3
1
1
16
1
0
3
4
19
18
1
1
6
20
20
0
1
4
8
1
5
3
oksammit
whewellit
whewellit
oksammit
whewellit
kalcit
whewellit
kalcit; whewellit
whewellit
whewellit
kalcit; whewellit
weddellit
oksammit
kalcit; whewellit
whewellit; oksammit
whewellit
whewellit; oksammit
whewellit
kalcit
kalcit; whewellit
whewellit
whewellit
kalcit
kalcit
kalcit
whewellit
whewellit
kalcit
kalcit
kalcit
kalcit
kalcit
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Tab. 5: XRD data for sample No. 19521.
°2θ
d-[Å]
Rel. int. [%]
Mineral
14.00
14.93
15.32
17.21
19.57
23.07
24.41
29.46
30.10
30.75
31.49
32.18
34.38
34.79
36.03
37.82
38.23
39.47
40.87
43.23
45.88
46.51
47.17
47.58
48.58
50.06
50.95
52.82
54.36
56.65
57.48
58.20
60.78
61.29
6.3216
5.9292
5.7808
5.1478
4.5325
3.8526
3.6436
3.0291
2.9663
2.9053
2.8385
2.7792
2.6065
2.5767
2.4909
2.3769
2.3526
2.2810
2.2062
2.0909
1.9764
1.9510
1.9251
1.9096
1.8726
1.8206
1.7909
1.7319
1.6863
1.6234
1.6020
1.5838
1.5227
1.5113
47
9
3
1
1
7
7
100
3
1
2
0
1
1
11
2
2
16
0
14
0
1
6
16
17
0
0
0
0
2
6
1
4
2
oksammit
whewellit
whewellit
oksammit
whewellit
kalcit
whewellit
kalcit; whewellit
whewellit
whewellit
kalcit; whewellit
weddellit
oksammit
oksammit
kalcit; whewellit
oksammit
whewellit
kalcit
whewellit
kalcit; whewellit
whewellit
whewellit
kalcit
kalcit
kalcit
whewellit
whewellit
whewellit
whewellit
kalcit
kalcit
kalcit
kalcit
kalcit
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Next step was to treat stećak no. 62 by emerging it in 5% AmOx solution for 24h. After
that, taken samples were prepared as cross-sections and measured from surface to depth by
µFT-IR spectroscopy. Results showed that calcium oxalate is present only on surface.
Measurements at depth of 1 mm showed only presence of calcium carbonate. Results are
shown in table 6 and figures 2, 3 and 4.
Tab. 6: Results of µFT-IR spectroscopy on samples from tombstone no. 62.
Sample No. - depth
Detected calcium oxalate
bands
Detected calcium
carbonate bands
20519 - surface
1620, 1315, 780, 665 cm-1
1425, 875, 710 cm-1
-
1380, 870, 710 cm-1
1610, 1315, 780, 665 cm-1
1410, 875, 710 cm-1
-
1390, 870, 710 cm-1
1620, 1320, 780, 665 cm
1410, 875, 710 cm-1
-
1390, 870, 710 cm-1
20519 - 1mm depth
20520 - surface
20520 - 1mm depth
20521 - surface
20520 - 1mm depth
surface
1 mm depth
Fig. 2: FT-IR spectra of sample 20519 at surface and 1 mm depth.
surface
1 mm depth
Fig. 3: FT-IR spectra of sample 20520 at surface and 1 mm depth.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
surface
1 mm depth
Fig. 4: FT-IR spectra of sample 20521 at surface and 1 mm depth.
4. Discussion
During previous conservation works on stećci (2014), field tests on creation of artificial
calcium oxalate layer by poultice (Doherty et al. 2007, Pinna et al. 2011) or brushing
(Mudronja et al. 2013) didn`t show great results. After finding appropriate or similar
“standards” in surrounding quarries, we tried to create protective layer by emerging them in
5% AmOx solution (Mudronja et al. 2013; Vanmeert et al. 2013). XRD measurements
showed similar creation of calcium oxalate layer on surface of all the treated limestones. In
addition, some ammonium oxalate (oksammit) bands were detected, which is a left over of
the treatment. It will be dissolved with first rain so it does not represent a problem. After
successful laboratory tests we immersed the whole stećak in ammonium oxalate bath for
24h using a crane on site (Fig. 5).
Fig. 5: The improvised pool with ammonium oxalate bath, Crljivica.
We tried to measure on site the thickness of created calcium oxalate layer using µFT-IR
fitted with transmission fibers. Results showed creation of protective layer on surface, but
mapping of oxalate bands beneath surface was very difficult with this technique because of
the resthralen effect (Ricci et al. 2006). We determined that below a depth of 1 mm there is
no calcium oxalate. For more precise thickness measurements, other techniques like µXRD
(Vanmeert et al. 2013) or µRaman (Doherty et al. 2013) could be more appropriate.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
5. Conclusion
In order to create a protective layer of artificial calcium oxalate on surface of the
tombstones, ammonium oxalate was applied on the stone by poultice (24 h), brushing
method (1, 2 and 3 hours) and by total immersion (24 h). Treatment by immersion of stone
sample (in laboratory) showed best results. Only with this type of treatment we can say that
protective layer of calcium oxalate was created on entire surface, which is needed for
protection. After that the same treatment was applied on the whole tombstone on the site.
Unfortunately, the investigations was limited because of technical and financial issues.
Mentioned limitations of µFT-IR technique could not resolve depth creation of CaOx, so
we could just approximate this value according to literature. Further investigations are
planned for future.
Acknowledgements
The project is supported by the Ministry of Culture of the Republic of Croatia.
References
Doherty, B., Pamplona, M., Selvaggi, R., Milliani, C., Matteini, M., Sgamellotti, A.,
Brunetti, B., 2007a, Efficiency and resistance of the artificial oxalate protection
treatment on marble against chemical weathering, Applied Surface Science,
253(10), 4477-4484.
Doherty, B., Pamplona, M., Matteini, M., Sgamellotti, A., Brunetti, B., 2007b, Durability of
the artificial calcium oxalate protective on two Florentine monuments, Journal of
Cultural Heritage, 8(2), 108-121.
Matteini, M., 2008, Inorganic treatments for the consolidation and protection of stone
artefacts and mural paintings, Conservation Science in Cultural Heritage, 13-27.
Mudronja, D., Vanmeert, F., Hellemans, K., Fazinic, S., Janssens, K., Tibljas, D., Rogosic,
M., Jakovljevic, S., 2013, Efficiency of applying ammonium oxalate for protection
of monumental limestone by poultice, immersion and brushing methods, Applied
physics. A, Materials science & processing, 111, 109-119.
Pinna, D., Salvadori, B., Porcinai, S., 2011, Evaluation of the application conditions of
artificial protection treatments on salt-laden limestones and marble, Construction
and Building Materials, 25, 2723-2732.
Ricci, C., Miliani, C., Brunetti, B.G., Sgamellotti, A., 2006, Non-invasive identification of
surface materials on marble artifacts with fiber optic mid-FTIR reflectance
spectroscopy, Talanta, 69, 1221-1226.
Vanmeert, F., Mudronja, D., Fazinic, S., Janssens, K., Tibljas, D., 2013, Semi-quantitative
analysis of the formation of a calcium oxalate protective layer for monumental
limestone using combined micro-XRF and micro-XRPD, X-ray spectrometry, 42,
256-261.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
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1200
INFLUENCE OF WATER EVAPORATION ON THE
DEGRADATION OF WALL PAINTINGS IN HAGIA SOPHIA,
ISTANBUL
E. Mizutani1*, D. Ogura1, T. Ishizaki2, M. Abuku3 and J. Sasaki4
Abstract
Hagia Sophia in Istanbul has been suffering from severe degradation such as exfoliation of
the wall paintings and interior finishing materials that is mostly associated with salt
crystallization at and near the wall surfaces. The purposes of our study are to elucidate the
physical mechanism of degradation of the wall paintings and then to propose suitable
measures to prevent the degradation. In this study, because degradation by salt
crystallization is likely to occur in places where a large amount of moisture evaporates, we
performed a numerical analysis of simultaneous heat and moisture transfer using a model of
the exedra wall, in which accumulation and evaporation of infiltrated rain are highlighted.
The results suggest that evaporation from the middle-layer mortar caused the exfoliation of
the interior finishing materials. We also developed a prediction model of the room
temperature and humidity of Hagia Sophia, in order to quantify the influences of solar
radiation and heat and moisture generation by visitors on evaporation at and near the inner
wall surfaces. Based on simulation results, it should be particularly pronounced that
reducing the transmission of solar radiation through windows is an efficient way to reduce
evaporation and to mitigate the subsequent degradation of the inner wall.
Keywords: porous materials, rain water, salt crystallisation, heat and moisture transfer,
evaporation
1. Introduction
Hagia Sophia, in Istanbul, has been suffering from severe degradation such as exfoliation of
the wall paintings and interior finishing materials mainly due to salt crystallisation within
the walls, especially at the exedras of the second cornice (Sasaki et al., 2012). Moisture
accumulation and evaporation significantly affect salt crystallisation. Therefore, in this
study, we investigate the influence of the indoor and outdoor climate and wall composition
on moisture behavior within the wall. This is done via a field survey and numerical analysis
1
E. Mizutani* and D. Ogura
Graduate School of Engineering, Kyoto University, Japan
be.etu@archi.kyoto-u.ac.jp
2
T. Ishizaki
Tohoku university of Art and Design, Japan
3
M. Abuku
Faculty of architecture, Kindai University, Japan
4
J. Sasaki
Center for the Global Study of Cultural Heritage and Culture, Kansai University, Japan
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
of heat and moisture transfer. In our previous study, we demonstrated that the main factor
of exfoliation of the interior finishing materials due to salt crystallisation was the
accumulation and evaporation of infiltrated rainwater at the middle-layer mortar
(Mizutani et al., 2015a and b). Ideally, restricting the penetration of rainwater from the
outer surface would be an effective countermeasure. However, completely blocking the
penetration pathway of rainwater is difficult because of the architectural size and
complexiity of Hagia Sophia. Besides, accumulated water in a wall might remain even after
the countermeasures are applied to the outer walls. Therefore, this study investigates the
effectiveness of controlling the indoor climate to limit the evaporation near the interior
surfaces using a prediction model to reproduce the room temperature and humidity. In this
paper, we discuss the influence of heat and moisture generation from visitors and the
transmission of solar radiation and other forms of heat transfer through windows on
evaporation at and near the inner wall surfaces.
2. Degradation and moisture content of the inside walls at exedra
of the 2nd cornice.
Figures 1 and 2 give respectively a vertical section of Hagia Sophia and photographs of
degradation of the inner walls at the exedra of the 2nd cornice. We have conducted
deterioration survey and measurement of the moisture content of the outer and the inner
walls since 2010. Fig. 3 shows the moisture content measured using a contact-type TDR
moisture content sensor at the 2nd cornice. The moisture content tends to be higher at the
semicircular-shaped walls called the exedra, and a high moisture content of > 20% was
confirmed at all the exedras. As Ogura et al. (2012) noted, locations, where remarkable
degradation of the inner walls with exfoliation of the inside stucco and middle-layer mortar
due to salt crystallisations is confirmed, generally correspond to locations of a high
moisture content. The exedras are considered to be corners where rainwater intensively
concentrates due to the geometry of the roofs and walls. Therefore, rainwater tends to
infiltrate the outer wall surfaces, causing a high moisture content and the consequent
degradation of the inner wall surface at the exedras (Mizutani et al., 2015a and b).
Fig. 1: Section of Hagia Sophia.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 2: Exfoliation of inner stucco (left) and middle-layer mortar
with salt crystallisation (right)
Fig. 3: Location number at 2nd cornice (a) and measured values of moisture content (b).
3. Fundamental equation of heat and moisture transfer
We use simultaneous heat and moisture transfer equations (Matsumoto, 1978) as
fundamental equation of numerical analysis of moisture migration and evaporation within
wall in Chapter 4 and 5. Heat and moisture balance equations are respectively:
cρ 𝑑𝑇 ⁄𝑑𝑡 = ∇ ∙ (𝜆𝛻𝑇) + 𝑟∇ ∙ (𝜆′𝜇𝑔 ∇𝜇 + 𝜆′ 𝑇𝑔 ∇𝑇)
(Eq. 1)
𝜌𝑤 (𝜕𝜓⁄𝜕𝜇 ) 𝜕𝜇 ⁄𝜕𝑡 = ∇ ∙ (𝜆′𝜇𝑔 ∇𝜇 + 𝜆′ 𝑇𝑔 ∇𝑇 + 𝜆′𝜇𝑙 ∇𝜇 + 𝜆′ 𝑇𝑙 ∇𝑇)
(Eq. 2)
where cρ, 𝑇, λ, 𝑟, 𝜇, 𝜌𝑤 and 𝜓 refer to respectively the specific heat capacity for volume
[J/m3 K], the temperature [K], the heat conductivity [W/m K], the latent heat [J/kg], the
water chemical potential [J/kg], the water density [kg/m3] and the moisture content [m3/m3],
and 𝜆′ 𝑇 and 𝜆′𝜇 are respectively the water conductivity for the temperature [kg/m s K] and
that for the water chemical potential [kg/m s (J/kg)]; the subscripts g and l indicate water
vapor and liquid water respectively.
4. Investigation of influence of infiltrated rainwater by analysis of wall model
We performed a numerical analysis of the heat and moisture transfer with a model of the
exedra wall (Fig. 4), to confirm the relation between the accumulation and evaporation of
infiltrated rainwater and degradation of the interior wall surfaces at the exedra. The analysis
1203
(inside)
(outside)
Solar
radiation
Night
radiation
heat
moisture
3
㎝
Measured Value at Hag
Temperature and Humidity
Indoor
3
㎜
)
120㎝
Table1 Analysis conditions
Outdoor
Stucco(
Brick Structure
(Connection Mortar)
Middle-layer Mortar(
rainfall
Temperature
(2010/9/26~2011/9/26)
Precipitation
3 times of amount of
(This value was estimat
)
Solar radiation
Fig. 4: Schematic diagram of the analysis
(inside)
3
㎜
)
moisture
3
㎝
Calculated Value of ver
from measured value o
Hagia Sophia
Table1:
Analysis conditions
conditions in Section
4.
Table1
Analysis
in Chapter
4
Outdoor
heat
(2010/9/26~2011/9/26)
and Measured Value at Hag
Humidity
Fig. 4 Wall model for analysis
Stucco(
㎝
conditions (Tab. 1) and hygrothermal material properties are kept the same as the past study
(Mizutani et al., 2015a). The severely deteriorated wall of the north-facing exedra is
analysed. The vertical radiation for the north-facing walls is calculated by decomposing the
total measured horizontal solar radiation into the direct and diffuse components using the
equations of Bouguer and and Berlarge. Judging by the roof shape, three times the amount
of measured precipitation was assumed to flow at the outer surface of the exedra.
Middle-layer Mortar(
cture
on Mortar)
13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Measured Value at Hagia Sophia
Temperature and Humidity
(2010/9/26~2011/9/26)
Indoor
Measured Value at Hagia Sophia
Temperature
and
Humidity
(2010/9/26~2011/9/26)
Precipitation
3 times of amount of measured precipitation,
(This value was estimated from the roof shape.)
)
Solar radiation
el for analysis
Calculated Value of vertical radiation at North
from measured value of horizontal radiation at
Hagia Sophia
Fig. 5 shows the calculated values of moisture content in the cases for which we considered
rainfall and no rainfall. In the rainfall case, the moisture content of the connection mortar
and middle-layer mortar sharply rose. The annual change of moisture content in the
connection mortar is large. Winter is the rainy season, and the moisture content of the
connection mortar reaches approximately 0.42 m3/m3 of the saturation of moisture content.
On the contrary, the annual change in the moisture content of the middle-layer mortar is
slight.
Fig. 6 and shows the average annual distribution of liquid and moisture fluxes near the
inner surface as well as the annual change in the amount of evaporation at main evaporation
locations near the inner surface, respectively. It can be said that evaporation mainly occurs
from the middle-layer mortar. Change of the amount of evaporation between stucco and
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
middle-layer mortar, namely 0.8cm from the inner surface, is so large that both of
evaporation and condensation occur mainly because of the change of indoor temperature
and humidity. The amount of evaporation is large in summer, when evaporation occurs not
only from the middle-layer mortar but also from the connection mortar. It might be said that
evaporation from the middle-layer mortar is related to the exfoliation of the stucco, which is
the main symptom of degradation confirmed at the exedra (Mizutani et al., 2015a and b).
a)
b)
Fig. 5: Annual change of calculated values of moisture content with no rain (a)
and with rain (b).
a)
b)
Fig. 6: a) Average annual distribution of liquid and moisture fluxes near the inner surface;
b) Annual change in the amount of evaporation near the inner surface
5. Influence of Room Temperature and Humidity on Evaporation
5.1. Modelling for analysis of room temperature and humidity
To estimate an influence of the room temperature and humidity on evaporation at and near
the inner wall surface, we develop a numerical model of the room temperature and
humidity of Hagia Sofia. Using this model, we investigate how to control the inside climate
to restrain the evaporation. This section accounts for the influence of heat and moisture
generation from visitors and the transmission of solar radiation and heat through windows
on the evaporation. The walls are treated as a one-dimensional uniform structure. The
simultaneous heat and moisture transfer equations (Matsumoto, 1978) are used as the
fundamental equation of the walls. The analysis model is composed of two rooms, as
shown in Fig. 7. The lower room, composed of the ground floor and gallery (see Fig. 1), is
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
called the visitor zone. The windows and doors are opened during visiting hours. The upper
room, composed of the second cornice and dome cornice in Fig. 1, is called the cornice
zone. The dimensions of the rooms, openings, walls, floors and roofs are estimated based
on the architectural survey of Van Nice (1965). The air of each room are represented as a
single mass.
The heat and moisture generated from one person are taken at 80 W and 64 g/h,
respectively. The daily number of visitors is based on the monthly average of 2013. It is
assumed that the staying time is 30 min. The visitors, who generate heat and moisture, stay
in the visitor zone during the opening time.
Fig. 7: Schematic diagram of the analysis model.
5.2. Boundary conditions
A third type of boundary condition is applied to the inner and outer wall surfaces. The
temperature, humidity and precipitation are based on the data measured every 30 min
outside and inside Hagia Sophia from September 26, 2012 to September 25, 2013. Solar
radiation on the walls facing each direction is calculated by decomposing the total
measured horizontal solar radiation into the direct and diffuse components using the
equations of Bouguer and and Berlarge. A boundary condition for the bottom of the ground,
which is 13.2 m below the floor, is the annual average value of the outside temperature. The
air change rates between the inside and outside and between the visitor and cornice zones
were determined to identify the measured values of temperature and humidity.
5.3. Comparison of the calculated and measured values of temperature and humidity
Fig. 8 shows the calculated and measured values of room temperature and humidity in the
visitor (a) and cornice zones (b). The calculated values of the humidity ratio for the visitor
zone and cornice agree with the measured values throughout much of the year. The
calculated values of the daily change of temperature are somewhat different in summer, but
the annual changes of temperature in the visitor zone and cornice generally agree with the
measured ones. We use these analysis conditions and results as reference values for the
following investigation.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
a)
b)
Fig. 8: Annual variation of temperature and humidity ration
in visitor zone (a) and cornice zone (b).
5.4. Influence of heat and moisture generation from visitors on evaporation from the
inner wall surface
Hagia Sophia is the most popular sightseeing spot in Istanbul; it has approximately 3
million visitors annually. Out past study observed that the measured values of the annual
average temperature on the opening day were 0.2–0.5° higher than that on the closing day.
It can be assumed that the heat and moisture generation from visitors influences the indoor
climate. Figures 9a and 9b show the number of visitors and provide a comparison between
the calculated amount of evaporation at the wall of the cornice zone in the reference case,
together with the heat and moisture generation of cases with and without visitors. The
relative humidity of the cornice zone in the reference case is slightly higher than that in the
case without visitors. Furthermore, the amount of evaporation from the middle-layer mortar
in the case without visitors is a slightly higher than that of the reference case, especially in
spring. Therefore, it can be said that the heat and moisture generation from visitors restricts
water evaporation, although it is quantitatively insignificant.
a)
b)
Fig. 9: a) Average daily number of visitors of each month; b) Difference in amount of
evaporation due to heat and moisture generation from visitors.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
5.5. Influence of heat loss and regain from windows on evaporation
The transmission of solar radiation through many windows that Hagia Sophia has is
considered to affect the room and wall surface temperatures, so we investigate the influence
of solar transmittance on the room temperature and humidity and the evaporation at and
near the wall surfaces. To study the influence of the windows on evaporation, the solar
transmittance of the windows is taken at 0.7 as the reference value or one fourth of that.
Fig. 10a and 10b show the calculated values of respectively the temperature and amount of
evaporation in the cornice zone. With a decrease of solar transmittance, the room
temperature decreases, especially in spring and summer because of a relatively large impact
of solar radiation. The decrease in the room temperature in these seasons would suppress
evaporation in the middle-layer mortar.
Furthermore, the influence of the heat transmission coefficient, i.e. the conductivity of the
window, is investigated. The heat transmission coefficient of the window is taken at 6.3 as
the reference value or one fourth of that . Fig. 10c and Fig. 10d show the calculated values
of the room temperature and the amount of evaporation in the cornice zone, respectively.
The room temperature of the case with a lower heat transmission coefficient is significantly
higher than that of the reference case in autumn and winter when the outdoor temperature is
lower than the indoor temperature. The room temperatures of both cases in spring and
summer do not differ. The decrease in the heat trasmission can increase the indoor air and
wall temperature specially in autumn and winter; as a result, the evaporation would increase
throughout the year, when the heat conductivity performance of the window is improved.
a) Difference in room temperature
b) Difference in amount of evaporation
c) Difference in room temperature
d) Difference in amount of evaporation
Fig. 11: Difference in room temperature and amount of evaporation.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
6. Conclusion
We investigated accumulation of infiltrated rainwater in the masonry and the influence of
its subsequent evaporation at and near the interior wall surfaces that would lead to
degradation associated mostly with salt crystallisation. This was done by numerical analysis
with a model of the exedra wall that takes into account out long-term on-site measurement
data of the indoor and outdoor environment. The results showed that infiltrated rainwater
mainly evaporates at the middle-layer mortar and would thus cause exfoliation of the inner
stucco, which becomes significant in summer. Furthermore, we developed a numerical
model that can sufficiently reproduce the room temperature and humidity, in order to
investigate the influences of the indoor climate conditions on the evaporation. The
simulation results show three main findings:
- Heat and moisture generation by visitors only slightly affects water evaporation.
- Reducing the transmission of solar radiation through the windows can reduce
evaporation in spring and summer.
- Increasing the thermal resistance of the windows promotes evaporation.
Based on the simulation results, it should be particularly pronounced that reducing the
transmission of solar radiation is an effective way to restrict evaporation at and near the
wall surfaces and thus to mitigate the subsequent degradation of the inner walls. On the
other hand, the number of visitors is of no importance from a viewpoint of restricting
evaporation. The influence of ventilation on the evaporation is to be investigated in the
future.
Acknowledgements
This work was partly supported by JSPS KAKENHI grant numbers 21226014 and 26709043.
We extend our gratitude to them. We are deeply grateful for understanding and cooperation of
this research given by curators and staffs of Aya Sophia Museum.
References
Sasaki J., Yosida N., Ogura D., Ishizaki T., Hidaka K. 2012. Study of salt crystallization on
the inner wall of Hagia Sophia, Istanbul, Turkey, Science for Conservation 51:
303-312. (in Japanese)
Mizutani E., Ogura D., Ishizaki T., Abuku M., Sasaki J. 2015a. Influence of infiltration of
rain water on degradation of the wall paintings in Hagia Sophia, Journal of
Environmental Engineering 80: 1001-1012. (in Japanese)
Mizutani E., Ogura D., Ishizaki T., Abuku M., Sasaki J. 2015b. Influence of infiltrated rain
water on degradation of the wall paintings in Hagia Sophia, Energy Procedia 78:
1353-1358.
Ogura D., Ishizaki T., Koizumi K., Sakaki J., Hidaka D., Kawata K. 2012. Deterioration on
the wall and indoor and outdoor environmental conditions in Hagia Sophia,
Istanbul, Turkey. Science for Conservation 51: 59-76. (in Japanese)
Matsumoto M. 1978. Energy conservation in heating cooling ventilating building: heat and
mass transfer techniques and alternatives (ed. Hoeogendoorn C.J. and Afgan
N.H.), Washington : Hemisphere Pub. Corp., pp.1-45.
Van Nice R.J. 1965. Saint Sophia in Istanbul: an architectural survey, Washington,
Dumbarton Oaks.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
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1210
CONSERVATION OF MAGAI-WAREISHI-JIZO, A BUDDHA
STATUE CARVED INTO A GRANITE ROCKFACE ON THE
SEASHORE
M. Morii1*, N. Kuchitsu1, T. Kawaguchi2, H. Matsuda3 and S. Tokimoto3
Abstract
The Magai-Wareishi-Jizo statue, carved on granite by stone mason Nenshin in A.D. 1300,
is located in Mihara City, Hiroshima Prefecture, Japan. It is located near the seashore now
and the whole image sinks under water at high tide. A global sea level change curve
indicates that the sea level must have been lower around A.D. 1300 and that the statue was
not fully immersed when first built. The present condition of frequent sinking must be due
to subsequent sea level change which was not assumed at the beginning. Macroscopically
speaking, the weathering rate of this statue is not regarded as so fast because it is carved on
a core stone which is hard. However, compared with a replica made 24 years ago, it is
revealed that the scaling is advancing little by little. Investigations are required from
various viewpoints and appropriate measures are hoped to be executed. The authors carried
out the conservation of Magai-Wareishi-Jizo in 2011. In this conservation, they carried out
reattachment of loose parts by acrylic resin. As the restored parts were sunk under sea level
because of the tide, drain holes were installed in order to help displace sea water in a cavity
of the adhesive part.
Keywords: granite, core stone, seashore, scaling, attachment, acrylic resin
1. Introduction
Ever since Buddhism was introduced to Japan in the 6th century, many Buddhist works of
art, such as stone pagodas and stone Buddha, have been created out of stone. The
techniques for creating these works continued to develop over the years, with influence
from overseas and master stonemasons were brought over from China to assist in the
reconstruction of the Great Buddha Hall (Daibutsuden) of Nara’s Todai-ji temple. At the
end of the 12th century, the offspring of those Chinese stonemasons remained in Japan, and
it became increasingly common for hard rock, such as granite, to be used in carvings. The
Magai-Wareishi-Jizo statue was carved in the 13th century, at a time of much activity in the
creation of stone artworks. The statue of Buddha is carved quite deeply into the granite
surface, and the inscriptions of “2nd Year of Shoan” (1300) and the name “Nenshin,
1
M. Morii* and N. Kuchitsu
National Research Institute for Cultural Properties, Tokyo, Japan
morii@tobunken.go.jp
2
T. Kawaguchi
Act-Biz Cooperation, Japan
3
H. Matsuda and S. Tokimoto
Mihara city education board
*corresponding author
1211
13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Buddhist sculptor” still remain to the right of the statue. The fact that it still bears the
artist’s name and the year of production makes this statue a valuable piece of cultural
heritage.
The statue stands on the shoreline, which means that, as well as the usual effects of the
external environment, it is also highly susceptible to the effects of tidal activity and
seawater spray. In fact, the sea level at high tide during spring tides comes up to the face of
the Buddha and the statue is almost completely submerged in seawater. In contrast, when
the tide goes out, the water level recedes to the point where it is possible to climb down to
the beach and view the statue from head on (Fig. 1). Considering that it has been standing
there, in an environment where stone-made structures are generally susceptible to
deterioration, for 710 years, the statue is in remarkably good condition.
In recent years, however, dirt and grime on the surface of the work and some peeling on
both the statue and the inscription have been observed. The authors therefore ascertained
the current condition of the statue and repaired some of the peeling. In this article, the
authors will report on the current condition of the Magai-Wareishi-Jizo statue and policies
for its restoration. The article will also report on the methodology for re-attaching the
peeling sections as a means of mitigating the effects of seawater, which poses a significant
deterioration risk to cultural properties made of stone that are located on the coast, and on
the results of field trials of that methodology.
Fig. 1: Magai-Wareishi-jizo statue; a) Situation at low tide; b) Situation at high tide.
2. Overview of the Magai-Wareishi-Jizo
The Magai-Wareishi-Jizo is a 0.88-meter tall relief of a seated Jizo (bodhisattva) facing out
to sea, carved into a granite boulder that is about 2.5 meters high, 4.9 meters wide, and 3.7
meters thick. It is located on the shoreline next to the Mukota Port Ferry Terminal on Sagi
Island (Mihara, Hiroshima Prefecture) in the Seto Inland Sea. On the right side of the
statue, an inscription of kanji characters can also be observed, which reads “2nd Year of
Shoan” (1300) and “Nenshin, Buddhist sculptor.” In the city of Mihara, there is a stone
pagoda built in 1249, which was said to have been created by a stonemason from Nara, and
a number of stone pagodas known to be the work of Nenshin are still in existence in the
city. They include the Hokyoin-to pagoda at Beisan-ji temple, which bears the inscription
“1st Year of Geno” (1319) and “Nenshin, builder.” It is presumed that the “Nenshin,
Buddhist sculptor” who carved the stone Buddha, and the “Nenshin, builder” who built the
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stone pagodas in Mihara are one and the same person, and that he may have given himself
different titles depending on what he was creating.
Most of Sagi Island is made of granite from the Late Cretaceous period. The granite
boulder into which the Buddha has been carved is exceptionally hard and in good condition
compared to the cliff faces on the same coast line and nearby stone Kasatoba (carved stone
pillars with hat) from the 17th century, which have decomposed badly and become fragile.
This granite boulder may be presumed to be an unweathered rock known as a “core stone.”
Its outward appearance differs from that of the decomposed surfaces nearby, which often
leads to the mistaken impression that it was brought to the site from elsewhere, but it is
believed to be an embedded rock that was originally part of a larger rock body (Fig. 2).
Because the statue is situated on the water’s edge, it is currently highly susceptible to the
effects of the tides. At low tide, the entire boulder is exposed above the water’s surface, but
at high tide, some or all of the statue is submerged. The area submerged at high tide differs
greatly day by day, but on most days, it comes up to at least the level of the Buddha’s chest.
The surface of the statue up to that point is covered in black algae, making the lower half of
the boulder appear black and dirty to the naked eye. During spring tides, however, the water
level rises even higher, and at the peak of high tide in those periods, the statue is sometimes
observed to be completely submerged to the top of the Buddha’s head.
Fig. 2: Comparison between the boulder on which the Magai-Wareishi-Jizo statue is
carved and the surrounding granite cliff face.
3. Conservation status of Magai-Wareishi-Jizo
The boulder on which the Magai-Wareishi-Jizo statue is carved is made of granite.
Compared to the decomposition of the surrounding cliff faces, which are of a similar
geological make-up, and of nearby stone structures that were erected after the statue was
carved, it has remained relatively unweathered. On a macroscopic level, if we assume that
the current rate of weathering is markedly rapid, the shape of the entire boulder should have
changed greatly from that of a core stone. It would have been no surprise, for example, if
the rock had taken on a gourd-like shape, with the area closest to the water’s surface at high
tide becoming indented. In reality, however, the boulder is believed to have retained the
characteristic core stone shape, so it is presumed that that kind of erosion has not been
significant. In other words, it is believed that, since 1300, when the statue was carved, there
has been no erosion significant enough to change the shape of the boulder, and it is difficult
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to believe that weathering is currently taking place at a rate that would cause the boulder
itself to disappear in the near future.
However, visual inspection of the statue has confirmed that there has been some partial
surface peeling that has obviously occurred in recent years. To identify the peeling sections,
the authors attempted a comparison with a replica of the statue that was cast in 1988 and is
currently on display at the Hiroshima Prefectural Museum of History. This comparison
confirmed deterioration in six places on the statue and the inscription that had occurred in
the past twenty years approximately. For example, peeling of about 1 mm diameter was
found on the chin of the stone Buddha (Fig. 3). Moreover, the deterioration is concentrated
around the peak high water line, and it is believed that the peeling may be caused by tidal
activity, that is, the repeated pattern of soaking at high tide and drying out at low tide.
Further, examination of the dark green areas found on the lower half of the Buddha’s body
confirmed the growth of algae in that area. Algae growth was also observed on the boulder
in the area between the ground and about 40 cm above ground, but there was none observed
above that line. Algae were also found on the stone lanterns in front of the statue, so the
algae growth is believed to be caused by the effects of the sea water.
Fig. 3: Confirmation of deterioration by comparison with replica.
4. Conservation measures
4.1. Past conservation measures
There are records of restoration work having been performed on the Magai-Wareishi-Jizo
in 1976. These records show that, at that time, it was believed that there was a great risk
that the interaction of a number of influences, such as erosion by the seawater, the repeated
drying and soaking caused by tidal activity, the effect of changes in temperature over the
course of the day in the sections submerged by the sea and those that are not, and the effects
of microorganisms and algae, could accelerate the weathering of the granite rock. It was
also believed that it would be impossible to eliminate all of those influences. For this
reason, restoration work consisted mainly of reinforcement of the granite with silicone
resin, repairs of cracks and peeling with epoxy resins, and injection of bonding agents.
However, as far as the authors could confirm during their field survey, it appears that most
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of the repairs were done on the back of the rock, and the work on the front was confined to
reinforcement alone.
4.2. Restoration policy
Despite the sculpture being regularly submerged under the sea at high tide, the statue itself
and the inscription have remained remarkably intact. The main deterioration at this point in
time is surface peeling, and the authors determined that a minimal level of measures to
prevent peeling was required to protect the statue and the inscription. Also, in terms of
bonding the peeling areas back onto the stone, it was decided to keep the use of bonding
agents to a minimum, in order to eliminate the impact of the difference in the thermal
expansion coefficients of the rock itself and the bonding agent. Moreover, because the bond
strength of the bonding agent would be reduced if it were to get wet before manifesting, a
restoration schedule was established that took into consideration the properties of the
bonding agent and the surrounding environment. Details are as Tab. 1.
4.2.1. Bonding method
Because the loss of the carved sections of the stone statue itself and the inscription would
greatly reduce the value of the sculpture, a minimal level of bonding was necessary. It was
decided, therefore, to spot-bond the areas affected by peeling and the areas that were lifting
away with an acrylic resin (Fig. 4. The black sections are the areas adhered with the acrylic
bond). Also, because no salt precipitation or plant growth was observed behind the peeling
sections, it was decided to ignore the deterioration caused by water inside the rock (salt
weathering, etc.) and to leave holes to allow any water infiltrating the peeling areas at high
tide to escape, in particular, for water to escape from the bottom sections.
Fig. 4: Method of bonding peeling sections.
4.2.2. Schedule of conservation
Bonding agents generally require time to harden. To prevent any adverse effect of moisture
or seawater while it was hardening, a season with a relatively large number of sunny days
was chosen, and it was decided to undertake the conservation measures at low tide during
neap tide periods, so that the area being worked on would not be submerged during high
tide.
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4.2.3. Conservation procedure
The conservation measures were carried out in November 2011. The areas of surface
peeling on the statue and inscription considered most at risk were selected and the bonding
agent applied. The procedure was conducted in the following order: (1) advance survey; (2)
determination of locations in need of restoration; (3) advance trials; (4) bonding of peeling
sections; (5) follow-up observation.
4.2.4. Advanced survey
The state of deterioration of the statue and inscription was ascertained before the work was
undertaken. As described earlier in this article, compared with when the replica was
produced, the authors found many areas of damage. For example, the chin of the
bodhisattva image is rounded on the replica, but in comparison, there has clearly been
peeling on the original sculpture in that area.
4.2.5. Determination of parts of restoration
Based on the advance survey, the areas for restoration was confined to the Buddhist image
itself and the carved surface of the inscription. Surface peeling was also observed on the
areas at the bottom of the Buddha relief that were dark green (algae), but these areas were
deemed unsuitable for the use of bonding agents due to their being wet for longer periods,
so conservation of those areas was deferred on this occasion. Also, because the purpose of
this work was not to reinforce the surface but to adhere the peeling sections, it was decided
to defer work on peeling of less than 1 mm in width, where there was a risk of the resin
attaching to the surrounding stone, and to only treat sections of 1 mm or more in width
which were in danger of falling off completely.
4.2.6. Advance trials
Advance trials of the bonding procedure were performed on a section of surface peeling on
the left side of the statue. In the trial, the resin’s hardening time was measured, and methods
for accelerating hardening and the composition of the thickening agent were decided. The
state of hardening and changes in colour of the bonded sections after submersion were also
checked.
4.2.7. Bonding of peeling sections
After the restoration methodology and schedule were decided based on the results of the
advance trials, the bonding agent was applied to the peeling sections. The resin was not
applied to the entire back surface of the peeling section; instead a hole for seawater that
entered the peeling section to drain out was created (Fig. 5). For smaller sections, however,
to ensure that the bonded section did not become detached, no drainage hole was made and
the surface was closed up completely. Because the area of peeling on the chin of the stone
Buddha had expanded, cracks of less than 1 mm were also bonded by filling them in with
resin. Subsequently, any grade differences from the surface were filled in with resin mixed
with stone powder.
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Fig. 5: Bonding peeling sections.
Tab. 1: Restoration policy.
Detail
Acrylic resin
Thickener
Compounding ratio
Bonding
Acceleration of
hardening
Colour tone
Acrylate (Liquid A: oxidizing agent, Liquid B: reducing agent)
Stone powder
1:2 (resin : thickener, capacity ratio)
*paste
Bonding the edge of the peeling section using bamboo skewer
Heated with a dryer for 2 hours
4 colours (white, yellow, black and brown) *slightly dark colour
4.3. Follow-up observation
Three months after the restoration work was done, follow-up observations were conducted
of the restored areas. No changes in the bond strength or colour tone were observed.
However, because these repairs were performed in a special environment, although a
bonding agent appropriate to the conditions was used, further regular follow-up
observations will be needed to determine whether or not the effectiveness of the repairs can
be maintained.
5. How the statue would have looked when it was first carved
The boulder on which the Magai-Wareishi-Jizo was carved is a granite core stone, and in
the 700 years since it was created, there has been only slight weathering on a macroscopic
scale. So what would the stone Buddha have looked like when it was first carved? If we
look at the curve of global sea-level change, the year 1300 coincided with a period of
marine regression in the Middle Ages known as the Paria Regression, and on a global
average, sea levels may have been around one meter lower than they are today (Fig. 6).
Topical elevation and sedimentation in the area would need to be studied, but if it was the
same on Sagi Island, then sea levels at the time the statue was carved would have been
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lower than they are today, and it is likely that the statue would not have been submerged at
high tide. In other words, the original concept may have been that, with the stone Buddha
located on the water’s edge, the water level would have come up to just below the Buddha
himself at high tide, which would make it appear as though the sitting Buddha was floating
on the water. With today’s higher sea levels, however, the statue is almost completely
submerged at high tide, something that the sculptor would not have intended.
Fig. 6: Global sea level change (from Fairbridge, R. W., 1961).
6. Conclusion
In addition to ascertaining the state of deterioration of the Magai-Wareishi-Jizo visible
today as it stands on the shoreline, the authors undertook those conservations measures
which were possible to carry out in the given circumstances in which the statue could not
be moved. Regarding the bonding of the peeling sections in particular, various innovations
were performed, such as including holes for drainage of seawater that had entered behind
the peeling section with the tide. As a result of these conservation measures, follow-up
observations three months after the work was performed showed that there were no major
problems and the work has remained in a good condition to date.
References
Katayama, K., 1961, "Akikoku Sagi-shima Wareishi-Jizo, Shoan Ninen Mei Magaibutsu",
"Shiseki to Bijyutsu", 314, 143-154 (in Japanese).
Kawakatsu, M., 1998, "Nihon Sekizou
9784490105032, 418p (in Japanese).
Bijyutsu
Jiten",
Tokyo-do
Shuppan,
Ikeda, H., 1998, The World of Granite Landforms, Kokon-shoin, 9784772216791, 206p (in
Japanese).
Mihara City Education Board, 2012, Report of conservation of Magai-Wareishi-Jizo statue,
Important Cultural Properties of Hiroshima Prefecture, 30p (in Japanese).
Hayakawa N. and Kawanobe W., 2001, The Study to Control Water Contents by Various
Sillicone Derivatives Usuki-magaibutsu, Science for Conservation, National
Research Institute for Cultural Properties, Tokyo, Japan, 40, 69-74 (in Japanese).
Fairbridge, R. W., 1961, Eustatic Changes in sea-level, in L. H. Ahrens, K. Rankama, F.
Press and S. K.. Runcorn (eds), Physics and Chemistry of the Earth vol 4, London:
Pergamon Press, 99-185.
1218
EVALUATION OF THE PRESERVATION STATE OF THE HOLY
AEDICULE IN THE HOLY SEPULCHRE COMPLEX IN
JERUSALEM
A. Moropoulou1, K. Labropoulos1, E. Alexakis1*, E.T. Delegou1,
P. Moundoulas1†, M. Apostolopoulou1 and A. Bakolas1
Abstract
The Church of the Holy Sepulchre (Church of the Resurrection) in the city of Jerusalem is
one of the most important historical sites of Christianity and according to tradition is the
scene of Jesus Christ’s death and resurrection. Holy Aedicule is one of the Holy Pilgrimage
Sites of the Complex, and is the place where Jesus has been buried and resurrected. During
the British Mandate, the structure of Holy Aedicule was strengthened by the installation of
a metal supporting frame to restrain the façades’ deformation that was macroscopically
observed and is still evident. To evaluate the preservation state of The Holy Aedicule,
characterisation of building materials, decay diagnosis and construction phase
determination have been performed using Non Destructive Techniques (NDT) in situ, and
analytical techniques in lab after sampling. In particular, based upon the historic
documentation of the Monument, Ground Penetrating Radar (GPR) measurements provided
a satisfactory discrimination of the construction phases. Additionally, samples were
investigated by analytical techniques like X-Ray Diffraction (XRD), Simultaneous
Differential Thermal and Thermogravimetric Analysis (DTA/TG) and Mercury Intrusion
Porosimetry (MIP), to characterize building materials, as well as to diagnose decay and
pathology of the historic structure.
Keywords: diagnostic study, non-destructive testing (NDT), building material, analytical
techniques, decay
1. Introduction
The Church of the Holy Sepulchre (Church of the Resurrection) is one of the most
important historical sites of Christianity. Within this Church, the Holy Aedicule is built,
which contains the tomb of Jesus Christ. The current Aedicule structure is the result of
various construction phases (Fig. 1), damages and destructions, reconstructions and
protection interventions (Lavvas 2009, Mitropoulos 2009, Montefiore 2012, Moropoulou
2016). The Church dates back to 325AD, when Emperor Constantine I ordered the
construction of a basilica incorporating the tomb of Christ, within the Holy Aedicule
(Fig. 1a). The Tomb was carved outside, possibly in a polygonal form, with an entrance on
its eastern side (Fig. 1a), whereas the interior had a rectangular form and on its northern
side the arcosolium. At the start of the 7th century, the exterior surfaces of the polygonal
1
A. Moropoulou, K. Labropoulos, E. Alexakis*, E.T. Delegou, P. Moundoulas,
M. Apostolopoulou and A. Bakolas
School of Chemical Engineering, National Technical University of Athens, Greece
alexman@central.ntua.gr
*corresponding author
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monolithic Aedicule were covered by marble plates, columns and metal fences to protect it
from the visiting pilgrims. This building was damaged by fire in 614 when. The Church of
the Holy Sepulchre was damaged by fire in 614 when the Persians invaded and destroyed
Jerusalem. The Aedicule’s exterior and interior surfaces and decorations were destroyed,
including partial destruction of the burial chamber, along its east-west axis (Fig. 1b). In
622, Christians were allowed to rebuild churches and monasteries. Modestus, the abbot of
the Monastery of St. Theodosius, rebuilt the Church of the Holy Sepulchre and destroyed
parts along the east-west axis of the Aedicule were restored with masonry (Fig. 1c). In
1009, the Caliph of Egypt El-Hakem ordered the complete destruction of the church; the
Holy Aedicule is destroyed down to ground level. During the reign of Constantine
Monomachus, Patriarch Nikiforos persuaded the Emperor to offer money for the
reconstruction of the Holy Sepulchre (1027-1048). Parts destroyed by Al-Hakim were
restored with masonry, the Aedicule regaining its former Constantinean plan form, and its
exterior surfaces covered with stone plates, enveloped by 12 columns (Fig. 1d). After the
arrival of the crusaders (1099) the Church of the Holy Sepulchre was renovated in a
Romanesque style and added a bell tower. A vestibule (Chapel of the Angel) was added at
the eastern side of the Aedicule in 1119 (Fig. 1e). Following various conquerors, Jerusalem
fell in 1517 to the Ottoman Turks, who remained in control until 1917.
Fig. 1: The construction phases of the Holy Aedicule of the Church of the Holy Sepulchre
throughout history (Mitropoulos 2009).
In 1808, an accidental fire became uncontrolled, which caused the dome of the Rotunda to
collapse over the Aedicule, inflicting to it severe damage. According to historic sources
(Moropoulou 2016), The Holy Tomb remained intact but the Aedicule structure was
heavily damaged and buried under the Rotunda dome ruins. After permission, the official
architect Nikolaos Komnenos rebuilt the Aedicule in the contemporary Ottoman Baroque
style, effectively embedding the remaining core of the burial chamber within the new,
larger, Aedicule structure. The restored Church was inaugurated on 13 th September 1810
(Fig. 1f).
Since the 1810 reconstruction, in all external faces, except the west end, the marble shell
presents a strong buckling. By 1947, the deformation of the external construction of the
Aedicule was already as intense as today, forcing the British Authority (to take immediate
measures in the form of an iron “frame”, along the flanks, which through strong wooden
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wedges prevented any further outward movement of the stones already affected by the
buckling mechanism. More recently, the National Technical University of Athens, after
invitation from is All Holiness, Beatitude Patriarch of Jerusalem and All Palestine,
Theophilos III, signed a programmatic agreement with the Jerusalem Patriarchate and
implemented an innovative research titled "Integrated Diagnostic Research and Strategic
Planning for Materials, and Conservation Interventions, Reinforcement and Rehabilitation
of the Holy Aedicule in Church of the Holy Sepulchre in Jerusalem". Within this
framework, based upon the historic documentation provided by the Patriarchate Technical
Bureau, an array of non-destructive techniques in conjunction with materials
characterization were performed to elucidate the construction phases of the Holy Aedicule
and the materials they are composed of, in order to assess the preservation state of the
Aedicule, and to provide basic layering information for the assessment of its current state
against static and seismic loads.
2. Methods and Techniques
2.1. Non Destructive Testing - Ground Penetrating Radar (GPR)
Ground Penetrating Radar (GPR) is an established non-destructive electromagnetic
technique that can locate objects or interfaces within a structure. GPR was utilized in order
to reveal information about the interior structure of the Aedicule, i.e. the interior layers of
its masonries, as well as the assessment of their preservation state and cohesion, in the
conjunction with macroscopic deformations. The ground penetrating radar system used in
this survey was a MALÅ Geoscience ProEx system with 1.6 GHz and 2.3 GHz antennae.
The MALÅ Geoscience Groundvision 2 software was used for data acquisition. The GPR
scans were processed with the MALÅ Geoscience RadExplorer v.1.41 software, after
application of the following filters: DC removal, Time zero adjustment, Amplitude
correction, and Band pass filtering.
2.2. Analytical (in-lab) Techniques
Sieve analysis was performed according to Normal 27/88 (Normal 27/88 1988) in order to
analyze the mortar aggregates grain size distribution and to calculate the binder aggregate
ratio. The sieves used were according to ISO 565. Differential Thermal and ThermoGravimetric Analysis (DTA-TG) provides qualitative and quantitative information
regarding the composition of the samples (Mettler Toledo 651e). The temperature range
applied was 25-1000°C and the heating rate was selected at 10°C/min (Moropoulou et al.,
1995). X-ray diffraction (XRD) provides information regarding the mineralogical
composition of the materials (Advance D8 Diffractometer of Bruker Corporation) (Normal
27/88 1988, Moropoulou et al., 1995). The microstructural characteristics of the samples
were studied through the use of Mercury Intrusion Porosimetry (MIP) with the use of a
Pascal 400 Thermo-Electronics-Corporation (Normal 27/88 1988).
3. Sampling
A number of historical mortar and building stone samples deriving from the façades and the
construction faces of the Holy Aedicule were collected for their characterization with the
analytical-laboratory techniques. The examined samples that are presented in this study are
coming from the South outer façade and the restoration mortar of Architect Komnenos. The
samples were obtained by Core Sampling on selected areas in the ground and the façades in
order the particular materials to be acquired.
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4. Results and Discussion
4.1. Non Destructive Testing
In Fig. 3a, over the plan of the Aedicule, the basic scan areas of the exterior and interior of
the Aedicule are presented. The red quadrants represent the basic survey areas. The
markings B1-B5 and N1-N5 corresponds to the north and south arch areas at the exterior
surfaces of the Aedicule. The description of the analysis of the GPR scans is presented in
Fig. 3b, which corresponds to a horizontal scan on area N4 at a height of 130 cm above the
interior floor level. For the conversion of the scan in Fig. 3b/A into a two-dimensional
section distance - depth (X axis vs. Depth – Z axis), the calculation of the pulse velocities
throughout all observed layers is required. For this purpose, stone blocks of the parapet at
the roof and stone block from the seat outside the entrance to the Aedicule were used as
standards to calibrate the pulse velocities for the GPR analysis, with the aid of, the
velocities and dielectric constants were calculated and used in the velocities models of the
remaining areas, representing the exterior stone panels and the holy rock, as they have
similar synthesis. Based on this calibration, a velocity of v=11.58 cm/ns (σ=1.02 cm/ns)
was calculated. It should be noted that the stone ashlars that were used for the construction
of the Bell Tower of the Church of the Holy Sepulchre had a velocity of v=10.48 cm/ns, as
measured during a previous diagnostic study with non-destructive techniques by the
research team of NTUA (Labropoulos and Moropoulou 2013).
a)
b)
Fig. 2: a) Plan of the Aedicule (at a height of 130cm from the interior floor); b) Overall
process of conversion of a GPR scan into a graph distance - depth
It should be noted that the scan after its processing with the aforementioned filters still
remains a distance – time graph. Specifically, the horizontal axis corresponds to the
displacement of the antenna over the surveyed surface, whereas the vertical axis of the
graph corresponds to the time elapsed between the moment when the electromagnetic pulse
is emitted from the antenna on the surface, its diffusion within the masonry, its encounter
with an interface of materials of different electrical properties, its partial reflection towards
the exterior surface, and its detection by the receiver antenna. The amplitude of the
reflected pulse is attributed with shades of grey, where black and white correspond to
maximum intensity of a pulse with positive or negative polarity correspondingly, whereas
grey corresponds to zero intensity of the detected pulse. Figure 3b/B presents with a blue
color the palmograph at position X=0.07 m from the beginning of the scan, where the
various reflections per time lapse (blue line peaks) are visible, and in particular the
reflection of the exterior panel / Komnenos construction phase at approximately 3ns. For
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the calculation of the pulse velocity of the Komnenos construction phase, scans in the N2
area were calibrated, where most probably the masonry consists mainly by stone/marble
panels (exterior and interior) and one internal building phase. Following these, Fig. 3b/C
and Fig. 3b/D present the application of the velocity model on scan H004. The various
layers are identified by the user and are depicted on the scan. From the exterior surface and
inwards, the various layers are shown. Grey: exterior stone panel, Yellow: Komnenos
construction phase, Blue: Crusader’s construction phase, Brown: Holy Rock of Golgotha,
Light Green: Masonry layer between Holy Rock of Golgotha and interior marble panel.
Green: Interior marble panel.
Figure 4 presents in a descriptive approach the various layers within the Aedicule structure,
as analyzed by GPR and retains the plan of the current structure and the exterior boundary
of the 11th/12th century building (red outlines). The BN3 plane and the longitudinal axis
conceptually define the four quadrants A1 – A4 of Fig. 3a. Starting from the southwest
quadrant A4 of the Aedicule, and analyzing with the aforementioned methodology the
various detected internal interfaces, from the south exterior towards the interior of the Holy
Sepulchre, the following are revealed: a) exterior panel, b) Komnenos construction phase,
c) Crusaders construction phase, d) Holy Rock, e) masonry between Holy Rock and interior
panel, and f) interior panel.
a)
b)
Fig. 3: Layering within the Holy Aedicule (cross-section at height level 130cm and 160 cm,
left and right, respectively) as identified by GPR analysis (Moropoulou 2016).
The exterior panel has a varying thickness of 10-15 cm, and corresponds to the first zone
(0-15 cm) at the respective GPR scans of the exterior surfaces. Moving towards the interior,
an interface is observed at a depth of 30-40 cm. The layer between the exterior panel and
this interface corresponds to the Architect Komnenos construction phase, and is indicated in
Fig. 3a as a yellow colored zone. Moving further towards the interior, the GPR scans reveal
the presence of a second interface, at a depth of approximately 50-60 cm. The layer
between the red dashed curve – internal boundary of the Komnenos construction phase –
and this second interface, corresponds to the 12 th century masonry, i.e. the Crusaders
construction phase. It should also be noted that the 12th c. masonry appears to have an
increased thickness, approximately 30 cm eastwards (area N3), in comparison with a
thickness of 20cm westwards (area N4, as well as throughout quadrant A1). This
observation, in conjunction with a) the slight rotation of the Holy Tomb in respect with the
longitudinal axis of the Aedicule and b) the different location, towards the north, of the 8 th
pillar of the Crusaders phase, in relation to its location at the original dodecagon building,
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can lead to the theory that the Holy Rock solid volume, or at least whatever remained from
its successive carvings, did not have a canonical dodecagon plan in full correspondence
with the pillars of the original dodecagon building, but possible had a transverse dimension
slightly smaller than the longitudinal one. Therefore, the addition to the Holy Rock of the
12th century masonry, possibly reinstated the canonical geometry on the apparent volume of
the Holy Rock. The revealed layers within quadrant A1 of the Aedicule are the same as that
of quadrant A4. The 12th century masonry appears, however, to have a thickness of
approximately 20cm, throughout quadrant A1, in contrast to the case of quadrant A4.
Regarding the Chapel of the Angel, and based on the analysis of GPR scans, there are
indications that on the northern side and on the eastern side parts of the Crusaders’ masonry
were retained (Fig. 3), on which deep carving was performed to its interior, to facilitate the
northward expansion of the Chapel. The old wall was retained – on the north part of the
Chapel of the Angel – probably to the full length of the Chapel, up to the façade area
(Moropoulou 2016). The retained height is probably approximately up to 1,5m above the
interior floor level, this corresponding to the height of the entrance of the northern staircase
and its first three steps. Above that height, the masonry is most probably entirely new,
constructed during the 1810 restoration works. Correspondingly, at the southern part of the
Chapel of the Angel, GPR analysis indicates that retaining of Crusaders’ phase masonry
occurs only at the southeastern corner (Fig. 3), up to height similar as the one on the
northeastern corner.
4.2. Building Material Characterization
4.2.1. South Façade Building Stone
Based upon the XRD pattern of Fig. 4a the sample mainly consists of carbonate minerals
(CaCO3), most particularly micrite calcite, approximately 98%, which in places becomes
microsparitic, while quartz crystals, clay minerals, opaque metallic mineral oxides and iron
hydroxides are found at < 2%. This stone is characterized as a micritic fossiliferous
limestone. With regards to the Microstructural Analysis (Fig. 4b), the building stone’s
Cumulative Volume 1.21 mm3/g, Bulk Density 2.67 g/cm3, Total Porosity 0.32%, Average
Pore Radius 0.005 μm and Special Surface Area 0.39 m2/g.
a)
b)
Fig. 4: Outer façade building stonet: a) XRD pattern and b) Pore size distribution.
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4.2.2. Architect Komnenos Restoration Mortar
According to the XRD pattern of Fig. 5a and the thermal analysis results (Fig. 6) and, the
examined are characterized calcitic with a slightly hydraulic as it presents high or even very
high percentages of natural bound water (hygroscopic). The important mass loss observed
in the temperature range 200-600οC, is attributed to four factors:
1.) Saturation of aluminate compounds of the marly limestone in water, which has led
to the intense disintegration of the mortar, simultaneously diminishing its
mechanical properties;
2.) Presence of organic compounds in the mortar composition which can be validated
through FT-IR measurements;
3.) Presence of ettringite; ettringite is crystallized with 16 crystalline waters, and it is
produced by the corrosion of the crust of larnitic rocks. The characteristic peaks of
ettringite can be found in XRD pattern of Fig. 5a;
4.) Large mass loss in the temperature range from 200 to 600 oC is due to the slightly
hydraulic nature of the mortar which provided high mechanical strength to the
mortar at the time of its application. With regards to the microstructural analysis
(Fig. 5b), the mortar’s cumulative volume 570.5 mm3/g, bulk density 0.98 g/cm3,
total porosity 56.03%, average pore radius 0.24 μm and special surface area
15.25 m2/g.
a)
b)
Fig. 5: Restoration mortar: a) XRD pattern; b) Pore size distribution.
Fig. 6: Differential thermal analysis and thermogravimetry graphs.
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Acknowledgements
The authors would like to express the gratitude to His Beatitude the Patriarch of Jerusalem
Theophilos III who initiated the program agreement by NTUA with title “Integrated
Diagnostic Research Project and Strategic Planning for Materials, Interventions
Conservation and Rehabilitation of the Holy Aedicule of the Church of the Holy Sepulchre
in Jerusalem”, His Paternity the Franciscan Custos of the Holy Land, Rev. f. Pierrebattista
Pizzaballa and His Beatitude the Armenian Patriarch in Jerusalem, Nourhan Manougian
who that authorized His Beatitude the Patriarch of Jerusalem Theophilus III and NTUA to
perform this research.
References
Labropoulos, K. and Moropoulou, A, 2013, Ground penetrating radar investigation of the
bell tower of the church of the Holy Sepulchre, Int. J. of Construction and
Building Materials, 47, 689-700.
Lavvas, G., 2009, The Holy Church of the Resurrection in Jerusalem, The Academy of
Athens; Greece.
Mitropoulos T., 2009, The Church of Holy Sepulchre – The Work of Kalfas Komnenos,
European Centre of for Byzantine and Post-Byzantine Monuments, Israel.
Montefiore, S., 2012, The Biography Paperback, Phoenix; Jerusalem, Israel.
Moropoulou, A., Bakolas, A., Bisbikou, K., 1995, Characterization of ancient, byzantine
and later historic mortars by thermal analysis and X-ray diffraction techniques, Int.
J. Thermochimica Acta, 269/270, pp. 779-795.
Moropoulou, A., 2016, Materials & Conservation, Reinforcement and Rehabilitation
Interventions in the Holy Edicule of the Holy Sepulchre, National Technical
University of Athens, Greece.
Normal 27/88, 1988, Caratterizzazione di una malta, C.N.R. – I.C.R., Roma, Italy.
Pringle, D., 2007, The Churches of the Crusader Kingdom of Jerusalem, A Corpus,
Volume III, the City of Jerusalem, Cambridge University Press, United Kingdom.
1226
CONSERVATION OF MACHU PICCHU ARCHAEOLOGICAL
SITE: INVESTIGATION AND EXPERIMENTAL RESTORATION
WORKS OF THE “TEMPLE OF THE SUN”
T. Nishiura1*, I. Ono1, A. Ito2, H. Fujita3, M. Morii4, F. Astete5 and C. Cano6
Abstract
Machu Picchu archaeological site, which is called “Ancient capital in the sky”, is one of the
most important and famous world-heritage. It was the special place of the Inca Empire in
the sixteenth century located on the high ridge in Peru. There are about 200 remaining
structures built of stones (granite) at the site of 13,000 km2. Systematic conservation
measures for the structures has not been applied, except emergency ones by the regional
office. Thus, the authors have started the project for the conservation of the remaining
structure, especially for the preservation and restoration of “Temple of the Sun”, which is
one of the most important structures in the site, in cooperation with the Ministry of Culture
of Peru. There are three major problems on the Temple of the Sun. One is that the stones of
the structure have cracks caused probably by lightening thunderbolts. Another problem is
that the structure became unstable because some of the joint parts among the stones are
open since it was excavated. The third one is the growth of lichens causing chromatic
alterations on the surfaces. The main activities of the project are reported.
Keywords: Machu Picchu, world heritage, stone structures, Temple of the Sun, granite
1. Introduction
Researches on deterioration and conservation of Machu Picchu archaeological site have
typically been approached from geological or civil engineering aspects of study due to its
unique setting of its mountain top location. In addition, many anthropological studies have
been made.
1
T. Nishiura* and I. Ono
Professor, Kokushikan University, Japan
nishiura@kokushikan.ac.jp
2
A. Ito
Kansai University, Japan
3
H. Fujita
Niigata of International and Information studies, Japan
4
M. Morii
National Research Institute for Cultural Properties, Japan
5
F. Astete
Office for Conservation and Administration of Machu Picchu Region, Ministry of Culture, Peru
6
C. Cano
Cusco University of Art, Peru
*corresponding author
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In regard to individual condition of granite dimension stones, a local conservation office
had been in charge of taking care of responsive emergency measures, however, a
comprehensive survey, research or restoration project has not yet undertaken. Therefore,
Japanese cooperation project under the cooperation of Cuzco Regional Office of Ministry
of Culture, Peru and Office for Conservation and Administration of Machu Picchu Region
was now established to take on in situ conservation and restoration technique research
particularly for Temple of the Sun.
Fig. 1: Machu Picchu site.
Fig. 2: Temple of the Sun.
2. Temple of the Sun
2.1. General
Temple of the Sun is one of the most significant remaining structures in Machu Picchu
archaeological sites. The dry stone technique employed to stick up stones on top of natural
stone bed is remarkable and considered to be the best construction technology in Machu
Picchu ruins. The sacred chamber situated on top of the sacred burial is dedicated to the
Sun. On Eastern wall, there are two windows, from one of which the sunlight comes
through on the winter solstice and on the summer solstice from another. When the building
was in use, it is said that the golden statue was placed on the natural rock pedestal with a
large bronze mirror set on the northern window to reflect golden sunlight.
2.2. Present Condition
Granite material degradation is most obvious in the Temple of the Sun. Exfoliation,
delamination, fissures, cracks of both large and small and missing parts are all detected in
the stones used in the structure. The cause for these damages is considered to be heat.
Granite as of its mineral composition is sensitive to fire and excess heat (remark: above 573
when quartz changes the structure. Gaps between stones caused by secondary phenomena
are bringing the building to a danger of collapse. Recent growing of lichens on the surface
is also noted. This is a cause of surface change of appearance.
There are two theories for the cause of hyper heating. One is of man-made fire during the
excavation time (1912-15). The excavation team cut down trees and dead branches and
burns them during the archaeological excavation survey inside the temple. The high
location of the site and circular protected high wall would have offered good conditions for
wood burning. It is common hearsay information among the locals.
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Another theory is the thunderbolt. After Machu Picchu site was abandoned, the large
bronze mirror was said to have attracted the thunderbolt. The area where the mirror was
supposed to be situated was damaged most severely. The stones of the area were specially
worked on for setting a mirror. If a manmade fire is to be a cause, a lot of substantial black
carbon would have been left on the stone surface, but it is not so obvious. This is also a
supportive evidence for the thunderbolt theory. However, the large bronze mirror or
similar objects have not found.
Close comparisons of historical photographs to present condition do not support evidence
of dismantling and reassembling of stones (Fig. 3). Fissures of one area, however, seem to
be progressive more aggressively. We continue comparison survey with historic
photographs to confirm. If there was no hyper heating damage at the discovery time,
thunderbolt must have occurred after the excavation period. Since the mirror was not found
at the discovery, the facts may support more for the manmade fire damage theory. We are
still investigating and not yet come to a conclusion, but are inclined toward thunderbolt
theory.
2.2.1. Extreme damage at the northern opening
There are traces of severe degradation of interior wall of the sacred chamber. Especially
surrounding the northern opening is most evident. This opening was said to be the place
where a big bronze mirror used to be. The stones used in the area were cracked and many
pieces were lost. The movements of the stones are also found that made the structure
unstable (Fig. 4). For stabilization of this area, substantial repair and consolidation of stone
material is necessary.
Fig. 3: Upper: 1915, Lower: 2013.
Fig. 4: Severe damage of the
northern opening area.
2.2.2. Exfoliations and cracks found on the interior curvilinear wall
Exfoliations and cracks are evident of interior curvilinear wall of the chamber. This is
typical damage phenomenon when granite was under hyper heating (Fig. 5).
2.2.3. Missing pieces of the edge stones
Many of the edge stones of the walls lost its pieces due to cracks of the material stones
(Fig. 6).
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2.2.4. Stone movement and vertical gaps arising
Movements of the dimension stones of horizontal directions, due to some kind of shocks
such as earthquakes, created vertical gaps among stones. These gaps seem to have already
been evident during the time of excavation, but the rate of progress was not yet measured.
Peruvian restoration technologists filled these gaps, some of which are as large as 5cm, as
emergency measures using special clay mixture of reversible materials.
2.2.5. Fissures in natural rock pedestal
Numbers of cracks are found in the natural rock pedestal in the sacred chamber. These
cracks pass through the rock completely in longitudinal direction. The upper part must
have been detached. The special clay mixture is presently filled in these fissures to prevent
excess water to fill the fissures and plants to grow there (Figures 3 and 7).
Fig. 5: Cracks and detachments.
Fig. 6: Missing parts of edge stones.
Fig. 7: Decay of natural rock pedestal.
2.2.6. Stone surface degradation
Graining or sugaring is not so evident on these stone surfaces. Growth of lichens evident
on the exterior walls changes colors (greying) and appearances of the ruins. The manual
cleaning with wire brushes were provided two years ago, but now the situation was brought
back to the before cleaning state.
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3. Investigations
3.1. Climate Condition
The meteorological observation station is set in the mountainside from the Sentry Hut to the
Inca Bridge in Machu Picchu site. Temperatures, humidity, precipitations, wind velocity
and directions, and sunlight amount are recorded at this station. We were able to access the
data of the last several years provided by the Peruvian side. In order to analyze fully we
need to get an access to the raw data, which is in discussion. The interim analyses with the
given data are as follows:
Fig. 8: Monthly maximum and minimum
temperature.
Fig. 9: Monthly average humidity.
Data was of monthly reports since September 1998 until August 2013. Fig. 8 shows
monthly highs and lows of the temperature during the recorded period. The rainy season of
the region is normally from November till March. The dry season is from May to August.
The temperature difference during the rainy season is smaller than the dry season. Fig. 9
shows monthly mean relative humidity. As is in Fig. 8, differences correspond to the rainy
and dry seasons, and mean relative humidity of over 80% throughout the year. Fig. 10
shows means of monthly-accumulated precipitation during the recorded period. The total
annual precipitation at the observation station records quite high, 2,150 mm, and 70% of
which are concentrated during the rainy season. The site is thus said to be in relatively high
in humidity, which is the geographical situation surrounded by the mountains with
vegetation. The high concentration of heavy precipitation as much as 300 mm in a month
during the rainy season is not so uncommon, but that can lead into landsides of the site or to
the access roads in the buffer zone.
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3.2. Three-Dimensional Surveying of Temple of the Sun
In order to accurately measure the present condition of the Temple of the Sun, 3D
measuring using total station was made.
Fig. 10: Monthly precipitation.
Prior to the measuring survey, we went over previous measured datum points closely and
utilized all usable points and data. Additional points were then measured from these
measured points. Using these newly measured points, we obtained plane table outfits inside
of the Temple of the Sun and produced a precise contour map of the area. The map is
captured by the 3D data points including usable points especially for photographic
measuring and scanning.
For the purpose of recording degradation condition of stones, fissures and cracks, we used
photogrammetry to produce 3D imaging. By capturing 3D data, scale of stone to stone
relationships and sizes of gaps are quantitatively measurable.
We used 3D scanning function of the total station to monitor the rate of displacement
degree and to make a model. For scanning, vertical and horizontal measuring pitch degree
must be determined. In this case, the exterior pitch is not completely even due to lack of
foundation on exterior wall. In order to create an accurate model, additional measuring will
become necessary. The model created this time was to adjust visual perception.
3.3. Tests in Situ
3.3.1. Injection of resins into cracks of a rock
As a testing of conservation measure, we injected resin into fissures of a natural rock in the
site with a gap opening of 0.6mm. In order to avoid spilling of the resin, we applied
ethylene vinyl acetate copolymer adhesives and then to applied stone powder and grains to
treat the stone surface before injecting 100 cc of epoxy polymer emulsion using syringe. If
we use manual pump injector, agent will reach further and will become more effective.
3.3.2. Application of a biocide against Lichens
In August of 2012, testing of biocide agent was applied on places where lichen infestations
are widespread on a natural rock in the site. The biocide was applied on four area (0.1m2)
on four sides on north, south, east and west of the natural rock (about 500g/m2). After a
year, obvious effect is not yet evident, while another testing place with the same biocide
agent set outside of the site in March of 2012 shows more apparent effect (Fig. 11).
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3.3.3. Reattachment of detached stone brocks to the natural rock pedestal in Temple of the
Sun
Stone pieces of the pedestal rock had been detached for the section of about 60 cm in
length. There were three detached pieces left as a remnant. We experimentally put these
three pieces back to where they had been and filled in missing parts with an artificial stone.
The specification used for the experimental restoration is as follows. Technically there was
no particular difficulty in application (Fig. 12).
1) Wash the surface with water where detachment occurred.
2) Apply epoxy adhesive of grease texture and attach the fallen pieces pressing with
wooden mullet and then to remove the piece once to see if the adhesive is evenly
spread on the joining surface.
When uneven application of the adhesive is
noticed, add it to even out.
3) Set in the piece again with pressure and remove again. Confirm attachment of
entire joining surface and press the piece firmly. Leave it until the adhesive
completely cured.
4) The joint line left at the restored part is camouflaged with powdered artificial stone
of a mixture of ethylene vinyl acetate with both fine and grainier granite powder
with small amount of lime. This will bring a result of natural appearance and
acceleration of curing.
Fig. 11: Application of a biocide against
lichens.
Fig. 12: Reattachment of detached brocks to
the original position of the pedestal rock.
4. Measures for the Conservation
4.1. Principle
The primary, but the most substantial issue is whether to disassemble the stone wall or keep
it as it is. The both approaches have merits and demerits which have a relation opposite
each other.We have been considering the issue from various angles generally together with
the Peruvian government, experts for restoration and academic experts. And, presently we
plan to respect the discussion between UNESCO and Peruvian government, stabilizing
method will be the basic approach.
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4.2. Conservation measures
4.2.1. Capping on the top of the structure
In order to avoid further decay of the structure, protection from rainwater to penetrate down
into the structure is prim. For that purpose, application of water-proofing layer on the top
(capping) is effective. As a possible material for capping, cement mortar is very effective.
But, cement is not desirable because it is irreversible, has inappropriate appearance and
contains soluble salts which may cause secondary decay.
Clay mixture is then an alternative material for capping. Quality of the base clay must be
very high. Mixture should contain lime and water-repellant to increase durability and
water-resistance property. In Machu Picchu site, good quality clay mixture prepared by a
local technician had been used for filling gaps, cracks and missing parts. Generally
speaking, the clay obtained from the granite bed is known to be high in quality. For these
reasons, use of this clay is considered to apply.
4.2.2. Consolidation and restoration of stone
Prior to the above mentioned capping, consolidation and restoration treatments to the
decayed stones are necessary. The techniques to provide these treatments are available, but
they take time and toil when disassembling is not an option
4.2.3. Filling the gaps between stones
Displacements of stone blocks created unwanted gaps among the stones. The opening can
be as large as 5cm in width. For such gaps, Clay mixture mentioned above was used to fill
in and so far they are working.
A new method, that durable and irreversible synthetic resin is injected into inner part of the
gaps and then the clay mixture is apply to the outer part of them, is currently suggested by
the Peruvian professional group. This method is easy in technique, but should be discussed
from the point of view of conservation philosophy. Now we are considering.
4.2.4. Restoration of the rock pedestal
Large crack found in the rock pedestal is confirmed to be causing complete detachment of
upper part. But the condition is stable due to the clay used to fill in these gaps and the
weight itself of upper detached piece. However, we noticed that the movement is still
progressive and we would have to make a decision on when we remove the detached piece
and place it back before the fall. This work requires some kind of heavy machinery or an
equivalent. Skilled technicians who are able to maneuver them in the extreme condition are
required as well. At that time, the heavy blocks should be jointed and the missing parts
filled. The specifications of the method and skilled technicians who could operate the
restoration are in search. In this summer, precise investigation in situ will be conducted for
this work.
4.2.5. Elimination of lichens, and consolidation and hydrophobic treatment of stone
surfaces
Since the cohesion of the stones is quite good, impregnation treatment with silicone
consolidant is not necessarily needed. It can be applied as preventive treatment against
future deteriorations.
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As for the elimination of lichens from the surface of the stones, the biocide which has been
tested in situ is showing good effect. Probably use of this biocide will be suggested. After
lichens are disappeared, the surface of the stones will be perhaps impregnated with
hydrophobic silicone consolidant, though this treatment is still in discussion.
5. Acknowledgment
The “Project for Conservation of Machu Picchu Archaeological Site” is supported mainly
by JSPS KAKENHI Grant Number 24404001, and partly by The Asahi Shinbun
Foundation (Grants for conservation of cultural properties), The Sumitomo Foundation
(Grant for the Protection, Preservation & Restoration of Cultural Properties outside Japan)
and Center for the Global Study of Cultural Heritage and Culture, Kansai University. We
sincerely thank them.
References
UNESCO, Historic Sanctuary of Machu Picchu, (whc.unesco.org/en/list/274, accessed 10th
October 2009).
Nishiura, T. et al., Conservation of the Machu-Picchu Archaeological Site: Investigation
and Experimental Restoration Works of “Temple of the Sun”, The Journal of
Center for the Global Study of Cultural Heritage, and Culture, Vol.1, Kansai
University, 67-79.
Nishiura, T. et al., Conservation of Machu-Picchu Archaeological Site: Investigation and
Experimental Restoration Works of “Temple of the Sun”, in proceedings of
International Symposium on Conservation of Ancient Sites on the Silk Load in
2014, Dunhuang, China, 98-101.
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1236
LAS CASAS TAPADAS DE PLAZUELAS – STRUCTURAL
DAMAGE, WEATHERING CHARACTERISTICS AND
TECHNICAL PROPERTIES OF VOLCANIC ROCKS IN
GUANAJUATO, MEXICO
C. Pötzl1*, R.A. López-Doncel2, W. Wedekind1 and S. Siegesmund1
Abstract
The building stones of the pyramids of Plazuelas were analysed in terms of their pore
space, water transport and retention properties, as well as their mechanical properties and
weathering characteristics. Based on mineralogical composition, different types of tuff
could be distinguished. In a field survey the structural damages and their intensities were
mapped in situ at every wall of the main building. The field investigation uncovered
substantial types of damage in the used tuffs. The specimens for the laboratory
investigations were prepared parallel and perpendicular to the lamination to distinguish
effects of the anisotropy. The data shows that the pore space properties have the largest
influence on additional rock properties (e.g. hygric expansion) of the tuffs, and hence the
largest influence on the weathering resistance of the stones. Due to the local climatic
conditions, some of the building stones, which would be commonly classified as unsuitable,
could be classified as a proper building stone.
Keywords: tuff, weathering characteristics, technical properties, damage mapping
1. Introduction
The suitability of tuffs as building stones is strongly dependent on the environmental
conditions. Therefore it is not always possible to give a general statement in terms of their
application. In Mexico tuffs were used as raw material for the construction of churches,
pyramids and other monuments. Due to infrastructure and availability rocks in the
immediate vicinity were usually used. In the federal state of Guanajuato (Mexico) the
Chichimecas, a sophisticated predecessor culture of the Aztecs that populated the adjacent
Bajío region, created the pyramids of Plazuelas at approximately 450 AD (Castañeda López
and Gutiérrez Lara, 2014). The central temple complex, which is also known as Casas
Tapadas, consists of four pyramids and an adjacent ballgame court (Fig. 1) and is possibly
connected to the worship of their gods. Because the pyramids were enlarged at least three
times, one can find a minimum of three phases of construction. Around 900 AD the
complex was abandoned due to a fire, which has been documented to date in the form of
discoloration of the façade leaving considerable structural damages. In 1998, after the
1
C. Pötzl*, W. Wedekind and S. Siegesmund,
Geoscience Centre of the Georg August University Göttingen, Germany,
christopher.poetzl@gmx.de
2
R.A. López Doncel
Geological Institute, Autonomous University of San Luis Potosí, Mexico
*corresponding author
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temple complex was buried for several centuries due to sedimentation, the Casas Tapadas
were officially rediscovered and excavated in the following years.
The building stones of the pyramids experienced more than a thousand years of weathering
processes and show damages and weathering characteristics equivalent to that length of
time. To make sustainable and effective protection for the preservation and conservation of
these valuable cultural assets, the consolidated scientific findings of the physical and
mechanical properties of the building stones as well as their weathering characteristics are
indispensable.
Fig. 1: a) View from the south over the ballgame court to the main pyramids; b) West side
of the central pyramid with the main entrance; c) South side of the central pyramid.
2. Materials and methods
In this investigation seven different tuffs and volcanic rocks from Guanajuato were
analysed. Mineralogical composition and whole rock chemistry were analysed by both
optical and geochemical methods (polarized light microscopy, X-ray diffraction (XRD) and
X-ray fluorescence (XRF) spectroscopy). Matrix and bulk density as well as the porosity
were measured by hydrostatic weighing according to the DIN 52 102. The pore radii
distribution was determined by mercury intrusion porosimetry. The capillary water
absorption was measured according to DIN ISO 15148. The water vapor diffusion was
measured according to DIN ISO 12572. The sorption was measured according to the DIN
ISO 12571 in a climate chamber. The tensile strength measurement was determined by
means of the Brazilian test. To determine the weathering behavior of the tuffs during
temperature changes, a thermal expansion experiment was carried out in a climate chamber
under dry and wet conditions. The moisture expansion of the rocks was determined by
hydric wetting of cylindrical samples under water–saturated conditions. The specimens for
the laboratory experiments were prepared parallel and perpendicular to the lamination to
distinguish potential effects of anisotropy. To investigate the resistance of the rocks to salt
stress, a salt-weathering test according to the DIN EN 12370 was performed. As an index of
salt resistance the numbers of test-cycles were used till a 30 % of weight lost was
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established. In a field survey the lithologies, the structural damages and their intensities
were mapped in situ at all four sides of the main pyramid of the Casas Tapadas.
3. Results
3.1. Petrology and mineralogy
The volcanic rocks range in age from Paleogene to Quaternary (Cotler Avalos et al., 2006),
with chemical compositions that vary from basaltic andesite to rhyolitic tuff. The
petrographic analyses of each rock sample were done on orientated thin sections under a
polarization microscope (Fig.2).
Fig. 2: Illustration of the volcanic rock samples described in detail. Top: Polished section.
Bottom: Thin section under polarized light
The Toba rosa (TR) is a white to reddish rhyolitic tuff with grey clasts embedded in a
characteristic flow texture. It mostly consists of a hypocrystalline matrix of quartz, feldspar
with approximately 20 % vitric material and clasts and melting lenses up to 50 mm in
length. TR is the most used rock on the pyramid. The Toba blanco laminado (BL) is a white
to yellowish green rhyolitic tuff with a clearly recognizable lamination. Altered rocks of
this type show a reddish colour. The reddish to brown clasts are less than 1 mm in size.
Grey, extremely elongated clasts can be found between the layers. The Toba lapilli amarillo
(LA) is a yellow to greenish porphyritic lapilli tuff with a dacitic composition. The
proportion of clasts shows strong variations, while clasts can show sizes over 5 cm and
often show andesitic composition. Variations of compact layers of ash and layers mostly
consisting of clasts also occur. The rocks appear to be very porous and show many gas
inclusions. It is the second most used building stone in the pyramid. The Andesita oscuro
de Sierra de Penjamo (AO) is a microcrystalline andesite black in colour and only shows up
in certain areas of the pyramid in the form of slabs of up to 5 cm of thickness. AO consists
of feldspar phenocrysts with an average size of 0,2 mm with a slight orientation. The Toba
lapilli beis (LB) is a beige porphyritic lapilli tuff with a clearly acidic composition
(rhyolitic tuff). It shows slightly orientated brown clasts of pumice with sizes up to 3 cm.
The Tezontle de Plazuelas (TE) is a red pyroclastic rock with a composition of a basaltic
andesite. It appears similar to the basaltic bomb named Tezontle, which can be found
nearby Mexico City. Due to many gas inclusions, the rock appears to be very porous and
lightweight but strongly welded with a recognizable lamination. The Toba lapilli rosa (LR)
is a beige to reddish rhyolitic tuff with red to brown clasts of pumice. The clasts are slightly
orientated and show sizes up to 5 cm. The cryptocrystalline matrix makes up about 70 % of
the rock. The volcanic lithic clasts mostly consist of feldspar.
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3.2. Petrophysical properties
Whenever possible the measurements were done in three perpendicular directions of the
rocks. The direction parallel to the bedding/lamination is defined as X, the direction parallel
to the bedding and perpendicular to the lamination is defined as Y and the direction
perpendicular to the bedding is defined as Z.
3.2.1. Pore space properties, water transport and retention properties
AO shows the lowest porosity with 0.63 vol% while having the highest bulk density with
2.73 g/cm3. TR and BL show a medium porosity of 21.1 % and 14.68 vol% and medium
bulk densities of 2.05 and 2.23 g/cm3, respectively. The remaining rocks show high
porosities up to 32.7 % and low bulk densities ranging between 1.56 to 1.81 g/cm3 (Tab.1).
Pore radii distributions show either a unimodal distribution like AO, LB and LR or bimodal
unequal like TR, BL, LA and TE (Fig.3). The amount of micropores in the rocks ranges
between 9 to 85 % (Tab.1). Microporosity is defined as the pores <0.1 µm and capillary
pores are defined as pores between 0.1 to 1,000 µm (Klopfer, 1985). The rock with the
highest amount of micropores is LA with 85 %, followed by AO with 81 % and TR with
70 %. The remaining rocks show microporosities less than 30 % (Tab. 1).
Tab. 1: Pore space properties, moisture transport and retention properties.
Stone type
Toba rosa Toba blanco
Toba lapilli
Andesita
Toba lapilli Tezontle de
Toba lapilli
(TR)
laminado (BL) amarillo (LA) oscuro (AO) beis (LB) Plazuelas (TE) rosa (LR)
Effective porosity (vol%)
21.1
14.68
29.98
0.63
32.42
32.7
29.39
Matrix density (g/cm3 )
2.6
2.62
2.23
2.75
2.5
2.63
2.56
Bulk density (g/cm3 )
2.05
2.23
1.56
2.73
1.69
1.77
1.81
Average pore radius (µm)
0.09
0.59
0.04
0.05
0.51
2.24
0.62
Microporosity (%)
70
28
85
81
11
21
9
X
14.93
7.79
21.84
0.96
62.85
7.9
56.17
Y
12.41
7.13
35.87
0.99
60.5
7.9
58.36
Z
10.88
4.01
44.49
0.99
59.92
7.13
42.33
27
49
51
3
5
10
27
X
41.39
32.92
14.89
58.66
18.34
18.28
14.3
Y
39.56
22.3
-
-
8.88
32.69
11.36
Z
54.72
33.26
17.51
-
13.27
63.39
14.81
28
33
15
-
52
71
23
0.0097
0.0054
0.0474
0.005
0.0132
0.01
0.02
w value (kg/m2 √h)
Anisotropy (%)
µ value
Anisotropy (%)
max. moisture content u
The w value of the investigated rocks varies considerably. LA, LB and LR show the highest
values with up to 62.85 kg/m2√h (LB). The lowest w value is shown by AO with
0.96 kg/m2√h. The w values of TR, BL and TE range between 4.01 to 14.93 kg/m2√h. The
rocks show anisotropic behavior up to 51 % (Tab.1). With up to 71 % (TE) the rocks show
strong anisotropic behavior of the µ value. The highest µ values are shown by TR, BL, AO
and TE with up to 63.39 (TE). The remaining rocks show µ values ranging between 8.88 to
17.51. The highest u value is shown by LA with 0.0474, followed by LR with 0.02 and LB
with 0.0132. The remaining rocks show u values below 0.01. The least u value is shown by
AO with 0,005. Except for TE, all rocks show higher w values with rising porosity and all
rocks show higher water vapor diffusion with rising porosity (Tab.1).
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3.2.2. Mechanical properties
TR has the highest tensile strength with 13.23 MPa, followed by AO with 11.16 MPa. The
remaining rocks show tensile strength ranging from 5.42 to 2.47 MPa (Tab.2). The tuffs
show medium to high anisotropic behaviour of up to 48 % (LA). Except for TR, all rocks
show lower tensile strength the higher their porosity (Tab. 1 and Tab. 2).
Tab. 2: Mechanical properties.
Stone type
Toba rosa Toba blanco
Toba lapilli
Andesita
Toba lapilli Tezontle de
Toba lapilli
(TR)
laminado (BL) amarillo (LA) oscuro (AO) beis (LB) Plazuelas (TE) rosa (LR)
Splitting tensile strength (Mpa)
X
13.01
4.51
4.73
11.16
5.3
5.42
4.67
Y
13.23
6
4.07
-
5.2
5
4.74
Z
10.81
4.42
2.47
11.2
3.57
4.53
3.52
Anisotropy (%)
18
26
48
0
33
16
26
3.2.3. Thermal expansion, moisture expansion and salt weathering
The thermal expansion of the rocks under dry conditions shows relatively low values
ranging between 0.017 to 0.028 mm/m and low anisotropies (Tab. 3). Under wet conditions
the thermal expansion of TR triples, BL doubles and LA quadruples. Even the anisotropic
behaviour increases up to 45 % for TR. The thermal expansion of LB, TE and LR does not
change much under wet conditions (Tab. 3).
Tab. 1: Thermal expansion under dry conditions and wet conditions, hydric expansion and
salt weathering.
Stone type
Toba rosa Toba blanco
Toba lapilli
Andesita
Toba lapilli Tezontle de
Toba lapilli
(TR)
laminado (BL) amarillo (LA) oscuro (AO) beis (LB) Plazuelas (TE) rosa (LR)
therm. expansion (mm/m) dry
X
0.017
0.022
0.01
-
0.028
-
0.023
Z
0.019
0.021
0.011
0.017
0.026
0.017
0.022
Anisotropy (%)
11
5
9
-
7
-
7
X
0.0335
0.038
0.038
-
0.0275
-
0.0285
Z
0.0605
0.04
0.0425
0.024
0.03
0.0175
0.0255
Anisotropy (%)
45
5
11
-
8
-
11
X
0.351
0.186
0.659
-
0.057
0.085
0.007
Z
0.392
0.183
0.736
0.061
0.054
0.031
0.022
Anisotropy (%)
11
2
10
-
5
64
68
19
19
11
> 40
> 40
> 40
33
therm. expansion (mm/m) wet
hydric expansion (mm/m)
Salt weathering (cycles)
The hydric expansion of the rocks in the X and Z direction is shown in Fig. 3. It shows
values that are partially multiple times higher than the thermal expansion and ranging
between 0.007 mm/m for T10 and 0.736 mm/m for LA. In general the rocks show higher
values for the Z direction and the anisotropy is very high for TE with 64 % and LR with
68 % (Tab.3). Every rock reaches the maximal expansion after a short time. The
microporosity has a large influence on the hydric expansion (Snethlage et al., 1995). In
Fig. 3 we can show a good correlation of the microporosity and the hydric expansion. The
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salt weathering test shows a low resistance in TR and BL with 19cycles and 11 cycles in
LA until destruction. LR shows a medium resistance with 33 cycles and AO, LB and TE
were not affected by salt bursting even after more than 40 cycles. Except for AO, the rocks
show lower resistance against salt weathering when having a high microporosity (Tab. 1
and 3).
Fig. 3: Hydric expansion correlates with the microporosity on the right.
3.2.4. Salt weathering and moisture expansion related to the pore space properties
A high porosity allows the water uptake and distribution to take place and thus letting the
water in the rock interact with the present clay minerals (Ruedrich et al., 2011). Salt
weathering is favoured due to high porosity and a bimodal pore radii distribution of the
tuffs as capillary pores provides the transport for salt solutions and micropores lower the
resistance of the rocks against salt crystallization. We could verify the findings from
(Punuru et al., 1990; Fitzner and Basten, 1994; Benavente et al., 2004) that the pore radii
distribution affects the stone’s durability as a key factor.
3.2.5. Mapping and in situ investigations
Some of the main deterioration and weathering effects are caused by back weathering
(Fig. 4a), fracturing (Fig. 4b), salt efflorescence (Fig. 4c) and scaling (Fig. 4d). These
phenomena are often found in shady areas or areas close to the ground (Fig. 5), where water
or moisture is permanently or temporarily available. The damage types were classified
according to the glossary on stone and deterioration patterns of the International Scientific
Committee for Stone (ISCS – ICOMOS, Anson-Cartwright, 2010). By mapping all four
sides of the pyramid (Fig. 5) and combining the different lithologies with the types of
damage and their intensity, we could detect the main damage sources and the building
stones most susceptible to it quantitatively. Fig. 6 shows a clear correlation of increased
damage intensities and an increased use of the Toba lapilli amarillo (LA) on the north and
west side of the pyramid. The percentages of high to very high damage intensities can be
related to LA. The rocks of the Toba rosa (TR) mostly show medium damage intensities.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 4: Some of the main damage phenomena in the building stones of the pyramids of
Plazuelas. a) Back weathering of clasts and components; b) Extensive fracturing and
craquele; c) Salt efflorescence; d) Scaling; e) Discolouration due to moisture area; f)
Biological colonization.
a)
b)
Fig. 5: Mapping of the south side of the pyramid;
a) Lithographic mapping; b) Mapping of damage types.
1 = 1st construction stage,
2 = 2nd construction stage,
3 = 3rd construction stage.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 6: Quantitative analysis of lithologies and damage intensities.
4. Conclusion
In combination with an increased hydric expansion, the rocks are in a situation where
availability of water can mean both an advantage and a disadvantage. Due to precipitation
the salt is washed out of the rock surface, which lowers the salt crystallization on the one
hand, but increases the hydric expansion on the other hand. By comparing the distribution
of the salt crusts at the different sides of the buildings clarifies how these circumstances are
connected to the exposition of the building stones in the pyramid. Since the main wind
direction is ESE during the rainy period, salt at the south side and east side gets washed out
before it can crystallize. According to this, salt weathering only occurs in areas close to the
ground where rocks can absorb the salt in solution by capillary water at any time. On the
east side this process is lowered due to the influence of the wind. The north and west side of
the pyramid shows an extensive distribution of salt efflorescence all over the façade due to
the lack of influence from the precipitation. On the other hand, hydric expansion only
occurs to a minor degree on these sides.
We were able to show that the building stones of the pyramids of Plazuelas partially
suffered serious damage due to salt weathering and hydric expansion. We could approve
that the pore space properties have a strong influence on the weathering behaviour of the
rocks. Especially the pore radii distribution seems to play an important role. While
providing a good water transport due to capillary pores as well as the availability of
micropores, which lower the resistance against salt crystallization, a bimodal pore radii
distribution with a high amount of micropores has proven to be inappropriate. Despite the
fact that laboratory investigations show high hydric expansion and low resistance against
salt weathering due to a high amount of micropores, the Toba rosa (TR) has proven to be a
suitable building stone under the existing environmental conditions at the Casas Tapadas.
Conservation measures will be challenged by the need of minimizing the salt contamination
while facing the risk of hydric expansion.
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Acknowledgements
Our work was supported by the Consejo Nacional de Ciencia y Tecnología (CONACyT),
Projects Ciencia Básica (CB-130282) and Cooperación Bilateral (191044). We are grateful
to G. Hartmann and K. Wemmer of the GZG for their help with the mineral analysis.
References
Anson-Cartwright, T. (Ed.) (2010), Illustrated glossary on stone deterioration patterns:
Illustriertes Glossar der Verwitterungsformen von Naturstein, Monuments and
sites Monuments et sites Monumentos y sitios, Vol. 15, 1st ed., ICOMOS,
International Scientific Committee for Stone (ISCS); Imhof, Paris, Petersberg.
Benavente, D., del Cura, M.G., Fort, R. and Ordóñez, S. (2004), “Durability estimation of
porous building stones from pore structure and strength”, Engineering Geology,
Vol. 74 No. 1, pp. 113–127.
Castañeda López, C. and Gutiérrez Lara, G. (2014), “La Arquitectura de Plazuelas”, in
Viramontes Anzures, C. (Ed.), Tiempo y Región. Estudios Históricos y Sociales:
Volumen VII: Ensayos sobre cultura material entre las sociedades prehispánicas
del centro-norte y occidente de México.
Cotler Avalos, H., Mazari Hiriart, M., Anda Sánchez, J.d., Garrido Pérez, A. and Pérez
Damián, J.L. (Eds.) (2006), Atlas de la Cuenca Lerma-Chapala: Construyendo una
visión conjunta, Instituto Nacional de Ecología, México, D.F.
Fitzner, B. and Basten, D. (1994), “Gesteinsporosität--Klassifizierung, meßtechnische
Erfassung und Bewertung ihrer Verwitterungsrelevanz”, in Jahresberichte aus dem
Forschungsprogramm Steinzerfall, Steinkonservierung. Band 4, 1992, Ernst,
Wilhelm & Sohn, Verlag für Architektur und technische Wissenschaften GmbH,
Berlin, Germany, pp. 19–32.
Klopfer, H. (1985), “Feuchte”, in Klopfer, H. (Ed.), Lehrbuch der Bauphysik.
Punuru, A.R., Chowdhury, A.N., Kulshreshtha, N.P. and Gauri, K.L. (1990), “Control of
porosity on durability of limestone at the Great Sphinx, Egypt”, Environmental
Geology and Water Sciences, Vol. 15 No. 3, pp. 225–232.
Ruedrich, J., Bartelsen, T., Dohrmann, R. and Siegesmund, S. (2011), “Moisture expansion
as a deterioration factor for sandstone used in buildings”, Environmental Earth
Sciences, Vol. 63 No. 7-8, pp. 1545–1564.
Snethlage, R., Wendler, E. and Klemm, D.D. (1995), “Tenside im Gesteinsschutz-bisherige
Resultate mit einem neuen Konzept zur Erhaltung von Denkmälern aus
Naturstein”, Denkmalpflege und Naturwissenschaft-Natursteinkonservierung I.
Verlag Ernst & Sohn, Berlin, pp. 127–146.
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1246
DESALINATING THE ASYUT DOG IN THE MUSÉE DU LOUVRE
O. Rolland1*, V. Vergès-Belmin2, M. Etienne3, H. Guichard3,
S. Duberson3 and P. Bromblet4
Abstract
The Asyut dog is a one meter high sculpture which is part of the collections of the Louvre
Museum in Paris, France. It was carved in Egypt during the Ptolemaic period, out of a fine
grained limestone, and was found broken into multiple fragments within the frame of an
archeologic campaign in the early twentieth century. The sculpture was restored in the
twentieth century using plaster of Paris, iron and brass rods. Since at least four decades it
shows degradation patterns typical of the action of soluble salts. A general superficial
granular disintegration is observed along with little cracks and scales. Deep cracks linked to
the corrosion and rust formation on iron rods endanger the structural stability of the
sculpture. These deep cracks boke apart the fragments. We took advantage of this
dismantling to use some of these fragments for soluble salts analyses and careful
desalination trials. Sodium chloride (halite) is the most abundant crystallized phase and
most probably takes a prominent role in the degradation, although its equilibrium relative
humidity is far higher (75%) than the relative humidity range in the museum showcase
where the dog is presented (33-65%). Further analyses of the salts extracted from a
fragment of the statue by immersion in water and evaporation at room temperature reveal a
contamination by a very hygroscopic mixture (a brine) the equilibrium relative humidity
(ERH) of which is lower than 33%. We suggest that the unexpected sodium chloride
empowerment of the statue deterioration may be due to the presence of this hygroscopic
brine, which would facilitate the transfer of sodium and chloride ions toward the surface,
thus feeding almost constantly halite crystallization. We propose to call such a hygroscopic
mixture a “transporter brine”.
Keywords: limestone, sculpture, salt, desalination, museum, climate, transporter brine
1. Introduction
The Asyut dog is a life sized sculpture, one meter high, which was carved out of a fine
grained limestone and painted in Egypt during the Ptolemaic period. It was found broken
1
O. Rolland*
Independent conservator, 3 rue du Gué, F-37270, Montlouis sur Loire, France,
olivierrolland@wanadoo.fr
2
V. Vergès-Belmin
Laboratoire de recherche des monuments historiques (CRC-LRMH USR 3224), France
3
M. Etienne, H. Guichard, S. Duberson
Department of Egyptian Antiquities, Musée du Louvre, Department of Egyptian Antiquities, France
4
P. Bromblet
Centre interdisciplinaire de conservation et de restauration du patrimoine, Marseille, France
*corresponding author
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into multiple fragments during an archeologic dig close to a burial site for dogs and wolves,
sacred animals of the local divine canid Oupouaout. Other dog statues are known around
this site, but this is the only one close to the burial site. It entered the Louvre collection in
1923, from a gallery, the year after its probable discovery by Wainwright during Lacau’s
excavations in Asyut. In the 1930’s it was already presented in a showcase, which suggest
that it was judged fragile. It is supposed to have given its name to the “dog stair” in the
museum. After a stay in a box, since 1997 it is one of the jewels of the animal-gods room,
the nineteenth room of the ground floor of the ancient Egypt department (Fig. 1a).
It is only since 2001-2002 that powdering was noticed near the tail. However, photos of the
dog showed degradation patterns typical of the action of soluble salts since at least four
decades. In 2010, superficial granular disintegration and powdering was observed on all the
surface of the statue, especially on its back and even more at the lower part of it; besides,
little cracks and scales were seen on the head and some very little scales were seen in a
whitish zone on the lower part of the back. Stone powder and millimetric fragments were
regularly observed on the floor of its showcase (Fig. 1b). In addition to these surface
deterioration patterns, deep cracks were observed in the legs (Fig. 2) thus endangering the
structural stability of the sculpture. Rust was visible behind the right thigh near the tail.
a)
b)
Fig. 1: a) The Asyut dog in its window case in the Musée du Louvre before restoration
(Photo: Christian Descamp, Musée du Louvre); b) Stone powder and flakes in the
showcase of the Asyut Dog in the Musée du Louvre (Photo: Philippe Bromblet, CICRP).
2. Diagnosis
Radiography and tomography were performed to collect evidence on the metal rods present
inside the stone. A metal detector discriminated non-magnetic rods, in the head and front
legs, and magnetic rods in the rear part of the animal. UV photos made more visible the
fillings and the small plaster of Paris repairs between stone fragments. It appeared clearly
that deep cracks developed mainly in these gypsum repairs and that their initial cause was
the expansion of the iron rods due to rust development in the rear part of the dog.
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To understand powdering and little cracks, we looked at the climatic conditions which had
been registered in the showcase during the year before the study: the relative humidity
varied between 33% and 65%, the temperature varied between 14°C and 25°C. These
conditions were supposed to be the usual ones. We do not know the past climatic conditions
but we can suppose that formerly it might have been sometimes much more humid, at least
during the probable sea transport.
Four samples were taken from the statue (Fig. 2): two samples (ref PA1 and PA2) are mixes
of superficial stone powder and salts collected by brush respectively on the lower part of
the back (PA1) and on the left side of the statue (PA2); Sample 3 is a little piece of stone
taken in a crack with a chisel; Sample 4 consist of stone powder collected by drilling from 3
to 4 cm depth (Pd1). The little stone fragment was used for petrographic analysis: a fine
grained limestone from the Nile Valley was identified.
Fig. 3: Localisation and results of the samples and
analysis on a decay map of the dog.
Samples PA1-2 were first analysed by X-ray diffraction (Bruker D8 Focus diffractometer
(Co Kα radiation) equipped with a Lynx’Eye detector operating with an aperture of 1 °2θ):
halite (sodium chloride) was detected as the major phase, gypsum (calcium sulphate
dihydrate) was detected as a minor phase and natron (sodium carbonate decahydrate) could
also be identified as a very minor component. These results suggest that the surface
deterioration of the statue is probably mainly due to halite crystallization. The equilibrium
relative humidity (ERH) of this salt is 75%, and we have seen that the relative humidity in
the showcase is always under 65%. In these conditions, halite alone should not be
destructive, it should stay its crystallised form.
Soluble sodium and magnesium, chlorides, nitrates and sulphates were quantified in the
samples PA1-2 and Pd1, following the solubilisation procedure of the Italian standard
NORMAL 13/83. Anions were analysed by ion chromatography (DIONEX DX 500 fitted
with an analytical column AS 9 HS) and sodium by Atomic Absorption Spectroscopy
(VARIAN AA240FS).
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In the surface samples (PA1-2) sodium and chlorides are very abundant while sulphates and
nitrates show respectively low and very low concentrations (Tab. 1). At 3-4 cm into the
stone (Pd1), sodium and chlorides concentration is divided by 100, sulphates are divided by
two, nitrates and magnesium have approximately the same concentration.
Tab. 1: Ionic contents at the stone surface (PA1-2) and at 3-4cm depth (Pd1).
Sample
Sulphate
[wt%]
Chloride
[wt%]
Nitrate
[wt%]
Sodium
[wt%]
Magnesium
[wt%]
1.91
1.79
0.77
23.38
33.80
0.19
0.23
0.11
0.18
15.25
21.70
0.07
0.02
0.01
0.02
PA1
PA2
Pd1
3. Desalination test
The dog had to be disassembled to remove the iron rods, so we decided to take this
opportunity to desalt a part of it. We chose a part without any polychromy, a fragment of
the right thigh. The desalination was performed by the bath method. Three successive baths
of demineralised water (added with calcium carbonate) were necessary to complete the
desalination (Bromblet et al. 2011). Water was moved constantly using an aquarium pump.
Fig. 3: Conductivity of the three successive desalination baths of the fragment of the right
thigh.
The desalination was monitored by electric conductivity measurements (Fig. 3). The
fragment was removed from each bath as soon as the conductivity became relatively
constant over the time. We used as less water as possible, in order for gypsum and other
relatively low soluble components to be less removed than very soluble salts such as
chlorides and nitrates. We think that all the salts in the object are part of its history and that
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removing only the largest part of the most soluble salts should be sufficient to stop the
decay. As expected, the first bath contained much more salt than the second one, which
contained more salt than the last one.
4. Characterization of the first bath water
Once the fragment was removed, a sample of the first bath was kept in a fridge for analysis
and the rest was left to evaporate at low temperature (between 20 to 32°C on a heater).
Drying process started in an open container, and then in a hermetically closed box, using a
cup containing calcium chloride oversaturated solution (ERH=33.3% at 20°C) as a
desiccant. In this way we concentrated the soluble salts extracted from the brine of the
stone fragment. The obtained extract contained millimetric halite crystals and a brownish
precipitate the nature of which remained unidentified (Fig. 4a). Such a mixture containing
very soluble and hygroscopic salts in solution was probably present in the statue before
desalination.
The brine was separated from the halite crystals and brownish precipitate. Quantitative
analyses of the soluble species in the water and in its corresponding brine were performed,
using the same analytical techniques as before desalination (Tab. 2). The brine, compared
to the bath, is relatively enriched with nitrates and depleted in sodium, chlorides and
sulphates (Fig. 4b and 4c), Chloride and sodium drop is logical since crystallized halite has
trapped these ions. Sulphates depletion may be due to the crystallization of sulphates
(gypsum, aphthitalite? maybe into the brownish precipitate described above).
b)
a)
c)
Fig. 4: Macrophotography of the evaporation residue from the first desalination bath
showing big halite crystals and smaller brownish crystals (a); Weight proportion of ionic
species (% of mass) in the first bath (b) and its corresponding brine (c).
Tab. 2: Ionic composition of the first bath and its corresponding brine in g/l.
Sodium Potassium Magnesium Calcium Chloride Sulphate Nitrate pH
Bath
71.5
12.4
8.5
46.85
111.87
30.56
211.98 6.8
Brine
185.6
266.5
184.1
633.2
518.0
1.5
4146.7 7.3
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As the brine still contains chlorides, other very hygroscopic chlorides such as calcium
chloride might be present This may at least partly explain why it is not possible to get the
brine in a dry state at room climatic conditions (T~22°C, RH=50%). It is clear that calcium,
sodium or potassium nitrates are not sufficiently hygroscopic to be responsible for such a
behaviour, as their ERH at 20°C are respectively 53.6%, 75.4% (Arnold and Zehnder
1990) and 97.3% (Schwarz H.-J., SaltWiki 2015). The mix has a very low mutual
deliquescence relative humidity (Linnow 2007).
5. Discussion and conclusions
The reasons for the structural deterioration of the statue are clear: rust related expansion,
likely accelerated by chlorides.The analytical results confirm that salt crystallization is
responsible for the surface deterioration of the statue. Halite is the main crystallized salt.
Nitrates, although present, are not identified as crystallized phase: this is quite strange as
potassium is present in the system and its nitrate is less soluble than halite (313 versus
356 g/L) and has a high equilibrium relative humidity (ERH=93.7% at T=20°C). We
observe that the disintegration of the surface heavily contaminated with halite occurs at
relative humidity far lower than halite equilibrium relative humidity. The presence of other
salts may decrease halite equilibrium relative humidity, but we have raised another
interpretation, or maybe just another way to describe the same phenomenon, that we would
like to share with the scientific community: the simple fact that water is present into the
system due to the hygroscopic salts might make it easier for some ions to move towards the
surface at a rate depending on climatic conditions in the showcase and probably on the
concentration and distributions of other ions . In other words, the feeding of the stone
surface by deleterious ions might be partly due to the transfer of these ions in the brine
within the capillary network of the stone. We propose to name this process “transporting
brine hypothesis” (Fig. 5). If it is confirmed, it might concern a large number of objects and
monuments, indoors as outdoors, probably in more complex ways. Nevertheless this
hypothesis has to be confirmed through additional experimental work and investigations
such as the measurement of the sorption isotherm of the brine, and of the stone before and
after desalination. The way we obtained the brine most probably should be optimized also,
as there are some discrepancies between the composition of the bath water and the one of
the brine, in terms of cations/anions balance. Those discrepancies might be due for instance
to bacterial activity (bacteria may in certain conditions extract sulphur and nitrogen from
the salt solution in the form of SO2 and N2), to losses in process of brine collection. The
very slight pH increase of the salt solution from 6.8 to 7.3 during the evaporation process
suggests that carbonates may be more present in the brine than in the bath water.
Eventually the bath desalination procedure we followed was efficient and did not damage
the stone. Considering these results, it was decided recently to desalinate all the other
fragments, of the statue, except the head because of its large polychromy remains. We will
wait for the results of current desalination baths on fragments (neck and ears) bearing
smaller remains of polychromy before deciding whether the head can be desalinated safely.
Fragments are currently in different baths according to their size, and each bath is
monitored by electric conductivity, density and temperature sensors. The data are accessible
24/24 and 7/7 with remote control and transmission by a GSM modem, and a weekly visual
control. When we write this paper on December 2015, the ears and front legs, small parts in
the same bath, are still immersed in their second bath, whereas the body, the larger part, is
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
just at the beginning of its first bath. The polychromy remains seem in good condition. We
begin to evaporate the first bath of the little parts and we plan to do so with each first bath.
Presently the operation goes on as foreseen.
Fig. 5: The transporter brine hypothesis.
References
Arnold, A. and Zehnder, K., 1990, Salt weathering on monument. First symposium on the
conservation of monuments in the Mediterranean basin, ed F. Zezza, Brescia,
grafo, p.31-58.
Bromblet, Ph., Vergès-Belmin, V., Franzen, C., Aze, S., Rolland, O., 2011, Toward an
optimization of the specifications for water bath desalination of stone objects, Salt
weathering on buildings and stones sculptures, Proceedings from the International
Conference, 19-22 october 2011, Limassol, Cyprus , p.397-404.
Linnow K., 2007, Salt Damage in Porous Materials: An RH-XRD Investigation,
Fachbereich Chemie, Universität Hamburg.
Schwarz H.-J., SaltWiki, http://193.175.110.91/saltwiki/index.php/Nitrate (accesseded
23/12/2015).
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
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1254
INVESTIGATION OF SALT CRYSTALLISATION IN A STONE
BUDDHA CARVED INTO A CLIFF WITH A SHELTER BY
NUMERICAL ANALYSIS OF HEAT AND MOISTURE
BEHAVIOUR IN THE CLIFF
N. Takatori1*, D. Ogura1, S. Wakiya2, M. Abuku3,
K. Kiriyama4 and Y. Kohdzuma2
Abstract
Motomachi Sekibutsu is a stone Buddha statue that was carved into a cliff in Oita City,
Japan, around the 11th – 12th century. Salt precipitation, mainly due to a high ground water
level, has been observed at Motomachi Sekibutsu. In this study, we elaborate phenomena
that the precipitation of crystals is caused by evaporation and a decrease in solubility due to
temperature changes. To do so, we examine the heat and moisture behaviour on and near
the surface of Motomachi Sekibutsu by numerical analysis and investigate the influence of
the environment in the shelter on the damage to the statue. Simulation results show that
evaporation generally occurs deep inside the external corner and the surface is mostly dry.
In particular, assuming that the amount of water evaporation is proportional to the amount
of salt precipitation, salt precipitates deep inside the corner in summer to autumn and near
the surface in winter.
Keywords: shelter environment, heat and moisture transfer, water evaporation,
sodium sulphate, calcium sulphate
1. Introduction
Motomachi Sekibutsu is a stone Buddha statue carved into a cliff in Oita City, Japan. It has
always suffered from the influence of moisture penetration through the cliff because the
statue is not and cannot be separated from the cliff. Therefore, at Motomachi Sekibutsu,
various preservation measures have been taken: main measures are constructing a shelter to
intercept wind and rain and boring a tunnel behind Motomachi Sekibutsu to decrease the
ground water level. However, the main factor of degradation, salt damage, has not been
prevented yet.
1
N. Takatori* and D. Ogura
Graduate School of Engineering, Kyoto University, Japan
takatori.nobumitsu.62a@st.kyoto-u.ac.jp
2
S. Wakiya and Y. Kohdzuma
National Institutes for Cultural Heritage, Japan
3
M. Abuku
Faculty of Architecture, Kindai University, Japan
4
K. Kiriyama
Graduate School of Advanced Integrated Studies in Human Survivability, Kyoto University, Japan
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Our ultimate aim is to suppress degradation from salt damage by rebuilding a shelter
covering the Buddha statue and controlling the interior environment. The precipitation of
crystals is considered to be caused by water evaporation and a decrease in solubility due to
temperature changes, the former of which is the main focus of the current study. We
examine the heat and moisture behaviour in Motomachi Sekibutsu via numerical analysis
and account for the seasonal changes of the position of evaporation.
2. Background
2.1. Surrounding Environment
As shown in Fig. 1a, Motomachi Sekibutsu is covered with a wooden shelter of
approximately 7 m wide, 5 m long, and 3.5 m high. However, Motomachi Sekibutsu has
suffered from the influence of the surrounding environment, including heat transmission by
the roof or walls, ventilation into the front door, solar radiation transmission into windows,
and rainfall penetration into the cliff behind the statue.
Motomachi Sekibutsu is composed of tuff, which is a porous material; thus, heat and
moisture transfer through the cliff to the statue. In addition, ground water around
Motomachi Sekibutsu is located approximately 1 m below the ground level. Therefore, it is
estimated that Motomachi Sekibutsu is considerably affected by ground water and remains
a high moisture content environment.
a)
b)
Solar
radiation
Ventilation
Window
Door
Stone
Buddha
Temp. and RH
Measured Point
Fig. 1: a) Exterior of the shelter; b) Plan of Motomachi Sekibutsu.
2.2. State of salt precipitation
At the Buddha of healing, which is located at the centre of Motomachi Sekibutsu, salt
conspicuously precipitates and deterioration by salt damage is ongoing. Na2SO4 and CaSO4
were mainly found on the statue by the Oita City Board of Education (1996). Na2SO4 is
considered to be the most destructive salt (Goudie 1997); therefore, deterioration from
precipitated Na2SO4 is a concern.
On the Buddha of healing shown in Fig. 2a, salt crystals are conspicuously found below the
waist. Moreover, there are few salt crystals on the head. Fig. 2b shows the result of ion
chromatography analysis of ions absorbed by paper placed on the surface of the statue for
desalination (Oita City Board of Education 2014). It can be observed that on the right knee,
all ions except Ca2+ are detected from November to December. In this study, we consider
only heat and moisture transfer and do not consider salt transfer. Therefore, we assume that
salt accumulates with water evaporation (Ogura 2013); thus, we investigate the amount of
salt precipitation based on the amount of water evaporation.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
a)
b)
Amount of salt precipitation
(mEq/g-paper/day)
From Jul. to Sep.
From Nov. to Dec.
From Jan. to Mar.
0.06
0.04
0.02
0
Na+
Ca2+
The Right Knee
Na+
Ca2+
The Left Knee
c)
Salt crystals and
algae on the internal
corner
Fig. 2: a) The ‘Buddha of Healing’, b) Salt precipitation on knees; c) Right knee.
There are some differences in the positions of salt precipitation from the waist to foot
because of the difference in shapes. The right hand is in the most conspicuous location
where salt precipitation differs at each part. The right hand is convex and contains few salt
crystals. Fig. 2c shows that salt precipitates and algae grow on the internal corner, which is
the secluded part. Moreover, on the knee, salt crystals are found, although they are on the
external corner.
3. Numerical Analysis
3.1. Method for numerical analysis
Here, we present a method of numerical analysis to determine the heat and moisture
behaviour in the stone Buddha, including the cliff. Heat and moisture balance equations for
porous materials are as follows (Matsumoto 1984):
𝜕𝑇
Heat balance
: cρ
Moisture balance
: 𝜌𝑤 (
𝜕𝑡
′
= ∇ ∙ {(𝜆 + 𝑟𝜆′𝑇𝑔 )∇𝑇} + ∇ ∙ (𝑟𝜆𝜇𝑔
∇𝜇),
𝜕𝜓 𝜕𝜇
𝜕𝜇
)
𝜕𝑡
= 𝛻 ∙ [λ𝜇′ (𝛻𝜇 − 𝑛𝑥 𝑔)] + 𝛻 ∙ (λ′𝑇 𝛻𝑇).
In this analysis, we use the explicit finite difference method and the space lattice width is
minimized 1 mm near the surface. Moreover, we calculate the amount of evaporation as
follows:
Amount of evaporation:𝑊 = −
𝜕𝜌𝑤 𝜓
𝜕𝑡
− ∇𝐽2𝑤 ,
where cρ is the apparent heat capacity of the material [J/m3K], 𝜌𝑤 is the density of water
[kg/m3], t is time [s], T is temperature [K], 𝜓 is the volumetric moisture content [m3/m3], 𝜇
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
is the chemical potential of water [J/kg], r is the heat of phase change from vapour to liquid
[J/kg], 𝜆 is the thermal conductivity [W/(m ∙ K)], λ′𝑇 is the moisture conductivity related to
temperature [kg/(ms·K)], λ′𝑇𝑔 is the vapour conductivity related to the temperature gradient
[kg/(ms·K)], λ𝜇′ is the moisture conductivity related to the chemical potential gradient of
′
water [kg/(m·s·(J/kg))], λ𝜇𝑔
is the vapour conductivity related to the chemical potential
gradient of water [kg/(m·s·(J/kg))], 𝑛𝑥 is the unit vector vertically downward [-] (1 if it is
vertically downward and 0 if it is horizontally downward), and 𝐽2𝑤 is the liquid water flow
[kg/m2s].
3.2. Analysis target
In this analysis, we analyze the two-dimensional plane whose centre is the Buddha of
healing. The analysis model is the cliff containing the stone Buddha shown in Fig. 3c
because Motomachi Sekibutsu is influenced not only by the room environment but also by
the temperature and humidity of the cliff behind the stone Buddha.
As shown in Fig. 3c, the cliff, including the stone Buddha statue, consists of two-layered
tuff and soil. The heat and moisture properties of tuff and soil are decided in reference to
paper which Li Yonghui et al. (2010) used; however, we modified the saturated hydraulic
conductivity of tuff to be 2.20 × 10−9 [m/s]. The coefficients of heat transfer used are
9.3 W/m2 K and 23.3 W/m2 K inside and outside the roof, respectively, and the coefficient
of moisture transfer was calculated using the Lewis relationship. Fig. 3d shows the space
lattice width and the positions used when examining the results.
a)
b)
Moisture Conductivity
Volumetric moisture content[m3/m3]
0.5
0.4
0.3
Tuff
0.2
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
1.E-08
1.E-09
1.E-10
1.E-11
1.E-12
1.E-13
0.1
0
1.E+06
Chemical potential of water : -μ[J/kg]
1.E+06
1.E-07
Soil
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E-14
1.E+00
1.E-15
Chemical potential of water:-μ[J/kg]
c)
d)
rain
Near the surface : the space lattice width
50mm
soil
10mm 1mm
convention
Neumann boundary condition
insulation, prevention of water
:
Buddha
statue
tuff
room
P1
Transmitted
30mm 20mm
convention
Buddha
statue
water table
P2
P3
P4
Head
Thigh
Body
Leg
P5
Neumann boundary condition
:insulation, prevention of water
Dirichlet boundary condition : Temp16.7℃ the chemical potential of water -7kJ/kg
Fig. 3: a) Equilibrium moisture content; b) Moisture conductivity of tuff; c) Analysis
model ; d) Analysis positions.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
3.3. Analysis conditions
Tab. 1 shows various room conditions used in the analysis. Initially, we performed steadystate analysis to determine the influence of the heat and moisture behaviour arising from the
shape of the statue and ground water on the stone Buddha statue. Next, we performed
unsteady-state analysis to determine seasonal differences.
Tab. 1: Calculation conditions.
Temp. and RH
inside the roof
Temp. and RH
outside the roof
Solar
radiation
Rainfall
Steady
Constant※1
Constant※1
0
0
Unsteady
Measured※2
Measured※2
Estimated※3
Measured※2
※1 The constant value is the annual average value in Oita City: Temp 16.4°C, relative humidity
(RH) 69%.
※2 The measured value used is the annual value from April 2013 to March 2014. Room
temperature and RH in the shelter were measured by Oita City Board of Education (2014), and the
outside temperature, RH, and rainfall in Oita City were measured by the Japan Meteorological
Agency. Rainfall was applied only to the top of the cliff, and half the measured value was used,
considering the influence of rainfall blocking by trees.
※3 The amount of solar radiation was calculated to divide the measured global solar radiation
into direct and sky radiation, considering the shape of the roof, the transmittance of the glass, and
the solar azimuth.
As boundary conditions, the bottom of the ground is the Dirichlet boundary condition:
temperature is 16.7°C at 12 m below the ground level and the chemical potential of water is
7 kJ/kg. As a result of preservation measures, the ground water level is 1 m below the
ground level. The vertical plane of the side of the ground is the Neumann boundary
condition: there is no heat and moisture flux.
4. Results
4.1. Steady-state analysis
In this section, we present the results of the steady-state analysis. We focus on the influence
of the shape of the stone Buddha statue and ground water on the heat and moisture
behaviour.
Fig. 4a indicates the temperature, water content, and amount of evaporation on the surface
of the statue. The positions corresponding to Fig. 4a are shown in Fig. 3d. The water
content on the head and P4 is low; the amount of water evaporation from the same positions
is also low. On the other hand, the water content on P3 and P5 is high, and the amount of
evaporation is also high. The head and P4 are the external corners that are strongly
influenced by room temperature and humidity because a wide portion of these areas is
exposed to air. On the other hand, P3 and P5 are the internal corners that are strongly
influenced by the deep part of the statue.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
a)
b)
c)
d)
Fig. 4: a) Heat and moisture behaviour on the surface of the Buddha statue; b) Weather
conditions from April 2013 to March 2014; c) Annual distribution of moisture content on
parts; d) Amounts of evaporation and moisture content with depth from P4.
4.2. Unsteady-state analysis
Next, we present the results of the unsteady-state analysis. We focus on the fluctuation of
the water content and evaporation in the statue with seasonal changes of room temperature
and humidity. We especially focus on P4, which is strongly influenced by room conditions.
Then, we examine changes in the amount of evaporation.
4.2.1. Weather conditions
Fig. 4b shows annual weather conditions used in the unsteady-state analysis as well as the
solar radiation that enters P4. As shown in Fig. 4b, the temperature and RH inside the
shelter fluctuate more slowly than those outside. The amount of solar radiation is the
highest during the winter solstice because of the placement of windows.
4.2.2. Depth of evaporation
Fig. 4c shows the annual fluctuation of the water content on parts shown in Fig. 3d. There
is a low water content on P1 and P4, and the water content only increases by July. On the
other hand, there is a high water content on P3 and P5. The water content intensely
fluctuates throughout the year only on P2. The surface of P4 tends to be dry because it is
the external corner. Therefore, the water content on P4 increases from June to July when
the room humidity increases. It is believed that the water content on P4 is high throughout
the year because it is the internal corner and strongly influenced by ground water.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Fig. 4d shows the monthly average value of water content and the amount of water
evaporation from the surface to deep part. The horizontal axis indicates the distance from
the surface; the 0-mm point is the surface. In July, the water content is high from the depths
to surface; therefore, water evaporates mostly on the surface. However, water evaporates
only slightly on the surface when the water content is low; it evaporates mostly from the
deep part of the statue. Fig. 4d shows that water mostly evaporates where the water content
increases rapidly.
5. Discussion
First, we discuss the results of the steady-state analysis. With the fluctuation of room
conditions, water evaporates not only on the surface but also from a deep part of the
Buddha statue at the external corner; on the other hand, water evaporates near the surface at
the internal corner when the ground water level is sufficiently high to keep the deep part of
the statue nearly saturated. Consequently, assuming that salt accumulates with water
evaporation, it is considered that salt precipitates in the deep parts of the head and P4,
which are the external corners. In contrast, on P3, which is the internal corner, salt
precipitates mainly near the surface.
P1
P2 P3
Evaporation(g/m3s)
20
16
P5
P4
Difference by the shape
Don't find
salt crystals
12
Evaporation
8
salt crystals on
the internal cornaer
4
0
Head
Body
Thigh
Leg
Fig. 5: Positions of salt precipitation.
Next, we discuss the seasonal changes of salt precipitation determined by unsteady-state
analysis. On P4, which is the knee of the Buddha of healing, water evaporates mainly from
the deep part from summer to autumn and near the surface in winter. Therefore, assuming
that the amount of water evaporation has a proportional relation with the amount of salt
precipitation, salt precipitates in the deep part from summer to autumn and near the surface
in winter. However, Fig. 2b shows that a remarkable amount of Na2+ was detected on the
knee in winter. This does not correspond with the analyzed results. We believe that this is
because the solubility of Na2SO4, which mainly precipitates in Motomachi Sekibutsu,
decreases with decreasing temperature. Moreover, the amount of Ca2+ detected on the right
knee was the highest in winter. This tendency of salt precipitation corresponds with the
analyzed results. On the other hand, the amount of Ca2+ detected on the left knee was the
highest in autumn. This may be because the amount of solar radiation is different on the
right and left knees, especially in winter. To confirm these inferences, it is necessary to
analyse the amount of solar radiation incident on the right and left knees.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
6. Conclusion
With focus on studying the relation between the depth of salt precipitation and that of water
evaporation at Motomachi Sekibutsu, we developed a two-dimensional model of
Motomachi Sekibutsu. Using this model and assuming that salt precipitation is caused by
water evaporation, we analysed the heat and moisture behaviour, and contrasted the
simulated moisture distribution with the positions of salt precipitation observed by a field
survey. At Motomachi Sekibutsu that is suffering from the strong influence of ground
water, evaporation tends to take place deep inside the external corner and near the surface
of the internal corner. In particular, on the knee, water evaporates in an area where the
water content increases rapidly. Assuming that the amount of water evaporation is
proportional to the amount of salt precipitation, it is considered that salt precipitates in the
deep part from summer to autumn and near the surface in winter.
References
Goudie, A.S., Viles, H.A., 1997. Salt weathering hazards, John Wiley and Sons, Chichester,
pp.106-107.
Ogura, D., Abuku, M., Hokoi, S., Iba, C., Wakiya, S. and Uno, T., 2014, Measurement of
salt solution uptake by ceramic brick using γ–ray projection, in: Proceedings of the
3rd International Conference on Salt Weathering of Buildings and Stone
Sculptures, Brussels, Belgium, October 14-16, 2014, pp.529-532.
Scherer, G.W., 2004, Stress from crystallization, Cement and Concrete Research, 34,
pp.323-330.
Japan Meteorological Agency. 2014. http://www.jma.go.jp/jma/index.html, accessed at 27
November, 2014.
Yonghui, L., Ogura, D., Hokoi, S. and Ishizaki, T., 2010. Effects of excavation and
emergency preservartion measures after excavation on hygrothermal behavior in
stone chamber of Takamatsuzuka tumulus, Journal of Environmental Engineering,
658, pp.1041-1050.
Matsumoto, M., 1984, Shin Kenchikugaku Taikei, Chapter 10 (in Japanese), Shokokusya,
pp.105-134.
Oita City Board of Education. 1996. Kunishiteishiseki Oita Motomachi Sekibutsu
Hozonsyurijigyo Hokokusho (in Japanese), Oita, Sohrinsha.
Oita City Board of Education. 2014. Oita Motomachi Sekibutsu Heisei 25 Nendo
Tyosagyomuitaku Hokokusyo (in Japanese), Oita, Sohrinsha.
Flatt, R.J., 2002, Salt damage in porous materials: How high supersaturations are generated,
Journal of Crystal Growth, pp.435-454.
1262
SCIENTIFIC EXAMINATION OF A PAINTED THRACIAN TOMB
DISCOVERED NEAR ALEXANDROVO VILLAGE, BULGARIA
V. Todorov1*, K. Frangova2 and T. Marinov3
Abstract
The Thracian tomb discovered near the village of Alexandorovo has been dated to the IV
century BC. It comprises dromos, antechamber and round burial chamber with a false
dome. The walls are made of local tuff stone and covered with painted plaster. The
construction and its paintings have survived in their original state without any repairs or
alterations made at any time of the tomb’s existence. Only evidence of processes of natural
deterioration is present: lack of adhesion between plaster and stonework, white veils on the
paint layer and local damage on the floor plaster due to water percolation. The petrological
study revealed that the tomb had been built of crystal-vitroclastic rhyodacitic tuff stone. It
also established that there was an ongoing process of zeolitization of the stones closest to
the ground, due to permanent moisture exchange. The soluble salts and mineral
nanoparticles deposited on the paint surface formed a white veil, the composition and
morphology of which were studied by means of SEM/EDX and XRD. Clay particles
deposited between the stone and the plaster had caused stratification in the upper parts of
the tomb and plaster damage in the lower parts. The mercury porosimetry investigation of
the pore size distribution showed the small pores to be entirely filled up. This added to the
tomb decoration’s uniqueness and presented a rare chance for the modern scientific
examination of an authentic encaustic wall painting technique.
Keywords: tuff, zeolitization, damages and causes, painting technique,
preservation measures
1. Introduction
In the late 2000, the Bulgarian archaeologist Dr. Georgi Kitov unearthed another Antiquity
structure – a painted Thracian tomb buried under a tumulus near the village of Alexandrovo
in South-East Bulgaria. According to its discoverer, the tomb dates to the mid IV BC and,
although there is no burial inventory (the tomb had been looted prior to its formal
discovery), it is of the quality and status of the already internationally renowned tombs in
Kazanlak and Sveshtari, included in UNESCO’s List of World Heritage Sites (Kitov 2001).
1
V. Todorov*
National Academy of Art, Department of Conservation, Sofia, Bulgaria
todorov.valentin@abv.bg
2
K. Frangova
Royal Danish Academy of Fine Arts, Institute of Conservation, Copenhagen, Denmark
3
T. Marinov
University of Mining and Geology, Sofia, Bulgaria
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
All premises within the structure are covered with painted decoration. At the far end of the
dromos, the traditional battle scenes are depicted, while in the burial chamber, opposite the
entrance, the Ancient master has placed the scene “Welcoming of the Hero”. At the very
centre of the burial chamber itself, there is an unique frieze with hunting scenes – an
invaluable evidence of the lifestyle and traditions of the ancient Thracians (Franks 2012).
The universal cultural, historical, artistic and scientific value of the mural paintings
prompted the Cultural Fund of the Japanese government to grant financial support (USD
3.5 million) for the creation of the Museum of the Thracian Art in South-East Rhodopes. A
full-scale museum copy of the tomb was also erected with this funding in order to meet the
needs of cultural tourism. The painting technique used within the tomb places the
monument among the very rare examples of use of wax in the Antiquity. Its integrity and
authenticity pend no questioning thus making the site one of exceptional interest to science.
A wide-scope research plan to investigate the building and the decorative skills of the
ancient masters was developed, aiming at establishing the materials used for both the
construction, and the paintings. It also aimed at determining the alterations and decays, as
well as the reasons for them. The observations and the research proved that the painting
process started on fresh mortar (buon fresco) and was finished using wax, identified by
GC/MS either as a paint binder or as a coating. The monochrome red and black bands,
which also contain wax, were executed in the so-called stucco lustro technique. The results
of the painting technique research have already been published (Todorov 2011).
2. Condition of the tomb
The tomb near Alexandrovo does not differ in its architectural and constructional
characteristics from other tombs from the same period. It comprises approximately 13 m
long dromos, antechamber with rectangular shape and a round burial chamber
(i.e. a beehive tomb) (Fig. 1a). It is built of local stone, native to the area of the East
Rhodopes – volcanic tuff. The stone blocks are of different sizes, placed in horizontal
layers. Each consecutive layer is smaller in diameter than the previous one, so that a socalled false, or corbelled, dome is formed. The face of each stone in the interior has then
been worked up with a flat chisel, so that a smooth 2.5-3 cm wide frame is formed. The rest
of the surface has been finely finished with a pointed chisel. The masonry has been laid
using a dry building technique, which requires perfect fitting of the building blocks, usually
done by additional in situ processing of each stone. No traces of additional metal clamps
are found.
About 20% of the original mortar in the burial chamber and in the antechamber was
discovered highly fragmented and on the floor. The damages on the murals found in situ are
mainly located in the North half of the burial chamber, up to 1 m above floor level.
Interestingly, the size of the damaged area coincides in height with the size of the entrance
to the burial chamber. In addition, it is important to note, that at the exact place where the
mortar layer is missing from the wall, there is a cavernous damage on the floor rendering
(Fig. 2a). This coincidence is explained with water percolating from above. The plaster in
the burial chamber is completely separated from the stonework (Fig. 2b).
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b)
a)
Fig. 1: a) Section of the tomb; b) A hunting scene (detail)
with part of the ornamental friezes.
The decorated surfaces in the burial chamber are divided into eight horizontal bands, of
which four are monochrome, two have polychrome ornamented friezes and two – figural
compositions (Fig. 1a). The main frieze is at eye level and depicts hunting scenes in which
four horse riders, four foot-hunters, nine dogs, two boars and two deer can be seen. The
paint layer of the swastika frieze is partially missing due to flaking. The scene “Welcoming
the Hero” situated opposite the entrance of the burial chamber is almost unrecognizable due
to powdering of the paint layer. The monochrome-painted areas are affected by salts’
efflorescence and in some areas there is visible spot (pitting) damage, caused by
subflorescences. It is obvious that the tomb has been affected by serious natural disasters in
the past (i.e. earthquakes), which have caused detachment of large fragments of the
building stones, cracking and scaling. In addition to that, human influence is also present,
as evidenced by the destruction of the original stone door to the burial chamber by ancient
looters.
3. Materials and methods
The samples were collected based on a preliminary research which established the use of
wax either as paint binder or as surface treatment (Todorov 2011). Unlike the initial
samples collected from the ornamental frieze, the ones for the current research were
selected among the detached red band fragments accumulated on the burial chamber’s
floor, thus avoiding further damage to the original. Each sample analysed included both
paint layer and mortar. Stone samples were collected from the base and approximately
20 cm above the entrance of the burial chamber. Samples for salts investigation were
collected from the antechamber from the layer between the detached paint-mortar layer and
the stonework. The stone and mortar samples were analysed petrographically using thin
sections as well as by SEM/EDS. The porosity of the stone samples was determined by
mercury porosimetry. The presence of salts was demonstrated by conductivity
measurements of water extracts. These salts were characterised by SEM/EDS and their
phase composition determined by XRD.
4. Results
4.1. Petrological characteristics of the stone used to build the tomb
The false dome of the burial chamber is built of crystal-vitroclastic tuffs, astonishingly
uniform in their colour, structural and textural characteristics. For the base of the dome,
zeolite-containing rocks are used. The tuff is white to light grey with massive texture and
crystal-vitroclastic structure comprising vitroclasts (volcanic glass), crystalloclasts and
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
lithoclasts. The vitroclasts make up to 40% of the rock. They are usually angular or rounded
pieces, partially transformed to zeolites and clay minerals. Such transformations are only
observed in the periphery and the micro-cracks of the vitroclasts, with the centres of the
latter appearing fresh and isotropic under a microscope. The crystalloclasts (or the primary
minerals) are represented by quartz, sanidine, plagioclase (oligoclase), biotite, monoclinic
pyroxene and amphibole (Fig. 2a). Rhyolitic and middle range vulcanites represent the
lithoclasts (Fig. 2b). As supplementary minerals, there are apatite, zircon, titanite, and
tourmaline. The rocks are almost entirely transformed to zeolites, with a main mineral
being clinoptilolite (63%) (Figures 2c, 3a, 3b and 3c).
a)
b)
c)
Fig. 2: a) Plagioclase, quartz, biotite, sanidine and vitroclasts; b) Zoned plagioclase,
quartz, glassy rocks and rhyolitic lithoclasts; c) Zeolite-containing rock - vitroclasts
transformed to zeolite minerals.
a)
b)
c)
Fig. 3: a) Zeolite: deep narrow crack in a stone from the burial chamber’s base. Elemental
composition of the needle-like crystals (mass %): C-36.59, O-38.64, Na-0.37, Mg-0.28, Al3.71, Si-17.56, K-1.35, Ca-1.50; b): Volcanic ash in the same stone. Elemental composition
(mass %): C-38.41, O-36.95, Na-0.16, Mg-0.09, Al-17.58, Si-3.66, K-2.72; c) Crystal
matter between the mortar and the stonework, antechamber. Oxide composition (mass %):
1) SO3-57.53, CaO-42.4 (gypsum) and 2) MgO-1.67, Al2O3-16.85, SiO2-65.17, SO3-2.08,
K2O-6.28, CaO-4.09 (clinoptilolite).
4.2. Mineral composition of the mortar
The stonework of the two chambers of the tomb and adjoining part of the dromos is
plastered with two layers of mortar, consisting of lime and mineral filler. Both layers are
astonishingly even in their thickness. The first one (laid directly on top of the stone
masonry) is about 3-5mm thick, greyish-white in colour and grainy in structure. The filler is
mainly crystalloclasts and vitroclasts. At the base of the first mortar layer, there is a finegrained clay mass, containing clay minerals and sericitic mass. The crystalloclasts and
lithoclasts described above are found on top of this layer (Fig. 4a). The second layer is also
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of constant thickness (3-4mm), white in colour and with micro-grained structure. A
secondary calcite can also be detected, deposited in some of the larger pores as a result of
the carbonization of the calcium hydroxide from the binder (Fig. 4b).
The only exceptions of the described stratigraphy are the monochrome (red and black)
bands in the burial chamber, executed in stucco lustro technique. They are laid over
additional layer of mortar, applied on top of the main one, so that they are different in
thickness compared to the other painted areas.
a)
b)
Fig. 4: Burial chamber a) First mortar layer: quartz and traces of clay-carbonate cement;
b) Second mortar layer: single quartz grains and carbonate cement.
4.3. Morphology and composition of the white veil and salts
In order to determine the composition of the salts three samples were collected from
different areas in the tomb. The measured conductivity of the aqueous extracts of the stone
and the mortar samples proved the presence of water-soluble salts. Their composition was
determined by XRD (BRUKER E-8 Advance) and EDS. Unfortunately, the salts were
present only in micro quantities and the analysis of their composition by x-ray diffraction
proved impossible. This necessitated the collection of additional samples, this time
consisting of secondary deposits – the white veils on the red band in the burial chamber
(sample Al-S1a) and the white powder crystallized between the stone and the mortar in the
antechamber (sample Al-S1b). These new samples allowed for better readings, so the actual
composition of the salts was determined as containing gypsum, calcium carbonate (both
calcite and aragonite), calcium aluminate and clinoptilolite (Fig. 5). The calcite and the
aragonite both originated from the lime mortar, the clinoptilolite – from the building stone.
5. Discussion
When the tomb was discovered, the inner temperature measured at 12-14oC and the relative
humidity – at 96%. An important issue in the interpretation of the results of the analyses of
the materials is the presence of a humidity gradient starting at the peak of the dome and
decreasing towards the floor. This phenomenon is explained by the military activities that
took place in the region during the Balkan War and WWI around 1915. Those included the
digging of a trench and the building of an observation post on top of the tumulus. The
trench collected atmospheric moisture (rain and snow) for almost a century, significant part
of the water actually penetrating the burial chamber and the antechamber through the soil.
There are a few reasons why we should reconsider the generally accepted belief that, when
buried underneath a thick layer of soil, the chambers of such constructions exist in an
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environment of stable temperature and humidity. In reality, a permanent moisture exchange
with the environment takes place, both directly (through the difference between the
temperature and the humidity levels in the interior and the external atmosphere), and by
diffusion (through the soil layer in front of the dromos), while the tomb is still covered. We
have no means of guessing the length of these exposure periods. As is obvious from the
section of the tumulus (Fig. 1), the dromos’ entrance is covered with significantly thinner
layer of soil compared to the layer over the burial chamber. It is also apparent that there is a
temperature and humidity gradient starting from the humid soil of the tumulus through the
chambers and the dromos out to the atmosphere. The mechanism of humidity transportation
is diffusional and is influenced by the daily, seasonal and annual climatic fluctuations. The
tomb’s construction and position within the tumulus only advances the process, while the
long dromos functions as a chimney-stack. The missing mortar, detached and fallen off,
corresponds with this phenomenon and is to be seen only at the height of the entrances of
the chambers and the dromos, i.e. it coincides with the path through which the humidity is
transported.
In the tomb both subflorescences and efflorescences are present, however the
subfflorescences are predominant. It can be suggested that the efflorescences are related to
the periods when the dromos was opened, i.e. when the humidity exchange was more
intensive. The presence of two types of damage effects – irregular white veil spots and
pitting, could be explained only by the disrupted vapour permeability of the paint layer,
related to the use of beeswax.
The building stone itself plays a special part in the weathering processes. Humidity is the
worst adversary of tuffs, influencing mainly the susceptible components of the rock, such as
clay minerals and zeolites, and causing their degradation. The weathering of vitroclasts
(volcanic glass) gives rise to zeolites and clay minerals. In the burial chamber, especially at
its base, vitroclasts constitute about 40% of the tuffs’ mass and are completely transformed
to zeolites and clay minerals. The main mineral in the zeolite-containing rocks is the
clinoptilolite, comprising as much as 63% of their contents. In comparison, the sanidine
content is about 14%, smectite – 8%, albite – 10% and quartz – 4%. On account of its
advanced stage of zeolitization, the rock is identified as tuff containing clinoptilolite and
zeolite. Zeolites are natural ion-exchanging minerals, influencing the ionic balance between
the stone and the mortar. The diffractogram of sample Al-S2a shows that the clinoptilolite
is predominantly present as clinoptilolite-Na and clinoptilolite-K and not as much as
clinoptilolite-Ca. This means that the potassium and sodium ions originating from soil salts
are trapped i.e. are chemically bound.
Moisture carries and deposits the products of weathering to the border area between the
mortar and the stone, to the porous structure of the mortar and to the surface of the paint
layer. Their exact location is dependent on the size of the dispersed minerals.
Montmorillonite clays are highly susceptible to humidity fluctuations. This explains why
the lower parts of the wall paintings bear the worst damage and why most of the mortar in
this area is detached.
Analysis of the surface white veils also proves that their origin lies in the weathering
products of the tuff and the mortar. A very interesting scientific fact is that the watercarried extracts of the mortar’s binder have recrystallized in both polymorphic forms –
calcite and aragonite (Fig. 5), while usually either one or the other form would be present.
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An interesting phenomenon is the discovery of gypsum among the white efflorescence and
at the border area between the stone and the mortar in the antechamber. The location and
distribution of the gypsum were obviously related to the path of the moisture’s penetration
in the tomb. The additional research showed that the gypsum in the white efflorescence was
of anthropogenic origin. In the period 1951-1994 in the nearby town of Dimitrovgrad
(approximately 10km away as the crow flies), a chemical factory for the production of
synthetic fertilizers and sulfuric acid was in operation. The air pollutants from the factory
were transported aerially to the site of the tomb. This is yet another proof of the existence
of moisture exchange between the tumulus, chambers and dromos and their surrounding
atmosphere. The analysis of the porous structure by means of mercury porosimetry showed
that the total volume of the pores is highly reduced, the finest of the pores of the stone and
the mortar (pore sizes under 500 nm) were completely filled up by products of stone
decomposition (Fig. 6).
Fig. 5: XRD analysis of Al-S1a. Identified minerals include calcite, aragonite,
quartz, gypsum, dolomite; all minerals are secondarily crystallized.
Pore sze distribution
100
70
60
80
Al S-1, Vp=0.07 cm /g
Pore content [%]
Pore content [%]
3
60
40
50
Al S-1
1000 - 1500 nm - 12%,
1500 - 2500 nm - 13%,
2500 - 3750 nm - 12%,
3750 - 7500 nm - 63%.
40
30
20
20
10
0
0
2500
5000
7500
Pore size [nm]
0
0
1000
2000
3000
4000
5000
6000
Pore size [nm]
Fig. 6: Integral and differential micro-porosity of sample Al-S1.
The finest pores are filled up.
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6. Conclusions
The clarification of the decay processes and their mechanisms causing the damaging of the
stone and the mural paintings in the tomb allowed for the development of a long-term
concept for the preservation of both the built structure and the wall paintings. The main
proposed actions are:
-
-
-
To separate the tomb from the tumulus so that the drying process is redirected
from the interior to the exterior. The main goal is to deposit the water-transmitted
salts and erosion products into the stone rubble layer around the tomb.
To stop the moisture exchange and the percolation of water in the burial chamber
through insolation.
To re-install the adhesion between the stonework and the mortar, which would
preserve the painted decoration.
To execute minimal conservation treatment to locally stabilize the powdering paint
layer, located in the lower areas of the tomb, close to the floor.
To preserve the authentic state of the wall paintings as a precious evidence of the
ancient painting techniques to be studied in the future. The white veil is not to be
removed and no further cleaning is to be undertaken.
To disallow access to the tomb and to create conditions as close as possible to the
historical microclimate by passive measures.
To develop a plan and methodology for distant observations (monitoring) of the
condition and emergency actions when and if needed.
Most of these measures and actions have already been implemented. The recreation of the
historic microclimate in the tomb using passive measures is forthcoming.
Acknowledgements
The authors would like to express their sincere gratitude to Mr. Werner Schmidt, wall
paintings conservator, ICCROM collaborator, for the cooperation and the encouragement to
investigate into the painting technique; to Dr. Dario Camufo, CNR, Italy, and Dr. Thomas
Warscheid, LBW Bioconsult, Germany, for the valuable advice on historical microclimates
and bio-protection of the tomb; as well as to Dr. Esther von Plehwe-Leisen, Germany, for
the discussions on building stone damage.
References
Kitov, G., 2001, A newly found Thracian tomb with frescoes, Archaeologia Bulgarica, 5
(2), 15-29.
Todorov, V., 2011, The Thracian Tomb at Alexandrovo, SE Bulgaria: Preliminary
observations on its painting technique, in Interdisziplinäre Forschungen zum
Kulturerbe auf der Balkanhalbinsel, Nikolov, V., Bachvarov, K., Popov, H. (eds.),
Sofia, 323-334.
Franks, H.M., 2012, Hunters, Heroes, Kings: The frieze of the tomb II at Vergina,
The American School of Classical Studies at Athens, ISBN 978-0-87661-966-7.
1270
CASE STUDY OF THE EPISCOPAL GROUP OF FREJUS
(FRANCE): DIAGNOSIS AND TREATMENT OF CLAY
CONTAINING SANDSTONES IN MARINE ENVIRONMENT
M. Trubert1, B. Brunet-Imbault2*, P. Bromblet3 and C. Guinamard2
Abstract
The episcopal group of Fréjus concentrating 16 centuries of architecture is located at 2km
from the sea. Six different sandstone patterns of local Permian sandstones were identified
and a list of damages (granular disintegration, craquele, scaling, moist area and salt
efflorescences) was localized on mappings. The analysis of the environmental context and
the implementation of the masonries indicate that the damage expression strongly depends
on the stone’s orientation. Moreover, we can recognize two sandstone patterns which are
mainly affected by a high level of decay: an original pattern of coarse sandstone and a
restoration pattern of fine sandstone. Petrographic analysis, petrophysic measures (porosity,
water capillarity, water vapour permeability and thermo-hydric dilation), salt analysis,
micro-scanning observations and clay activity evaluations were conducted. Our results
indicate that the on-site scaling thickness can be related to the thermo-hydric dilation values
and to the clay swelling capacity. Furthermore, the salt analysis indicates a contamination
in chloride and sodium due to the marine environment. The contamination is enlarged by
nitrates in capillary rising areas and by sulfates due to the urban environment as well as
locally used gypsum mortars. The intrinsic properties, like dilation properties with water,
are then the dominant factor in the sandstone damages but the salt contamination and water
transfers are aggravating factors. Therefore, solution based on buthyldiammonium chloride
was tested to evaluate the feasibility of dilation stabilization. Tests performed on samples in
laboratory indicate, for the two main sandstone patterns, the impact of the application
protocol on the depth of penetration. The tests show a significant effect of the solution on
the hydric dilation decrease. In parallel, a consolidating protocol based on tetraethoxysilane
(TEOS) has been tested. These tests are encouraging for the treatment feasibility, they will
be extended by an on-site experimental restoration phase.
Keywords: sandstone, clay, swelling, conservation, treatment
1
M. Trubert
Architecte en Chef des Monuments Historiques, Fontainebleau, France
2
B. Brunet-Imbault* and C. Guinamard
Cabinet d’études Studiolo, Paris, France
3
P. Bromblet,
Centre Interdisciplinaire de Conservation et de Restauration du Patrimoine, Marseille, France
*corresponding author
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
1. Introduction
The episcopal group of Fréjus (Var – France) is composed of the baptistery, the cathedral
church, the canonical buildings including the cloister and the bishop’s residence. This
remarkable group presents a subtle range of colors due to the use of various local Permian
sandstones. The Mediterranean sea is located 2 km south from the building. The
conservation issue of the episcopal group is to define protocols permitting conservation and
restoration of damaged sandstones. The main issue is to distinguish the influence of the
marine environment from the intrinsic properties of the sandstones in the degradation
process. Damages can, indeed, be caused by the components and microstructure of the
stone itself, more specifically the clay inclusions. Although the effect of clays on the
sandstone, and especially swelling clays, is well-known, the discrimination of the
predominant factor leading to the observed damages and the feasibility of long-term stone
preservation is yet an unsolved issue, especially in the marine environment. Firstly, we
focused on the identification and classification of the factors involved in the development
of different damages. Secondly, we tested stabilization and consolidation protocols.
2. Materials and methods
2.1. Building stones and degradation patterns
The episcopal group was built with local Permian sandstones. The macroscopic
examination of the building’s stones allows distinguishing six different sandstone patterns.
e
c
d
b
a
f
Fig. 1: details of the 6 different sandstone patterns.
The detailed sandstones on the previous photos are:
a) Type 1: fine wine lees colour sandstone
b) Type 2: coarse wine lees colour sandstone including rock fragments of several cm
c) Type 3: fine red sandstone of restoration
d) Type 4: yellow sandstone
e) Type 5: grey-green sandstone
f) Type 6: grey-green restoration sandstone
The episcopal group presents pathologies affecting stones in terms of sandstones reactivity
in their environment but does not present structural disorder of masonries. Pathologies
affect the different sandstone patterns, main damages consist of granular disintegration,
craquele, scaling, moist area and salt resurgences.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
a
b
Type 1 sandstone
North exposure
Type 6 sandstone
Portal sculpture
South
e
d
Type 5 sandstone
East exposure
c
–
Type 4 sandstone
Bump stone cutting South
Type 2 sandstone
South exposure
f
Type 1 sandstone
South exposure
Fig. 2: Details of craquele, scaling and granular disintegration patterns.
Craquele is a degradation level which evolves towards the scaling (Fig.2a and 2f); it is due
to constraints which occur in stone subsurface, under the superficial epidermis part, on the
total stone surface. The observed craquele pattern seems to be characteristic of a
degradation mechanism due to intrinsic properties of the stone. The picture f detail shows
that it is not significant of interactions with joint mortars. The picture e documents the
yellow type 4 sandstone scaling. It shows that the more the stone is exposed to the
imbibition-evaporation phenomena, the more it scales. The stone cutting in bumps on the
bell tower enhances the degradation. Scaling affects the 6 sandstone patterns of the
episcopal group of Fréjus; nevertheless, the grey-green of types 5 and 6 sandstones are
particularly damaged. So craquele and scaling affect as much, and even in a spectacular
way, the type 6 grey-green sandstone used in a recent restoration (less than 30 years ago).
Besides, granular disintegration is a phenomena which widely affects the type 2 coarse
wine lees sandstone (Fig. 2c), especially in capillary rising zones.
The analysis of the environmental context and the implementation of the masonries
indicates that the damage expression strongly depends on the stone’s orientation. Indeed, if
epidermis are locally remained undamaged on the north and east façades, all of the
sandstones of the south and west façades have scaled. Moreover, very important granular
disintegrations occur in the lower part of the south baptistery façade, in possible area of
capillary rising. We can also recognize two sandstone patterns which are mainly affected by
a high level of decay: an original pattern of coarse sandstone (type 2) and a restoration
pattern of fine sandstone (type 6).
2.2. Sampling
Type 1 sandstone being the most present on the episcopal group and particularly affected
by damages and type 2 sandstones being the most strongly affected by damages, they can
be considered as representative of the conservation issue of the episcopal group. So they
have been used for the first characterization of the building sandstones. In addition, each
specific sandstone pattern has been sampled to characterize stone properties and specific
fraction in order to try to highlight discrimination factors. Sandstone fragments sampling
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
includes the different degradation stages in order to search the degrading agents. Stone
powders have then been sampled in various areas of the episcopal group as well as in
different heights and different depths to evaluate the salt contamination of the masonries.
2.3. Analysis
The characterization of the building sandstones includes petrographic analysis, vapour
permeability, porosity and water capillarity according to the NF EN 1936 and NF EN 1625
(1999) standards. Microscopic observations have been performed on craquele and scaling
patterns with a scanning electron microscope coupled with an EDX Phenom Pro X probe.
In order to determine the dimensional variations of the different sandstone patterns with
temperature and water exposures, the thermo-hydric dilations were measured. Clay activity
of fine sandstone fraction (< 2mm) has been evaluated. The test consists in adding
methylene blue to an aqueous suspension of the 0-2mm size fraction of the crushed
sandstone, the solution adsorption is verified after each addition by determination of free
colouring agent on filter paper according to the recommendations of the NF 933-9 standard.
Salt analyses were performed with an ionic chromatography Dionex DX 120 according to
the Italian "Normal 13/83" standard. Analyses have been performed by BPE laboratory
(France).
2.4. Treatment tests
Clay stabilization and stone consolidation were tested on the types 1 and 2 sandstones. The
size of the treated samples was of 10×10 cm2 and type 1 and 2 sandstone samples with
cohesive surface were selected.
Tab. 1: Protocol of the treatment tests.
Sample
I EP-2
II EP-2
I KC-2
II KC-2
I AP-2
II AP-2
Stone
1st application
2nd application
Type 1
Type 2
Type 1
Type 2
Type 1
Type 2
Estel 1000 40% - Solvent 60%
Estel 1000 70% - Solvent 30%
Brush in saturation
Estel 1000 25% - Solvent 75%
Brush in saturation
Estel 1000 50% - Solvent 50%
Cellulose compress (Arbocell)
Antihygro
Cellulose compress (Arbocell)
Antihygro
Brush in saturation
Brush in saturation
The used products for the trials are:
- Antihygro (Remmers) : solution based on buthyldiammonium chloride
permitting the stabilisation of swelling clays
- Estel 1000 (CTS) : consolidant based on tetraethoxysilane (TEOS) in solution
with White-Spirit solvent; concentration is calculated in volume
- Compresses are made with cellulose fibers of type Arbocell BWW40
3. Results
3.1. Sandstone characterization
3.1.1. Petrography and petrophysic
Type 1 sandstone is an arkosic and type 2 is a protoquartzite sandstone including 5 to 25 %
of rock fragments, orthoses, micas and clays.
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13th International Congress on the Deterioration and Conservation of Stone: Case Studies
Tab. 2: Summary of petrographic and petrophysic analysis.
Parameters
Open porosity
Bulk density
Water capillarity
Vapour permeability
Petrographic class
Unit
Type 1
Type 2
%
kg/m3
gm-2s-0.5
g/m²hmmHg
10.5
2216
37.7
0.167
Arkosic sandstone
15.3
2130
24.7
0.457
Lithic sandstone
Results are significant of distinct properties of the type 1 and type 2 sandstones. For an
open porosity value 50% more important, the type 2 sandstone presents a vapour
permeability 3 times more important than the type 1 sandstone, with a capillarity 30%
lower. The comparative analysis of type 2 sandstone porosity and capillarity provides
indications of the pore geometry that is a macroporal microstructure fitting with the coarse
macroscopic appearance of this sandstone type.
3.1.2. Thermo-hydric dilation
The thermos-hydric dilation measures allow to evaluate the rock deformation potential
under water and temperature exposures. Samples are gradually plunged into water and
measures are made during 96 hours using a retractometer and a digital micrometric
comparator. Concerning the thermic dilation, samples were exposed to a thermal interval of
60°C (from 20°C to 80°C).
Tab. 2 provides the reached values for the asymptote in stabilization phase for the 5
sandstone patterns; we cannot have a sample of sufficient size for the type 6 sandstone only
present on the sculptures of the portal.
Tab. 3: Hydric and thermic dilation values.
Sandstone
Type 1
Type 2
Type 3
Type 4
Type 5
Hydric dilation at saturation
(mm/m)
0.20
0.24
0.11
0.17
0.14
Thermic dilation
(K-1)
3.16·10-5
3.30·10-5
2.60·10-5
3.21·10-5
3.88·10-5
The thermal dilation values are homogeneous while the hydric dilation values are very
different according to the various sandstone patterns. The type 3 red sandstone used in
restoration has a hydric dilation lower 45% than the type 1 wine lees sandstone and 54%
than the type 2 wine lees sandstone which presents the most important hydric dilation
value.
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3.1.3. Clay fraction
The clay activity has been evaluated with the methylene blue test. The table 3 provides the
adsorbed colouring agent weight for 100 g of dry 0-2 mm sandstone fraction. This try
indicates at the same time the presence of clays in significant proportion in the different
sandstone patterns and the swelling capacity of these clays adsorbing the colouring agent.
Tab. 4: Blue methylene values.
Blue methylene value (MB)
Sandstone
Type 1
Type 2
Type 3
Type 4
Type 5
Type 6
0.40
0.99
0.34
0.42
0.34
0.63
Moreover, the scanning electron microscope (SEM) permits to observe the in situ clay
figures. Observations in the damaged areas of scaling indicate fracture formation where
clay layers are opened (Fig. 3c).
a
b
250 µm
c
300 µm
60 µm
Fig. 3: SEM images of clays inside type 2, 5 and 6 sandstones.
3.2. Salt contamination
Quantification of cations (sodium and potassium) and anions (chloride, sulfates and
nitrates) indicates a salt contamination especially on west and south exposures. Sodium
(until 0.16% on scaling patterns) is associated to chloride (until 0.24%), indicating by there
even the origin of the contamination due to the marine environment. Local contaminations,
over stone conservation thresholds, are determined for the sulfates in the baptistery, on the
south baptistery wall and under the bell tower cornice, in the bell opening intrados. Lastly,
nitrates over threshold in the lower part of the façades and in the baptistery are significant
of capillary rising.
3.3. Efficiency of the treatment and feasibility
Measurements of consolidant absorption and action depth by reaction to dithizone after
reticulation show that microstructural differences between types 1 and 2 sandstones require
specific application protocols; brush can be used for the type 1 sandstone but compresses
must be used to reach a significant penetration depth for the type 2 sandstone which is
significantly less capillary.
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Tab. 5: Consolidation and clay stabilization effects on sandstone.
Sample
Type 1
I EP-2
I KC-2
Type 2
II EP-2
II KC2
Type 1
I AP-2
Type 2
II AP-2
Absorption
2
(g/cm )
Action
depth
Porosity
(%)
(mm)
Water
capillarity
Vapour
permeability, D
(g.m-2.s-0.5)
(g/m2.H.mmHg)
10.5
9.8
10.4
15.3
2
11.2
5
9.4
Penetration depth
0.0625
0.25
37.7
0.167
8.9
0.139
3.1
0.135
24.7
0.457
6.2
0.358
4.5
0.363
Hydric dilation (mm/m)
0.20
0.13
0.24
0.15
3
4
0.0625
0.25
(mm)
0.0625
5
0.0625
3
Consolidation test provides until 38% of porosity decrease for the type 2 while it provides
until 7% of porosity decrease for type 1 sandstone. Vapour permeability is preserved in all
consolidating protocols with around 20% of decrease which allows to preserving the fluid
transfers. However, consolidation with tetraethoxysilane has a strong effect on water
capillarity reducing it of 80-90%. Clay stabilization tests indicate a significant hydric
dilation decrease of 35%.
4. Result analysis
Analytical investigations show that damages are due to combined factors. The saline
contamination due to the marine environment, some local gypsum mortar use and capillary
rising enhance the damages. Nevertheless important scaling is observed even in areas where
the salt contamination is not significant.
Scaling thickness
(mm)
Hydric dilation
(mm/m)
Type 3
Red
Type 5
Grey-green
Type 4
Yellow
Type 1
Wine lees
Type 2
Coarse
wine lees
a few mm
a few mm
2 to 5 mm
until 10 mm
until 15 mm
0.11
0.14
0.17
0.20
0.24
Fig. 4: Sandstone classification according to scaling thickness and hydric dilation.
Classification of the various sandstone patterns according to their common scaling
thickness determined by on-site reading is correlated to the hydric dilation. More the
scaling is thick or more the disintegration is strong, more higher the hydric dilation is; this
is an intrinsic factor of the stones which is in relation with the clay activity. Indeed, most
low clay activities are measured for types 3 and 5 sandstone and largely strongest clay
activity is determined for the type 2 sandstone. The bar chart shows that the blue methylene
value is a discriminant factor. If the various sandstone patterns have important clay
activities, type 2 and 6 sandstones have significantly the most important values and these
are the ones which react in the most spectacular way.
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East
East
West
West
East
West
Fig. 5: Bar chart according to hydric dilation and methylene blue values.
5. Conclusions
Intrinsic property, especially hydric dilation related to clay activity, is the dominant factor
in the damage mechanisms particularly craquele and scaling patterns but salt contamination
and water transfers, such as capillary rising, are aggravating factors. Our study shows the
feasibility of dilation stabilization by application of a solution based on buthyldiammonium
chloride. Furthermore, the consolidating protocol tested to enhance the sandstone cohesion
leads to capillarity reduction while preserving fluid transfers thanks to permeability.
Capillarity reduction is a side effect of the tetraethoxysilane treatment which is favorable to
the conservation of such sandstones containing swelling clays. However, tests indicate the
impact of the application protocol on the depth of penetration. Buthyldiammonium chloride
has a significant effect on the hydric dilation decrease but the penetration depth remains
weak with regard to the scaling thickness. Laboratory tests are encouraging for the
treatment feasibility; nevertheless, they will be extended by a next on-site experimental
restoration phase on several limited areas of masonries which must be desalinated before
the treatment.
References
Berthonneau J., 2014, Le rôle des minéraux argileux dans la dégradation de la pierre, Ph.D.
thesis, University of Aix-Marseille, France.
Mertz J.D., 2006, Salt damage, dilation and actual practices in sandstone conservation,
Colloque des architectes de cathedrals à Strasbourg, 153-156.
Furlan V., Félix C., Queisser A., 2000, La pierre du portail peint de la cathédrale de
Lausanne : nature, état de conservation et consolidation, 9th Int. Congress on
Deterioration and Conservation of Stone, Venice, vol 2, 633-640.
Félix C., 1995, Peut-on consolider les grès tendres du plateau Suisse avec le silicate
d’éthyle, “Conservation et restauration des biens culturels, Montreux, 266-274.
1278
THE POLYCHROMED BETHLEHEM PORTAL OF HUY,
BELGIUM: EVALUATION AND MAINTENANCE OF A 25 YEAR
OLD TREATMENT
J. Vereecke1*, L. Rossen2, K. Raymakers2 and M. Stillhammerova1
Abstract
Built around 1430 at the entrance of the cemetery of the Collegial of Huy, the Bethlehem
portal has been modified and restored many times. The Royal Institute for Cultural Heritage
(KIK/IRPA) carried out the last restoration in 1988-1989. Twenty five years later, in 2014,
a maintenance treatment of the portal was decided upon at the end of the global restoration
of this side of the collegiate church. In addition to the conservation treatment, this was also
a unique opportunity to evaluate the efficiency of the previous 1988-89 treatment. We
examined the reports and work site diaries to have a clear idea of the state of conservation
before this treatment and to understand the materials, methods and techniques of the
treatment itself. The conservation state of the portal, and therefore the efficiency of the past
treatment was firstly evaluated through visual observation. To the unaided eye it appeared
perfect except for decolouration of the blue wash layer applied on the background. The
purpose of this maintenance treatment was to return the portal to its condition after the
restoration of 1988-89 by light removal of dust and a soft superficial cleaning. Even if the
25 years old treatment might nowadays be considered as quite “heavy” (products used and
the methods applied) and would not to be employed these days, we must admit that it did,
and still does work perfectly well.
Keywords: ethyl silicate and epoxy consolidations, acrylic and PVA as fixatives for
polychromies, water repellent, old treatment evaluations
1. Introduction
Built around 1430, the Bethlehem portal has been modified and restored many times. The
last restoration realised by the IRPA/KIK in 1988-1989 was published in de VI
international congress on deterioration and conservation of stone of Torun in 1988 (De
Henau et al., 1988). Twenty-five years later, in 2014, a maintenance treatment of the portal
was decided upon at the end of the global restoration of this side of the collegiate church. In
addition to the conservation treatment, this was also a unique opportunity to evaluate the
efficiency of the previous 1988-89 treatment. We examined the reports and work site
1
J. Vereecke* and M. Stillhammerova
Jacques Vereecke sprl, Belgium
jacquesvereeckesprl@hotmail.com
2
L. Rossen and K. Raymakers
Vof Raymakers-Rossen, Belgium
*corresponding author
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diaries to have a clear idea of the state of conservation before this treatment and to
understand the materials, methods and techniques of the treatment.
Fig. 1: Portal in the 1930, © KIK/IRPA, Bruxelles.
2. Conservation state before 1988-89 and this treatment
The portal is originally built with three kinds of stone. The base and lintel was carved from
local blue limestone. For the arches and sculptures, a softer material was chosen: an
organoclastic Bajocian yellow limestone quarried in Dom-le-Mesnil. The background of the
portal consists of Maastrichtian limestone (soft bioclastic calcarenite of the UpperCretaceous) briquette carefully jointed. The bed of the Virgin is also carved in this stone.
When restored in 1890, they substituted deteriorated original stone with an oolithic
Bajocian limestone (French Jaumont limestone). The blue stone and the stone of Jaumont
were in good condition. The Maastrichtian limestone did not suffer from sulfatation but
shows disintegration and was strongly eroded. The Dom-le-Mesnil stones show a lot of
sulfatation decay such as blistering and micro cracks. Salts analyses showed the presence of
sodium, ammonium and calcium phosphates and sulphates. Layers of whitewashes covered
the original polychromy, all sensitive to water.
The first step of the treatment consisted of taking away pigeon’s nests and excreta. Then the
salt crystals on the surface, the encrustation of dust and the whitewashes were removed
mechanically. During this procedure, the original polychromy was fixed, and the stone was
consolidated where necessary. At first, the stone consolidation was carried out by injecting
ethyl silicate (Goldschmidt Tegovacom V). After unsatisfactory result, it was decided to
consolidate with injections of epoxy resins (Araldite AY 103-HY956 diluted with methanol
10%). These operations were repeated until the desired result was achieved. A mortar
composed of lime stone powder mixed with pva emulsion (10%) was used. The background
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was overpainted with a blue paint composed of a mixture of casein and lime with blue
pigments. As finishing layer, a water-diluted silicone was applied over all the surfaces of
the portal. For protection against pigeons, a nylon net with 3 centimetres square was placed.
Fig. 2: Portal after treatment in 1989, © KIK/IRPA, Bruxelles.
3. Understanding the methodology of treatments applied in 1988-89
Given the very good state of conservation after 25 years where no evidence of any kind of
decay was visible, we decided it was too interventionist to make any destructive analyses.
However, for a better understanding of the conservation status we thought it was important
to map in diagram form the treatment done in 1988-89. In the interest of continuity and
comprehension we employ the same format used at that time in the treatment reports and
worksite diaries including written notes and drawings / diagrams. This compilation
concerns only information about the consolidation of the stone and fixing polychromy and
the application of the water repellent.
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3.1. Stone consolidation
It was carried out in several partial stages corresponding to the areas where the restorers
were working. Some areas have been consolidated once, others up to five times, with a
minimum period of three weeks between applications, which mean that the silicate was
completely polymerized before the new application. We find also mentions of a muchlocalized consolidation with a mixture of ethyl silicate (Wacker OH) supplemented with
Paraloïd B72. We do not know when that treatment was performed: before, during or after
the individual impregnation with ethyl silicate, but we think it is probably just a test and
that this type of treatment was not used. Some elements were not consolidated with ethyl
silicate (based on documents consulted). The result after five campaigns of impregnations
was considered insufficient and (after testing), consolidation with epoxy resin (AY103 /
HY956) diluted in methanol (100 cc resin diluted with 20 cc of solvent) was decided upon.
The consolidation with the epoxy resin was not applied everywhere, which implies that the
condition of some of the stones were found to be sufficiently good (unless there is a gap in
the reports).
Fig. 3: Localisation of the five treatments with ethyl silicate.
Fig. 4: Localisation of the treatment with a mixture of ethyl silicate supplemented with
Paraloïd B72 (left) and consolidation with epoxy resins (right).
3.2. Fixation of the Polychromy
Polychromy was fixed with PVA glue. When necessary, the fixing was repeated, so some
areas have been treated many times. It is mentioned that following repeated fixing there
was the formation of a whitish film on "Joseph". One restorer used an acrylic adhesive
(Primal AC33) to carry out fixation. The diagrams show the areas mentioned in the
documents. It must also be considered that these are maybe local fixings and therefore not
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necessarily the complete ‘shaded’ area was treated. From our observations, not all the areas
treated have been recorded in the treatment documentation. The current state of the
polychromy is very good. We have not found any lifting paint, or a disturbing whitish veil
(bloom).
Fig. 5: Localisation of the treatment with PVA (left) and Acrylic (right).
3.3. Water-repellent treatment
After a satisfactory test, it was decided to apply the water-repellent on all surfaces of the
portal. The product used was Rédésil S. We found the water repellent present and active on
all surfaces. It certainly played an important inhibitory role against weathering elements,
the formation of black crusts (sulfatation) and the attachment of dirt deposit.
3.4. The blue background
The blue lime wash applied on the background is the only intervention that has not aged
well. It has discoloured to a green-greyish tone. Lime wash, made with lime caseinate and a
blue pigment was applied in order to restore a sufficiently homogeneous background to
push the sculptures into relief.
100 µm
Fig. 6: Microphotograph of cross-section of blue background
(optical microscopy using reflected light).
The pigment used was not mentioned in the report but SEM/EDX and Micro Raman
spectroscopy analyses of the rests of blue still preserved in the depth of the stone proved the
presence of cerulean blue and titanium IV oxide (rutile type). As Cerulean blue, cobalt tin
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oxide CoSnO3 is considered to be a very stable pigment, the discoloration of surface paint
layer could only be explained by degradation and yellowing of the lime-casein medium
used.
4. Maintenance treatment in 2014
The goal of the maintenance treatment was to return the portal to the state in which it was
immediately after the 1988-89 treatment. The dirt was superficial and not compact and had
little cohesion. We tested soft, dry pencil erasers. After several tests, we selected the ‘Firm
gum Milan, the pan miga 4020’. This is a pencil eraser made from a synthetic rubber
compound having a neutral ph. The entire portal was cleaned using this method except the
background, which was too fragile. The three lower baldaquins, having more compact dirt,
could not be successfully treated with the erasers. Areas where superficial dirt showed
greater cohesion, mainly in the lower part of the ogive and more particularly in areas with
horizontal surfaces, another cleaning method had to be determined in order to achieve a
uniform cleaning of the whole portal. First we tested solvents and solvent mixtures based
on Dr. Masschelein-Kleiner’s list (1981). Despite the water sensitivity of polychromy
layers as described in the reports we dared test solvents and gels containing water because
of the presence of a water repellent. Only mixtures of isopropanol / ammonium hydroxide
and water (90/10/10 and 50/25/25) gave results, dissolution of dirt, but the friction of the
cotton swab caused a significant abrasion of the polychromy layer. Secondly, we tested
solvent gels with the idea to limit the friction. Gels posed the problem of their elimination:
gel residue remained on polychromy surfaces. Following the disappointing and
unsatisfactory result, we decided to test the micro sandblasting with low pressure and mild
abrasives (calcite and glass micro balls) or very fine alumina oxide (240 mesh, 320 mesh
and 400 mesh). This proved a good solution: regular and easily controllable. The cleaning
was performed with a Sand master machine speed of 3, an outlet nozzle with a diameter of
1.2 mm, a pressure of 1 bar and an alumina oxide 320 mesh.
Fig. 7: Localisation of the treatment with 'soft rubber pencil eraser' (left) and micro
sandblasting (right).
Before retouching the background, it was important to evaluate the effectiveness of the
repellent. To do this, we initially made a water flow test on the surface. In view of the rapid
percolation without water absorption, we decided to place Karsten pipes. They were applied
for ten minutes without any absorption! This proves that the repellent was still active. Due
to the presence of the water repellent, retouching, usually made with water-based products,
was problematic. They were restricted to a reintegration of the current green / blueish
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background. Retouching with lime wash was not considered because of the water repellent.
We tested silicates products (Beeck), acrylic (Golden), but they formed an unsightly film
which remained visible after drying. We tested gouache paint which gave a satisfactory
cosmetic result. However, because of worries concerning the adhesion of the gouache to the
background, we tested this by rubbing the dry gouache with a wet micro-sponge: the
gouache was resistant to this. Therefore we retouched the most important gaps with
gouache.
5. Conclusions
Following the conventions of today, we probably would not use the same methods,
materials and techniques as in this 1988-89 treatment, however, one cannot fault their
results. The fixing of the polychromy is still good; stones and mortars repair are in a good
state of preservation; the water repellent is still active. Only the painted background
presents colour alterations from blue to greenish grey. There are few localized zones, well
protected, which present a blue appearance probably close to the original state of the
whitewash applied in 1989. The maintenance treatment with its main goal of going back to
the state after the restoration of 1988-89, was achieved with a light removal of dust, soft
superficial cleaning treatment and a retouching treatment of the discoloured blue
background.
Fig. 8: Portal after maintenance treatment in 2014.
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Acknowledgements
We would like to thank the restorers of the stone workshop of the KIK/IRPA to allow us to
consult all the data concerning the treatment executed in 1988-89.
References
De Henau, P., Van Molle, M. and Annaert, M., 1988, Etude et conservation du portail
polychrome dit de Bethléem à Huy”, Proceedings of the 6th international congress
on deterioration and conservation of stone, Torun, Ciabach, J. (ed), Nicholas
Copernicus University Press Department, 680-686.
De Henau, P., Annaert, M., Kockaert, L. and Van Molle, M., 1995, in Le portail
polychrome dit “Le Bethléem” à Huy, Extrait du Bulletin de l’Institut royal du
Patrimoine artistique, XXV, 1993, Bruxelles.
Masschelein-Kleiner, L., 1981, Les solvants, Cours de conservation 2, Institut Royal du
Patrimoine Artistique, Bruxelles.
1286
EXPLORING THE PERFORMANCE OF POMPIGNAN
LIMESTONE AS EXTERIOR CLADDING AND PAVERS IN THE
MID-ATLANTIC REGION OF THE UNITED STATES
R. Wentzel1* and M. Coggin1
Abstract
Herein presented is a case study outlining an investigation of the suitability of Pompignan
limestone as an exterior finish at an unnamed, architecturally significant installation.
Included in this study are the forensic investigation techniques employed as well as results
from petrographic examination and analysis involved. Also provided are descriptions of the
methods by which the stone was installed as exterior pavers and as exterior wall cladding.
Ultimately, this case study concludes that Pompignan limestone has several inherent
characteristics which negatively affect its performance and durability in exterior exposures
in regions subject to freeze/thaw cycles matching that of the mid-Atlantic region of the
United States. Specifically, stylolite features found in the limestone enable moisture
entrapment, leading to freeze/thaw damage. The freeze/thaw expansion propagates parallel
with the face of the stone along microscopic vein features filled with secondary
mineralization. The net result of both occurrences is a reduction in strength and durability
of the Pompignan limestone installed and exposed per this case study.
Keywords: limestone, Mid-Atlantic, Pompignan, performance, stylolite
1. Introduction
This paper discusses the findings and conclusions of an investigation into the causes and
origins of catastrophic cracking in Pompignan limestone installed as exterior pavers,
cladding, and capstones in the Mid-Atlantic geographic region of the United States. Both
installed and attic stock examples of pavers and cladding from the project were acquired for
purposes of petrographic analysis. This analysis was undertaken with the goal of
determining both the causes of the cracking and the appropriateness of Pompignan
limestone for use as an exterior finish within the region in which it was installed.
Capstones were not removed for analysis.
2. Existing Conditions
Thermally finished Pompignan limestone pavers sized 55.9 cm square by 5.1 cm thick (22”
square by 2” thick), mounted on plastic composite shims atop pedestals, with open joints,
were encountered at the project location. Failed pavers exhibited cracking and/or
delamination.
1
R. Wentzel* and M. Coggin,
Thornton Tomasetti, Inc., United States of America
rwentzel@thorntontomasetti.com
*corresponding author
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Fig. 1: Typical failed paver.
Thermally finished Pompignan limestone cladding sized 55.9 cm by 29.8 cm by 4.13 cm
thick (22” × 11 3/4” × 1 5/8”) installed on stainless steel anchors grouted into field cut kerfs
were encountered at the project location. Façades featuring Pompignan limestone were
built as cavity walls, acknowledging the fact that moisture will work its way through the
limestone veneer. Approximately 3.5 cm (1 3/8”) of air space was left between the veneer
and waterproofed insulation board on CMU serving as a structural exterior wall. A flexible
backer rod was installed in each joint between each individual stone, and silicone sealant
applied in front of the backer rod to a plane virtually flush with the surface of the stone
cladding. Failed cladding stones exhibited vertical cracking or semi-circular cracking at the
kerfs.
Fig. 2: Typical failed cladding.
Encountered at the project location, but not analysed, were thermally finished Pompignan
limestone coping stones. Featuring various lengths, the coping stones measured 27.9 cm
(11”) wide, 9.4 cm (3 11/16”) thick on the high side and 8.1 cm (3 3/16”) on the low side.
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3. Material Testing
Based on observations of deterioration in the paving, cladding, and cap stones, petrographic
analysis of pavers and cladding stones was undertaken in an effort to determine causation
of observed deterioration. Selected representative samples of cladding and pavers were
acquired from the project owners on site attic stock. Two fragments from broken kerf
spalls, a piece of cladding, and a paver removed from in situ were also acquired. Tab. 1
describes 12 pieces submitted for petrographic analysis.
Tab. 1: Matrix showing material application, area from which it was obtained and size.
Sample ID
Location
Dimensions (cm)
Dimensions (in)
Cladding 1
Attic Stock
55.9×29.8×4.1
22×11.75×1.6
Cladding 2
Attic Stock
55.9×29.8×4.1
22×11.75×1.6
Cladding 3
Attic Stock
55.9×29.8×4.1
22×11.75×1.6
Cladding 4
Attic Stock
55.9×29.8×4.1
22×11.75×1.6
Cladding 5
Attic Stock
55.2×29.8×4.1
21.75×11.75×1.6
Cladding 6
Attic Stock
55.2×29.8×4.1
21.75×11.75×1.6
Paver 1
In situ
55.9×55.9×5.1
22×22×2
Paver 2
Attic Stock
55.9×55.9×5.1
22×22×2
Paver 3
Attic Stock
55.9×55.9×5.1
22×22×2
Sample #1 (Shard)
In situ
Spall – 15.9 length
Spall – 6.25 length
Sample #2 (Shard)
In situ
Spall – 15.2 length
Spall – 6 length
Cladding 7 (Stone)
In situ
30.5×22.9×4.1
12×9×1.6
3.1. Petrographic Facilities
Highbridge Materials Consulting, Inc., Pleasantville NY provided petrographic examination
and analysis of the stone pavers and cladding.
3.2. Analysis/Test Sample Selection Criteria
The cladding from the Owner’s attic stock had been stored outside in a vertical orientation.
These unit items were highly desirable for analysis purposes as they shared both of those
characteristics with installed cladding, although kerfs for anchors had not been cut.
Owner’s paving attic stock was also stored outside stacked in a horizontal orientation, again
mimicking the installed position of these units and again providing a highly desirable item
for analysis.
Units selected from attic stock represented the most pristine examples remaining in stock
and featured undamaged edges and no visible cracking. Units removed from in situ were
selected due to obvious cracking. Analysis of attic stock material presented an opportunity
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to view stone characteristics with stresses limited to those related to water absorption,
thermal cycling and in situ stress relief following quarrying.
4. Analysis and Testing Results
4.1. Petrographic Analysis
Petrographic examination was conducted in accordance with ASTM C 1721. The analysis
and interpretation was performed by an ASTM C 956 Section 4 qualified petrographer.
4.1.1. Visual Appearance
All samples received were similar in appearance, presenting as a dense, compact limestone
with medium greenish grey colour. Fresh surfaces (intended for exposure when installed)
were uniform with a lithographic to slightly grainy texture. Fresh surfaces also showed as
roughly planar with a slight textured relief. Faint linear ripples with very low relief were
just visible at the surface when viewed under low angled lighting:
The remaining five surfaces in full dimensioned samples were cleanly saw cut.
No bedding surfaces, sedimentary laminations, or other depositional structures were
visible in the samples. Veins or other secondary mineralizations were not visible in
the samples.
4.1.2. General Summary of Petrographic Findings
Sample analysis revealed a dense calcitic limestone with no petrographically observable
microscopic pore structure. The stone exhibited a fine grain, homogeneous texture. No
distinct bedding fabric was found to be present.
Original geological structures were noted to be present as two localized planar elements.
Both elements can be considered as discrete planes of relative weakness and also as
avenues for moisture infiltration through an otherwise dense and cohesive limestone matrix.
Stylolitic cleavage is one structural element present in an orientation both parallel and
perpendicular to the stone face, though the former appears dominant. Microscopically thin
calcite veins represent the other type of structure present; however these veins manifest
strictly in a perpendicular orientation to the stone face and are not visible to the eye in the
samples.
4.1.2.1.
Stylolites
A stylolite is a type of geological cleavage across which dissolution has occurred during
compaction of the original sediment. Insoluble matter such as clay and other silicates
collect at the dissolution plane. Stylolites in the stones examined manifested as saw toothed
bands in both horizontal and, less commonly, vertical planes as oriented to the intended
exposed face of the stone. The more notable stylolites usually presented as a single
continuous to semi-continuous seam located somewhere between mid-depth and the inside
surface of the stone. Stylolites within the plane of paving stones were noted to exhibit a
series of incipient microcracks oriented parallel to the stone face in its installed position.
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Fig. 3: Microcracks parallel to stone face.
Fig. 4: Stylolite feature. Arrows indicate saw tooth nature of stylolite.
4.1.2.2.
Veins
Veins are geological crack openings that have healed with secondary mineralization. These
are not visible to the eye in the samples and were only identified petrographically. Veins
manifested in the stone roughly perpendicular to the finished stone surface in thin sets of
two or three closely spaced planes. Vein spacing is unknown; however one set is found in
almost every linear inch of material subjected to petrographic study. Vein thickness ranges
from approximately 0.025 to 0.075 millimetres (0.00098 to 0.00029 inches).
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All veins are filled with secondary calcium carbonate that is coarser grained than the calcite
found in the adjacent host stone. Due to the thinness of the vein structure, only two or three
crystals are generally found across the vein width. It was observed in examples exhibiting
cracking from service that said cracks almost always follows a path between individual
crystals.
Fig. 5: Calcite healing at petrographically observed vein (shown at arrow).
5. Failure Modes
5.1. Paver Cracking
Two failure modes were identified in paving stones; both are closely related to the preexisting geological structure. One is a fracture that splits the stone coincidental with a
microscopic vein set. The other is an incipient in-plane crack with secondary gypsum
crystallization coincidental with main stylolitic surfaces.
Fig. 6: PPL photomicrograph revealing nature of failure at paver crack. The crack was
epoxied together (blue area) for sample preparation.
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Fig. 7: Typical delaminated Paver.
5.2. Cladding Cracking
Microcracks present within the stone structure represent an incipient plane of weakness
oriented parallel to the stone face. Crack opening thicknesses are approximately 0.025
millimetres (0.00098 inches).
5.3. Miscellaneous
Pyrite and glauconite are present in all of the petrographically examined stone. Both
minerals are capable of oxidative weathering producing a red iron oxide that could manifest
as “rust” spots.
6. Conclusions
Based on the petrographic analysis completed at our direction, it is apparent that
Pompignan limestone used as exterior paving and cladding in the Mid-Atlantic region of
the United States exhibits several characteristics that negatively impact its performance and
durability. These undesirable characteristics include stylolite and vein geologic features.
As Pompignan limestone is exposed to moisture and cyclical freeze/thaw, the stylolite
features allow moisture to penetrate the stone. This moisture freezes and expands, opening
a crack at the stylolite which results in more moisture being able to penetrate the stone.
The typical multicyclic freeze/thaws that occur in the winter and spring in the Mid-Atlantic
region of the United States exacerbate this condition.
Pompignan veining features have lower-strength value than the surrounding stone. At the
case study location, paver failure was always coincidental with veining, as was coping
stone failure, said failures which occurred solely under the self-weight of the stone.
Based on the forensic efforts outlined in this case study in combination with the relative
petrographic analysis, we opine that the presence of open seams is fully attributable to the
characteristics of the stone and not to failures in the installation method. The use of
Pompignan limestone for exterior paver installations on pedestals and as exterior cladding
in regions with a climate similar to the Mid-Atlantic region of the United States is not
recommended.
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ABSTRACTS
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CONSERVATION:
MECHANISMS OF CARBONATE-OXALATE
TRANSFORMATION:
EFFECTIVENESS OF PROTECTIVE TREATMENTS FOR
MARBLE BASED ON OXALATE SURFACE LAYERS
A. Burgos-Cara1*, C. Rodríguez-Navarro1 and E. Ruiz-Agudo1
Abstract
The widespread distribution and the severity of the weathering processes suffered by
numerous stone-built historical and artistic complexes of our cultural heritage make it
crucial to undertake conservation strategies for the stone materials in these monuments, in
order to preserve them for future generations. In particular, the design of treatments that
protect the surface of carbonate rocks (e.g. marble) from etching by acidic or saline
solutions is an urgent need. Current urban atmospheres, with a high concentration of
pollutants such as SO2 and NOx, are a significant hazard for building elements made of
carbonate stone due to their susceptibility to chemical attack. Since ancient times, oxalate
patinas formed on building elements have had an important protective role over these
materials. Nowadays, because of the current high levels of pollution in urban and industrial
centres, the proliferation of microorganisms that excrete oxalic acid during their
metabolism and the formation of protective oxalate patinas related to the activity of such
microorganisms has declined, which adds to the own negative side effects of harmful
contaminants. The poor knowledge on the mechanisms controlling the carbonate–oxalate
transformation at the nanoscale, as well as the lack of an in-depth understanding of the
factors that determine the extent of coverage or adhesion of the oxalate layers to the
carbonate substrate has limited the development of effective procedures for marble
conservation that mimic the natural process of oxalate patina formation. It is the aim of this
work to investigate the mechanism of the replacement of calcite and dolomite by calcium
oxalate, as well as to evaluate the effects of pH, oxalate concentration, and fluid-to solid
ratio on this transformation. With this idea, the formation of calcium oxalate protective
layers on the surface of two types of marble (a calcitic marble -Macael White- and a
dolomitic marble -Yellow Triana-) as a possible protective treatment to chemical
dissolution processes are studied in this work. This has been done by a combination of
Scanning Electron Microscopy (SEM), bidimensional X-Ray Diffraction (2D-XRD) and
Atomic Force Microscopy (AFM) techniques. Finally, the efficacy of such a treatment as a
protective protocol for marble surfaces was assessed by performing water absorption and
drilling resistance tests, by determining the resistance to acidic solutions and the colour
variation after the oxalate treatment. The textural evidence found in this research show that
the replacement of calcite and dolomite by calcium oxalate (whewellite) is an interfacecoupled dissolution-precipitation reaction. Calcite and dolomite pseudomorphs were
1
A. Burgos-Cara*, C. Rodríguez-Navarro and E. Ruiz-Agudo
Departamento de Mineralogía y Petrología, Universidad de Granada, Spain
aburgoscara@ugr.es
*corresponding author
1297
13th International Congress on the Deterioration and Conservation of Stone: Abstracts
obtained under acidic conditions, when spatial coupling between the dissolution of
carbonates and nucleation and growth of whewellite occurs. Also, the existence of
structural similarities between calcite and whewellite appears to result in the promotion of
whewellite crystallization, since the formation of other Ca-oxalate phases was not detected
in our experiments. Experiments performed using marbles cubes as substrates demonstrate
that these layers effectively protect carbonate surfaces from chemical weathering, without
significantly affecting the water properties of the stone, maintaining the coherence with the
substrate and being only slightly perceptible to the human eye.
Keywords: oxalate, marble, protective patinas
1298
13th International Congress on the Deterioration and Conservation of Stone: Abstracts
CONSERVATION:
PRESERVATION OF BUILT CULTURAL HERITAGE USING
NANOTECHNOLOGY BASED COATINGS: RESPONDING TO
CONSERVATION VALUES?
J.J. Hughes1*, L.P. Singh2, P.C. Thapliyal2, T. Howind1 and W. Zhu1
The application of surface treatments on buildings is common, to protect or to functionalise
surfaces (e.g. consolidation, water repellence, self-cleaning). Many applications clearly
have performance and sustainability benefits for mainstream construction. This is also the
case for the built Cultural Heritage, though inappropriate application of materials has been
blamed in the past for damage to buildings. Conservation philosophy emphasises the
safeguarding of original material fabric, and the preservation of age value, through the
maintenance of authenticity and integrity, and often appearance and function. This implies
that the replacement of old materials with new in cultural heritage objects, is a special case.
The same criteria for specification or for measuring a successful outcome compared with
repairs to non-historic structures, where newness or visibly improved function is valued, do
not apply. The application of coatings and treatments that penetrate into a surface layer to
alter the properties of a material is a sensitive subject for heritage objects. Such material
applications are subject to (well established) criteria for the selection of treatments,
including that it has no effect on appearance, be re-treatable or that it should even be
reversible. Any surface treatment should of course also achieve the desired physical affect,
which is usually to overcome loss of cohesion between constituents, to improve durability
and to be compatible with the historic fabric. However this is achieved, the application of
any treatment should not adversely affect the authenticity of the object or building.
Drawing on other work, we can show that perceptions of authenticity are however,
contextual, and that practitioners attach great importance to operational parameters such as
health and safety alongside material performance characteristics. Therefore decision
support for choosing treatments, may need to accommodate this variability in the criteria
for selection, not just on the basis of material performance characteristics. In addition, a
full understanding of the aesthetic, mechanical and physical properties of surface coatings,
in addition to the practical application methods and risks is important and needs to be
defined for untried coating formulations, especially in Cultural Heritage applications.
Keywords: coating, conservation values, cultural heritage, nanotechnology
1
J.J. Hughes*, T. Howind and W. Zhu
School of Engineering and Computing, University of the West of Scotland, Paisley, Scotland,
United Kingdom
john.hughes@uws.ac.uk
2
L.P. Singh and P.C. Thapliyal
Organic Building Materials Group, CSIR-Central Building Research Institute, Roorkee, India
*corresponding author
1299
13th International Congress on the Deterioration and Conservation of Stone: Abstracts
CONSERVATION:
INNOVATIVE DEVELOPMENTS IN THE FIELD OF STONE
CONSERVATION BY THE ACRYLIC RESIN TOTAL
IMPREGNATION PROCESS OF NATURAL STONES BY THE
JBACH COMPANY
G. Scholz1, R.J.G. Sobott2, H.W. Ibach1
Abstract
The complete saturation of historically and culturally valuable stone monuments and
sculptures with MMA (methylmethacrylate) and the subsequent polymerization in the pore
space of the object is carried out by the JBACH company for 40 years. More than 20,000
stone objects with a wide range of petrophysical parameters were conserved in this time
period. Well-known examples are sculptures from the Cologne Cathedral, Sanssouci Palace
in Potsdam or the Royal Palace of Huis ten Bosch in The Hague. Compared to the standard
impregnation process with 100% MMA the new development is based on a decrease of the
monomer content in the impregnation solvent (formulations A and B) which as a principal
innovative feature reduces the polymerization temperature below 80°C and consequently
the thermal strain in the objects. The petrophysical properties of weathered rocks, sandstone
as well as marble, benefit very much from the conservation process with respect to the
mechanical strength and capillary water uptake. For instance, the flexural strength of the
fine-grained Udelfanger sandstone is raised from 4 to more than 34 N/mm², while the
capillary water uptake is reduced from 9 kg/m²h0.5 to practically nil. The optical
microscopy of thin sections of this sandstone after conservation reveals a lining of the pore
walls with PMMA which effectively seals the pore throats against the infiltration of water,
while the central parts of larger pores remain open. In the case of marble we no longer
observe a complete filling of the slit-like pores with PMMA containing small vacuoles but
delicate cellular PMMA structures instead. The results are no less than a great improvement
of the already very successful and efficient acrylic resin total impregnation process and of
great importance for the preservation of cultural heritage in the form of stone objects. The
successful conservation must be completed by a professional installation of the objects at
their original site which avoids rigid emplacement and guarantees compensation of possible
thermal strain by expansion joints.
Keywords: acrylic resin, marble, conservation, Udelfanger sandstone, total impregnation
1
G. Scholz* and H.W. Ibach
JBACH GmbH, Scheßlitz, Germany
g.scholz@ibach.eu
2
R.J.G Sobott
Labor für Baudenkmalpflege Naumburg, Naumburg (Saale), Germany
*corresponding author
1300
13th International Congress on the Deterioration and Conservation of Stone: Abstracts
DIGITISATION:
MONUMENTUM:
DIGITAL 3D MODELLING AND DATA MANAGEMENT
FOR THE CONSERVATION OF DECORATED STONE BUILDINGS
L. De Luca1, J.-M. Vallet2*, P. Bromblet2, M. Pierrot-Desseilligny3,
X. Brunetaud4, F. Dubois5, M. Bagneris1, M. Al Mukhtar4,
F. Cherblanc5, O. Guillon2 and J. Tugas6
Abstract
The investigations that are made on a building for conservation purposes need an important
work that is transcribed in a variety of numerical and printed data: surveying data and
scientific imagery, damage mapping, photographic collections, historical archives, physical
and chemical data etc. Given the difficulty to collect, compare, analyse and validate data
prior to restoration, the approach we present aims to mobilize various disciplines
(architecture, conservation, mechanics, and computer sciences) to define a novel
information processing chain including metric surveys, analysis of surfaces, geometric
models of structures, heterogeneous documentary sources management, temporal data, etc.
By the way of MONUMENTUM project which is an on-going research project (20132017) funded by ANR (French National Agency for Research), we are designing and
developing an open and expandible web platform for the capitalisation and the management
of knowledge needed for the understanding and analysis of degradation phenomena
affecting historic buildings. This objective requires the definition of a common and
continuous process that establish a technological and conceptual interconnection between
the stages of 3D digitization, semantic annotation and structuring of the geometric model
(including multi-layers analysis of surfaces), characterisation of the state of the building
and management of restoration actions. Based on three case studies that present
conservation issues on stones (Castle of Chambord and Caromb’s church in France) and
wall paintings (Notre-Dames des Fontaines’ chapel in France), it concerns the image-basedmodelling of architectural heritage, the development of a 3D information system for the
1
L. De Luca and M. Bagneris
UMR CNRS/MCC « MAP », Marseille, France
2
J.-M. Vallet*, P. Bromblet and O. Guillon
CICRP, Marseille, France.
jean-marc.vallet@cicrp.fr
3
M. Pierrot-Desseilligny
ENSG/IGN, Marne la Vallée, France
4
X. Brunetau and M. Al Mukhtar
UPRES PRISME, France
5
F. Dubois and F. Cherblanc
UMR CNRS/ Université Montpellier 2 « LMGC », Montpellier, France
J. Tugas
CRMH, DRAC-PACA, Aix-en-Provence, France
*corresponding author
6
1301
13th International Congress on the Deterioration and Conservation of Stone: Abstracts
management of conservation data and also a numerical modelling tool (FEM-DEM) for the
physical and structural analysis.
Keywords: conservation, stone, 3D information system, modelling, web platform
1302
13th International Congress on the Deterioration and Conservation of Stone: Abstracts
CASE STUDIES:
INVESTIGATION OF BUILDING STONES USED IN THE ALAZHAR MOSQUE (HISTORIC CAIRO, EGYPT)
N. Aly1*, A. Hamed1, Á. Török2, M. Gomez-Heras3 and M. Alvarez de Buergo3
Abstract
Al-Azhar was the first mosque built in Fatimid Cairo and the first theological college, and
has played a continuous role in the history of Cairo from its foundation to the present day.
A long series of restorations and enlargements were made at Al-Azhar during the Mamluk
and Ottoman periods. More additions and restorations were carried out in the nineteenth
and twentieth centuries. Mokattam Limestone is the main building material used in the
construction of the Al-Azhar mosque and all Historic Cairo. The site in the center of Cairo
makes it susceptible to various factors of weathering and pollution. Limestone core samples
were extracted from different facades of the Al-Azhar Mosque, including new and old
stones. The samples investigated and analyzed by means of different techniques, such as
Polarizing microscopy, Scanning Electron Microscope (SEM), Ion Chromatography (IC)
and Unconfined Compression Strength (UCS) besides, non-destructive techniques [i.e.
Ultrasound Pulse Velocity (UPV) and Rebound Hardness (Leeb). The analyses revealed
that all the samples contain different amounts of salts mainly chlorides, sulphates and
nitrates which also noticed filling the stone pores in SEM images. The presence of salts
affects the strength, P-wave velocity and rebound hardness measurements and indicates that
the Al-Azhar building stone is under deterioration.
Keywords: cultural heritage buildings, stone decay, non-destructive testing (NDT)
1
N. Aly and A. Hamed
Faculty of Petroleum and Mining Engineering, Suez University, Egypt
neven.ali@suezuniv.edu.eg
2
A. Török
Department of Construction Materials and Engineering Geology,
Budapest Technical University, Hungary
3
M. Gomez-Heras and M. Alvarez de Buergo
Geosciences Institute IGEO (CSIC, UCM) Madrid, Spain
*corresponding author
1303
13th International Congress on the Deterioration and Conservation of Stone: Abstracts
CASE STUDIES:
THE EFFECT OF REBURIAL ON STONE DETERIORATION:
EXPERIMENTAL CASE STUDY, OXFORD, ENGLAND
N. Zaman1* and H. Viles1
Abstract
The practice of reburial/backfilling, either partially or fully, of stone ruins is a method of
site management and preservation that is of interest to cultural heritage site managers
worldwide due to the expense and limited resources agencies often face in site maintenance
and restoration. Some sites have implemented reburial to some degree, including Chaco
Canyon National Historical Park (United States), Aztec Ruins National Monument (United
States), Rose Theatre (England), Laetoli hominid trackway (Tanzania), and at various sites
in Italy, Israel, and North Africa for the preservation of ancient mosaics. This method of
site preservation is dependent upon the assumption that soil conditions that were conducive
to preservation of the ruins pre-excavation are reestablished upon reburial/backfilling. Yet
to date there has been extremely limited research done to assess whether this is the case and
being cause for the primary hesitation on the part of site managers in implementing partial
or full reburial/backfilling of sites. This research aims to bridge this gap by investigating
whether soils used to protect cultural stone through the method of reburial/backfilling of
sites are benign or likely to cause alteration to the stones due to the environment they
facilitate. The effects of a reburial/backfilled soil environment versus surface exposure on
the weathering of stone materials are examined through a case study at Wytham Woods in
Oxford, England. Limestone and sandstone blocks were buried at differing depths for two
years in fill material consisting of the native soil on site, a clay rich silt loam. The
limestone and sandstone samples were pre-weathered in the laboratory prior to burial in
order to simulate weathered cultural stone. A corresponding set of limestone and sandstone
blocks were left exposed at the surface for two years. Weathering of the limestone and
sandstone blocks were assessed by examination of changes in weight, the Young’s modulus
of elasticity, and surface hardness after burial and surface exposure. In situ soil moisture
and temperature measurements were monitored continuously with emplaced soil sensors
connected to dataloggers and soil samples were taken for chemical and physical analysis
before burial and upon excavation. An on-site weather station was used to obtain above
ground environmental data including temperature, relative humidity, rainfall, and solar
radiation. Results from all stone and soil analyses were used to assess whether burial in this
case enhanced preservation or promoted alteration of cultural stone to a stronger degree
than being left exposed to surface conditions.
Keywords: reburial, backfill, stone weathering, soil
1
N. Zaman* and H. Viles
School of Geography and the Environment, University of Oxford, United Kingdom
noreen.zaman@ouce.ox.ac.uk
*corresponding author
1304
13th International Congress on the Deterioration and Conservation of Stone
LIST OF AUTHORS
Caner-Saltık, E.N.
839
Caneva, G.
915
Cano, C.
1227
Carmona-Quiroga, P.M.
703
Caruso, F.
923
Casanova Municchia, A.
915
Castelvetro, V.
847, 855
Charalambous, C.
711
Charola, A.E.
1069, 1129
Cherblanc, F.
1301
Chiantore, O.
847, 855
Coggin, M.
1287
Colella, M.
1089
Coltelli, M.-B.
847, 855
Çömez, S.
839
A
Abdel-Wahab, M.
1041
Abuku, M.
1201, 1255
Aguiar, J.
653
Al Mukhtar, M.
1301
Alexakis, E.
1219
Aloiz ,E.
1069
Alonso, J.
663
Alvarez de Buergo, M.
1303
Aly, N.
1303
Andraud, C.
785
Apostolopoulou, M.
1219
Araiza-Garaygordobil, G.
1051
Arnold, T.
879
Arosio, F.
1089
Astete, F.
1227
Auras, M.
1077
D
D’Amen, E.
761
Dağ, F.K.
839
Dajnowski, A.
719
Dajnowski, B.
719
De Luca, L.
1301
De Roy, J.
999
Del Lama, E.A.
811
Delegou, E.T.
1219
Ďoubal, J.
729
Downes, S.
963
Drdácký, M.
687
Duberson, S.
1247
Dubois, F.
1301
B
Bagneris, M.
1301
Bakolas, A.
1219
Ball, R.J.
671
Balloi, A.
1089
Barov, Z.
679
Bartoli, F.
915
Benchiarin, S.
1111
Bianchi, S.
847, 855
Bîrzu, C.
1097
Böhm, K.
879
Bonazza, A.
1137
Bourgon, J.
785
Boyes, N.
1103
Bracci, S.
653
Bresciani, V.
1089
Bromblet, P.
1247, 1271, 1301
Brunetaud, X.
1301
Brunet-Imbault, B.
1271
Burgos-Cara, A.
1297
E
Erdil, M.
839
Espinosa-Gaitán, J.
Etienne, M.
1247
Ettl, H.
1077
F
Fassina, V.
Fermo, P.
Flatt, R.J.
Fontaine, L.
C
Cabello-Briones, C.
Caner, E.
839
695
XXIII
1111
1137
923
999
745
13th International Congress on the Deterioration and Conservation of Stone
Forster, A.
769
France, C.
1129
Frangova, K.
1263
Franković, M.
663
Franzen, C.
753, 1119
Franzoni, E.
761, 803, 947
Fregni, A.
761
Frühwirt, T.
955
Fujita, H.
1227
I
Iba, C.
1145
Ibach, H.W.
1300
Ioannou, I.
711
Ishizaki, T.
825, 1201
Ito, A.
1227
J
Jablonski, M.
Jakutajć, J. M.
Jandejsek, I.
G
Gabrielli, R.
761
Gembinski, C.
1009
Gerdwilker, C.
769
Gerns, E.
777
Ghaffari, E.
889
Gherardi, F.
847, 855
Giaccai, J.
1129
Godet, M.
785
Gomez-Heras, M.
1303
Górniak, A.
793
Graham, C.A.
1017
Graziani, G.
761, 803, 947
Grissom, C.
1069, 1129
Grossi, C.M.
817
Grossi, D.
811
Guichard, H.
1247
Guillon, O.
1301
Guinamard, C.
1271
Gulotta, D.
1137
Güney, B.A.
839
1153
831
687
K
Kang, S.
703
Karacsonyi, S.
889
Karbowska-Berent, J.
831
Kardara, E.
1025
Kawaguchi, T.
1211
Kiesewetter, A.
1119
Kiriyama, K.
1255
Kohdzuma, Y.
1255
Koizumi, K.
1145
Kozub, B.
1031
Kozub, P.
1031
Kraus, K.
753
Krist, G.
889, 1171
Kuchitsu, N.
1211
L
Labropoulos, K.
1219
Lawane, A.
1181
Lawrie, K.
1059
Lazzeri, A.
847, 855
Leroy, E.
785
Lezzerini, M.
847, 855
Little, N.C.
1129
Livingston, R.A.
1069, 1129
Long, E.S.
863
López-Doncel, R.A.
981, 1051, 1237
Łukaszewicz, J.W.
793, 831
Luxford, N.
963
H
Hamed, A.
1303
Hartleitner, W.
1077
Haselberger, M.
1171
He, L.
905
Henry, A.
671
Hoornaert, L.
999
Howind, T.
1299
Hughes, J.J.
1299
Hunt, B.J.
817
Huysmans, S.
999
Hyslop, E.
769
M
Marelli, I.
XXIV
1089
13th International Congress on the Deterioration and Conservation of Stone
Marinković, V.
1189
Marinov, T.
1263
Martín-Chicano, A.
745
Mas-Barberà, X.
871
Matsuda, H.
1211
McGibbon, S.
1041
Meier, T.
1077
Meinhardt, J.
879
Milchin, M.
889, 1171
Mısır, Ç.T.
839
Mizutani, E.
1201
Molin, G.
1111
Monnier, J.
785
Morii, M.
1211, 1227
Moropoulou, A.
1219
Moundoulas, P.
1219
Mudronja, D.
1189
Q
Quarto, A.
R
Raymakers, K.
1279
Rieffel, Y.
981
Rodríguez, M.A.
871
Rodríguez-Navarro, C.
1297
Rohatsch, A.
847
Rolland, O.
1247
Rossen, L.
1279
Roveri, N.
761
Rüdrich, J.
981
Ruiz Bazán, I.
1089
Ruiz, S.
871
Ruiz-Agudo, E.
1297
N
Niccolai, L.
Nishiura, T.
Nuño, M.
1089
S
847
1227
671
Sacchi, B.
653
Saheb, M.
785
Salvadori, B.
653
Salvini, S.
939
Sano, K.
1145
Sasaki, J.
1201
Sassoni, E.
761, 803, 947
Scherer, G.W.
803, 811, 947
Scholz, G.
1300
Siedel, H.
955, 1119
Siegesmund, S.
1237
Signori, F.
855
Simon, S.
1017
Singh, L.P.
1299
Smacchia, D.
855
Smith, N.
1059
Sobott, R.J.G.
1300
Sotgia, C.
1089
Soto-Zamora, M.Á.
1051
Šperl, M.
687
Stanley, B.
963
Stillhammerova, M.
1279
O
Odgers, D.
671
Ogura, D.
1201, 1255
Ono, I.
1227
Ottosen, L.M.
897
P
Pan, A.
905
Pantet, A.
1181
Pascucci, S.
915
Pérez, L.
871
Pesce, G.L.
671
Pfefferkorn, S.
1119
Piao, C.
1145
Pierrot-Desseilligny, M.
Poli, T.
855
Pomonis, T.
1025
Pötzl, C.
1237
Praticò, Y.
923
Pummer, E.
931
1301
T
Takatori, N.
Taniguchi, Y.
XXV
1255
1145
13th International Congress on the Deterioration and Conservation of Stone
Tavukçuoğlu, A.
839
Thapliyal, P.C.
1299
Thomassin, J.H.
1181
Thorn, A.
971
Todorov, V.
1263
Tokimoto, S.
1211
Toniolo, L.
847, 855, 1137
Torney, C.
769
Török, Á.
1303
Tracey, E.A.
1059
Trubert, M.
1271
Tugas, J.
1301
W
V
Y
Vallet, J.-M.
1301
Vereecke, J.
1279
Vergès-Belmin, V.
785, 1247
Verhulst, N.
999
Vicenzi, E.
1129
Viles, H.
1304
Viles, H.A.
695, 703
Vinai, R.
1181
Vizcaino-Hernández, I.E.
1051
Yang, S.
905
Yoshioka, M.
1145
Young, D.
991
Young, D.A.
863
Wakiya, S.
1255
Wangler, T.
923
Watanabe, K.
1145
Weber, J.
847, 889
Wedekind, W.
981, 1237
Weise, S.
1119
Wentzel, R.
1287
Wichert, J.
955
Will, R.
777
Wiśniewska, B.
793
Z
Zaman, N.
Zhu, W.
XXVI
1304
1299
13th International Congress on the Deterioration and Conservation of Stone
LIST OF KEYWORDS
3
C
3D information system
1302
3D photo monitoring
1031
3D surface geometry
1017
3D survey
1089
3D-modelling
1051
calcareous stone
793
calcination
1129
calcite
803
calcium phosphate
803, 947
calcium sulphate
1255
calcium-oxalate
1189
captive-head washing
991
carbonate stones
831
Carthage marble
777
cemetery
1153
cemetery conservation
939
Central Park Obelisk
1009
clay
1271
cleaning
729, 785, 1077, 1089
climate
1247
Close-Range Digital Photogrammetry
1051
coating
1299
compatibility
769
compatible treatment
729
conservation
663, 719, 729, 939,
981, 1059, 1119, 1137, 1171, 1271,
1300, 1302
conservation of stone
1077
conservation planning
769
conservation practice
1017
conservation treatment
839, 1009
conservation values
1299
consolidants
811
consolidation
687, 745, 769, 793,
831, 839, 848, 855, 889, 923, 931,
955, 1279
convergent photogrammetry
1089
core stone
1211
cracks in stone
687
crust
999, 1077
cultural heritage
663, 817, 1031,
1299, 1303
cultural heritage buildings
1303
cyanobacteria
915
Cyprus
711
A
ablation
719
acid attack
803
acrylic and PVA as fixatives for
polychromies
1279
acrylic resin
1211, 1300
additives
663
adhesives
663
African local houses
1181
ageing
703
alveolar weathering
981
ammonium citrate
653
ammonium oxalate
803, 1189
analytical techniques
1219
application
889
application techniques
679
archaeological sites
695
architectural heritage
848
attachment
1211
B
bacillus cereus
831
backfill
1304
bedrock
879
benzalkonium chloride
863
biocide
863, 915
biodeterioration
915
biological growth
863
biomineralisation
745, 831
bio-restoration
1089
black crust
999, 1077
block copolymer
855
building material
1219
burial
817
XXVII
13th International Congress on the Deterioration and Conservation of Stone
D
F
damage mapping
1237
damages and causes
1263
database schema
1025
decay
695, 897, 1137, 1219
decorated stone elements
1097
delamination
999, 1069
demineralisation
931
dense limestone
831
deposition
1137
desalination
981, 991, 1247
design of experiment (DoE)
923
deterioration
1189
deterioration mapping
999
deterioration patterns
1111
diagnostic study
1219
diammonium hydrogen phosphate (DAP)
793
digital documentation
1009
digitalisation
1051
digitisation
1041
dissolution
803
dolomite
839
drilling resistance
671
durability
1111
façade cladding
777
fatty acid
711
field recording
1009
film properties
905
fire
1129
fragile tuff
1145
fragments
871
freeze thaw
671
frost
817
frost damage
825
frost heave phenomenon
E
H
earthquake
1171
efficiency tests for conservation
treatment
839
efflorescence
1103
Elbe sandstone
1119
electro-desalination
897
environmental monitoring
1145
environmental pollution soiling
1103
epoxy consolidation
1279
ethanol
947
ethyl silicate
923, 971, 1111
ethyl silicate consolidation
1279
evaluation
729
evaporation
1201, 1255
exhibition
1097
existing conditions
1009
Hagar Qim
695
heat and moisture transfer
1201,
1255
heritage management
1059
historic building materials
761
hybrid latex
855
hydric properties
955
hydrogen peroxide
963
hydroxyapatite
793
825
G
GC-1
719
geospatial data capture
1059
Gotland sandstone
793
grain loss
947
granite
719, 1211, 1227
gravestones
1017
green conservation
939
grouting repairs
1153
guidelines
1181
gypsum crust
785
I
index quality
1181
infilling cracks
831
injectable grout
971
interactive re-lighting
1017
iron yellowing
785
Itararé sandstone
811
XXVIII
13th International Congress on the Deterioration and Conservation of Stone
mould
museum
J
Joliet limestone
777
N
K
Kathmandu Valley
KSE
879
963
1247
nano-dispersive calcium hydroxide
solutions
839
nanolime
671, 745
nanomaterials
848
nanoparticle
785
nanotechnology
1299
natural weathering
703
non-destructive testing (NDT)
1219,
1303
1171
L
laser
785
laser ablation
1103
laser cleaning
719, 1077
laser scanning
1041
laterite
1181
leaching
761
lime
663
limestone
711, 719, 777, 793, 831,
889, 963, 1189, 1247, 1287
limestone decay
695
lithium silicate injectable grout
971
O
obelisk
719
old treatment evaluations
1279
onsolidation of calcareous stones
793
oxalate
1298
M
P
Machu Picchu
1227
magnetism
871
magnets
871
maintenance
1041
maintenance and repair
1059
mapping
999, 1031, 1237
marble
777, 1089, 1129, 1153, 1298,
1300
marble decay
1137
masonry
1181
mechanical properties
955
medieval tombstones (stećci)
1189
metadata
1025
Metigo MAP
999
Mid-Atlantic
1287
mobile applications
1009
modelling
1302
moisture transfer
1255
monitoring
695, 817, 879, 1137,
1145
monitoring and care concept
879
monument
1103
monument mapping
1031
painting technique
1263
Patan
1171
penetration depth
955
performance
1287
permeability
905
photocatalytic activity
703
photogrammetry
1129
Pińczów limestone
793
pinning repairs
1153
Platteville limestone
777
point cloud
1031
Pompignan
1287
porous limestone
831, 889
porous materials
1201
POSS-based copolymer
905
poultice
863
poultices
879
pre-consolidants
811
pre-investigation
1119
preservation
817
preservation measures
1263
preventive conservation
753, 1137
projects
1025
XXIX
13th International Congress on the Deterioration and Conservation of Stone
protection
753, 761, 848, 855
protective measure
825
protective patinas
1298
protective performance
905
Puerto stone
745
sodium sulphate
1255
soft nanomaterials
905
soil
1304
soiling
1103
sorptivity
711
stone
653, 663, 719, 729, 817, 1171,
1211, 1302
stone blackening
1137
stone conservation
848, 931, 939,
1025, 1097, 1119
stone consolidation
745
stone decay
1303
stone deterioration
1051, 1189
stone restauration
1097
stone structures
1227
stone weathering
1304
stonemasonry
1041
strengthening
931
stylolite
1287
sulphate
897
surface erosion
1137
surface treatment
1145
surfactants
811
survey
1103
sustainability
939
swelling
1271
swelling clay
811, 1271
swelling clay-bearing sandstones
923
swelling inhibitor
923
R
rain
761
rain water
1201
reburial
1304
recarbonation
1129
repair
1041, 1153
resin
1211
reversible stone adhesive
679
risk assessment
753, 769
rock weathering
1145
Romanesque portals
999
RTI
1017
rust removal
653
S
salt
981, 1247
salt attack
991
salt crystallisation
671, 1201
salt decay
897
salt deterioration
1119
salt reduction
879
salt weathering
991
sandstone
769, 793, 811, 897, 955,
971, 1069, 1119, 1153, 1271, 1300
scaling
1211
scheduled monument
1103
sculpture
871, 1089, 1247
seashore
1211
self-cleaning
761
self-cleaning coating
703
self-stabilisation
855
SEM/EDS
793, 839
shelter
825, 1255
shelter environment
1255
shelters
695
siloxane polymers
1111
skills development
1041
smart ventilation
963
sodium dithionite
653
sodium hexametaphosphate
653
T
technical investigations
679
technical properties
1237
TEM
785
Temple of the Sun
1227
TEOS
745, 889
thermal ageing
947
thermal diffusivity
947
thermosetting polymethyl methacrylate
679
TiO2
703
tombstones
1189
total impregnation
1300
toughness
687
Tournai cathedral
999
Tournai stone
999
XXX
13th International Congress on the Deterioration and Conservation of Stone
transporter brine
1247
travertine
915
treatment
1271
tuff
1145, 1237, 1263
water repellency
711
water repellent
915, 1145, 1279
weathered stone degradation
671
weathering
753, 981, 1145
weathering characteristics
1237
web platform
1302
wettability
711
winter cover
753
world heritage
1227
U
Udelfanger sandstone
ultra-violet
963
unions
871
1300
X
V
XRD
vacuum
889, 931
vacuum circulation process
955
Vermont marble
1129
vernacular architecture
1181
839
Z
zeolitization
W
water content
825
water evaporation
1255
XXXI
1263
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