Conserving Stone Heritage: Traditional and Innovative Materials and Techniques

292 Pages·2022·11.125 MB·English

by  Francesca Gherardi, Pagona Noni Maravelaki

Cultural Heritage Science
Francesca Gherardi
Pagona Noni Maravelaki Editors
Conserving
Stone Heritage
Traditional and Innovative Materials
and Techniques
Cultural Heritage Science
Series Editors
Klaas Jan van den Berg, Cultural Heritage Agency of the Netherlands
Amsterdam, The Netherlands
Aviva Burnstock, Courtauld Institute of Art, London, UK
Koen Janssens, Department of Chemistry, University of Antwerp,
Antwerp, Belgium
Robert van Langh, Rijksmuseum, Amsterdam, The Netherlands
Jennifer Mass, Bard Graduate Center, New York, NY, USA
Austin Nevin, Head of Conservation, Courtauld Institute of Art,
 London, UK
Bertrand Lavedrine, Centre de Recherche sur la Conservation des Collections,
Muséum National d’Histoire Naturelle, Paris, France
Bronwyn Ormsby, Conservation Science & Preventive Conservation,
Tate Britain, London, UK
Matija Strlic, Institute for Sustainable Heritage, University College London,
London, UK
The preservation and interpretation of our cultural heritage is one of the major
challenges of today’s society. Cultural Heritage Science is a highly interdisciplinary
book series covering all aspects of conservation, analysis and interpretation of
artworks, objects and materials from our collective cultural heritage. The series
focuses on science and conservation in three main fields
• Art technology
• Active conservation and restoration
• Preventive conservation and risk management
The series addresses conservators and conservation scientists at museums,
institutes, universities and heritage organizations. It also provides valuable
information for curators and decision makers at museums and heritage organizations.
Cultural Heritage Science comprises two subseries, one focusing on advanced
methods and technology for conservation experts, the second presenting the latest
developments in conservation science. All titles in the book series will be peer
reviewed. Titles will be published as printed books and as eBooks, opening up the
opportunity to include electronic supplementary material (videos, high-resolution
figures, special data formats, and access to databases).
More information about this series at https://link.springer.com/bookseries/13104
Francesca Gherardi • Pagona Noni Maravelaki
Editors
Conserving Stone Heritage
Traditional and Innovative Materials
and Techniques
Editors
Francesca Gherardi Pagona Noni Maravelaki
Investigative Science School of Architecture
Historic England Technical University of Crete
Portsmouth, UK Chania, Greece
ISSN 2366-6226 ISSN 2366-6234 (electronic)
Cultural Heritage Science
ISBN 978-3-030-82941-4 ISBN 978-3-030-82942-1 (eBook)
https://doi.org/10.1007/978-3-030-82942-1
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We dedicate this book to Susanna Bracci, for
her remarkable contribution and inspiring
dedication to heritage science.
Preface
This book intends to provide guidance to heritage stakeholders for the design and
selection of materials and techniques for natural and artificial stone conservation,
with a focus on cleaning, consolidation, protection, and repair mortars. It aims to
bridge the gap between laboratory studies and conservation interventions, by link-
ing together the diverse scientific areas involved in the preservation of stone heritage.
The design and implementation of conservation treatments for historical build-
ings is a complex and challenging task, as a deep knowledge of the working proper-
ties and performance of the available conservation materials and methods is
required. The variety of decay patterns often encountered in historical buildings is
the result of the use of several types of materials in their construction, which, in
turn, are subjected to different micro-environments.
In the past decades, climate change has impacted the decay processes and their
kinetics, with the rise in the concentration of air pollutants and the increase in sur-
face recession, erosion, and biofilm formation as a result of more frequent and
aggressive precipitations. The changing climate has been affecting the properties
and durability of stone substrates, highlighting the crucial role of conservation treat-
ments needed to tackle these problems. In this context, many research studies have
been focused on the developments of materials specifically designed for stone heri-
tage conservation, often utilising nanotechnology. Thanks to the possibility to adapt
their properties, these innovative treatments are very versatile, and they often dis-
play high compatibility with the historical substrates, as well as new functional
properties. This book showcases recent developments in the application of new
materials, methods, and testing techniques for stone conservation, with a focus on
future outlooks.
A great deal of research succeeded in the full characterisation of different classes
of products available on the market, as well as newly developed materials for stone
conservation. Despite the promising results, only a few studies have included in
their design experiments relative to the investigation and monitoring of the changes
occurring in the treatments after long-term natural weathering. Indeed, few applica-
tions and assessments of the performance of conservation treatments on naturally
aged substrates in trial areas in historical buildings are available. The effectiveness
vii
viii Preface
of some products can be very different once applied onsite, as environmental and
operational factors can affect the application methodology and the curing of the
products. The long-term monitoring of conservation treatments is crucial for the
evaluation of their suitability for built heritage conservation, in order to provide
guidelines for their selection and application.
In the last decades, several groups and national standardisation bodies have been
working in the set-up of guidelines and recommendations for the testing and evalu-
ation of materials and methods for stone conservation. However, by comparing the
number of European (EN) and American Society for Testing and Materials (ASTM)
standards for materials used in the building sector (e.g. concrete, cement, polymeric
materials), it is clear that there is still some work to do in the standardisation of
protocols and procedures in conservation, especially regarding onsite testing, and
the definition of common threshold values for the assessment of their efficacy. In
this sense it is particularly interesting to confine the standard guidelines within the
framework of reversibility, retreatability, and compatibility, which are the pillars in
each conservation treatment.
In some of the case studies illustrated in this book, the selection of a specific
treatment able to meet every performance requirement was not possible, due to the
substrate characteristics (mineralogical composition, porosity, etc.) and their decay
patterns. This is particularly true for the selection of consolidants and protective
treatments, whose working properties are sometimes not compatible with historical
surfaces. As mentioned above, the concepts of compatibility and reversibility/retrea
tability of conservation treatments are important requirements for treatments in
heritage conservation, and they have been defined and discussed in this book.
To avoid the selection of unsuitable products, a condition survey in each of the
areas under investigation should be carried out, aiming to identify the type of stones,
their state of preservation, their exposure to the environment, and any past conserva-
tion treatments. These studies combined with the setup of treatment trial areas are
essential to achieve successful results. The possibility to test several formulations is
critical for the selection of the technical parameters (materials, methods, and equip-
ment) and working protocols to be followed. Decision support tools and “incompat-
ibility risks” assessment have been proposed by different scholars to make
comparisons among several options and help in the selection of the treatments for
the specific case study. In addition to the implementation of these tools, we believe
that the collaboration of different professionals (conservators, architects, scientists,
etc.) in the decision-making process is important to solve complex problems, and it
is instrumental in the success of the conservation interventions. The chapters in this
book provide the state of the art on traditional and innovative materials and methods
for stone conservation, highlighting current trends and future perspectives. Each of
them critically examines one phase of the conservation intervention: preliminary
investigations, condition assessment, and mapping of the deterioration patterns; sur-
face cleaning, with a specific focus on laser technology; consolidation; protection;
repair mortars and grouts; and onsite assessment and monitoring of conservation
treatments.
Preface ix
In Chap. 1, Gulotta and Toniolo present different strategies to carry out the con-
dition assessment of stone surfaces to identify and map the deterioration patterns,
by discussing international standards and providing guidelines. As showcased by
the reported case studies, this preliminary phase is crucial for the design of the most
accurate conservation interventions for built heritage.
In Chap. 2, Maravelaki provides an overview of the main cleaning techniques
used in the past and the future trends in cleaning interventions. The importance of
the nature of the substrate, deterioration patterns, micro- and macro-environmental
factors, specific guidelines, interdisciplinary, and people awareness are discussed.
Particular focus has been given on the best methodologies and materials for mechan-
ical and chemical cleaning applied in case studies, while innovative nanogels, nano-
fluids, poultice, micelle solutions, and microemulsions for stone cleaning and
desalination are also described.
In Chap. 3, Pouli introduces the reader to the basic concepts of laser cleaning,
while highlighting the critical and decisive parameters that enable the laser light to
selectively remove unwanted layers and encrustations from the surface of cultural
heritage. The case studies presented are good practices of laser cleaning referring to
different substrates, encrustations, and environmental conditions. Emphasis has
also been given to the necessity of monitoring the cleaned surface with reliable non-
destructive techniques.
Chapter 4 by Delgado Rodrigues highlights the main challenges in stone consoli-
dation. It provides guidelines to the professionals in their decision-making process,
by helping to understand complex deterioration patterns in their specific case stud-
ies, propose potential solutions, and select and implement the best procedure in
terms of materials and methodologies. Some practical examples are discussed,
describing issues and factors to consider in order to identify the best solutions.
Chapter 5 by Gherardi gives an overview on properties, effectiveness, and dura-
bility of several classes of protective treatments. Indications on performance
requirements, working properties, and the criteria for the selection of the materials
for specific case studies are discussed. The recent developments in terms of sustain-
ability and environmental impact in the use of innovative technologies and nanoma-
terials in stone protection are also explored, with recommendations for further
studies.
In Chap. 6, Apostolopoulou and Moropoulou present the design parameters of
conservation mortars related to compatibility and durability issues. The design takes
into account the physico-chemical and mechanical characteristics of the historical
materials, as well as the environmental stresses of the monument, the raw materials
used, and any architectural or geometric characteristics that influence the perfor-
mance of the restoration mortars. Principal component analysis (PCA) is a decisive
tool to discriminate the most high-performance and compatible restoration mortars.
Chapter 7 by Papayianni deals with repair mortars/grouts for reinstatement of
stone units found in archaeological sites, ancient theatres, castles, monasteries,
arched bridges, and industrial buildings. The repair mortars/grouts are designed
while taking into account the original stone characteristics and the environmental
conditions. Improved compositions of the repair materials were designed using
x Preface
additives, ensuring they are compatible to the historic ones in terms of colour, tex-
ture, and good adhesion to substrate. The case studies presented confront practical
issues of applications and how these can be overcome.
Finally, in Chap. 8, Bracci and Sacchi provide a review on the main invasive/non-
invasive techniques used onsite for the evaluation of conservation treatments (clean-
ing, consolidation, and protection of stone). Testing protocols for the assessment of
the effectiveness of the treatments and for the long-term monitoring of their proper-
ties are discussed, together with threshold values for the selection of the most appro-
priate materials and methods to be implemented in the conservation interventions.
While writing this book, we have been discussing several topics and concepts
with colleagues and practitioners working in the conservation of built heritage. We
are grateful for their time and support, which was fundamental in bridging scientific
studies with conservation practice. We would specifically like to acknowledge
Thorsten Schneider and Annelies Kersbergen, editors for Springer Nature, for invit-
ing us to publish this book and for their great support during these months; the
editorial board of the “Cultural Heritage Science” series; the reviewers for their
feedback and comments; and Michael Schredl, for proofreading the chapters.
We would like to give our profound thanks to the authors of each of the following
chapters for their excellent work, their perseverance, and their dedication to this
book, especially in the challenging past year.
Portsmouth, UK Francesca Gherardi
Chania, Greece Pagona Noni Maravelaki
Spring 2021