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The design of treatments for the conservation of stone in historical buildings and works of art is a challenging task, as a deep understanding of the working properties and performance of the available products and methods is required to tackle complex decay patterns.

The chapters in this book illustrate the state of the art on traditional and innovative materials and methods for stone conservation, examining current trends and future perspectives. Each of them is focused on describing the consequent phases that complement the spectrum of the conservation intervention: preliminary investigations, condition assessment, and mapping of the deterioration patterns; surface cleaning, with a specific focus on laser technology; consolidation; protection; repair mortars and grouts; and onsite assessment and monitoring of conservation treatments. The performance of the applied conservation interventions is criticized and discussed with an aim of providing the specialists with specific tools for stone conservation.

This book intends to bridge the gap between laboratory studies and conservation interventions, by linking together the diverse scientific areas involved in the preservation of stone heritage. Different case studies are included, highlighting specific conservation challenges and their solutions in order to understand and overcome them. The aim is to guide conservators, conservation scientists and heritage stakeholders in the selection of compatible and sustainable materials and techniques for Conserving Stone Heritage.



Chapter 1. Preliminary Investigations, Condition Assessment, and Mapping of the Deterioration Patterns

Although generally assumed as long-lasting and extremely stable materials, natural stones are subjected to complex and interconnected damaging actions over the prolonged exposure time usually associated with heritage sites. Therefore, evaluating and monitoring the state of conservation of the stone surfaces of the built heritage is integral to the design and management of appropriate and effective preservation strategies. This chapter provides a critical overview of different approaches for the condition assessments of the stone surfaces, by examining international standards, guidelines, and methodologies for the identification and mapping of the deterioration patterns. The application of theoretical frameworks to precisely describe and evaluate the actual complex field conditions requires multidisciplinary contributions and an appropriate and sustainable diagnostic support. Selected case studies are also presented to discuss objectives and challenges in applying condition assessment strategies to the long-term evaluation of past conservation treatments, to inform and design suitable conservation strategy for historic façades, and for the preservation of modern architecture.
Davide Gulotta, Lucia Toniolo

Chapter 2. Surface Cleaning: Implications from Choices & Future Perspectives

In this chapter, an overview of the main cleaning techniques used in the past and trends in cleaning interventions are presented and discussed. The requirements for the selection of the best cleaning methodology according to the substrate, deterioration pattern, and micro- and macro- environmental factors are discussed. An overview of different classes of cleaning methods is presented, with a particular focus on the best methodologies and materials for mechanical and chemical cleaning. In particular, the application of innovative nanogels, nanofluids, poultice, micelle solutions, and microemulsions for stone cleaning and desalination are described. Some case studies summarising results published in the literature on the use of mechanical, chemical, and nanogel cleaning are presented and discussed. Raising awareness, providing specific guidelines, and establishing collaboration amongst experts from different disciplines in charge of carrying out diagnostic, cleaning, and evaluation methods are highlighted in this chapter.
Pagona Noni Maravelaki

Chapter 3. Laser Cleaning on Stonework: Principles, Case Studies, and Future Prospects

The use of laser light to selectively remove and/or precisely reduce unwanted layers and encrustations from the surface of cultural heritage (CH) objects and monuments was systematically investigated during the past 30 years bringing about a significant breakthrough in the field. This chapter aims at briefly introducing the reader to the basic concepts of laser cleaning, while highlighting the critical and decisive parameters that determine an efficient and successful laser ablation on stonework. Limitations ensuring a safe process are discussed, and good practice guidelines for laser cleaning interventions are presented, with emphasis to their practical implementation in three laser cleaning projects with different conservation challenges. Finally, ongoing issues related to careful assessment and reliable monitoring of the process are discussed.
Paraskevi Pouli

Chapter 4. Stone Consolidation. Between Science and Practice

This chapter deals with basic considerations about stone consolidation and aims to advance thoughts and clues to help professionals bridge the gap between science and practice. Scientific literature and personal experience serve to support and interpret the complex and intricate difficulties raised by practical consolidation needs. The reasons for these difficulties stem from the often-complex patterns of deterioration, the high potential risks of obtaining a very high or very low consolidation action, the uncertainty of medium- and long-term behaviour, and the lack of adequate guidelines for selecting a product and configuring a treatment consolidation solution for the intended objective. The purpose of this chapter is to help professionals to adapt existing knowledge on stone consolidation issues to each specific case and help them to make decisions, keeping in mind that there is no universally applicable product or treatment and that universal recipes should be clearly discarded. It is assumed here that the user works with products available on the market and, therefore, this chapter is not sufficiently detailed and is not intended to serve as a guide for testing or certifying new products or treatment techniques to be introduced to the market.
José Delgado Rodrigues

Chapter 5. Current and Future Trends in Protective Treatments for Stone Heritage

This chapter provides a background on stone protection, taking into consideration the performance requirements, working properties, and the criteria for the selection of the most appropriate materials for specific case-studies. The main classes of protective treatments (water repellents, antigraffiti coatings, inorganic treatments, limewashes, salts inhibitors, etc.) are explored, along with information about their properties, performances, and durability once applied to naturally weathered stone surfaces. Recent trends in the development of innovative and nanostructured formulations with antibacterial, depolluting, and antifouling properties for stone protection are also examined, providing recommendations for further studies. The chapter emphasises the crucial role of multidisciplinary teams to understand and solve complex problems and challenges that arise in built heritage protection.
Francesca Gherardi

Chapter 6. Mortars for Restoration: Set-up Parameters and Developing Mortar Design Areas

Designing mortars for restoration work is a crucial step in any conservation project. Mortars are complex, composite materials and their characteristics are dependent upon the raw materials used, as well as several design parameters. Especially in the case of monument protection, it is important to design a mortar with required characteristics to ensure its compatibility in relation to the historical materials, and its effectiveness in terms of the restored monument’s mechanical performance. In this chapter, first, a discussion is made on the effect of the design parameters and raw materials of a mortar on its characteristics, taking into account international literature. Following this, an interdisciplinary methodological approach is presented, focused on the design of restoration mortars, considering the characteristics of the historical materials of the monument, the environmental stresses it is subjected to, and the vulnerability of the structure to mechanical stresses. This approach considers any architectural or geometric characteristics which may set limitations to which the restoration mortar must abide by. Principal component analysis (PCA) is used to correlate and examine mortar characteristics within a combined space, where compatibility and performance are simultaneously achieved.
Maria Apostolopoulou, Antonia Moropoulou

Chapter 7. Repair Mortars/Grouts for Reinstatement of Stone Units in Historic Structures

Stone units (shaped or unshaped) are the components of many historical masonries found in monuments such as archaeological sites, ancient theaters, castles, monasteries, arched bridges, and industrial buildings. A great variety of locally available stones have been used in the past, but nowadays the old quarries/deposits do not often exist. Therefore, there is need to reinstate old stone units with mortars/grouts to produce artificial stone pieces to replace the missing parts in restoration works. These repair mortars/grouts should fulfill conceptual, functional, and technical requirements with respect to their compatibility with old stone (color and texture harmonization, good adhesion to substrate, resistance to environmental conditions, no secondary reaction products, etc.). Furthermore, before the selection or design of a repair material (mortar/grout), a systematic analysis of the original stone pieces and environmental conditions affecting their degradation should be well understood and considered. Improvement to the composition of repair materials should be made by using additives and taking measures for good practice in the execution of old stones reinstatement or replacement works.
Three selected case studies concerning two archaeological sites and an ancient theater are also presented. Problems confronted in practice are recognized, and possibilities to overcome them are suggested.
Ioanna Papayianni

Chapter 8. In situ Assessment of Conservation Treatments and Monitoring of Their Effectiveness

In this chapter an overview of the main invasive/non-invasive techniques used in situ for the evaluation of conservation treatments is provided. The conservation treatments considered are cleaning, consolidation, and protection of stone, mainly for architectural heritage. After a brief introduction, a paragraph is dedicated to the current process of drafting the standards, starting from previous experiences. In each paragraph dealing with conservation treatments, a reminder of commonly used laboratory tests carried out on stone samples, following either standardized protocols or not, are briefly reported. Details about testing protocols and threshold values for the selection of the best conservation treatment and for the monitoring will be described.
This chapter is not a technical description of each single technique but rather an introduction to the different possibilities of application of in situ methods.
Susanna Bracci, Barbara Sacchi


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