FALL 2010
The Conservation of Decorated Architectural Surfaces
Some Perspectives
By Leslie Rainer
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Throughout history humans have decorated the surfaces of domestic, religious, and monumental architecture. These elements have ranged from painted plasters found in the earliest human settlements to contemporary public murals, with precursors found in prehistoric rock art decorating the surfaces of caves, cliffs, and natural shelters. It is a universal human impulse to embellish the spaces where we live, work, and worship. Decorated architectural surfaces of great aesthetic, historic, and cultural value constitute a significant portion of our cultural heritage.

The term decorated architectural surfaces refers to an astonishing array of treatments, from wall paintings and mosaics, textured plaster finishes and scagliola, stucco and relief elements, to cast stone, tile, and terracotta facings. Materials can be manipulated to achieve a great variety of effects, making the diversity of architectural surfaces enormous. However, one thing they have in common is that they are all directly applied to the surface of a building, monument, or freestanding wall and become an integral part of the architectural system.

Decorated architectural surfaces are complex, exhibiting stratigraphies with heterogeneous materials in numerous layers, from plasters to paints and coatings and—in the case of gilding, mosaics, and other cladding—various other applied materials. Moreover, decorative schemes may be superposed, with original and subsequent historic layers covered by more recent schemes. While the most immediate perception of decorated architectural surfaces is frequently of embellishment and ornament, they can simultaneously serve as the protective skin of the underlying structure. As such, decorated surfaces are intrinsically tied to the architectural system, inevitably suffering from deterioration factors affecting the building, monument, or site where they are located. Additionally, the larger context of the building and its surface may shift over time, and changing values may affect the significance of the decorated scheme. As the interface between the structure and its surroundings, decorated surfaces are often architectural elements of great value and, at the same time, the most vulnerable.

From mosaics and wall paintings on archaeological sites to earthen plasters on historic buildings to contemporary outdoor murals, the materials used to decorate architectural surfaces are diverse, and the contexts in which they are found vary greatly. This combination of factors presents conservators with difficult challenges. The experts needed to address conservation specialize in paintings, objects, stone, and architectural conservation, and they often require support from allied professions, including materials science, engineering, and architecture, as well as the artisan trades. The GCI has sought to address the conservation of decorated architectural surfaces over the last twenty years by carrying out research, implementing projects, and convening professionals through its field projects, scientific program, education, and dissemination.


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One of the most challenging issues in conserving decorated architectural surfaces is their preservation in situ. In the past, because of their value and significance, many architectural features were detached from their supports, as this was believed to be the best way to preserve them. Wall paintings and mosaics, in whole or in part, were routinely removed from archaeological sites to retain what archaeologists considered prized elements for study and display. However, in removing them, the elements became objects divorced from their context. Evidence of the original materials and technique of execution was often lost, as was their location and orientation on the supporting wall, vault, or ceiling. This diminished the value of the detached architectural elements, as well as the significance of the space from which they were removed. Moreover, a majority of these detached fragments ended up in storage areas inaccessible to the public.

Since the 1960s, conservation practice has advocated for the in situ preservation of wall paintings, plasters, and mosaics in order to retain both the integrity of the architectural ensemble and the context of the surface. In current practice, detachment of wall paintings and mosaics is commonly considered to be the very last resort when there is no alternative for their conservation in situ. This has created challenges to the physical preservation and maintenance of the extant surfaces and their interpretation, because of a number of factors, including environmental conditions, structural issues, and site management.

One specific challenge has been the need to reattach wall paintings and plasters to their support. Early attempts to preserve wall paintings and plasters in situ used pins and anchors to hold them in place. These anchors were not only aesthetically intrusive, they also put stress on points adjacent to already detached or weakened areas, at times leading to further damage. In the 1980s scientists and conservators from ICCROM (International Centre for the Study and Preservation of Cultural Property in Rome) developed the first injection grouts to reattach wall paintings, mosaics, and plasters to their architectural supports. Over time, a variety of commercial and custom-mix injection grouts has been developed. In spite of their increased availability, there has been little systematic research into the properties and performance characteristics of injection grouts specifically for architectural surfaces.

To address this gap, GCI scientists and conservators are carrying out laboratory and field research to develop test methods for the evaluation of these injection grouts, to provide practitioners in the field with tools to make informed decisions on the use of specific grouts for different cases.

The GCI has also addressed the conservation of decorated architectural surfaces in situ in several of its field projects. Oneof the most complicated cases has been the conservation of wall paintings in situ at the Mogao Grottoes, a fourth- to fourteenth century Buddhist Silk Road site near Dunhuang, China. The aim of this work, undertaken in collaboration with the Dunhuang Academy as part of a larger project on the conservation of the site, was to conserve the wall paintings in Cave 85, a representative cave temple at Mogao. The wall paintings showed a particularly complex set of conservation issues, including detachment of plasters from the substrate, damage to the paint layer by salt efflorescence, flaking paint, alteration of organic colors due to light exposure over time, and visitor impact. Conservators, conservation scientists, and engineers worked together to develop a diagnostic methodology for solving the numerous problems affecting the wall paintings and to mitigate damage to the fragile and exquisite painted earth plasters. As a result, the conservation of Cave 85 has become a model project for the conservation of other cave temples at the site and in the region.


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As in situ preservation has become the accepted approach for decorated architectural surfaces, the need to address issues of the surrounding site when planning for the conservation of a decorated architectural surface has become ever more evident. These architectural surfaces are affected by problems of the building or monument on which they are applied, and they can also be impacted by natural and human threats to the larger site of which they are part—a situation that requires an integrated approach to their conservation.

An example of the way in situ conservation of decorated features has led to conservation of the surrounding site can be found in the GCI's work in Egypt. In 1986 the GCI, in collaboration with the Egyptian Supreme Council of Antiquities (SCA), undertook the conservation of wall paintings in the 3,200-year-old tomb of Queen Nefertari, wife of Ramses II. Located in the Valley of the Queens, the multichambered tomb contains a highly sophisticated wall paintings scheme. The project, comprehensive for its time, included documentation, environmental study, conservation treatment of the wall paintings, and technician training. Following the project, visitation has been restricted, and the tomb can only be visited with special permission from the SCA. Continued monitoring by the GCI has shown that the tomb is overall in stable condition, with the greatest threat coming from visitors and film crews causing unintentional damage, underscoring both the importance of monitoring and maintenance over time and the need for controlling the effect of visitors on the site.

With a larger view of site conservation issues, the GCI returned to the Valley of the Queens in 2006. In its current project, the GCI is working with the SCA to develop and implement an integrated plan for the whole valley to address the most significant threats to the site, including structural issues of the tombs, rare but devastating flash floods, and mass tourism. While this project addresses broad site conservation issues, the heritage at the heart of the Valley of the Queens includes numerous tombs and wall paintings and plasters that risk damage and loss if larger issues are not addressed in a holistic conservation and management program.


A very different set of issues arises when considering decorated architectural surfaces on buildings still in use and for which regular maintenance and renewal are important both for the survival of the building and for the skills and traditions that created it. This is of particular concern for plasters, finishes, and paintings on earthen architecture, especially in climates where seasons of heavy rainfall may rapidly degrade surfaces.

In some cultures, buildings may be torn down and reconstructed, and then replastered or repainted, resulting in the loss of original decorated surfaces. However, artisans trained in plastering, painting, and finishing these surfaces ensure the survival of the tradition, though earlier schemes may be sacrificed. This cycle can pose a dilemma for conservators trained to conserve original materials.

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In the late 1990s, the GCI and the Ministry of Culture and Communication in the Republic of Benin confronted the complexities of working with a living tradition in their collaborative project to conserve polychrome bas-reliefs from the ajalala (reception hall) of King Glélé at the Royal Palaces of Abomey. This project presented a unique example of a site with a living tradition in the care of heritage professionals trained in the conservation of material culture. When the ajalala was demolished in 1988 and a new one was built in its place, the bas-reliefs that had adorned the original structure's facade were detached and placed in heavy earth and cement frames, in a process that converted them from integral architectural elements to museum objects. Fifty panels from the ajalala were preserved as part of the museum's collection, while artisans reconstructed the building and created new bas-reliefs in their place.

Royal ceremonies are still held at the reconstructed ajalala, and museum visitors can view the original bas-reliefs in an exhibit, which also provides interpretation of the history and tradition of bas-reliefs in Abomey and the conservation project. Since the project's completion, there has been greater attention to the polychrome bas-reliefs on royal and religious buildings in Abomey, and other projects have aimed to conserve historically significant buildings and treat bas-reliefs in situ. A conservation plan for the site is ensuring the preservation of the physical heritage, while artists in Benin continue to create bas-reliefs, preserving the living tradition.

Conservation professionals have begun to recognize that intangible living traditions are as valuable to preserve as physical materials. Traditions that maintain earthen finishes—such as plastering, repainting, and renewal of surfaces—are essential to the physical maintenance of these buildings and their preservation as living cultural heritage. In 2004 the GCI and the National Park Service organized an international colloquium to explore these and other issues related to the conservation and care of decorated surfaces on earthen architecture.1 The colloquium brought together conservation professionals working in different contexts—from archaeological sites to historic buildings, living traditions, and museum settings—to start a dialogue on the range of issues faced in the conservation of diverse surface treatments on earthen architecture.


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Over the last forty years, significant numbers of public murals were created by public arts programs in the United States through neighborhood beautification projects, artist commissions, and programs for youth. Exterior murals, often executed with modern paint materials not necessarily formulated for outdoor use, are showing signs of deterioration due to exposure to ultraviolet light, harsh environmental conditions, vandalism, and neglect. These contemporary examples of decorated architectural surfaces face conservation problems ranging from flaking paint, deterioration of coatings, and graffiti, to complete overpainting.

A multipronged approach is critical to link the issues of long-term care and maintenance of murals with ongoing scientific research on paint degradation and protective coatings to preserve them over time. Several institutions, including the GCI, are conducting research into modern materials,2 including paint degradation, which on murals is exacerbated by exposure to ultraviolet light and atmospheric pollutants. Scientists and conservators at the GCI are also conducting research into anti-graffiti coatings to evaluate the performance of different categories of protective coatings on murals. Just as important, the GCI has worked with arts administrators responsible for public art programs to address the importance of maintenance for murals and other public art. Having a maintenance plan in place when new murals are created (and then carrying it out) is an effective preventive conservation measure that minimizes the need for costly, large-scale treatments.


As illustrated in the examples mentioned here, the conservation of decorated architectural surfaces is a multidisciplinary area of conservation that draws on wide expertise. Conservators specializing in paintings, stone, and architecture must work together with architects, engineers, and scientists, combining their knowledge to address issues of both structure and surface. Furthermore, projects involving restoration may draw on skilled artists and craftspersons to re-create lost elements. The conservator of decorated architectural surfaces, who may be specialized in one or several areas of materials conservation, requires multidisciplinary training that provides a working knowledge of the conservation issues of the entire architectural system—from the structure and substrate to the surface.

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A number of organizations are working to build capacity in this area. As an adjunct to the GCI's work at the Mogao Grottoes, a degree program in wall paintings conservation was established at Lanzhou University, China, in collaboration with the Courtauld Institute of Art Conservation of Wall Painting Department (the Conservation of Wall Painting Department itself was initiated by the GCI and the Courtauld Institute of Art in 1985). MOSAIKON , a large-scale collaborative initiative in which the GCI is involved, is under way to address education and conservation issues of mosaics in the Mediterranean region.

The continued need for capacity building in the conservation of decorated architectural surfaces is clear. The field requires integrated training that takes into account the variety of skill sets necessary to address both surface and structure in context. Fine arts conservation degree programs have begun to recognize the need to train conservators not only in the conservation of paintings, paper, textile, and museum objects but also in architectural surfaces. While programs in Europe have long produced wall paintings conservators, it is only more recently that some U.S. programs in art conservation and historic preservation have begun to include architectural finishes and murals in their curricula.3 However, few programs provide training in the conservation of the wide range of decorated architectural surfaces discussed here.

Conservators with such training are well positioned to communicate, to both professional colleagues and the public, the complex conservation issues of decorated architectural surfaces. By raising awareness of the significance and value of the diverse range of decorated architectural surfaces, we can ensure that increased attention and expertise will be brought to the conservation of these significant—and vulnerable— elements of built cultural heritage.

Leslie Rainer is a wall paintings conservator and senior project specialist with GCI Field Projects.

1. Colloquium on the Conservation of Decorated Earthen Architectural Surfaces, organized by the GCI and the U.S. National Park Service, September 22–25, 2004.
2. See Conservation Perspectives: The GCI Newsletter, vol. 24, no. 2.
3. Notably, a number of students have graduated from the Winterthur Museum/University of Delaware Program in Art Conservation (WUDPAC) with a specialized interest in the conservation of painted surfaces, including architectural finishes and murals. WUDPAC is also carrying out research on protective coatings and deterioration of acrylic paints used for murals. The graduate programs in historic preservation at Columbia University and the University of Pennsylvania both offer training in the conservation of architectural finishes.