The Use of Epoxy Resins for Stone Consolidation
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THE USE OF EPOXY RESINS FOR STONE CONSOLIDATION
CHARLES M. SELWITZ The Getty Conservation Institute, 4503 Glencoe Avenue, Marina del Rey, CA. 90292
ABSTRACT An overview on the causes and methods of treatment of stone deterioration is presented. The reasons for and prejudices against epoxy resins for stone consolidaton are described in terms of achieving deep penetration, improvement in mechanical strength and good water repellancy without the inhibition of water vapor transmission. Early work which failed to understand the nature of epoxy curing in solution is outlined, and more recent research, where this problem has been solved, is discussed.
INTRODUCTION In 1986, The Office of Technology Assessment of the Federal Government issued a report entitled "Technologies for Prehistoric and Historic Preservation" which pointed out that our country is losing important parts of its cultural heritage at an alarming rate1 . Preserving America's historic sites contributes to our quality of life, and that of future generations, by increasing our understanding of the history of the United States. It also provides economic benefits, such as jobs and increased tourism. The thrust of the OTA report was to promote the use of modem technologies as the most cost effective way of dealing with this problem. Accordingly, this presentation is about adapting a modern, technological workhorse for use in some special concerns in the preservation of heritage buildings and monuments. The concerns are the environmentally caused deterioration of sandstones, limestones, marbles and other building stones that are a critical part of the fabric of many historic structures. The technological workhorse I want to invoke are the epoxy resins. Chemicals, such as epoxy resins, are used to strengthen and to protect weathered stone by a process known as consolidation. The polymer typically is brought into the fragile, often highly porous stone in an organic solvent. This solvent is used to achieve a formulation of low viscosity which enables deep penetration to occur. After the solvent has evaporated it is hoped that the consolidant has penetrated deeply enough to reach into fresh, undeteriorated stone and remain as a thin layer over the internal surfaces and between stone particles. Ideally the consolidated product has greater mechanical strength, and is protected against attack by water or chemicals but still allows water to pass freely through the stone. There is some controversy about putting polymers into stone to provide stabilization. How can any organic material make inorganic rock stronger? In fact there is ample evidence that epoxy resins injected into cracked, crumbling concrete wharfs, bridges and buildings can rehabilitate these structures and provide many additional years of service. In November of last year, I was taken by boat to inspect Pier 187 of the Port of Los Angeles. This structure was built in 1920 but by 1957 it had deteriorated to the point where the concrete beams had large transverse cracks up to a half inch in width 2 . The
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