Efficiency of Epoxy Resins as Stone Preservatives

Earlier studies on stone conservation by Gauri [1] and Gauri et al. [2, 3] were concerned with impregnation techniques and with the changes rendered in the physical and chemical properties of stone as a result of impregnation treatments. While studying the reactivity of test specimens in dynamic, SO,-enriched atmospheres, Gauri et al. [3] found that certain epoxy resins provided more protection than other epoxy resins. They had also found that certain epoxy resins even increased the reactivity rather than providing protection to the treated stone. Specifically, the reactivity of specimens treated with Epi-Rez* 510 was less than the reactivity of the specimens treated with Epi-Rez 504, and certain specimens having thick coatings of Epi-Rez 504 were more reactive than the controls. One of the causes of this enhanced reactivity was thought to be the occurrence of perforations [3; Figs. 6, 7] resulting from frothing of the resin during polymerization and the escape of the solventvapor from deeper layers of treated stone. One of the purposes of this note is to present an additional, and certainly more effective, cause for such increased reactions. Another purpose of this note is to emphasize the need of laboratory testing of preservative treatments in concentrated atmospheres for accelerated weathering. The appraisal of this additional cause to enhance calcite-SO, reactivity has emerged from considerations concerning the chemistry of the resins applied in our treatments. Epi-Rez 510 is a bisphenol-A diglycidal ether. Epi-Rez 504 which, rather than providing protection, increased the reactions of treated specimens as compared with the untreated, is a mixture of Epi-Rez 510 and Epi-Rez 502. Epi-Rez 502 is an aliphatic diglycidal ether. To establish that it is the occurrence of an aliphatic group in the epoxy chain that causes an excessive