EVALUATING THE POTENTIAL DAMAGE TO STONES FROM WETTING AND DRYING CYCLES

Abstract

The literature on stone conservation often mentions that clay-containing stones can be damaged over time through cycles of wetting and drying (F�lix 1988). Several studies demonstrate the deleterious action of these cycles on stones consolidated with ethyl silicates [F�lix and Furlan (1994), F�lix (1995)]. However, to our knowledge, only one study (Wendler et al. 1996) demonstrates that these cycles can damage unconsolidated stone. The procedure is rather long and probably this is the reason for which so little work has been done to examine the importance of this damage mechanism.In this paper, we present a testing machine that has been developed to automate and accelerate the rate at which stone samples may be submitted to these cycles. Direct measurement of swelling indicates that swelling increases with the number of cycles, indicating progressive damage. However, the swelling can be durably reduced, although not completely eliminated by swelling inhibitors.We use a novel technique to examine the behavior of swelling stones, which consists in measuring the warping of a thin stone plate placed on two supports and which is wetted from above. Deflection and relaxation of the plate can be analyzed to extract free swelling, the ratio of wet to dry modulus and the sorptivity of the stone. However, agreement with separate measurements requires introducing a separate kinetic expression for the rate of swelling.