12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012 1 EFFECT OF SWELLING INHIBITORS AND SELF-RESTRAINT ON THE DURABILITY OF ETHYL SILICATES CONSOLIDANTS APPLIED TO CLAY- BEARING STONES Francesco Caruso, 1 Timothy Wangler, 1 Asel María Aguilar, 1 Heinz Richner, 1 Jakob Melchior 1 and Robert J. Flatt 1 1 ETH Zürich, Institute für Baustoffe, Physical Chemistry of Building Materials, HIF building, Schaffmattstrasse 6, 8093 Zurich (Switzerland). Email addresses: fcaruso@ethz.ch, wangler@ethz.ch, aselaguilars@ethz.ch, richnerh@ethz.ch, jakobme@student.ethz.ch, flattr@ethz.ch Abstract This paper presents the study of the role of a swelling inhibitor on the durability of a clay-bearing stone consolidated with an ethyl silicate. It is shown that when the samples are left to swell freely, the swelling inhibitor reduces the rate of weakening of the stone in cycles of wetting and drying. In the case where samples are restrained during the wetting, there appears to be a further reduction of the weakening for samples treated with swelling inhibitor before consolidation. However, this is not the case for samples consolidated without prior application of swelling inhibitors. The latter results require further work and improvement of experimental protocols to shed light on the possible role of self-restraint on the durability of consolidated clay-bearing stones. Keywords: clay-bearing stone, Villarlod molasse, swelling clay, ethyl silicate, swelling inhibitor 1. Introduction The preservation of stone-built cultural heritage is a challenge in material and conservation sciences. Many types of stones contain inclusions of clay minerals that may cause serious damage by dilatation during wetting and drying cycles, depending on the type, amount and distribution of the clay. The application of ethyl silicates consolidants can be used as a treatment to strengthen weathered stone, by allowing the formation of silica gel network that acts as a binder within the stone. However, in the case of swelling stones, these consolidants can lose their effectiveness after just a few cycles of wetting and drying (Felix 1994). A remedy to the damage is to use these in combination with swelling inhibition products (Wendler et al. 1991). Positive synergies have recently been demonstrated (Jiménez González 2008), which restore particular interest for in situ application for non- transportable monuments and facades. Furthermore, it is known that protruding elements get more damaged than facade ones in cycles of wetting and drying. This has been explained by the partial saturation of stone blocks, leading to partial expansion and lower stresses. This may also play an important role in increasing the durability of ethyl silicate consolidants with respect to laboratory tests performed on small and unrestrained samples. We examine whether the restraint felt by the consolidated part of the stones may also play such a role.