Preservation of limestone material culture with siloxanes

Abstract

For centuries, limestone has been used as a building material and as an art medium. Contrary to popular belief, limestone is not indestructible. Natural and unnatural environmental factors have taken their toll on monuments and sculptures throughout the world. Because of the porous structure of limestone, it is unfortunately relatively susceptible to degradation, especially under modern polluted atmospheric conditions. Over time this degradation takes the form of dissolution, peeling, and mineral build-up on the surface. This results in aesthetic changes and disfigurement to monuments and works of art. The purpose of this research was to determine if siloxane polymers are effective in the preservation of material culture made from limestone. To accomplish this, separate blocks of freshly cut limestone were put through a series of tests before and after being treated with a variety of siloxanes/alkoxysilane mixtures, and alkoxysilanes. These tests included porosity and water absorption measurements, depth of penetration measurements and the effects of accelerated weathering. Several conclusions can be inferred by the data presented in this research. First, it was found that simple and inexpensive techniques could be used to determine the effectiveness of consolidants on limestone. Second, several siloxane/alkoxysilane mixtures and alkoxysilanes that were studied did protect limestone from water absorption, and accelerated weathering. There is still more data needed before a recommendation on the appropriate use of siloxanes in limestone conservation, but this research is a start in the right direction.