The Effectiveness of Silicones as Water Repellents When Applied to Various Types of Limestone

Abstract

Masonry structures are subject to cracking and staining as they undergo weathering. The cracking is apparently due to freezing and thawing of the masonry when it is wet. Staining is most common in smoky cities, but does occur to some extent everywhere. It is very costly to remove stains and to repair cracked masonry. For example, it was necessary to spend about $10,500 in 1953 to replace cracked limestone in the walls of the Kansas State College Library. Any method of preventing such damage would be very valuable. Two methods are available for preventing such damage. The first method, which should be employed as far as possible, is to construct buildings with types of limestone known to have a high natural resistance to freezing and thawing damage. The second method is to keep water out of the stone by means of either waterproofing agents or suitable water repellents. Recently there have appeared on the market two types of silicone preparations which give water repellency and stain resistance to masonry. They may be applied by brushing and spraying. One of them is a solution of methly silicone resin in a solvent such as toluene. This material has been reported by Anderegg (1) and (2) and by the General Electric Company (7) to give satisfactory water repellency to brick and concrete structures but was not recommended by the General Electric Company (7) for Indiana Limestone (Bedford). The second water repelling agent is a water solution of sodium methyl OH