By model experiments using slate plates, water-repellent agents such as silicone and organic titanium compounds were found to be the best for water-proofing and durability. Stone powder binders of ethyl silicate system were found to be best. In the experiments using tuff test pieces the following facts were found: 1) Water absorption and deterioration are proportional in their rates. 2) To prevent deterioration water-repellent substances should be used. 3) Water-repellent substances lose water proofing after physical destruction of the surface layer impregnated with repellents. 4) Durability of the stabilizing and consolidating resin is most important, and a modified ethyl silicate binder was found to be best.