Cast stone ornamentation and stuccoed surfaces of the California Building, erected in 1915, had deteriorated due to weathering. Increased water absorption, reduction of mechanical strength, and cyclical hydration of efflorescences had accelerated decay. Connecting iron bars had oxidized. Consequently, cast stone had fragmented in places; these areas needed repair. Heavy ornamentation that was determined to be a safety hazard was replaced by light weight replicas of artificial stone. Conservation procedures, developed from laboratory experiments, consisted of cleaning efflorescences (reduction of Na^2t to 0.02 percent of stone) and consolidating the cast stone with epoxy impregnation (to enhance compressive strength by 50%) The specifications for the artificial stone made from polymeric cement and inorganic aggregate were dependent upon these factors: bond and mechanical strength, water absorption, flammability, and linear expansion; these were determined using ASTM standards. The properties of the fabricated stone were similar to that of the cast stone. Since the completion of the work in early 1975, the building appears to be in a good state of preservation.