Impregnation Treatment with Hydrophobic Silane to an Important Stone Building Suffering from Freezing Damage in Cold and Heavy Snowfall District

An important historic stone building (1906) in a cold and heavy snowfall district, Otaru, Hokkaido, Japan, had been suffering from freezing damage because of frequent freeze-thaw cycles in early spring. In order to revive the cohesion of the damaged stones (porous tuft) and protect them from water penetration, impregnation treatment with hydrophobic silicone resin (a solution of the oligomer of methyl triethoxy silane in organic solvent) was executed. Several years later, a serious trouble occurred. The layers of some stones, into which the resin had penetrated, had become detached. Detailed investigation revealed that the cause and the mechanism of this trouble is as follows: Because the waterproofing of the roof was insufficient, snow water penetrated into the stones from the untreated side and the water froze to make ice crystals in the interface between resin-treated layer and untreated layer; the growth of the ice crystals led to the breaking of the stones. Thus, covering the roof with copper sheets was carried out. Now, more than 30 years after the conservation work, the condition of the building is good.