A porous, friable stone can be effectively consolidated and rendered resistant to the action of water, oxides of sulfur, oxides of carbon, and other atmospheric constituents by treating with an aqueous solution of a barium or strontium salt of a monoester of sulfuric acid, followed by hydrolysis. The treatment with the barium or strontium salt solutions effects impregnation of the stone in depth. Controlled hydrolysis from a homogeneous solution results in precipitation and deposition of well formed, granular barium or strontium sulfate throughout all those regions the salt solution has penetrated. This deposition of insoluble sulfate effects consolidation of the stone area, and inasmuch as the sulfate is highly insoluble and chemically inert, the stone is rendered resistant to attack. -- AATA