Reports investigations into the application of surfactants in stone conservation. Alkyl ammonium chlorides reduce the hygric dilatation of clay rich sandstones to half of the original value. Polysiloxane films can be tightly bound to clay mineral basal planes using aminoalkyl silane as a primer. The water uptake and hygric swelling are markedly reduced. Well defined mixtures of ethanolic alkyl silane and aqueous aminoalkyl silane solutions form stable microemulsions. They can be used as commercial conservation products which are compatible with the environment.