Method for the hydrophobic impregnation of fired ceramic molded bodies

A process for the hydrophobizing impregnation of fired clay moldings, comprising treating the fired clay moldings with an aqueous composition comprising:

• (A) at least one silane of the formula
• RaR1Si(OR2)3-a (I),
• in which
• R each independently, are monovalent, SiC-bonded hydrocarbon moieties having from 1 to 5 carbon atoms,
• R1 each independently, are monovalent, SiC-bonded hydrocarbon moieties having from 6 to 22 carbon atoms,
• R2 each independently are hydrogen or monovalent hydrocarbon moieties and a is 0 or 1,
• and/or partial hydrolysates of the silanes of formula (I) which have at most 5 silicon atoms in the partial hydrolysate,
• (B) at least one siloxane comprising at least 10 siloxy units, comprising units of the formula
• R3bR4c(OR5)dSiO(4-b-c-d)/2 (II),
• where
• R3 each independently are a monovalent, SiC-bonded, nitrogen-containing hydrocarbon moiety,
• R4 each independently are a monovalent, SiC-bonded hydrocarbon moiety that is unsubstituted or that optionally has halogen atoms as substituents,
• R5 each independently is hydrogen or a monovalent hydrocarbon moiety,
• b is 0, 1, 2 or 3,
• c is 0, 1, 2 or 3 and
• d is 0, 1, 2 or 3,
• with the provisos that b+c+d≦3, that in at least one unit b is not 0, and in at least 50% of all of the units of the formula (II) in the organopolysiloxane b+c is equal to 2,
• (C) acid,
• (D) optionally, emulsifier(s),
• (E) water, and
• (F) optionally, other substances.