A method of improving the hardness and/or the scratch resistance of a coating, which comprises adding, to the coating compositions used to produce the coating that is to be improved, a mixture of an adduct (A) with silane functionality and a catalyst (C) for the crosslinking of the silane groups, the adduct (A) prepared by an addition reaction of
- (a) at least one silane (Si) which has at least one functional group G′,
- and
- (b) at least one compound (O) which has at least one complementary functional group G″ and at least one surface-active radical,
- wherein the at least one functional group G′ of silane (S1) is reactive with the complementary functional groups G″ of the compound (O).