The invention relates to a hardenable mixture comprising at least one product of hydrolysis of an organosilane of general formula R aR bSiX(4-a-b) or of an oligomer derived therefrom, and at least one blocked polyisocyanate. In said formula, R represents a non-hydrolysable radical, R represents a non-hydrolysable radical carrying a functional group, X represents radicals which are the same or different and are selected from the hydroxyl group and hydrolysable substitution products of a hydroxyl group, a is equal to 0 or 1, b represents a value between 0 and 3, and the sum of a and b is equal to 1, 2 or 3, provided that at least one of the substituents R comprises an epoxy group as a functional group. The invention also relates to mixtures containing pigments and/or fillers, a method for producing cross-linked mixtures by reacting products of hydrolysis, namely modified polysiloxanes, with the blocked polyisocyanates, and to coatings and moulded bodies produced thereby.