The hydrolysis of compounds containing alkoxysilyl moieties catalysed by UV-generated protic acids, followed by condensation of in situ generated silanol groups, is proposed as an effective approach to formation of hard, silicate-type materials by a sol–gel process. It gives highly thermally stable materials which can be of value as precursors to silicon oxycarbide films. The effectiveness of the photocatalyst used in the process depends on the type of anion and seems to be limited, in some cases, by Si–F bond formation.