A composition characterized in that it contains (A) a polydiorganosiloxane having at least one silicon-bonded OX group, in which X represents hydrogen, alkyl or alkoxyalkyl, and at least one aminoalkyl or polyaminoalkyl acid salt substituent derived from a water-soluble organic or inorganic acid, (B) a silicon compound e.g. methyltrimethoxysilane which is soluble in (C) and which has per molecule more than two silicon-bonded groups reactive with the OX groups in (A), and (C) a water-soluble solvent for (A) selected from aliphatic alcohols, glycols and polyglycols and their ethers and esters.
The compositions are useful as coating compositions and in particular can be diluted with water for application as water repellents to masonry and similar substrates.