Abstract: A continuous process for the preparation of alkoxypolysiloxane in which silane or a silane mixture and a mixture of hydrogen chloride-containing alcohol and water is fed continuously into the lower region of preferably cylindrical stirred reactor, the reaction product formed together with excess hydrogen chloride-containing alcohol is drawn off continuously after residence time of 30 to 180 minutes at the upper end of the reactor and the undissolved, gaseous portion of hydrogen chloride is carried off at the head of the reactor, the temperature of the reaction mixture or the reaction product, as it flows through the reactor, being raised from a range of -17.degree. to +30.degree. C. to range of +30.degree. to +80.degree. C., the temperature gradient having to be at least 10.degree. C.

Abstract: A composition for making building materials water-repellent, before or after they are shaped, the composition containing organoalkoxysiloxanes of the formula ##STR1## in which R.sup.1 is an alkyl or aryl radical, R.sup.2 is an alkyl radical with 1 to 4 carbon atoms, a=0.8 to 1.5, and b is not greater than 2. The composition contains(a) 1 to 20% by weight of a mixture of organoalkoxypolysiloxanes of the aforementioned formula, 25 to 75% weight of organoalkoxysiloxanes having a b-value of 0.1 to 0.5 (siloxanes A) and 75 to 25% by weight of the organopolysiloxanes having a b-value 0.8 to 2.0 (siloxanes B), and in which the sum of a and b is not greater than 3,(b) 80 to 90% by weight of a water immiscible solvent and, if necessary,(c) known condensation catalysts.The organoalkoxysiloxane mixture has a surprisingly increased stability on alkaline walling. At the same time, a high depth of penetration and good surface effectiveness are observed.