Hydrophobic cementitious composition

The composition contains more than 0.15 wt% of organo-silicon compounds based on the cement content. These are based on at least one alkoxy-silane and at least one alkoxy-siloxane. Of the organo-silicon compounds, 5-95 wt% comprises R 1-Si-(OR 2>) 3. R 1> is an alkyl group with 1-16 carbon atoms and R 2> is an alkyl group with 1-4 carbon atoms. In addition, 95-5% comprises alkoxysiloxanes. Their general molecular and structural formulae, together with suitable variants, are further detailed in the text. The organo-silicon compounds are obtained by conversion of at least one alkoxysiloxane compound and at least one alkoxysiloxane. Conversion takes place at 150-200[deg] C. The composition is concrete or an artificial stone. In manufacture, an aqueous emulsion containing the organo-silicon compounds is added to a cement-containing, free-flowing mixture. Setting follows. Sufficient emulsion is used, to ensure that more than 0.15 wt% of organo-silicon compounds are added, based on the cement content. The emulsion added to the mixture contains 1-75 wt% of organo-silicon compounds. More than 2 wt% of aqueous emulsion is added to the mixture. The emulsion contains 1-10 wt% of emulsifier(s). They are anionic, cationic and/or non-ionic. The buildings or parts of them, which are constructed using the cited composition, are also claimed. An independent claim IS INCLUDED FOR the method of making hardened cement-containing compositions.