The invention relates to a building material composition containing a) a hydraulic binding agent, b) an aggregate, c) a copolymer suitable as a flow agent and d) an adsorption blocker, wherein the adsorption blocker has as its basic component a structural unit D-E-A obtained from the reaction of the individual components D, E and A, wherein E is represented by a compound having at least two reactive isocyanate groups, D is represented by a hydrophobic compound with at least one group reactive with isocyanates, A is represented by a hydrophilic compound with at least one group reactive with isocyanates.