A composition useful as a replacement for cellulose ether in cement, plaster or mortar compositions comprising i) one or more crosslinked vinyl brush polymers having pendant or side chain polyether groups, which at a pH of from 1 to 14 contains less than 10×10−4 mol of added anionically or cationically charged monomers or polymer repeat units, and having a relative weight average molecular weight (relative Mw) of from 250,000 to 50,000,000 g/mol, ii) one or more aromatic cofactors containing one or more phenolic groups or, in combination, one or more aromatic groups with at least one sulfur acid group.