Pulverulent polycondensation products are described, comprising a) from 5 to 95% by weight of a polycondensation product based on an aromatic or heteroaromatic compound (A) having from 5 to 10 carbon atoms or hetero­atoms having at least one oxyethylene or oxypropylene radical and an aldehyde (C) selected from the group of formaldehyde, glyoxylic acid and benzaldehyde or mixtures thereof, and b) from 5 to 95% by weight of a finely divided mineral support material having a specific surface area of from 0.5 to 500 m2/g (according to BET to DIN 66 131). The inventive pulverulent polycondensation products are outstandingly suitable in building material mixtures in an amount of from 0.1 to 5% by weight, based on the weight of the building material. The pulverulent polycondensation products have a number of advantages in this context, for example excellent storage stability, good liquefying action at low dosage and technically simple production.