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