The present invention provides a process for preparing polymer powders by
evaporating the volatile constituents from aqueous dispersions of
film-forming polymers P in the presence of drying assistants T selected
from the salts of oligomeric arylsulfonic acid-formaldehyde condensates
wherein prior to the evaporation of the volatile constituents the aqueous
polymer dispersion comprises at least 1.5% by weight, preferably at least
1.7% by weight, based on the polymer in the dispersion, of at least one
anionic surface-active compound AO having at least one C.sub.6 -C.sub.32
alkyl group; the polymer powders obtainable by the process; and their use
in binding mineral building materials.