Polyvinylacetal-grafted polymers in the form of their aqueous dispersions or water-redispersible powders, and based on emulsion or suspension polymerized base polymers of one or more monomers from the group consisting of vinyl esters, (meth)acrylates, vinylaromatics, olefins, 1,3-dienes and vinyl halides, and optionally, further monomers copolymerizable therewith, the base polymers grafted with polyvinylacetals having from 0 to 5.0 mol % of vinyl acetate units, from 75 to 95 mol % of vinyl alcohol units and from 0.1 to 20 mol % of acetal units which are derived from aldehydes having 3 to 7 C atoms, are useful as additives in construction compositions, as binders, and as adhesives, and may be dried to form readily water-redispersible polymer powders.