A biocide- and ammonia-free aqueous polymer dispersion is obtained by radically initiated multi-stage emulsion polymerization and comprising particles comprising at least a first polymer phase formed from a monomer composition I and a second polymer phase from a different monomer composition II. The first polymer phase has a glass transition temperature below 20° C., and the second polymer phase has a glass transition temperature above 20° C., both as determined by differential scanning calorimetry according to ISO 16805. The polymer dispersion further comprises at least one water-soluble alkali metal silicate, at least one water-soluble alkali metal or alkaline earth metal alkyl siliconate, or a mixture thereof and has a pH of 10.0 or higher.