FIELD: manufacture of building materials. SUBSTANCE: method of manufacturing product containing solidified gypsum and having elevated resistance to constant bending strain comprises providing mixture of calcium sulfate material with water and a reinforcing material including one or several salts or their anionic moieties selected from sodium trimetaphosphate, aluminum trimetaphosphate, sodium acid pyrophosphate, tetrapotassium pyrophosphate, trisodiumdipotassium tripolyphosphate, ammonium polyphosphate with 1000-3000 phosphate units, which mixture is then maintained under conditions appropriate to allow calcium sulfate material to form hardened gypsum. EFFECT: increased resistance to bending strain. 69 cl, 5 dwg, 19 cl, 12 ex
