Abstract: Paper-covered gypsum wallboard of increased racking resistance which has been strengthened by impregnation completely through the thickness of the cover paper, at least throughout certain critical areas, by coating and subsequent absorption thereinto of water-free polymeric solutions. A most significant improvement results from impregnation thereinto of a moisture-curing isocyanate resin, preferably a semiprepolymer of a polyisocyanate and a polyol in combination with a viscosity reducing solvent, such as mineral spirits or xylene, and a catalyst. Improved mobile home walls are formed with the impregnated areas of gypsum board back face paper disposed over and adhered to framing members with glue or the like.