A method of producing gypsum building board, comprises allowing a layer of an aqueous gypsum slurry to set so as to form a board, in which the improvement comprises mixing the gypsum slurry with an aqueous foam produced by foaming water containing at least one non-ionic alkylpolysaccharide foaming agent of the general formula (I) R—O-(G)x  (I) where: R represents a linear or branched alkyl group having from 6 to 20 carbon atoms; G represents a reducing saccharide moiety connected to R via an ethereal O-glycosidical bond; and x is 1 to 10.