A method for producing a set gypsum-containing product comprising an interlocking matrix of set gypsum wherein said method comprises applying to said set gypsum one or more enhancing materials selected from the group consisting of phosphoric acid; condensed phosphoric acids, each of which comprises 2 or more phosphoric acid units; and salts or ions of condensed phosphates, each of which comprises 2 or more phosphate units, and monobasic salts or monovalent ions of orthophosphates.