A dry mix particulate composition of a calcined oxide of Mg and/or Ca, an acid phosphate, and fly ash or equivalent, wherein the calcined oxide is present in the range of from about 17% to about 40% by weight and the acid phosphate is present in the range of from about 29% to about 52% by weight and the fly ash or equivalent is present in the range of from about 24% to about 39% by weight when sand is added to the dry mix, it is present in the range of from about 39% to about 61% by weight of the combined dry mix and sand. A method of forming a structural member is also disclosed wherein an aqueous slurry of about 8-12 pounds of water is added to dry mix and sand.