A method is provided for making inexpensive synthetic inorganic resins that are stable, mix easily with water and may be conveniently diluted to form an easy-to-use paste for commercial applications. The method uses environmentally friendly techniques to provide improved efficiencies in the commercial production of these resins. The resins are produced by the partial reaction of phosphoric acid with sparsely-soluble oxides, or sparsely-soluble oxide minerals, that are added to the phosphoric acid under controlled conditions. In certain specific embodiments, methods are provided for modifying synthetic inorganic resins so as to produce rapid-setting phosphate cements and ceramics having high flexural strength. Unique synthetic inorganic resin formulations are also disclosed. These formulations are phosphate-mineral based, non-volatile, tend to be non-flammable, do not contain any hazardous inorganic or organic compounds, and are chemically stable at relatively high temperatures, yet they are less expensive than most commercially available organic synthetic polymeric resins.