A modified alkali silicate composition for forming an inorganic network matrix. The modified alkali silicate matrix is made by reacting an alkali silicate (or its precursors such as an alkali hydroxide, a SiO₂ source and water), an acidic inorganic composition, such as a reactive glass, water and optional fillers, additives and processing aids. An inorganic matrix composite can be prepared by applying a slurry of the modified aqueous alkali silicate composition to a reinforcing medium and applying the temperature and pressure necessary to consolidate the desired form. The composite can be shaped by compression molding as well as other known fabrication methods. A notable aspect of the invention is that, although composite and neat resin components prepared from the invention can exhibit excellent dimensional stability to 1000 C. and higher, they can be prepared at the lower temperatures and pressures typical to organic polymer processing.