Comparison of results obtained in the polymerization of methyl methacrylate in sandstone using different initiation systems: benzoyl peroxide, Redox systems and radiation. With Redox polymerization it is difficult to find a compromise between the time needed for penetration of monomer into the stone and speed of polymerization. A serious defect is destruction of some of the samples during polymerization and this occur also when using radiation. No destruction of the stone samples occurred when the polymerization temperature was above 80 degrees C.