A study of the possible advantages and disadvantages of stone consolidation using methyl-methacrylate applied as monomer, in comparison with a polymethyl-methacrylate applied in solution. The treatment of two different stones, a Carrara white marble and pyroclastic tuff from Cerveteri (Rome), was studied. Measurement of different properties showed that the monomer gives the best results on both types of stone. Colour changes derive from both treatments, but the variations produced by the pure methyl-methacrylate monomer are stronger than those induced by the polymer solution. Further studies on artificial weathering are needed to assess ageing performance of the treatments.