Method and process using a supercritical fluid, with or without the aid of entrainers to solubilize a monomer, monomer mixture or polymer which may or may not include additives and entrainers; to carry the supercritical solvent mixture (40) thereby created into the wood matrix (34) via a pressure tank (12); to remove extractives from the wood; to precipitate the monomer or polymer within the wood; and to polymerize the monomer in situ in the wood.