Conditioner that is a liquid resin, gypsum sealing, and hardening material for models and dies. When applied to a gypsum surface, the conditioner penetrates into the porosities of the material. As the carrier evaporates, the resin-like material hardens and provides a sealing layer over the entire area to which it had been applied. As a result, all porosities are filled and considerable strength and increased abrasion resistance is imparted upon the gypsum surface.