PURPOSE: To expose a pattern at random and to obtain a special appearance, by applying a urethane resin paint or a urethane resin sealer onto the surface of a substrate board material, and top-coating the surface with an emulsion paint while the urethane resin is not ye cured.

CONSTITUTION: A urethane resin paint or urethane resin sealer is applied onto the surface of a substrate board material. Thereafter, the substrate is top-coated with an emulsion paint, e.g. an acrylic paint or the like, reactive to an isocyanate group while the previously applied urethane resin is not yet cured.