Abstract: Wood-based products, to which an overlay material is attached, are pretreated with an aqueous suspension of alkaline, inorganic, multivalent compound such as magnesium hydroxide and a binding agent and then allowed to dry fixing the antistaining compound on the surface of the wood member. Selected additives can be added to the aqueous suspension to enhance application and surface properties. Thereafter the treated members are installed, a typical application being as wood-based underlayment or structural subflooring in flooring construction. When a vinyl floor covering material is attached to the pretreated panel, the treatment functions as a stain blocker preventing unsightly staining of the vinyl floor covering over time.