Abstract: A composition for producing surface layers on wood or other substrates is formed from diatomite, expanded perlite, chopped glass fibers and a thermosettable resin mixed in specified amounts to provide a flowable mixture. When applied to the substrate as a layer about 1 to 2 cms. thick and the resin component has cured, a tough, impact-resistant, watertight surface is created on the substrate. The new compositions and surfacing methods are particuarly useful for refinishing the hulls of wooden boats.