Floors that have been finished with polyurethane are resistant to moisture and stains, but as with any surface finish, they can be scratched. The blend of water or petroleum bases with synthetic resins, plasticizers and other film-forming ingredients harden over the wood to protect the wood, but when the polyurethane is scratched it breaks the protective barrier. Repairing a scratch on the surface finish before the wood is damaged will protect your investment in your wood floor.
Remove any dust and dirt from the scratch with a broom or vacuum.
Sand the scratch and surrounding area with a sheet of 240-grit sandpaper. Apply light pressure to the sandpaper. Sand with the direction of the wood grain.
Dampen a clean cloth with warm water and wipe it over the affected area to remove any dust caused by the sanding. Allow the area to dry thoroughly.
Apply a matching color stain to the wood with a wood marker if the scratch has penetrated to the stained wood surface.
Dip the tip of a paintbrush into the polyurethane and wipe it on a dry paper towel to remove most of the polyurethane. This will allow the repaired area to blend with the rest of the flooring.
Brush the scratch with the dry brush. Never apply a heavy coast of finish. Additional coats of polyurethane can be applied after the first has dried for 24 hours if needed to smooth the surface.