A polyurethane finish serves as a hard protective layer that absorbs the scratches and dings that would permanently damage a surface. With each scratch or scuff, however, the polyurethane gloss begins to dull, eventually becoming dirty and worn looking. You can reverse this process by polishing the polyurethane with mild abrasives, creating a high-gloss look that gives your surface a smooth, bright and scratch-free appearance.
Saturate a 1000-grit sheet of wet/dry sandpaper in a bucket of water.
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Sand the surface of the polyurethane with the sandpaper, using small circular motions to remove any imperfections from the surface. Imperfections are often created during the application process and can include anything from sags in the polyurethane film to brushstrokes. Use the sandpaper until the surface is completely smooth.
Clean the surface with a pH-neutral cleanser and a sponge to remove any sanding debris. Rinse the polyurethane film with clean water, and then pat the surface dry with a clean lint-free cloth.
Squirt a small quarter-size circle of a fine-cut cleaner onto a soft cotton cloth.
Apply the cleaner to the polyurethane finish, spreading the cleaner across the surface using a back-and-forth motion in overlapping rows. The slightly abrasive cleaner will remove the tiny scratches created by the sandpaper, clearing away any dullness in the polyurethane. Allow the cleaner to dry completely.
Wipe the cleanser residue from the polyurethane with a damp, lint-free cloth. Examine the surface for dullness due to scratching. If the surface remains dull, apply the cleaner a second time. If not, then buff the finish to a bright shine using a clean, dry cloth.