Polyurethane is often used as a finish on surfaces that see extensive everyday use. The polyurethane forms a hard protective layer on the surface to which it's applied, absorbing the scratches and dings that would permanently damage the surface. This protection comes at a price, however, as with each scratch or scuff, the polyurethane dulls in gloss, eventually making the protected object appear dirty and worn. You can reverse this dulling process by polishing the polyurethane. With sandpaper and abrasive, you can bring out the shine in the polyurethane, creating a high-gloss look that makes your surface smooth, bright and scratch-free.
Saturate a 1000-grit sheet of wet/dry sandpaper in a bucket of water. 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 surface, spreading the cleaner across the surface using a back-and-forth motion in overlapping rows. The slight 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 piece of lint-free cloth. Examine the surface for dullness due to scratching. If the surface remains dull then apply the cleaner a second time. If not, then buff the finish to a bright shine using a clean, dry cloth.
Allow the polyurethane surface five full days curing time before you attempt to polish the material for the first time. Repeat the polishing process whenever the polyurethane begins to lose its gloss from use, taking care not to sand through the coating entirely and removing its protective properties.