High-gloss polyurethane is primarily used to seal and protect wooden surfaces. If you decide you want to add colour to your wood furniture, trim or fixtures, painting over existing polyurethane poses some challenges. High-gloss finishes require several coats of paint for full coverage, whereas matt surfaces take just one or two. For polyurethane-coated wooden items, you'll also find that natural wood oils will bleed through paint over time. Fortunately, with the right preparations, you can avoid these pitfalls for lasting coverage in fewer coats.
Sand the high-gloss polyurethane finish with 150-grit sandpaper. Sandpaper roughs up glossy surfaces for better paint coverage in fewer coats.
Wipe away the sandpaper dust with a moist rag.
Apply stain-blocking primer to the wooden polyurethane surface, using a paintbrush or paint roller. When you sand off some of the polyurethane gloss on a wooden surface, you risk exposing the raw wood. Certain wooden surfaces naturally release oils over time, and this will discolour your paint if you don't use a stain-blocking primer. If you're painting over nonwooden polyurethane surfaces, use a general-purpose primer.
Paint the surface with latex or oil-based paint after the primer has fully dried. A paintbrush is good for small items, and paint rollers are ideal for large jobs.
Apply additional coats of paint as needed after the first coat dries.