You can paint over a surface of polyurethane varnish if you prepare it properly. Polyurethane is typically hard, durable and glossy, and it is these qualities that make a finish vulnerable to chips and flaking. You don't have to remove all the varnish before you start painting. Preparation will pay off in the long run by providing a long-lasting finish.
Things You'll Need
- Clean, lint-free cloths
- Mineral spirits
- Wood filler
- Protective face mask
- Fine-grade sandpaper
- Liquid sandpaper (optional)
- Oil-based primer
- Oil-based topcoat
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Clean the surface with a cloth dampened with mineral spirits. Fill chips, holes or other damage with wood filler.
Sand the surface with fine-grade sandpaper. Wear a protective face mask; dust from polyurethane varnish is toxic. Roughen the surface enough so the paint will adhere to it. Remove dust with a clean cloth and mineral spirits. Alternatively, use a liquid sandpaper that will dissolve the gloss surface of the varnish. Follow the manufacturer's directions.
Apply a coat of primer to the wood. Don't skip this step; primer provides the proper surface to which a topcoat will adhere; it also disguises areas of filler. Allow to dry overnight.
Paint on the first application of a topcoat. Let it dry overnight, then lightly sand and wipe the surface with a clean cloth and mineral spirits.
Apply the second coat of topcoat. Allow the surface to cure for 72 hours before handling it or placing objects upon it.