Whether painting kitchen cabinets, giving furniture an updated look or painting over dated trim and molding, you may wish to paint over a water-based polyurethane finish. Because this process involves several different products, you need to properly prepare the surface to be painted if you want to get durable, good-looking results. When you're careful about when and how you paint over the polyurethane you can get a finished product you can feel proud of.
Water-based polyurethane has a slick finish which looks keeps other products from adhering to it. To prepare the polyurethane to accept paint, first wash it down with a grease-cutting detergent and water and dry it well. Next, scuff the polyurethane surface with sand paper. You can do this by hand, or if you want to do it more quickly, use a power sander with 200-grit sandpaper. Vacuum up the dust generated by the sanding, and make sure all dust and debris are removed from the area to be painted. Apply a layer of good-quality, oil-based primer, and allow the primer to dry for a full 24 hours before applying paint.
Once you have prepared the water-based polyurethane surface for painting, you must choose an appropriate day for painting. You'll get best results if you paint on a hot, dry day. Cool, damp conditions will cause the paint to cure improperly on top of the polyurethane, and you could end up with an orange-peel texture or deep cracks that go all the way down through the primer. Choose a nonrainy day that is at least 50 degrees Fahrenheit. Ideally, paint over polyurethane when the temperatures are above 70 degrees.
Coats and Dry Times
To get a solid finish, apply three coats of paint over the oil-based primer. Allow each coat of paint to dry for 24 hours before applying the next coat, especially if you're painting a floor or a piece of furniture that will need a durable finish. Applying the next coat before the first coat has had time to cure will cause the paint to bubble up or crack, and you'll have to remove the paint and start over, which is a messy and frustrating process.
Even if the water-based polyurethane was applied after 1978, if the surface you are working on predates 1978, don't sand the surface until you have taken precaution for lead-based paint and stain. Dust generated from lead-based products can be very harmful to children under the age of 6. Don't allow children into the work area, seal off the area and cover up floors and furniture that could be affected, and use a HEPA vacuum when cleaning up after sanding.