How to Polyurethane Over Water Based Paint

A polyurethane finish can prolong the life of paint and prevent ultra violet rays from causing it to fade. Unfortunately, when many do-it-yourselfers apply polyurethane over a water-based latex or acrylic paint, they end up with rampant flaking. If you want to avoid a similar outcome, choose a specific type of polyurethane, specifically formulated to bond with water-based finishes. Remove oils and foreign particles from the painted finish, before you apply the sealer, or the finish may fail.

Things You'll Need

  • Pressure washer

  • Wide-angle tip

  • Rags

  • Tack cloths

  • Professional painter's tape

  • Canvas drop cloths

  • Water-based polyurethane

  • Wooden stir stick

  • 2- to 3-inch polyester paintbrush

Step 1

Wash exterior painted finishes, using a pressure washer. Intense water pressure may strip the paint. Avoid this by using a low-pressure, wide-angle spray tip. Rinse interior painted finishes, using wet rags. Let the painted surface dry for four hours.

Step 2

Wipe down the painted finish, using tack cloths.

Step 3

Cover surfaces adjacent to the painted finish, using a low-tack tape. Spread drop cloths out beneath the finished surface.

Step 4

Open the can of polyurethane, then stir the clear finish, using a wooden stirring stick.

Step 5

Apply the polyurethane to the painted finish, using a 2- to 3-inch polyester paintbrush. Brush left to right, applying gentle pressure as you move your paintbrush.

Step 6

Look closely at the polyurethane finish to see if it is sagging. Quickly smooth these types of flaws before they have a chance to fully dry. Let the polyurethane dry for two hours.

Warning

Oil-based polyurethane will not bond to water-based paint. Be sure to select a compatible water-based polyurethane finish, or flaking will result.