How to Apply Polyurethane to Painted Wood

Written by ryan lawrence
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A clear polyurethane sealer can add a glossy finish to painted wood and protect the finish from premature wear. Unfortunately, when eager amateurs try to add polyurethane over the top of a painted finish, they frequently end up with noticeable peeling after only a few hours or days. This usually occurs because they fail to understand the importance of compatibility. While petroleum-based polyurethane sealers are well-suited for oil-based finishes, such as stains and enamels, they will not bond to water-based acrylic and latex paint. Choose the proper type of sealer based on the type of paint you're working with, or finish failure will result.

Skill level:
Moderate

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Things you need

  • Pressure washer
  • Wide-angle tip
  • Rags
  • White spirit
  • Professional painter's tape
  • Wooden stir stick
  • Water-based polyurethane
  • 2- to 4-inch polyester paintbrush
  • Solvent-based polyurethane
  • 2- to 4-inch natural-bristled paintbrush

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Instructions

  1. 1

    Rinse exterior painted wood, using a pressure washer. Be sure to equip the washer with a wide-angle tip that won't strip off the existing paint. Wipe down interior water-based paint, using wet rags; wipe interior oil-based paint, using a rag dampened with clean white spirit solvent. Let each surface dry for two hours.

  2. 2

    Attach painter's tape to any surface running adjacent to the painted wood.

  3. 3

    Open the container of polyurethane and stir the clear sealer, using a wood stir stick.

  4. 4

    Apply the correct type of polyurethane to the paint, using an appropriate paintbrush. Add water-based poly to existing water-based paint, using a polyester brush; apply solvent-based poly to existing oil-based paint, using a natural-bristled paintbrush. Apply gentle pressure with the brush and carefully smooth sags and/or runs before they have an opportunity to solidify.

  5. 5

    Let the polyurethane finish dry for two hours. Wash polyester brushes with tap water; wash natural brushes with white spirit solvent.

Tips and warnings

  • Don't apply water-based polyurethane over existing oil-based paint, or peeling will follow; likewise, don't add oil-based poly over the top of existing water-based paint.

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