How to Apply Polyurethane to a Stained Wood Door

Polyurethane provides a durable, washable finish for wood surfaces. A smooth, clear finish also enhances the natural grain of wood used for the door’s construction. As with most finishing projects, the preparation phase is the most critical part of the job. Providing a smooth, even surface for your finish makes the actual application of the polyurethane a simple task. For most interior doors, this is a job that will only need to be done once when done properly.

Flat work surface or two saw horses
Sandpaper, 150- and 220-grit
Sanding block
Paintbrush
Tack cloth
Can or small bucket
Paint stick
Mineral spirits
Polyurethane

Instructions

- 1
  Place the door flat on a clean work surface or across two sawhorses. The stain must be completely dry before applying polyurethane.
- 2
  Sand the door lightly in the direction of the grain using 150-grit sandpaper and a sanding block. Using a sanding block reduces the risk of gouging the surface of the door during the sanding process.
- 3
  Remove the sanding residue with a clean bristled paintbrush. Run your hand over the surface of the door to check for any rough spots. If you find any, remove them with light sanding and clean the door again.
- 4
  Sand the door again with 220-grit sandpaper attached to your sanding block. Apply light pressure and always work in the direction of the grain.
- 5
  Remove all sanding residue with a tack cloth. Fold and turn the cloth frequently to keep the surface clean while working.
- 6
  Pour a mixture of one part mineral spirits and two parts polyurethane into a can or small bucket and stir thoroughly with a paint stick. This thinned mixture acts as a sealer to fill the small holes in the surface of the wood. Apply this mixture with a clean brush. Use long stokes and follow the direction of the grain. Allow this coat to dry for at least 8 hours before proceeding to the next step.
- 7
  Apply an undiluted coat of polyurethane with a clean paintbrush. Use long, smooth strokes and follow the grain of the wood. Apply this coat within 24 hours, after the sealing coat is dry to the touch.
- 8
  Apply the final coat of undiluted polyurethane within 48 hours of the previous coat. The surface must be dry to the touch before you begin.

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