How to Apply Polyurethane

Sand the Surface 

• Sand your project with progressively finer grits of sandpaper.
  • Note: Paper with a higher grit number removes the deeper scratches left by paper with a lower-numbered grit.
  • Pro tip: Most projects need an initial sanding with medium sandpaper (100-grit) followed by a fine paper (150-grit) and then an extra-fine sanding with 220-grit.

Remove the Dust

• Once the wood is blemish-free, remove the dust.
  • Pro tip: Use a shop vacuum with a soft brush attachment, followed by a wipe-down with a clean, lint-free cloth moistened with mineral spirits.
• As a last dusting step, wipe the surface down with a tack cloth.

Seal the Surface

• Thin your oil-based polyurethane with two parts polyurethane and one part mineral spirits.
  • Pro tip: Pour the products into a glass jar and gently stir the mixture with a flat stir stick.
• Brush the sealer on with a natural-bristle brush using long, even strokes. Be sure to catch any runs.
  • Note: Some stains are self-sealing. Check the can for this information. If the stain is self-sealing, you can skip this step.
  • Pro tip: Never shake a can of polyurethane! You’ll introduce air bubbles into the mixture that’ll end up as bumps on the finished surface.
  • Pro tip: Use a good quality natural bristle brush to apply oil-based polyurethane. Exploded-tip synthetic brushes (with each strand divided into multiple strands at the tip) may introduce air bubbles into the finish.
• Load your brush by dipping it about 1 in. into the mixture and brush the wood with long, even strokes from end to end.
• Keep a wet edge by overlapping each pass until the surface is completely coated.
• Catch any drips with your brush and smooth them into the surface.

Apply the First Coat of Polyurethane

• Within 24 hours of applying the seal coat, brush on a coat of finish right from the can.
  • Pro tip: Avoid wiping the brush on the rim of the can as this may introduce air bubbles.
• Spread the varnish over the entire surface with long, even strokes.
  • Pro tip: Don’t use too much or you’re likely to get runs; use just enough to get a nice, even coat without dry spots. As soon as the surface is coated, brush over it again with the grain, from end to end.
• Overlap your strokes to get a uniform coating.
• Catch any drips, especially along the bottom edges.

Shave Off the Bumps

• Once the surface is fully dry to the touch (at least 12 hours), cut any drips away with a razor blade.
  • Pro tip: Be sure not to cut below the surrounding surface.

Wet Sand the First Coat

• After the first coat has dried for 24 hours, remove small blemishes by wet-sanding with 400-grit sandpaper mounted to a sanding block.
• Dip the sandpaper in water and use circular strokes to remove the blemishes and any dust bumps.
  • Pro tip: Use enough water to lubricate the sandpaper so you won’t burn through the delicate finish. Sand just deep enough to remove the blemish.
• When the surface feels smooth, wipe it with a moist cloth and then dry it with a clean, dust-free cloth.

Apply the Second Coat

• 24-48 hours after you apply the first coat, apply the second and final coat using the same procedure as the first.

Repeat Steps 5 and 6 if Needed

• Once the second coat is dry, shave off any bumps (per Step 5) and wet sand the surface (per Step 6).
  • Note: Only follow these steps if absolutely necessary. If you have to wet sand the second coat, you will need to polish the surface.

Polish the Surface if You Wet-Sanded the Second Coat

• Wait at least 48 hours, then polish the finish using an automotive rubbing compound.
• Dampen a clean, cotton cloth with water and apply automotive rubbing compound to the surface in a circular motion.
  • Note: The compound has a fine abrasive that’ll remove any scratches left by the 400-grit sandpaper and restore the luster in the polyurethane finish.
• After rubbing, let the surface dry and buff the finish with a clean, dry cloth.
  • Pro tip: If the finish is still a bit cloudy, apply more automotive polishing compound using the same method. Let it dry, then buff the surface.
  • Pro tip: For even greater luster, apply a polishing compound as the final step.