How to Apply Polyurethane

4 Simple steps to a finish as smooth as glass

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Getting a smooth, blemish-free finish with oil-based polyurethane is within your grasp if you follow the steps in this article. Oil-based polyurethane varnish brings out wood's natural beauty and grain. Our 8-step approach shows you how to apply the varnish successfully. A good-quality natural-bristle brush, a reasonably dust-free, well-ventilated space and some patience are all you need.

Tools Required

  • Sanding block
  • Shop vacuum

Materials Required

  • Automotive polishing compound
  • Automotive rubbing compound
  • Lint-free cloth
  • Mineral spirits
  • Oil-based polyurethane
  • Sandpaper
  • Tack cloth
  • Wet/dry sandpaper

Finish your woodworking project or furniture refinishing job with an oil-based polyurethane varnish to bring out the wood’s natural beauty and grain. Learn how to prep the wood surface and successfully apply a flawless finish with these detailed steps.

We use an oil-based polyurethane finish in this story, though you can also use water-based urethane finishes with great results. But the color and depth you get are no match for oil-based urethanes. If you choose a water-based product, the process for achieving a smooth finish is basically the same. Just be sure you use a tack cloth to clean off dust that’s appropriate for water-based finishes, like a cheesecloth moistened with denatured alcohol.

Have a lot of polyurethane to apply? Watch this video for the fastest way to get it done:

Project step-by-step (8)

Step 1

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.

Have an exhaust fan facing out through a window to remove vapors and crack a window at the other end of the room to let fresh air in. If you’re sensitive to fumes or can’t get good ventilation, it’s a good idea to wear a respirator with an organic cartridge. A fan placed near the workpiece is bad news and will only blow dust right on your project. The idea here is a gentle flow of air in and then out.

Step 2

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.