4 steps to a perfect polyurethane finish
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Wood Magazine

4 steps to a perfect polyurethane finish

Prepare your workpiece
Board with glue and scraper
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Pour the wood-grain filler directly
onto the workpiece and spread it
across the grain with a plastic putty
knife or plastic scraper to force it
into the pores.

Prepare your workpiece

A glass-smooth finish begins with a level, even surface. To achieve this on open-grain woods (oak, ash, walnut, or mahogany, for instance), first fill the pores with a wood-grain filler, photo right.

Quick Tip! Wood-grain fillers come in different colors; you can choose one to blend with the color of the workpiece for an even appearance, or select one that contrasts for more pronounced grain.

Scrape off the excess and let dry. Sand the workpiece to 220 grit.


 

Apply stain and poly
Staining board
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Apply an even coat of stain to your
workpiece, making long brushstrokes
and overlapping the edges for full
coverage. Wipe off any excess stain.

Apply stain and poly

Move to a low-dust setting: somewhere without lots of foot traffic and with dust-free surfaces. You can create such an area by hanging an inexpensive vinyl shower curtain in a corner of your shop. With your workpiece wiped clean, apply stain, photo right. (Skip the stain if you intend to leave your workpiece natural-color.) Let dry.

Prepare the polyurethane by reducing it about 10 percent with mineral spirits, unless you're using water-based polyurethane, which doesn't need thinning. Thinning the polyurethane makes it flow on more smoothly and reduces brush marks.

Quick Tip! To reveal flaws (bubbles, brush marks, etc.) as you work, shine a light at a low angle across the surface.

Brush on three thin coats with a foam brush (previous slide). (You can use a natural bristle brush with oil-based poly, but keep an eye out for loose brush hairs.) Coat the entirety of your workpiece, but don't brush excessively or you'll create areas with too little polyurethane. Allow each coat to dry fully. To give the subsequent poly layers something to bond to, sand lightly between coats with 320-grit sandpaper wrapped around a hard block. Note: The first coat needs the most sanding to appear smooth; don't worry if it doesn't look as flawless as you'd like at first.

After the third coat, sand with 320-grit, then 400-, and finally 600-grit sandpaper. Sand in alternating directions with each abrasive to make it easier to see whether you've removed the scratches from the previous grit. Sand with the grain on the final pass. Then, wipe off the dust with a rag dipped in mineral spirits.


 

Put on the polish
Spraying board
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Hold the spray nozzle 12/16" from
the workpiece and sweep the can
across the surface without stopping.
Apply only one thin coat.
Buff pad on board
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Apply a small amount of
automotive paste wax, working
in the grain direction to hide fine
scratches. Buff off the excess with
a clean, soft rag.

Put on the polish

The final coat gives your workpiece its smooth feel and flawless appearance, so give it extra attention. Spray on this coat using an aerosol polyurethane and let it cure overnight, photo right. Then, remove any dust nibs with 1,500-grit sandpaper or a piece of brown paper bag. Finally, using a soft cotton rag or polishing pad, buff the finish to a high shine using automotive paste wax, photo below right, which has fine abrasives that polish the finish even further.


More Resources

  • Choose your finishing brush wisely: woodmagazine.com/brushwithgreatness.
  • Watch a filled-pore finish in progress: woodmagazine.com/filledporevid.
  • Find more finishing tricks here: woodmagazine.com/finishingtricks.


 

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Wood Magazine