While you’ll only spend about 30 minutes working, each coat requires anywhere from 12 to 48 hours to dry.
Cost
$50–$100
You’ll wonder why everyone doesn’t do this themselves.
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What you'll need:
TOOLS
Natural-bristle brush
Sanding block or orbital sander
Exhaust fan
Respirator
Shop vac
Razor blades
SUPPLIES
Oil- or water-based polyurethane finish
Mineral spirits
80-grit sandpaper (if finishing new wood)
100- to 120-grit sandpaper
150- to 180-grit sandpaper
220-grit sandpaper
Two clean cloths
Automotive rubbing compound
Organic respirator cartridge
When you’re refinishing old wood furniture or floors, topping off the project with the right sealer can enhance the natural beauty of the wood’s grain and protect it for the future. Using polyurethane on wood creates a smooth surface that resists scratches and water damage. For your finish to work, however, you need to apply it properly. This guide will teach you how to apply polyurethane.
Preparing to Use Polyurethane
Before finishing hardwood floors or furniture, know that there are two major types of polyurethane finish. Each can provide great results with specific advantages and drawbacks:
Oil-based polyurethane is more durable and can withstand heat, making it better for pieces like kitchen tables. It provides better color and depth, developing an amber hue over time. On the other hand, it has a stronger odor and takes longer to dry.
Water-based polyurethane is less durable and better suited for desks, bookcases, and end tables. It goes on clear with little odor and dries more quickly but may require more coats for effective protection. It can also cost up to twice as much.
The application process for both types is similar. Never shake a can of polyurethane, or you’ll cause air bubbles that create bumps on your finished surface. Gently stir the mixture with a flat stir stick. Use a quality natural bristle brush for application and avoid brushes with exploded bristles.
Finally, create a safe workspace with proper ventilation. If possible, open a window and point an exhaust fan facing out to remove vapors. Crack another window at the opposite end of the room to let fresh air gently flow in. Don’t place fans too close to the work area or they’ll blow dust onto your project. You can also wear a respirator with an organic cartridge.
Remove the Old Finish
For the smoothest results with no blemishes, you’ll need to create a smooth surface completely free of any old paint, varnish, or finishes. Using a sanding block or orbital sander, sand your wood surface using progressively finer sandpapers.
For new wood, start with coarse 80-grit sandpaper. For previously finished wood, start with 100- to 120-grit medium sandpaper. After the entire surface is thoroughly sanded, wipe off any dust and grit with a clean microfiber cloth and move to a fine 150- to 180-grit sandpaper.
Repeat the process with extra-fine 220-grit sandpaper.
Remove the Dust
Thoroughly clean any dust from your smooth surface using a shop vac with a soft brush attachment. After vacuuming, wipe the surface down with a clean, damp cloth. If you’re using oil-based polyurethane, dampen the cloth with mineral spirits. If you’re using water-based polyurethane, dampen it with water. Finally, wipe it down once more with a dry cloth.
Apply the First Coat
Photo: ellinnur / Adobe Stock
Dip your brush into your can of polyurethane; use just enough to create a thin coat without any dry spots. The best way to apply polyurethane is to go with the grain in long, even strokes. Spread finish over the entire surface, overlapping strokes for a uniform coating. Catch any pools, drips, or runs as they form and incorporate them into your even coat.
Allow at least 12 hours for the first coat to become dry to the touch before moving to the next step. For oil-based stains, you may need to wait at least 24 hours.
Shave Off Any Drips or Bumps
Test the surface to ensure that it’s dry by lightly sanding an inconspicuous area. If it’s still wet, wait another hour. Once you’re certain the first coat is dry, use a razor blade to cut away any drips that can’t be sanded. Be careful not to scuff the wood or cut below the surrounding area.
Sand the First Coat
Dip fine 220- to 400-grit sandpaper in water and sand away any remaining dust or debris from the drying process using circular strokes. Use just enough water to lubricate the sandpaper so you don’t burn through the finish, sanding just deep enough to remove debris. Once the surface feels smooth, wipe it down with a clean, damp cloth and again with a clean, dry cloth.
Apply the Second Coat
Photo: Wirestock / Adobe Stock
Twenty-four to 48 hours after you apply your first coat, apply a second coat using the same long, careful strokes. Spread an even layer of polyurethane over the surface and let it dry completely again.
Repeat Steps 4, 5, and 6 as Needed
Once your second coat is dry, you can repeat step 4 to remove blemishes. If it’s absolutely necessary, you can repeat step 5 to wet sand the surface. If you do so, you’ll need to polish your surface (as in step 8).
If you wish to apply a third coat, wait to polish and repeat step six first. You should never need more than three coats of oil-based polyurethane, but you may need to apply up to 12 coats of water-based polyurethane.
Polish the Surface
Forty-eight hours after your final coat has dried, polish the finish by dampening a clean cloth with water and applying an automotive rubbing compound in a circular motion. This compound contains a fine abrasive that removes scratches left by the finest sandpaper. After rubbing, let the entire surface dry and buff it once more with a clean, dry cloth. Repeat as needed.
Frequently Asked Questions
What happens if I don’t sand between coats of polyurethane?
If you don’t sand between coats of polyurethane, your finish may not adhere properly. Debris that gets stuck to your finish can eventually cause peeling or leave your surface looking uneven.
How many coats of polyurethane should be used?
You should use no more than three coats of oil-based polyurethane. If working with water-based polyurethane, you may need up to 12 coats to get the results you want.
How do you apply polyurethane without brush marks?
To apply polyurethane without brush marks, use a quality brush with natural bristles. You can also thin your first coat of polyurethane by mixing two parts polyurethane with one part mineral spirits in a separate jar. This can help the flow of thicker finishes for a more even coat. Ensure you’re working in an environment heated to at least 70 degrees Fahrenheit.
Why does my polyurethane look cloudy?
Your polyurethane may look cloudy due to a zinc oxide buildup at the bottom of the can. Zinc oxide is added to some polyurethane finishes to create a satin or matte look. To fix a cloudy polyurethane, stir well with a flat stir stick and avoid storing your polyurethane in extremely hot or cold places.
Nick has been a copywriter in the home services industry since 2017, marketing for hundreds of flooring and home improvement providers throughout North America.
Nick has been a copywriter in the home services industry since 2017, marketing for hundreds of flooring and home improvement providers throughout North America.
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