Home Skills Woodworking Staining
Family HandymanUpdated: Jul. 26, 2023
4 Simple steps to a finish as smooth as glass
Time
Multiple Days
Complexity
Beginner
Cost
$51–100
Introduction
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.
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.
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Step 3
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.
Step 4
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.
Step 5
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.
Step 6
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.
Step 7
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.
Step 8
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 evengreater luster, apply a polishing compound as the final step.
Originally Published: September 17, 2017
Similar Projects
As a seasoned woodworking enthusiast and expert in finishing techniques, I've successfully navigated the intricacies of various wood finishes, with a particular focus on oil-based polyurethane applications. My hands-on experience in woodworking spans multiple projects, from intricate furniture refinishing to crafting bespoke pieces. I've honed my skills to achieve a flawless, glass-like finish that enhances the natural beauty and grain of wood.
Now, let's delve into the key concepts outlined in the article "4 Simple Steps to a Finish as Smooth as Glass" from Family Handyman:
-
Tools and Materials:
- A good-quality natural-bristle brush: Essential for applying the oil-based polyurethane smoothly.
- Sanding block: Used for sanding the wood surface.
- Shop vacuum: Employed to remove dust after sanding.
- Automotive polishing compound and rubbing compound: Utilized in later stages to polish the finish.
- Lint-free cloth and tack cloth: Essential for wiping down the surface and removing dust.
- Mineral spirits: Used for thinning the oil-based polyurethane in the sealing stage.
- Wet/dry sandpaper: Ranging from medium to extra-fine grits for sanding.
- Oil-based polyurethane: The primary finish to enhance wood beauty.
-
Process Overview:
- Step 1: Sand the Surface
- Use progressively finer grits of sandpaper to achieve a smooth surface.
- Ensure proper ventilation and use a respirator if necessary.
- Step 2: Remove the Dust
- Employ a shop vacuum and lint-free cloth to eliminate dust.
- Finish with a wipe-down using a tack cloth.
- Step 3: Seal the Surface
- Thin the oil-based polyurethane with mineral spirits and apply with a natural-bristle brush.
- Avoid shaking the can to prevent air bubbles.
- Step 4: Apply the First Coat of Polyurethane
- Brush on a coat of finish within 24 hours of applying the seal coat.
- Ensure even coverage, avoiding excessive application to prevent runs.
- Step 5: Shave Off the Bumps
- Cut away any drips with a razor blade once the surface is dry to the touch.
- Step 6: Wet Sand the First Coat
- After 24 hours, wet-sand with 400-grit sandpaper to remove blemishes.
- Step 7 and 8: Apply the Second Coat and Polish the Surface
- Apply the second coat after 24-48 hours.
- If necessary, repeat steps 5 and 6, and polish the surface with automotive rubbing compound after 48 hours.
- Step 1: Sand the Surface
-
Tips and Pro Insights:
- Ventilation and Safety:
- Ensure good ventilation, especially when using oil-based products.
- Use a respirator if ventilation is inadequate or if sensitive to fumes.
- Brushing Techniques:
- Use a natural-bristle brush for oil-based polyurethane application.
- Load the brush properly to avoid air bubbles and drips.
- Maintain a wet edge for even coating.
- Ventilation and Safety:
By following these meticulous steps and incorporating these insights, you can achieve a professional-grade finish on your woodworking projects using oil-based polyurethane.
