How to Apply Polyurethane to Wood

The two basic types of polyurethane are oil-based and water-based. Both have different pros and cons.

• Water-based polyurethaneis clear, low-odor and has a quick drying time. It is recommended for surfaces that see little exposure to heat or the elements. Water-based polyurethane works well for projects like desks, bookcases and end tables. It may require more coats.
• Oil-based polyurethane has more durability than water-based. It withstands heat better so it’s a good choice for projects such as kitchen tables or countertops. Oil-based does develop an amber tint over time. It also tends to have a stronger aroma and a slower drying time.

Different formulations of polyurethane create different levels of luster or sheen, so choose based on your preference.

• Flat or matte polyurethane leaves the least shiny coating and conveys the look of natural, unfinished wood.
• Satin polyurethane has a low to medium sheen that helps conceal dirt and scratches, making it popular for flooring.
• Semi-gloss polyurethane and gloss polyurethane have a higher level of sheen and reflectivity.

You’ll get the best results from your polyurethane topcoat if you remove any old paint, varnish or other finishes before polyurethane application. For a smooth coating, you’ll want the surface to be as smooth as possible.

• Prepare the wood by sanding it with a sanding block or orbital sander.
• Start with 120-grit sandpaper on refinished pieces and 80-grit on new wood.
• After sanding the entire surface thoroughly, wipe off the dust and all loose sandpaper grit with a clean cloth.
• Then, sand with 180-grit until you've removed all the marks left by the 120-grit, and the surface appears level.

If dust or other particles settle on wet polyurethane, they can create a rough surface. This defeats the goal of a smooth topcoat.

• After sanding, dust and vacuum the surface and room as thoroughly as possible.
• Wipe the surface with a damp, lint-free cloth or sponge.
• If you’re going to apply water-based polyurethane, dampen the cloth with water.
• If using oil-based, dampen the cloth with mineral spirits.

You can use a brush, rag or spray for your project. The best way to apply polyurethane will depend on the surface of the wood project.

• Brushes are best for flat surfaces such as tables or some chairs. Brushing a rounded, contoured or vertical surface is more likely to create drips. Apply a thin coat following the grain with a tapered, bristle brush.
• Rags or cloths are ideal for contoured surfaces. When applying polyurethane, use a clean microfiber towel. Apply each coat with the grain.
• An aerosol spray is good for hard to reach areas or surfaces with intricate designs like chair rails. Apply by holding the can 8 to 12 inches from the surface in a well-ventilated area.

Make sure to sand the polyurethane between coats. Sanding removes drips, bubbles and other uneven spots in each coat.

• Dry the first coat for a full 24 hours. If the coat feels tacky or sticky after that, let dry until it feels completely dry.
• Sand the topcoat with 180 to 220 grit sandpaper.
• Wipe off any residue after sanding.
• Repeat as needed.

• Apply 1 to 2 coats of stain when using a brush and 2 to 3 coats if you’re spraying the polyurethane.
• To keep outdoor dust and particles away from the surface, applying polyurethane should take place in a well-ventilated room indoors, with an open window or fan to circulate fresh air. This also helps clear the fumes of oil-based polyurethane.
• If sandpaper is inadequate to remove dried drips or other imperfections, shave them off with a razor.
• Before use, a can of polyurethane should be stirred, not shaken. Shaking can introduce air bubbles in the finish that could make an uneven coat.
• Minimize or eliminate brush marks. Choose a tapered brush, thin the varnish with mineral spirits and apply long strokes at a vertical angle.