Polyurethane is a durable, water-resistant finish that has largely replaced traditional shellac and varnish for wood projects. Because the versatile coating comes in different formulations, you can find an application method for various needs. Our guide covers how to apply it to achieve a beautiful, long-lasting finish, whether you’re finishing a broad tabletop, intricate chair spindles, or anything in between.
Types of Polyurethane Finishes
Understanding the different types of polyurethane available will help you choose the right product for your project.
Oil-Based vs. Water-Based Polyurethane
Oil-based and water-based polyurethanes each have their own strengths and ideal uses. Oil-based polyurethane is more durable and has a warm amber tone that enhances the natural beauty of wood. It’s perfect for high-traffic areas like floors or frequently used furniture.
Water-based polyurethane dries faster, has less odor, and maintains the wood’s natural color. It’s an excellent choice for lighter wood and for projects you need to complete quickly.
Gloss Levels: From Matte to High-Gloss
Polyurethane finishes come in various sheen levels, ranging from mattes to high-gloss:
- Matte finishes offer a subtle, low-shine look that’s great for rustic or modern styles.
- Satin provides a soft luster and is versatile for many applications.
- Semi-gloss adds more shine and is often used on trim or cabinets.
- High-gloss delivers a mirror-like finish that’s striking but can highlight imperfections, making it best for perfectly smooth surfaces or bold design statements.
Essential Tools and Materials for Applying Polyurethane
Gather the following equipment for a smooth, professional-looking polyurethane application.
Brushes and Applicators
For brush-on applications, use high-quality natural or synthetic bristle brushes designed for the type of polyurethane you’re using. Foam brushes can work well for smaller projects. For wipe-on polyurethane, make sure you have lint-free cloths or applicator pads. When spraying, choose a spray gun compatible with your polyurethane, or use aerosol cans for smaller jobs.
Sanding Materials
Use fine-grit sandpaper (120–220 grit) for preparing surfaces and very fine-grit (220–320 grit) for lightly sanding between coats. Sanding blocks or a random orbital sander can make the process easier and more uniform. Steel wool (0000 grade) is useful for final buffing or smoothing dried oil-based polyurethane.
Safety Equipment
Wear a respirator mask to protect against fumes, especially when using oil-based products or spraying. Safety glasses shield your eyes from dust and splashes. Nitrile gloves protect your skin from the chemicals in the finish.
Preparing Your Surface for Polyurethane Application
Taking the time to prepare your surface will give you better adhesion and a smoother result.
Cleaning the Surface
Start by thoroughly cleaning the surface to remove dust, dirt, or grease. Use a tack cloth to pick up fine particles that might interfere with the finish. For oily wood, we recommend wiping down the wood with mineral spirits to help the polyurethane adhere properly.
Sanding Techniques
Sand the surface with progressively finer grits of sandpaper, starting with 120-grit and working up to 220-grit. Sand in the direction of the wood grain to avoid scratches. After sanding, use a vacuum and tack cloth to remove all dust.
Dealing With Existing Finishes
If you’re applying polyurethane over an existing finish, check that it’s compatible and in good condition. Lightly sand the old finish to give a good bonding surface. For badly damaged or incompatible finishes, stripping the paint from the wood before applying polyurethane is helpful.
Brush-On Polyurethane Application
The brush-on method provides a thick, durable coating and is ideal for large, flat surfaces. It’s versatile and easy to use, making it the go-to technique for many woodworking projects.
When To Use Brush-On Polyurethane
Brush-on polyurethane is great for broad, flat, horizontal surfaces such as floors, tabletops, and chair seats. It forms a thicker coat, so the finish builds up faster than with other methods. Be cautious when applying to vertical or contoured surfaces, as drips and runs are more likely.
Step-By-Step Brushing Technique
Here is our recommended technique for brush-on polyurethane:
- Stir the polyurethane gently to avoid creating bubbles.
- Load your brush and apply the polyurethane in long, even strokes along the wood grain.
- Use light pressure to avoid leaving brush marks.
- Overlap each stroke slightly to ensure full coverage.
- Allow the first coat to dry completely before lightly sanding and applying the next coat.
Avoiding Bubbles and Drips
To decrease bubbles, avoid shaking the can and use a tipping-off technique: Unload the brush by slapping it against the inside of the can, then hold the brush vertically and drag it over the wet coating. For vertical surfaces, apply thinner coats to prevent drips and runs.
Wipe-On Polyurethane Application
Wipe-on polyurethane is a great alternative for surfaces where brush-on applications might create drips or uneven coverage. It’s less viscous than brush-on formulations, making it ideal for round, vertical, or contoured surfaces like crown molding, wainscoting, and stair balusters. It’s also less likely to create bubbles or brush marks, giving you a smoother finish.
Proper Wiping Technique
Here is our recommended technique for wiping on polyurethane:
- Pour a small amount of wipe-on polyurethane onto a lint-free cloth or applicator pad.
- Apply the finish in long, smooth strokes following the wood grain.
- Use light pressure to work the finish into the wood pores.
- Remove any excess with a clean cloth to avoid pooling or drips.
Building Up Multiple Thin Coats
Each wipe-on coat is thinner than a brushed-on coat, so you’ll need to apply more layers for adequate protection. Typically, we recommend four to six coats. Allow each coat to dry completely and lightly sand between coats for the best results.
Spray Polyurethane Application
Spray polyurethane is handy for hard-to-reach surfaces or when you need to cover a large area quickly. It requires some practice to master but can produce excellent results.
Mastering the Spray Technique
Here are our steps for applying spray polyurethane:
- Shake the can well before use.
- Hold the can 6–8 inches from the surface.
- Apply in light, even coats using a sweeping motion.
- Keep the can moving to avoid heavy buildup in one area.
- Allow each coat to dry before applying the next.
Ideal Projects for Spray Application
Spray applications are ideal for coating hard-to-reach surfaces on projects with many nooks and crannies. Think shutter louvers, chair spindles, wicker furniture, or intricate woodwork. Spray polyurethane is great for encapsulating flaking paint on vintage pieces or touching up scratched finishes. It’s also helpful for quick touch-ups or when you need to apply a finish in tight spaces.
Polyurethane Drying and Curing Process
Proper timing between coats and full curing will make for the best results. Drying time can vary based on several factors:
- Type of polyurethane (water-based dries faster than oil-based)
- Humidity and temperature of the environment
- Thickness of the applied coat
- Air circulation in the drying area
Generally, water-based polyurethane dries to the touch in 4–8 hours, while oil-based can take 24-48 hours.
When To Sand Between Coats
Once the previous coat is completely dry, lightly sand with 220–320 grit sandpaper or, if using oil-based polyurethane, 0000 steel wool. This creates a slightly rough surface for the next coat to adhere to and removes any dust nibs or imperfections. Be sure to remove all sanding dust before applying the next coat.
Final Curing
While polyurethane may feel dry to the touch after a few hours, it continues to cure and harden for several days or even weeks. For best results, wait at least 24 hours before light use and up to 30 days before subjecting the finish to heavy use or placing objects on it.