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.
For the oil based Polyurethane, the standard recommendation is to use a lambs wool applicator. But if you use one of those, be VERY meticulous about getting all the fibers and lint out of the applicator. I made that mistake on my first floor, just ran some blue tape over it a few times and started applying.
But when it comes to applying a smooth coat of clear finish, such as polyurethane, a foam brush is not my first choice. Instead of bristles, it has a blade. The blunt sides leave two parallel ridges of finish, like a snowplow on the highway. Also, the foam head contains air, which can leave bubbles in your finish.
Use a clean microfiber towel to apply polyurethane. Coat every layer against the grain. For difficult-to-reach places or surfaces with elaborate designs, like chair rails, an aerosol spray works well. Apply in a well-ventilated area while holding the can 8 to 12 inches above the surface.
Another way to get it nice an smooth is to do a rubbed finish. Instead of applying with a brush, use a rag or wool applicator. This will allow you to do multiple things coats and get a nice smooth finish. You can also use the silicone oil with this with the same caveat.
Two coats of finish are suggested for most interior projects. When sealing floors, you should apply three coats. However, do not apply more than two coats in one day. 220 grit sandpaper should be used between coats to remove any air bubbles, but avoid using steel wool.
Wetting your brush before applying polyurethane is not necessary and can actually hinder the application process. Instead, ensure your brush is clean and dry before dipping it into the polyurethane.
Waterborne polyurethanes usually require a minimum of 3-4 coats to be effective. Although there is some evidence that too many coats can result in a plastic-like finish, waterborne polyesters are thinner than other types and therefore require several more coats to provide the same protection for hardwood floors.
Sand it with 220 on a foam block, vacuum off, sand with 400, vacuum, 0000 steel wool, vacuum, tack rag, and apply your final coat with a wide foam brush. Before my "final coat", even if my previous coat was perfect, I sand with 400-600 and 0000 steel wool to make it silky smooth before that last coat.
I prefer to use a wipe-on poly because it goes on thinner and does not leave the brush marks. You could sand what you have to smooth it, then thin the poly about 50% and use it as a wipe-on. Using it as a wipe-on applies it in a thinner layer and with it thinner it will also dry faster.
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 below. Hold the spray nozzle 12–16" from the workpiece and sweep the can across the surface without stopping.
Too thick of a coat: Applying too thick of a coat can extend drying times, leading to issues with subsequent layers.
Make sure to sand the polyurethane between coats.
Polyurethane will dry to touch in 3 hours. Under ideal drying conditions, allow 6 hours before recoating. Overnight drying is recommended.
Thin your polyurethane with mineral spirits.
The mineral spirits will provide a more forgiving coat of polyurethane and will also help any bubbles in the finish to burst before it sets up and dries. Pour the polyurethane into a separate container and add some mineral spirits.
Make sure you are NOT shaking the can before opening. Stir thoroughly but gently and let it settle a bit before applying. Shaking will aerate the poly, filling it with tiny air bubbles.
If you're short on time, here's a quick overview: Composition: Polycrylic is water-based, while polyurethane can be oil-based or water-based. Application: Polycrylic applies in thin coats and dries quickly; polyurethane takes longer to dry.
A roller is the recommended method for applying some water-based polyurethanes, as well as some oil-based polyurethanes and moisture-cured poly finishes. Rollers are good for finishing multi-direction floors, like parquets.
Streaks and brush marks can be fixed by sanding and reapplying. Let the coat with streaks or brush strokes dry completely. Next, lightly sand with 220 grit sandpaper to remove the streaks or brush strokes. Then, remove the sanding dust.
Minwax® PolyShades® is an easy way to change the color of your currently stained or polyurethane finished wood. There's no stripping or heavy sanding necessary to remove the old finish!