Dust and other particles that dry in the polyurethane will result in an uneven surface. [1] X Research source
Never place a fan in your immediate work area, since this may lead to dust being blown onto your wood as you coat it. Purchase a respirator with an organic cartridge if you are unable to improve the room’s ventilation and/or if you are sensitive to fumes.
Also make sure the surrounding area is clear of any objects that you want to keep clean, just in case you make a bigger mess than you mean to.
If your polyurethane is oil-based, use mineral spirits to dampen your lint-free cloth. For water-based polyurethane, dampen your cloth with water. Some people use tack cloths for the dry wipe-down, but be aware that some tack cloths may include chemicals that will interfere with the polyurethane’s adhesion.
Dunk the bristles roughly an inch (2. 5 cm) into the polyurethane to load the brush. Brush with the grain in long, even strokes. After each stroke, run the brush back over any drips that need to be smoothed out. Overlap half of each previous stroke to reduce the chance of gaps and uneven coating. After each coat, reinspect it for any drips that need repairing.
Fold a clean cloth into a square, roughly palm-sized, to apply your coats. Dip an edge into the polyurethane. Wipe it onto the wood, following the grain. With each wipe, overlap half of the previous wipe for even coating.
Spray-on polyurethane creates very thin coats. Practice on a test area first to improve your technique.
Pure polyurethane takes roughly 24 hours to dry, but it should take less than that when diluted with mineral spirits. [11] X Research source
When brushing, go over the whole surface area with your brush again, without reloading it, once the first coat is complete. Smooth out any drips or runs. After that, give the polyurethane 24 hours to air-dry.
After the final coat use a piece of cardboard instead of sandpaper to buff the surface. This will give a nice polyurethane finish.
