Bubbles in Polyurethane on Wood Floors

Brush

• Using the wrong brush to apply polyurethane to wood floors can cause bubbles to form. When you apply the polyurethane, use a nylon brush for a water-based finish or a natural-bristle brush for an oil-based finish. Before you use the brush, soak it in water or mineral spirits. After the bubbles stop forming on the brush, wring out the excess water so it remains damp. Apply the polyurethane slowly, and avoid over-brushing the wood floors. Stir the polyurethane instead of shaking it.

Drying

• After you apply the polyurethane on the wood floors, it needs to dry properly to prevent bubbles from forming. Allowing the floor to dry too rapidly can cause bubbles to develop. Ventilate the room after the finish dries for one hour because the circulation of air could create bubbles. After the floors dry for one hour, ventilate the room to allow the solvent fumes to escape.

Sealing

• Apply a sanding sealer to the wood floors before you apply the top coat of polyurethane. Instead of sealing the wood with the polyurethane, use the sanding sealer to prevent bubbles from forming in the polyurethane. A sanding sealer hardens the wood grain and makes it easier to sand the surface smoothly. You can also thin the first coat of polyurethane up to 25 percent with mineral spirits. The thin coat seals the pores in the wood to prevent bubbles from forming when you add the other coats of polyurethane.

Remove Bubbles

• Sand air bubbles from the wood floor finish by buffing the wood floors with 150- or 220-grit screen paper. After you sand the surface, apply another coat of polyurethane. Screens are sanding discs that remove the finish without damaging the wood floors. Never use a screen on a waxed polyurethane floor because it can damage the surface. You need a floor polisher to use sanding screens. You can also sand the floors with a drum sander with 60-, 80- and 100-grit sanding discs. If you have a small spot that contains bubbles, use a 400-grit sanding block. If you do not have experience in sanding floors or using these tools, contact a professional. Improper sanding can cause damage and an uneven floor.