Polyurethane is a type of varnish with a resin that adds heat-, scratch-, water- and solvent resistance to the wood on which it's applied. To create a good resistant finish, multiple coats of the polyurethane may be required on the wood surface. Between each coat the polyurethane must be sanded with a light-grit sandpaper. The sanding between coats accomplishes two things: It removes defects from the applied urethane as well as small dust particles lodge in the dry finish.
Things You'll Need
- 320 or 400 grit sandpaper
- Tack cloth
Allow the first polyurethane coat to dry. Depending on temperature and humidity, it may take up to 24 hours for the urethane to thoroughly dry before the first sanding.
Fold the sandpaper over several times so it fits in your hand. Work the urethane finish with the grit side of the sandpaper lightly in one direction. Typically the sandpaper should be run over the surface in the same direction as the wood grain. Sand the finish once to remove any built up dust ridges on the finish.
Clean the surface with the tack cloth. Apply the second coat of urethane. Allow the product to dry as before according to label directions and environmental conditions.
Sand the urethane surface a second time in preparation for a third coat. Follow Steps 2 and 3 between each polyurethane application.