Varathane brand polyurethane varnish by Rustoleum is a standard polyurethane coating. It can be used over raw, painted or stained wood. Polyurethane is used as a top coat to provide the glossy clear coat normally associated with wood furniture. Proper preparation and application techniques will help prevent common problems such as hazy finishes and bubbles in the finish. Allowing the proper drying time between coats is the most critical of these techniques.
Wipe the surface to be varnished with a tack cloth to remove any dust or small debris from the surface. Work carefully to wipe the entire surface, looking for dust, hairs and small bits of lint that can cause bumps in the varnish.
Open the Varathane and mix it thoroughly in the can with a wooden paddle. Mix it slowly, without agitating, which can cause bubbles that will remain in your finish. Allow the varnish to set for five to 10 minutes to allow any bubbles to rise and break.
Dip the tip of a soft-bristled paintbrush into the Varathane. Start your application along one long edge working in long, straight, slightly overlapping strokes to ensure complete coverage. Work in the direction of the grain without working back over the varnish, which will leave brush marks and may cause bubbling.
Cover the entire surface with a medium-thick coat, spreading it evenly to prevent runs and drips in your polyurethane. Allow the varnish to dry according to the label instructions. Allow 24 hours if moisture is high or temperatures are at the low end of the recommended range.
Rinse the brush with lacquer thinner between coats and allow it to dry completely before reusing it.
Sand the surface of the polyurethane with a random orbit sander and 220-grit sandpaper. Sand any minor bubbles or bumps in the finish to level them. Wipe the fine dust from the surface with a tack cloth.
Apply a second coat of Varathane in the same way as the first. Work in a thinner coat, concentrating on preventing bubbles and reworking. Allow this second coat to dry thoroughly, leaving it overnight in damp or cool conditions. Sand the second coat as for the first and wipe with the tack cloth.
Add a third thin coat of Varathane and allow it to dry for at least 24 hours before returning the item back to normal use.
Use a lamb's wool applicator if applying hardwood floor varnish. It will speed the process and leaves fewer bubbles than a roller.