How to Remove Urethane From Wood
- 1). Apply a coat of chemical stripper to the painted surface with a paintbrush. Use a product recommended for urethane removal and spread it on liberally with the grain of the wood. Be sure it covers evenly and that there are no dry spots. Let the stripper work for the time recommended on the container, which can be anywhere from one to two hours to overnight. It will soften the finish material, and may even cause it to bubble up in some places.
- 2). Scrape off the stripper with a sharp paint scraper. Hold the scraper at a 30- to 45-degree angle and push it along the surface, going with the grain of the wood. If you can't get all the finish off, don't try to dig it out. Leave it for a second application of stripper.
- 3). Paint stripper over the areas of finish that you couldn't scrape off, wait for it to work, then try scraping these areas again. Repeat a third time if necessary.
- 4). Wash the surface with a rag moistened with solvent. Use water if the stripper is water soluble and lacquer thinner if not. Lacquer thinner is a stronger solvent than turpentine or mineral spirits and will clean better. It will also evaporate quickly without raising the grain of the wood.
- 5). Sand the surface with an orbital sander. Use 80-grit sandpaper if there are still areas with finish remaining on the surface. Work these areas with the sander until the finish is gone. If you managed to remove all the finish with the stripper, use 100-grit sandpaper to smooth the surface of the wood, remove any marks you made with the scraper and open the grain for a new finish.
- 6). Sand the surface again, this time using 120-grit sandpaper to remove sanding marks left by the coarser paper.
Source...