Polyester wood finish is made from a synthetic polymer that contains ester. There are many different formulas; the most common is made from polyethylene terephthalate. Polyester finishes provide the thickest and highest-gloss finishes available and are often used on expensive furniture pieces such as pianos. Stripping polyester finishes is a bit more challenging than typical varnishes, but it can be done.
Scoring the Surface
Penetrating the hard outer shell of this finish is the essential first step. Use an orbital sander with 100-grit sandpaper or similar sanding disk to scratch up the main surface, and an oscillating tool with 120-grit sandpaper on edges, corners and inaccessible areas. Work from one end to the other side to side in overlapping rows to ensure that the entire surface is well scratched. Use a damp cloth and wipe away the dust. Allow the surface to dry so that the scratches reappear and sand an area that is not well scuffed up. Use a hand sanding block for fine details.
Applying the Stripper
Select a stripper with methylene chloride as an active ingredient. This may have to be purchased at a paint store. Wear rubber gloves and eye protection when working with this highly caustic chemical. Use a chemical-resistant paint brush to brush the stripping agent onto the surface in a medium thick coat. Work in long, straight overlapping strokes to ensure proper coverage. Allow the stripper to set, keeping it moist with additional coats as needed, until the polyester begins to lift from the surface.
Removing the Finish
Use a scraper to remove as much of the polyester finish as possible, scraping it into a metal container. Reapply finish as needed to keep the surface wet. Use a nylon scrubber or rotary tool fitted with an abrasive brush or nylon brush accessory in detail areas. Wipe the surface down with a rag damp with lacquer thinner once the finish is removed to cut any film left behind. Allow the lacquer thinner to dry before moving on to prep the surface for a new finish.
Sand the surface with an orbital sander and an oscillating tool using multiple passes, each with a progressively finer grit of sandpaper or sanding disk. Start with, for example, 60-grit and sand the entire surface, then with 120-grit, then 240-grit. Work with the grain of the wood and work to sand each area as evenly as possible. Wipe the entire project surface down with a tack cloth after the final sanding pass to remove the fine sanding dust to prevent it getting caught in the new finish.