Q: I am building a set of bookcases from birch plywood with pine facing, trying to match those installed about 25 years ago. I chose to shellac the cases first to avoid blotching and perhaps get a more even finish. I’ve shellacked the new cases but now decided this was not a good idea. I know alcohol will soften the shellac, but how can I tell if the shellac has indeed been removed, and is this the best method to remove it? Should I decide it isn’t worth the trouble to remove the shellac, what will be necessary to paint over the shellac as well as over the older polyurethane?
A: Scrub the wood with denatured alcohol on nylon abrasive pads and wipe up the resulting slurry with paper shop towels. When the towels start to wipe clean rather than being discolored by the slurry, you have as much of the shellac removed as will be coming off. Sand the wood again with the final grit you used before and proceed with your finish. If you want to paint over any existing finish, the process is as follows. Clean the surface by scrubbing with mineral spirits or TSP on fine nylon abrasive pads. If you’re unsure of the compatibility of the existing finish with what you plan to apply, add one coat of Zinsser SealCoat™, a clear primer, before adding the topcoat.