Heat-resistant Clear Finish?
I used four coats of shellac and four coats of water-based polyurethane on a live edge eucalyptus tabletop slab, and it was really nice until my grandson used his laptop computer on it. The heat emitted from the computer formed large bubbles in the finish. Is there a clear finish that I could use to still show the beauty of the wood and prevent the heat damage? - Donald Little
Tim Inman: I'm guessing the bubbles are split between the shellac and poly surfaces. I love shellac and use it often. However, one thinned coat as a sanding prep/sealer would be plenty in your case. Poly does not like to bond well. It is one of its famous failings. Applying it to a built-up slick shellac surface is just asking for a failure - which I think you had. Some nice placemats used under the laptop or other hot things like a soup tureen would also provide good protection for the finish. A big stick to wallop the guy who doesn't use 'em would be good to have on display, too. Just sayin'...
Chris Marshall: Here's a case where "more" finish, or a combination of finishes, isn't always better. Did the shellac contain wax? If it did, that might also have been the problem. But even if the shellac was dewaxed, some water-based finishes are still incompatible with non water-based sealer coats. I know General Finishes, for one, does not recommend shellac of any sort underneath their water-based products. Read the fine print on the can (of both the shellac and the polyurethane) carefully, and be sure to heed those instructions. The "do's" and "don'ts" can make a difference in the long run.