Q: What is the best way to repair catalyzed polymer finishes on acoustic guitars? 
A: Polyester or UV cured finishes, either acrylic or polyester, are the most difficult to repair. There is a way to repair them with the same finish on them, but you must have a UV curing wand to do that. For small chips, I find filling them with cyanoacrylate (super glue) is about as good as anything else. With catalyzed lacquer and conversion varnish, you can burn in chips with burn in stick, if you are skilled at that, and you can blend repairs by deglossing the surface by sanding the guitar lightly with 500 or 600 grit paper, then respraying it with a coat of lacquer, catalyzed lacquer or conversion varnish.
Q: I’ve recently come into possession of a 1900 Lyon & Healy parlor guitar. It needs a lot of work including a good cleaning. I haven’t done a test yet for whether what little remains of the finish is shellac or lacquer but on the spruce top there are some splits in the meaty part of the wood between the grain. Not sure what the technical term is but it looks like it has some shallow valleys of exposed wood between the grain. Can you recommend a safe way, if any, to clean these out as they have collected some dirt?
A: You can clean it with mineral spirits on a white nylon abrasive pad. For what it is worth, Lyon and Healy did not start using spray lacquer until well after 1910, so my guess is that the finish is either shellac or spirit varnish. As for the terminology, if you are talking about areas where the soft early wood bands were eroded by strumming, leaving low areas between the late wood bands, the condition is called “washboarding.”
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