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I did a couple of coats of wash coat shellac on each outside top after sanding to 220 to protect the wood from debris and esp rosewood dust. But I accidentally did one inside surface while not paying attention. Will the brace joints, with tightbond original, be ok or should I sand back the shellac some? Thanks

Jon

You should sand back.

Absolutely. The glue will not adhere to a shellaced surface. It is a good reason for not applying a finish inside a guitar in case of regluing braces in case of repair.
Dave

Yep, sand back…

Controversial of course as guys like Benedetto and Bourgeois do a wash coat inside of their guitars. Obviously done after bracing so there is no shellac under the braces.

Sanding (or, much better, scraping, or even better yet, planing) the surface within fifteen minutes of gluing produces a measurably stronger glue joint, according to the Forest Products Lab.

There may or may not be a benefit to 'sealing' the wood on the inside with a thin coat of shellac. In theory it slows (but doesn't stop) moisture exchange, and so may help prevent (or delay) cracking, but it would be hard to prove that. It's not hard to show that you get a better glue joint without the shellac. Back when I did a lot of repairs we used to hate seeing guitars that were shellacked on the inside. It was always a pain to remove it to do the repair, and looked bad afterward unless you went to the even bigger trouble of putting the stuff back on.

I certainly respect your opinion as a long time and experienced luthier Alan. As I previously said though, there is no shellac under the braces of something like a Benedetto guitar so nothing to be detrimental to having to reglue them. Am I not understanding something?

I’m not Alan (remember Jessi Colter’s 1975 hit, I’m Not Lisa?), but I think the problem that shellac poses for repairs is that, sometimes, the repair is not as simple as regluing a brace that has popped off. Sometimes a cleat or patch needs to be glued to the top to reinforce a crack repair. Or so I am told. A sealer is very much a PITA in that situation.

It is frustrating that the part of the guitar most prone to cracking from dry weather is the top, so that makes the top the part of the guitar I would most want to seal with something that slows down moisture transfer. But that is also the part of the guitar where such a sealer is most in the way if a crack needs to be repaired. I figure there are smarter and more experienced builders than me who come down on both sides of this question, but in the end, I have chosen to not seal the inside, so that future repair people don’t trash me on the Internet. At least, not on this basis alone.

Thanks for the advice guys, this is a great forum and your sharing your collective knowledge is a real bonus for newbies like me. I hope to someday be accomplished enough to share rather than just take advice. Jon

That makes sense Don especially on an archtop where it is exceeding more difficult to reach inside. Having said that, it's also difficult to reach inside to place cleats. Magnets are a lot of help for both sanding and cleating but removing shellac would add a bit of time.

Re-gluing braces is not nearly as common as fixing cracks and applying cleats. It doesn't matter how easy or hard it is to place and clamp cleats if they won't stick. Removing finish is also much more time consuming than simply getting a cleat onto the right spot, even if it's an easy spot. If it's a hard spot...

Keep in mind, please, that the OP was about having applied shellac on the entire inside surface before gluing on the braces. IMO this will more or less guarantee that they'll peel up at some point.

Very true and thanks for getting the thread back on track Alan.

Hey there’s always crazy glue for repair…shellac shmellac…