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Still planning the repairs on my 1947 Martin D-28 "fixer upper".  I was looking at the repaired crack that runs the length of the back.  I believe it was repaired with cyanoacrylate.  When I rub my fingernail across the crack it catches badly, so apparently the repairman did not use a caul to line up the two sides and they are poorly aligned. Assuming I was willing to refinish the guitar, could I use acetone to dissolve the cyano, separate the crack, clean it and and re-glue with tight bond and clamping cauls?

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You'll want to reenforce inside w/cleats or a nice strip of spruce/crossgrain for added assurance.
Thanks for your reply, but,  yes,  I know all about cleats.  The question was whether it is feasible to separate the faulty repair with acetone and re-glue with Titebond and clamping cauls.

Call the repairman to verify what type glue he used if you're on speaking terms. 'cause if it's water based, acetone should not be used IMO.g'luck  If he was authorized it should be HHG which may need heat to soften and clean.

Acetone will dissolve the finish more likely than not so limiting it's action to only the crack would be dificult. The wood will wick it.  Have you tried a "four handed" approach with someone mildly heating the crack while you gently pull on it?  This way you might be able to get the adhesive to relax enough to reopen it and then hand scrape the ends.

 

Rob

Thanks for the ideas.  I was told by the previous owner that it was repaired with cyano.

If you're sure that it's CA I guess you could try applying CA remover applied to the crack with a pipette. I've never tried using it to re- open CA glued cracks, I only have it on standby in my 'shop in case I stick my fingers together (or worse). It works well for stuck-together fingers though, don't ask me how I know that :-)  

 

Grahame

Stephen,  Acetone will definitely dissolve the bond. You may be able to limit the finish damage by wicking small amounts into the joint from inside the guitar and then working it loose. 
Does acetone soften hide glue?

No

Heat and water loosen hide glue (maybe a tad a acetic acid, vinegar) - acetone will eat most everything else (including your safety glasses lens if you splash it high enough, or your eye glasses or plastic contacts if you're not wearing safety glasses, or your eyes, etc., etc.,)..  Nasty stuff but sometimes it's all that works.

 

Rob

awesome!   thanks.
Stephen , I beleive alcohol will soften hide glue while leaving finish ok . Though I haven't tried it.Added this for the record as you have a CA problem anyway.They say the alcohol removes all water from hide glue and this makes it weak.

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