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The back strip on this 1970mahogany dreadnaught has separated from the back plate on one side by about .006". See pic attached. The strip that covers the seam on the inside of the guitar is loose in a couple of places, but not along it's entire length. There is also a small section on the bottom of the neck block where I can fit a .003" feeler gauge under it by about 1/2". Other than that, all of the back braces seem to be stable without any loose spots.The back itself seems stable overall. If I squeeze the guitar sides, in an attempt to close that small gap and bring the back plates together, there is no movement.

What should be my course of action here. Is this just the celluloid back-strip shrinking over 40 years time?
Should I run some hide glue or Tite-Bond under the center seam and the neck block inside the guitar, and leave the back strip alone?
Should I fix what is loose inside the guitar, then run some kind of adhesive in that .006" opening on the back? Some CA glue or something very thin? Tite-Bond? Something to ensure that the back seam stay stable?

Thanks for any help!

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I'm starting to think that this is just the celluloid shrinking. There is no evidence that the joint is not strong. If I ran some CA along the length of that seam on the back, would that glue potentially harm the finish or the celluloid? Would I be better off using Tite-Bond for this?

(the guitar has been in high 40's to low 50's humidity for several days now, so it doesn't seem that the gap is going to close with additional humidity)

Or, the other option s to leave it alone, and replace the backstrip when I am ready

thanks
I agree that it's the celluloid shrinkage. But I would do the following: cut a thin piece of celluloid that fits in the gap, soften it with acetone and put in place. Wipe fast to avoid acetone ruins the finish. When hardened sand and brush. Hope well!!
Thanks Antonio - if it is in fact celluloid shrinkage, should i be worried about anything structurally, or is this just a visual issue? If its just visual, then i may let it be and move on with the other repairs.

(At this point, I really want to take care of the structural issues on this guitar and get some strings on it. It's been a work in progress for some time now.)

When I am ready to repair the celluloid: I don't know if I have the skill/tools to cut a piece of celluloid that thin. The gap is probably .006" at its widest point, but it is not uniform. Would it be easier to remove the existing back strip, cut a new one, then apply, level, etc. ??

If I remove the back strip altogether, I could then inspect the joint. Does the back strip add any additional structural strength to that joint?
I would try the C.A first because you can't use c.a after you use titebond .That is my experience any way. Bill.""""""""
Titebond isn't going to work after CA either. If I was going to fill it, I would be more inclined to thin down a strip of mahogany and work it in then CA. I just thinned some down to .010 for a neck reset shim and using a raiserblade could have shaved off a little more.
Some backstrips are inlayed into the back and some go all the way through. If it goes all the way through, removing it will be a little more involved. Being binding material I would think it would be inlayed but who knows. You might want to remove a piece of the crossgrain cleating that covers the back joint on the inside to see. Keep us informed. Good luck which ever way you go at it.

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