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I was going to put my neck on my new build when i noticed i had developed a crack in the back about 3 inches away from the neck block and about 4 inches long what is the best way to repair this and since my finish is already on it will i need to drop fill this area,

let me rephrase can i put the guitar in a higher humidity place such as a bathroom to allow the crack to close the wick in some titebond then put a couple of diamond patches on the crack inside?

I would use some thin CA, push down lightly by the crack to open it up a tiny bit then wick in some CA release the preasure that should do the trick but you will have to touch up the finish. When I say push down lightly I mean lightly you don't want to make the crack longer. It won't take much for the thin CA to run in there. That's what I would do.

Titebond won't wick into such a small crack. You need water like CA. I use 'Hot Stuff'. It's really too bad that you've finished the instrument already, but this crack needs to be stopped, ASAP. I'd sand down the area and hit it with the CA, both inside and out. You can always sand the inside again to clean it up.

What kind of wood and what kind of finish do you have on there? I hope for you that it's something easy to repair like shellac. Just to be on the safe side, I'd probably hit the "mirror" area on the other side of the center joint with CA just in case you have the same impending fault just waiting for you to re-finish the guitar before it delcares itself... Don't ask me how I know this...

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I'd like to be able to prove, just for once, that money wouldn't make me happy...

You can get titebond or hide glue into some pretty tight cracks. I glob some on and then massage it in to the crack, flexing the crack up and down so the glue is sucked in, you can be pretty vigorous without doing any further damage. I also use a little suction cup to force glue into tight cracks. You know it is working when you see beads of glue coming through the back the length of the crack. I prefer glue you can easily clean up on a nice new finish. Patches are probably not a bad idea.

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Jordan Aceto
Ithaca, NY

After making sure the crack is closed up tightly (humidifying the guitar if necessary), I'd recommend following Jordan's advice. It might be a good idea to clamp the area flat with cauls on the inside and outside as the glue dries, if you can figure out a way to clamp it* - that might be quite unnecessary, though. I would suggest cleating it, and, rather than applying CA to the mirror area of the other half of the back, if you can find the corresponding grain lines, you could cleat that side, too, as a preventive measure.

Presumably the crack is not on the glue joint, or you wouldn't be asking about cleating it - ?

*You might be able to put the guitar, back side down, in your radius dish (lined with wax paper, of course), and then put a radiused caul inside and clamp that down with go bars through the soundhole.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

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Magnets magnets magnets... And the stewmac scissor jack.

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Jordan Aceto
Ithaca, NY