MIMF

I have a guitar in the shop, one of my builds, and I'm trying to repair a crack in the top.
The guitar is about 3 years old and belongs to a friend of mine. This winter was extremely harsh in our area as far as cold temps and low humidity. I've seen problems everywhere this year, not just in instruments but also wood work in houses shrinking up that's been fine for years.
This particular guitar has been kept on a guitar stand, unhumidified and next to the fireplace and believe it or not, it cracked. The crack starts at the treble side edge of the tailblock and runs up to the bridge. I've been trying to get it humidified since about the middle of January. This past week it finally closed up. So glued it up with HHG and was going to let it sit overnight and then cleat it the next day. Actually looked pretty nice. But when I returned to the shop yesterday morning it had opened back up and I can't seem to get it to close back up again. I tried introducing moisture to the joint, rehumidifying over night, even tried using a bar clamp to try to close it up, but still have about a .010-.015" gap that I just cannot close. What do I do next?

let me jump back in here real quick before someone responds. A couple thoughts I've had:
1) I could just let it wait until the humid season gets into full swing and see if it closes up on it's own. I'd have to clean the glue out of the crack if I can; otherwise it will probably just keep it propped open even though it might want to close?

2) I could try a splint? I might even have the original spruce offcuts from this soundboard. If not I'm sure I have something very similar. My concern with this is blending the finish. This was one of my very first guitars and I used a pre-cat from Sherwin Williams. it doesn't burn in and probably will be a lighter color, at least for a while...

Over-humidifying to close up a crack often results in a repeat crack, as you are seeing here. Being that the guitar was severely dried out, the top may never return to its original width, so a splint is unfortunately probably the best way to deal with this. Original wood will help but will not ensure a perfect match. You have to have the grain running the same way and make sure you get any grain lines out of the picture. I would practice on scrap a few times if you have never done a splint to improve your technique. Making the split and splint an equal width and a slight tapered shape is the way to go.

I've done quite a few and never had one turn out that wasn't quite noticeable. So maybe someone else can jump in to describe how to lessen the visual effect.

Thanks Barry. I agree, I don't think there's any way to make this repair invisible. But the owner had already resolved that it was un-salvageable (no faith.) So being able to save it at all should make him happy.

Update: I got the splint in but I'm not overly happy with it. I couldn't find the original offcuts, it's probably a back graft, UTG, and soundhole patch in some guitars out there somewhere. the problem is, I was trying to match the color first. Big mistake as I have figured out that I will not be able to match the color and the grain isn't even close. I found another piece that matches the grain much more closely but it's a piece of torrified spruce. It's darker, but I've pretty much given up on color matching at this point. But I don't know if I can splint torrified sitka to regular sitka. Are there problems I might expect if I proceed with this? Right now it's my best option at matching the original soundboard.

The torrified spruce shouldn't be an issue. We are just talking about a thin splint here.

Thanks Barry. I'll proceed. This has been a rough one.

That's why the pay us the big bucks

I have the same repair at the moment. It has been a similar month here and I had 6 guitars in within 1 week with tops dat were concave or cracked..
I splint with the ubex tool, that seems to work quite well. But since you have the splint in already that is useless info i guess.
The colour matching is just hard. At the moment i am experienting with the glu products. another go to option for me is shellac and also airbrushing with natural tints. I guess you have to try till you find one that matches. I find it very hard to judge colours till they are on the wood.

that's why I try to stay away from repairs. I'm always afraid they won't be good enough. I sent the customer a picture and he said he likes it, it gives it character. not all customers would be so gracious about something like that.