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Well, I was away from my workshop for a few days, and when I returned this morning, I discovered that one of my builds had the centre seam joint opened as a result of the sudden drop in humidity while I was away. The temperature had dropped to -20 celsius, with the accompanying drop in humidity. And this guitar is completed, except for final sanding and finishing. Would appreciate any help in finding a solution for this crack. The joint was initially joined with hide glue.

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Under Compensated Nut!

Look at the silking on that pretty top!

This is why it's important to deal with the RH issues for where ever you are located as a very important part of guitar building. But you knew this...

I suspect that your jointing and/or HHG gluing process may need to be examined. Why you may ask? Because in our business we see cracks everyday and no we don't repair refridgerators.... Especially this time of year and we also sell a ton of guitar and case humidifiers as a result.

The reason why I think that the jointing and/or gluing process may have contributed to this joint opening up is what we typically see is the top cracking near the joint or somewhere else. Rarely do we see the actual joint come open. Come to think of it the last time that we did green, unseasoned wood was a contributor too.

Dimensional instability (green wood) is a long walk on a short pier and usually will be problematic again and again. If your top is well seasoned disregard the dimensional instability part of my post.

To repair step one is......... wash your hands. Seriously, since the guitar is not finished yet and even it if was "working" glue into the joint with your hands and fingers can stain the joint from contamination on your fingers, hands, etc. And then the joint will have a darken color and be visable. So wash those hands first!

Step two assuming that your HHG is well prepared and at proper temp (140ish - 145ish) is to reach in the box and from the inside and outside at the same time use your clean... fingers to work the joint open and closed as you press in the HHG. This needs to be done quickly or the glue will gel AND the crack needs to be closed from rehumidifcation. Good thing about HHG is that the residual in the joint can be reactivated as well. Warming the joint area carefully with a heat gun extends your open time too.

Before doing any of this prepare some wax paper and flat, flexible cauls that will be clamped over the crack to keep both sides level. Do dry runs on the clamping to be sure that you have what you need.

After working the glue into the joint and I like to use a camera or mirror to see little tiny beads of HHG on the inside which tells me that I am using enough glue. Squeeze-out is your friend.

Before any of this though bag the thing in a garbage bag with a large, wet, car washing type spounge for a couple of days. the crack needs to be capable of closing with rehumidification or all bets are off and it will have to be filled with additional material. Do you like sunbursts?

Anyway hopefully something here will help. BTW I would use high powered, rare earth magnets, the 3/4" ones with 40 plus pounds per square inch of clamping horsepower with wax paper down first, then the flexible caul (sheet plastic that is stiff enough but still flexible works, plexi too). Be careful if using the magnets those things can bite ya.....

Good luck, this can be fixed but give some thought to what you need to do to stabilize the RH in your shop, your jointing routine, HHG methods, and how seasoned the top was.

Thanks guys.
Hesh, I'm inclined to agree with you on the preparation of the joint. I was already suspecting that might have led to the opening of the seam. The top was seasoned similar to others I have used. Two similar tops in same room had no issues. So, I suspect that working glue into the closed joint may be only half of my problem/solution. A cleat on the inside of the box might help???

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Under Compensated Nut!

Absolutely and good thinking on your part. Several little, spruce cleats and it should hold. Be sure that your shop is back up to the RH that the guitar was built at or it will want to pull open again.

The Luthier who taught me, David Collins, always would ask me if I washed my hands first..... so now I do it too, ask folks.....hope I was not offensive which was the last thing that I would want to be.

I have never done this repair, so I am just throwing this out for answers to my curiosity.

Since HHG can be reactivated, would it work to bring the humidity up so the joint closes; wet the joint to provide water to soak the old glue; heat with a directed blower, perhaps adding water occasionally; then clamp across the guitar. After cooling, cleat the inside. Point is, can the step of working glue into the joint be skipped.

No, use Hesh's method. Couple of dry runs on clamping will pay large dividends. Good Luck

I believe it will be near impossible to close that seam to where it will be unnoticeable. Whatever the reason for the failure I think your best bet is to remove the top and replace it, or remove the top and braces, get a good joint and go from there. good luck.

Jack, I'm inclined to agree with you. But first I will try HHG treatment. Then if that fails, back to your suggestion. Meanwhile, thanks to all those folks who gave their advice.

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Under Compensated Nut!

If the guitar is for you go ahead and repair, if its for someone who will pay you for it they deserve a replaced top.

Fred

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Fred Tellier
http://www.fetellierguitars.com
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