Official Luthiers Forum!

I recently had one of my guitar come back for a repair after the centre seam opened up on the top. I figured this guitar had dried out so I put it into some intense humidity treatment (plastic bag and sponge treatment). After a few days the crack has closed up beautifully! Other than a small finish check that runs along the centre seam you can't see any visible signs there was separation. I thought that was great. Now the problem is how to go about gluing it. I figured I would just apply some pressure on the inside of the top to force the crack open. Then apply some new glue and clamp. The only problem is that when I took a look at it today and tried applying some pressure to the inside of the top I can't get it to open up at all. Maybe I'm not applying enough pressure, but I think if I press much harder I will damage the top.

Anyone have some suggestions on how to go about finishing this repair? Maybe there is a technique I am missing?

As to why the seam opened up in the first place that is a different issue, but I think I have that one nailed down. I was trying some new techniques on this guitar and builder error/dryness probably accounted for it.

Thanks

Josh

_________________
Josh House

Canadian Luthier Supply
http://www.canadianluthiersupply.com
https://www.facebook.com/canadianluthiersupply?ref=hl
House Guitars - Custom Built Acoustic Instruments.
http://www.houseguitars.com

Hi Josh,

I've had this happen to me as well. I used thin CA that I assumed got sucked in by the crack (couldn't really check, could I?). Afterward I cleated the crack and that was it. The guitar had since been back to dryness and the crack didn't open back.

I was afraid the CA would show, but it didn't. It was spruce, by the way. I might not have been so confident with cedar...

_________________
Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

I had a similar problem, though it was on an unfinished top, and someone suggested using hide glue thinned slightly applied the the crack while open as much as possible and then using a vacuum from the back side to suck the glue completely through the crack. It seemed to have worked for me (although at the time I had only Titebond, so I thinned it a bit and used that), but it might not be an option for you if the crack is unreachable with a vacuum hose. Good luck.

_________________
Aaron Craig

I had a couple that closed up tightly in the humidity bag and couldn't be sprung open. I let them sit out in the shop at 40% for a day or so and then I could just spring them open. I used diluted Tightbond and the moisture seemed to draw it into the crack. Used plexiglass cauls and when dry cleated them. Hopefully some of the experienced repair folks will chime in.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

If you vacuum, do NOT obstruct the sound hole. If you do, the top will suck in and self destruct. You would need to apply some kind of vacuum tool directly to just the seam area and move it along the seam.

I wonder if you could apply glue before humidification then heat it up to bond when dry and closed up?

_________________
"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

If you have cured glue in the crack the seam won't close…

What I would attempt is to use TB1 mixed 1:1 with warm water and try to massage some glue in the seam from the inside, and it doesn't hurt to do it from outside too. Clean up, then glue a couple of thin, feathered skewed grain cleats inside with HHG and finger pressure.

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

How about putting a thin coat of epoxy on each edge, a separate part on each side? When they close up and mix, voila. Just a thought.

_________________
"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

I don't see the reason to overhumidify a crack before gluing. If it has to go much over normal room humidity to close, it will just open up again when the guitar acclimates to normal humidity. If it doesn't close all the way at about 70%, it needs splinting.

You can blow the glue in from outside with compressed air. Much easier than sucking it in from the inside. Easier to clean up the finished side (although any mess left over is not nearly so well hidden). This is useful in places where the inside is not accessible.

Hide glue has good penetration and wicking when thinned, but Titebond will do OK, thinned about 1:1 with lukewarm water (not hot) as Laurent suggested. But there is no need to switch to hide glue for cleats. You can do a rub joint with Titebond (I don't know where this myth got started that the ability to glue without clamping is unique to hide glue); or clamp with magnets.

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Here's an odd variant of this question that I'm faced with right now.

I've had one of my guitars come back (for other reasons) with center seam opening between the bridge and tail, and I checked this with my own guitar which is this one's sister, and sure enough it is happening there too.

(1) These are the only tops I've ever joined using LMI white. Each is about 3 years old.

(2) These are flamenco guitars. There is a fan brace running right down the center seam, of course, and the brace seems still well attached in each case. The guitars sound fine. Since the joint is well braced from the back, I can neither open it up in order to work glue in, or clamp it shut under pressure. I can see the gap change with humidity (just moving it from my shop to the unregulated part of the house), but there is nothing loose in an obvious sense.

What would you do?

(Again, existing glue in joint is LMI white)

_________________
Jim Kirby
kirby@udel.edu

Hey guys,

Thanks for all the tips. There were a few things here I hadn't thought off. Not 100% sure which option I will end up going with, but the thinned Titebond and some cleats sounds like it might be the easiest. I've removed the guitar from the bag and will let it readjust to normal humidity before I proceed further.

Josh

_________________
Josh House

Canadian Luthier Supply
http://www.canadianluthiersupply.com
https://www.facebook.com/canadianluthiersupply?ref=hl
House Guitars - Custom Built Acoustic Instruments.
http://www.houseguitars.com

Thanks!!!!!! I've been saying that for years. Also I think it's a bad idea to try to close a crack caused by low humidity too quickly.

I wick thinned hide glue into cracks, then glue cleats with magnets. It's the only method I've ever used, but it works for me.

_________________
I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

At the suggestion of David Collins a few years ago, I now fix all repairs with slightly thinned Fish Glue. It has a much longer open time and allows me to get everything aligned and clamps applied before setting up. It works as well as HHG without the stress. Thanks again, David! (he always said I'd thank him later and I've been thanking him ever since)

_________________
JJ
Napa, CA
http://www.DonohueGuitars.com