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Ginridge
Mar-19-2014, 2:56pm
Hi Folks,

I've got a new mahogany "traveling" tenor uke made by Kala that I've been asked to do a center seam repair on. This instrument was hung in a local music store (humidified), but the seam opened up due to the extremely dry winter we've been having. When I got it, it was open perhaps a 16th of an inch. I've been able to get the seam to close through slow humidification, but these are always tricky fixes that frequently fail so I thought I'd ask for some advice.

My gut is to use hot hide glue on the theory that I've been told it will "wick" into the crack if it's tight and as it hardens, will pull the seam tighter. It's fairly well closed now so I'm concerned that if I used something like titebond it would be difficult to get enough glue into the crack to effectively work. I've also considered superglue but am concerned super glue won't be strong enough for this situation. Does anyone have any practical experience with this they can share?

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Complicating this is the fact that this is an unusually thin instrument (thus the "traveling" name) limiting access to install cleats inside.

116964

As usual, your thoughts would greatly appreciated!

testore
Mar-19-2014, 3:02pm
Yes use hide glue. Mostly because if you don't like the results you can wash it out and redo it. But if you have some strap clamps and a few small wedges of wood or plastic(tile wedges) then it's an easy fix. I've used tire inner tubes cut into strips for this job too if you don't have strap clamps.

sunburst
Mar-19-2014, 3:32pm
I'm not so sure about hide glue for the open seam. If it was glued with hide glue originally, than it's the best choice by far, If it was glued with AR, then hide glue might not hold.
I wonder if it is possible to contact Kala and find someone who knows what kind of glue was used...

Ginridge
Mar-19-2014, 4:56pm
Hmm, good point John. I've put a call and email into the Kala Service department and will report what they have to say.

Ginridge
Mar-19-2014, 8:33pm
I heard from Ryan Haugh at Kala and he said Tite bond or LMI white glue. I'll go that route.

multidon
Mar-19-2014, 8:34pm
Don't know how much difference this makes, but just wanted to point out the mahogany on those is laminate,

Ginridge
Mar-20-2014, 4:41pm
I'm sure some models are but on this particular model, I believe it's solid wood. I base this both on my own observations (I can match up specific grain patterns from the outside to the inside of the top in at least 2 locations) and a comment from the tech at Kala:

"Thanks for your understanding. Solid woods sound amazing but can be very temperamental. Best of luck!"

Nevin
Mar-20-2014, 5:48pm
You can thin tight bone with water if you need to.

PiccoloPrincipe
Mar-20-2014, 5:48pm
" I've been able to get the seam to close through slow humidification"

Good.

"My gut is to use hot hide glue on the theory that I've been told it will "wick" into the crack if it's tight and as it hardens, will pull the seam tighter. "

Absolutely correct.


" I've also considered superglue but am concerned super glue won't be strong enough for this situation. "

I would never use superglue on an instrument. Superglue (cyanoacrylate) is crap. Superglue is a crap fix imho. I hate the stuff and would never use it on a fine instrument.. Not to mention it will permanently discolor the wood, cannot be worked, its stability under tensile strength on the long term is still unknown. I would use it only on fingerboard cracks or chips, but even then I really prefer to use other wood fillers..


AS it is an apparently "unusually thin" instrument I question its value, or sound for that matter.
Sounds like a future headache for whomever, but it may need to be backed with a very fine thin piece of wood support and clamped.

As the instrument is so shallow, you may need to remove the back to do it properly..

Trust your gut.
If it tells you you should do that, then do it.

Like restoring old cars (and maybe everything else) ...often times we get that lazy feeling we are saving time by not removing the parts to get at what we need and can work around them, but in the end it was faster to remove them and get at what we needed to instead of goofing around...


Study hide glue. Few luthiers today know how to use it properly..
I would only ever use hide glue on a fine instrument.
It is completely reversible, can be manipulated like no other, hardens and dries stronger than the wood itself, and transmits sound better than any other glue known. Instruments hundreds of years old have survived intact with it...learn it, use it, live it.

There is a lot of info online...Practice on scraps.

Wood is very hygroscopic as you know. Moisture, steam, etc.. can make it bend like plastic, malleable like mush..

Wet rags, an iron, steam, hide glue, clamps, (and jute string if it is a crack on the top to bind the entire instrument while drying and guard against additional cracks or side deformation) all are used to remedy this and anything on an instrument perfectly..

..of course with that magic word "experience".

Here in Italy, it is all that is ever used.

Anyway, it feels to me it is going to need a very thin brace behind it..and frankly, while you're at it, you need to make several around the sides of the entire instrument as it will certainly happen again.

I would tell your client this.
As you know, braces are placed around the sides to protect against exactly this..

Best of luck.

CedarSlayer
Mar-21-2014, 6:54am
Hide glue will glue to hide glue and a lot of epoxies glue to epoxies. Other glues do not glue to glue. Tightbond is amazingly glue proof. I dilute tigntbond II and paint the surface of tables and objects to make them glue resistant.

If they used tightbond or LMI white glue, you will need to remove material until the glue is gone if you want a real bond. After removing that glue, the responsible thing to do is to use hide glue.

It is a very sad thing when fine and rare materials crafted with precision are transformed into a wondrous instrument that cannot be effectively repaired due to the use of the wrong glue.

Bob