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Gluing a tight crack with CA - Shellac First?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=44914		 Page 1 of 1
Author:  Pat Hawley [ Thu Jan 15, 2015 2:11 pm ]
Post subject:  Gluing a tight crack with CA - Shellac First?
I've presently got a guitar in my shop that has three cracks in the top. They seem to be closing up nicely with humidity. My intention is to wick CA into the cracks after they are tight. However, all the finish is off (I'm re-finishing the guitar) and I'm worried that if I run CA along the crack area it will also stain the top. Does it make sense to first brush on some thin shellac prior to gluing or will the shellac interfere with getting a good glue bond? I do brush the channel with shellac when installing a rosette with CA and the rosette seems to glue just fine but I've not much experience at gluing a crack with CA.

Thanks,
Pat
Author:  Barry Daniels [ Thu Jan 15, 2015 2:39 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
No, don't do that. If shellac gets in a closed crack then no CA will. I would suggest you rethink the glue and consider either HHG or Titebond. But either way, keep the shellac off until you glue the crack.
Author:  meddlingfool [ Thu Jan 15, 2015 3:03 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
Seems like thin hhg would be better.

That being said, ca tends to stain the endgrain. Since cracks would be lengthwise, the endgrain won't be exposed...

I'm sure folks with more repair experience will chime in soon
Author:  kencierp [ Thu Jan 15, 2015 3:18 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
No shellac necessary along the grain line -- CA has been my "completely closed" grain line crack repair adhesive of choice for about thirty years now, ever since I saw it in Don Teeter's repair publication. But I suppose that does not necessarily make it the best choice?
Author:  Barry Daniels [ Thu Jan 15, 2015 3:23 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
I use CA on tight cracks located on necks or other places that have no flexibility. But a crack on a top or back can usually be flexed a bit which allows you to rub Titebond or HHG down into the crack with your finger. I think this is a better long term solution and it usually looks better too.
Author:  Hesh [ Thu Jan 15, 2015 3:29 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
What Barry said.

Humidify until the cracks are closed on their own. Next wash your hands.... seriously, dirty fingers contaminate cracks and then we see a darker line for the rest of time.

With one arm in the box and the other outside run a bead of Titebond original over the closed cracks and while pumping the crack up and down with the arm in the box press the glue into the crack with the arm outside the box.

Once you can see little beads of glue in the inside with mirrors and lights cover with waxed paper, place a flat caul, and clamp level. We use powerful rare earth magnets that produce over 40 pounds of clamping per square inch but conventional long reach clamps work too. Use waxed paper and cauls inside too if using clamps.

It's super important that the cracks are swelled shut on thier own before gluing.

Once the glue dries install cleats in the inside.

Easy peazy. [:Y:]
Author:  Hesh [ Thu Jan 15, 2015 3:33 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
meddlingfool wrote:
Seems like thin hhg would be better.

That being said, ca tends to stain the endgrain. Since cracks would be lengthwise, the endgrain won't be exposed...

I'm sure folks with more repair experience will chime in soon


Yep HHG is good too but in this case Pat has multiple cracks to glue and may not have glued cracks prior so the longer open time of Titebond may serve him well.
Author:  meddlingfool [ Thu Jan 15, 2015 4:57 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
Makes sense...
Author:  Pat Hawley [ Thu Jan 15, 2015 10:13 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
Thanks for the suggestions fellows. Now that I know that staining shouldn't be a concern, I think I'll go with the CA as I'm far more confident in the CA's ability to wick into cracks than my ability to work in the Titebond.

Cheers,
Pat
Author:  Alex Kleon [ Thu Jan 15, 2015 10:56 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
Would excessive runout in a top be a subtle amount of end grain, and possibly be stained with CA?

Alex
Author:  James Ringelspaugh [ Sat Jan 17, 2015 6:32 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
Before using CA I'd test it inside the box under the fretboard or on an offcut if you built this guitar and still have one... I've had spruce that CA didn't stain at all, but some that stained badly. I don't know whether it's the particular spruce, the formulation the the CA or what that causes the staining but when it happens it's really ugly and if there's a way for it to penetrate deep into the wood it will.
Author:  Jim Watts [ Sat Jan 17, 2015 6:47 pm ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
James Ringelspaugh wrote:
Before using CA I'd test it inside the box under the fretboard or on an offcut if you built this guitar and still have one... I've had spruce that CA didn't stain at all, but some that stained badly. I don't know whether it's the particular spruce, the formulation the the CA or what that causes the staining but when it happens it's really ugly and if there's a way for it to penetrate deep into the wood it will.


I've experienced that too. :(
Author:  Michiyuki Kubo [ Tue Jan 20, 2015 6:06 am ]
Post subject:  Re: Gluing a tight crack with CA - Shellac First?
I've had maple stain from ca and it showed like neon yellow. Spruce as well but not as bad. I'd test it out on scrap beforehand.
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