Official Luthiers Forum!

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

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There are three kinds of people:

Those that make things happen,
those that watch things happen,
and those that wondered what happened.

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.

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

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?

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Ken Cierp

http://www.kennethmichaelguitars.com/

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.

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.

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.

Makes sense...

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

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There are three kinds of people:

Those that make things happen,
those that watch things happen,
and those that wondered what happened.

Would excessive runout in a top be a subtle amount of end grain, and possibly be stained with CA?

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

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.

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Jim Watts
http://jameswattsguitars.com

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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久保
美智え