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Need advice on how to repair a crack
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Author:  ClintB [ Fri Nov 07, 2008 12:16 am ]
Post subject:  Need advice on how to repair a crack
Hi all.

I have a koa back that I've just joined together. After I scraped and sanded the joint, I noticed a small crack starting on the lower bout a few inches from the centerline.

My question is: What should I use to repair it? My thoughts are either HHG or CA. The crack is only an inch long and is the only one as far as I can see. Must've happened while I was cutting the profile on the bandsaw.

If CA is the best choice, what viscosity is recommended?

Thanks

Clint
Author:  Alexandru Marian [ Fri Nov 07, 2008 6:16 am ]
Post subject:  Re: Need advice on how to repair a crack
MIght not hurt putting a crossgrain diamond spruce cleat too, where or after the crack ends....
Author:  Hesh [ Fri Nov 07, 2008 9:10 am ]
Post subject:  Re: Need advice on how to repair a crack
Clint I agree that HHG is a better choice but let's examine what caused the crack so as to eliminate this from happening to ya again.

Are you building with humidity control? Often cracks result from the guitar drying out and also proper humidity control can be helpful in closing the crack while gluing.
Author:  Brock Poling [ Fri Nov 07, 2008 9:26 am ]
Post subject:  Re: Need advice on how to repair a crack
Don't use CA.. you will see a dark line on Koa.

I would use either LMI white or HHG. If the crack closes up perfectly tight I would work a little in there and compression tape it closed from both sides. It will be fine. No need to cleat it. If it doesn't close up tight post a pic and we can give you some ideas on how to fix it.
Author:  ClintB [ Fri Nov 07, 2008 12:46 pm ]
Post subject:  Re: Need advice on how to repair a crack
Thanks for your help, guys.

Hesh, the humidity is controlled, but my dehumidifier went on the lam so it did rise to about 49%. Both my hygrometer and psychrometer agree so I don't think humidity caused it.

I'll go with the HHG and tape it shut. It's a very small crack so I'm not too worried about it.

One more question, though. The back is now at about .120" thick, and it seems/sounds good to me, but this is my first steel-string and my first time using Koa so I'm wondering if this is in the right range, or should I thin it a little?

Thanks again for your input. I love this forum [:Y:]
Author:  Brock Poling [ Fri Nov 07, 2008 12:51 pm ]
Post subject:  Re: Need advice on how to repair a crack
ClintB wrote:
One more question, though. The back is now at about .120" thick, and it seems/sounds good to me, but this is my first steel-string and my first time using Koa so I'm wondering if this is in the right range, or should I thin it a little?


You are going to get a lot of opinions on things like this, but I would go a LOT thinner. My last koa guitar was about .08" on the back. But I build very light.
Author:  Howard Klepper [ Fri Nov 07, 2008 1:11 pm ]
Post subject:  Re: Need advice on how to repair a crack
Cleat it. It happened for a reason. And put a cleat just beyond it. You might do the same on the other side along that grain line.

Too thick at .120". Koa in my shop usually s about .095" before finish sanding.
Author:  ClintB [ Fri Nov 07, 2008 3:13 pm ]
Post subject:  Re: Need advice on how to repair a crack
OK, so I'll go with the HHG and cleat to be safe. I'll do it symmetrically like you said Howard cause even if nothing else, the symmetry will look better looking in. Maybe I'll do something fancy for the shape of the cleats to make it look intentional.

Any rule of thumb for cleat thickness?

Thanks also for the advice for the thickness of the back. I really appreciate all the help.

-Clint
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