Official Luthiers Forum!

Hi

I was wondering how you folks would approach this situation. I’ve sprayed the final coats of nitro and noticed there was a crack that developed recently. Should I apply ca glue and touch up with nitro or should I approach it differently? How does lacquer react when applying ca glue?

Any help is appreciated

Carlos

Wait for others to answer about nitro, I have no idea about it. But….

The crack looks like it’s cross grain? Are you sure it’s a crack all the way through? Maybe stick your phone in the sound hole and take a pic of that area of the side while dumping Naptha on the crack area to see if it wicks through?

I wouldn’t expect a surprise crack that is cross grain.

If you do go CA I would use GluBoost thin.

Brad


Sent from my iPhone using Tapatalk Pro

_________________
Insta - https://www.instagram.com/cbcguitars/
Facebook - https://www.facebook.com/cbcguitars

Same disclaimer as Brad as to nitro. But...

Are you sure that's not a scratch in the finish rather than a crack in the wood? It does not follow a grain line at all. Are your linings that depth that it might be running along the bottom of a lining?
Looks more like a stray grit got dragged across the surface once and dropped off at the end of the swipe.
Same advice as to napha and photo. a little sharper focus or higher resolution on a picture would be great also.

Unfortunately it is a side crack. I can feel it on the inside and when I put pressure I can feel it separating slightly. It’s a hairline crack that the nitro covered until I put pressure on it and then it became visible.

Sorry that happened.

Others will for sure chime in on what to do. My guess is depending how far along you are toward leveling and buffing you can either take a step back and spray more coats or fix it with GluBoost post mortem.

Good luck!!


Sent from my iPhone using Tapatalk Pro

_________________
Insta - https://www.instagram.com/cbcguitars/
Facebook - https://www.facebook.com/cbcguitars

My opinion on repairs is to fix a problem as soon as I find it, and that includes backing up until going forward involves no compromises and workarounds. Do what ya gotta do, today, so tomorrow doesn't see a problem. With good fortune in a perfect world, no one will ever see that there once was a problem. What the builder will remember is the huge investment in time and care, and maybe materials, involved in making a problem disappear.

_________________
Peter Havriluk

Can you work CA glue into the crack from the inside?

CA will significantly disfigure nitro, even the fumes can cause a "discontinuity" on a smooth lacquer surface.
If you wick CA in from the inside, and let it do what it's going to do, you could likely recover nicely with a normal-ish finish repair, if one is even required.

I've never wicked CA in from the inside with a nitro finish on the outside. If you hit the fresh CA with accelerator, any potential lacquer damage might be minimized. I think a medium CA would stabilize the crack and reduce the likelihood of excess CA wicking under the lacquer on outside. THats the approach I would consider: Medium CA, promptly followed with a shot of accelerator, well rehearsed in advance.

Then there is the after-CA repair thing...easy enough.

Does your body have side reinforcement strips?

_________________
Measure Twice,

Karl Borum

Another option is to use thinned Titebond and use a suction cup or some other method to force the glue through the crack then put a clamp across the side. After it dries I would add a cleat in there. You can get a bag full of suction cups from Amazon for a few bucks.

I’d vote for the thinned tightbond and suction cup from the inside, spool clamped, followed by a cleat. You could even use Tightbond Dark which would hide any glue in the crack

Any irregularities on the outside could be handled by gluboost.

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

Thanks for the tips. I ended up applying ca glue from the inside and the crack stabilized. My plan is to spray 2 or 3 coats of nitro. I’ll let you folks know how it turns out.

I think that crack is evidence that there was a weakness in the wood's grain structure. I'd be thinking of an internal patch (cloth?) to support the crack in all directions. But this problem isn't, literally, in my hands.

Guitar sides are bookmatched. What's the other side look like?

_________________
Peter Havriluk

I was going to stay out of this one but I wanted to let Peter know he's exactly right we would be reinforcing the inside too.

Instead of cloth though we might use BJR (back joint reinforcement) strips that are very nicely beveled at the edges and extra material was removed. It's a cleat but in the form of a light weight, spruce strip. What's important for structural integrity is the clean, patch, etc. is cross grain.

It will show if someone peers into the inside of the instrument maybe with a flashlight but if the crack comes back open again it will show much worse....

Good job Peter.