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When I was french polishing this guitar I discovered a couple of hairline cracks in the back along some dark grain lines. I stripped the back and put thin CA glue on the crack which wicked in and the problem was solved. I went ahead and finished french polishing and completed the guitar. About a month later I noticed 2 more hairline cracks, also along dark grain lines on the back. These are in a different place than the first cracks. This is Indian Rosewood that was purchased from LMI and has been in my shop for years with controlled humidity. The finished guitar has also been kept controlled. I suspect that the wood for the back had hidden cracks that I was not aware of. I do not think these are new cracks forming. The back is a slightly different color than the sides and I have had none of these problems with the sides.

I'm thinking of stripping the back and spreading thin CA over the whole back to wick into these and any more hidden cracks. Then sanding and french polishing as before. Is this a good approach? Best way to keep the CA from running onto the sides? Wendy

It seems to me u need to do some cross grain reinforcement. Gonna be hard with top on, but its done on smaller scales all the time. Also, in a dark room, put a bright light in the body and see if cracks go all the way through. Pics please

There's no light showing through the cracks, they are hairline and tight, or don't go all the way through. But when I wicked thin CA in the earlier ones the CA did slightly come through to the inside. The CA was spotty on the inside so the whole length of the crack may not have gone all the way through. Those cracks were tight enough that the CA repaired them. These appear to be as tight. They are only visible because the finish is cracked. They are very difficult to see unless the light hits them just right but I will see if I can get a picture.

I have heard of soaking lower quality Brazilian Rosewood in CA to solve similar problems, which is why I thought to strip and spread CA over the whole back. I'm worried if I only repair the current cracks that new ones might appear later.

If you're going to strip the back again, then yes I would flood the whole back with CA.

I wouldn't let it pool, but squirt a bit and rub it around with a paper towel.

New username, same Pat Mac

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Pat

Why strip the finish? Just wick CA into the cracks, level and over polish.

I have not done this, so I am just parroting what I read on other posts. When spreading a large areas with CA, the fumes can be pretty bad, so you might want to do this outside and stand upwind.

That's really frustrating. Tell ya what, CA is quickly becoming my favorite pore filler and I do believe it will strengthen the plates. I used it on the last two guitars I built of Wenge and EIR. As bergman suggested you definitely want to do it outside. I have a breezeway garage and I open all the doors and have a big fan blow across the work bench when I do it. You can get oderless CA too but it's expensive.

The seeping through to the other side that you see is not in itself a sign that there is a crack. Most EIR is porous
enough that CA or shellac will wick right through. The method of applying the CA with a paper towel is good advice imo.

Michael N, I may try what you are suggesting and then wait and see if any new cracks appear before going the whole way with stripping and spreading with CA. That didn't work for me with the first cracks though. The glue would not wick in until I removed the finish. I wish I had just flooded the back with CA then, but I didn't know that more cracks would appear. The reason I am considering stripping and spreading CA over the whole back is as a safety net, in case there are more hidden cracks that are not showing yet.

These cracks are so tight that I have given up getting them to show up in a photo, I tried.
Maybe, as Ken suggested, the cracks might not go all the way through and the CA may have just wicked through the porous wood. In any case, I don't want to be dealing with this again if anything new shows up, so I am tempted to just take the finish off and spread CA after wicking it into the crack and be done with it. This has literally been the guitar from hell. Wendy

I had made a guitar from South East Asian rosewood several years ago that did the same as yours. I had many cracks in the back. They were small cracks, you could see them and feel them but they didn't open up. I did as you suggested, sanded back to wood, filled the cracks with CA and started back with pore fill. I believe it would have turned out well if I would have remembered to put the retaining clip on the nail that was holding the freshly epoxied body up near the ceiling. You guessed it, I bumped it and it came crashing to the concrete.

I am sure you won't make that mistake and if you just CA, sand and polish or do a refinish, it will fare much better than mine.

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Joe Beaver
Maker of Sawdust

I use Zpoxy as a pore filler and heat it with a heat gun to thin. It flows much better and I wonder if it were thin enough to fill the cracks that it might also help strengthen against future cracks?

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Thank You and Best To All

Larry, I would be worried about the Zpoxy being thinned enough to wick into such fine cracks. These cracks are so fine that they don't show at all on the unfinished wood. The only way I found them is when the finish cracks over the crack.

And Joe..... that's a nightmare!

Joe, I feel your pain....
Same thing happened to me once-bumped a guitar and it smashed on the floor. at least I was able to reuse the neck.

You could try it on a scrap and check the results. It's surprising how well it flows when heated. It may require near sanding back to wood to really have an effect

I think I am experiencing the same small cracks on a EIR body I am working on now. I clamped some reinforcement for a sound port and noticed the Titebond had been forced through in a couple places through what must be very small cracks as you're describing.

I'll heat the ZPoxy as I usually do when it comes time for pore filling but will keep my eyes open for any other cracks that may appear.

Good luck

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Thank You and Best To All

I thought CA on paper usually resulted in fire, or at least smoke and burnt fingers. Or does it somehow not go as crazy if it's fully saturated?

Yeah, same experience here - every time and avoid if possible but I have seen Glue Boost used as a pore filler with a cloth with no problems. Just not a technique I would use.

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Thank You and Best To All

I've not experienced this when using paper towels but I did make the mistake of smearing CA around with a cotton cloth once. Suddenly it got really hot on my fingers. I'm not saying paper towels aren't an issue, I just haven't experienced it. But, I also have never used paper towels to move a large amount of glue around.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

MUST have something to do with each formulation... Whenever I use the Bob Smith Industries stuff it smokes up a storm...

https://www.youtube.com/watch?v=-YNF0O7Zjvc

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Thank You and Best To All

Same as Bryan. Not saying it couldn't happen either. It does get kinda warm to the touch, probably has a lot to do with how much
one uses. I've pore filled a few necks this way. Just a few drops and rub into an area two or three inches. By then the CA starts to
harden, fold the paper towel and repeat. I wouldn't toss the used paper towel into the bin haphazardly when done either, stays on the
bench until the CA is fully cured. Btw I generally use Bob Smith. I think I musta used it as a neck pore fill when I had a couple maple
guitars on the go and didn't need to use my preferred West epoxy for the bodies. It did a fine job as I remember but I prefer the look
of epoxy.

I have a bottle of CA that instructs to not wear cotton or wool gloves or clothing when using CA, due to excessive heat generation.

Don't wear clothing? I don't use CA often but when I do I always wear clothes.

A good compound safety question to ask one's self before any shop task: What can go wrong if I do it this way, and how embarrassed would I be going to the emergency room if that happened?

To the OP, Wendy,

Did you pore fill the back before starting your FP?

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Thank You and Best To All

"Repairing guitar cracks with thin ca glue on Brazilian rosewood to fix invisible micro cracks"

https://www.youtube.com/watch?v=bzSaxfhPpFI

I will probably try this as a first step with my current EIR build...

"Note- This isn't pore filling.
I've never used ca as a final finish (like nitro etc). I know some that use epoxy as a final finish- it buffs apparently- ive not tried that either.
You can pore fill with ca, but use medium viscosity- i have other videos on this.
I will sand this back down to wood and pore fill after i bind it."

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Thank You and Best To All

Larry, Yes I actually pore filled twice. The first time I pore filled with shellac and EIR sawdust. When I stripped to repair the first cracks I then pore filled with Aqua Coat, which is what I pore filled the sides with after I wasn't crazy about the sawdust pore fill on the back.

This time I intend to strip, saturate with thin CA to fill any cracks and then I'm thinking of pore filling with med CA if needed. I did watch that video where you posted it on the latest CA pore fill discussion, thanks. I will probably spread with either a nitrile gloved finger or a dull razor blade or credit card. I have had issues with paper smoking so I wondered about that when paper towels were suggested.