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I asked this question in Josh H's thread about a center seam split, but it got buried a the end of the thread. I am hoping to get some feedback, as I'm really not sure what to do.


I've had one of my guitars come back (for other reasons) and noticed that the center seam is opening between the bridge and tail, and I checked this with my own guitar which is this one's sister, and sure enough it is happening there too.

(1) These are the only tops I've ever joined using LMI white. Each is about 2-1/2 years old.

(2) These are flamenco guitars. There is a fan brace running right down the center seam, of course, and the brace seems still well attached in each case. The guitars sound fine. Since the joint is well braced from the back, I can neither open it up in order to work glue in, or clamp it shut under pressure. I can see the gap change with humidity (just moving it from my shop to the unregulated part of the house), but there is nothing loose in an obvious sense.

What would you do?

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Jim Kirby
kirby@udel.edu

No bites? Bummer. OK, let me ask this - if I want to at least try to work some glue into the seam, what would be most compatible with what is in there already, and easiest to clean off the adjacent French Polished shellac finish?

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Jim Kirby
kirby@udel.edu

I would get it to open as much as possible and put a deluted 1:1 ratio of titebond to it. You want a glue with a long open time. Fish glue will also work if you heat the area up first to extend the open time. French polish can be redone at any time so your good there.

No answer from me, but, one thing to think about. Having used LMI White, won't that create issues with re-gluing with any glue? Don't you have to clean the old glue out? I'm, just asking!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

This is one of two things, dryness or dryness.
I would first "force" humidify them to see if the sep closes up. If so, gluing and preventing them from drying out again should do it.
I don't think it's your technique, any seam will give if the plates on either side of it shrink sufficiently, regardless of a brace underneath.
If the seam does not close completely, it may be that there was too much moisture content in the wood, or, the guitar was built under too high humidity.
I don't think it's the type of glue you used.

I was wondering that, but since the top is still well attached to the fan brace, I don't quite see how to clean anything out. Getting a knife point or even a razor blade into the gap would make things way worse than they are now. The gap barely shows as more than what could be interpreted as simply an ugly top join.

With the guitar dehumidified (i.e., sitting in Delaware heated house with uncontrolled humidity probably in mid 20's), I can get a .005 feeler into the gap for about 3/4" of the gap's length, starting close to the bridge. I CAN'T get the 0.0015 feeler into the gap from the tail to about the midpoint from tail to bridge, but the gap seems to be there as well. Since everything is pretty solid, it seems, I'd like to try to do whatever reinforcement would likely be beneficial, but not a lot more.

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Jim Kirby
kirby@udel.edu

ARRRGGG>>>>>Humidity in the Mid-twenties? no wonder.......!!!
Get those things into 35% plus (45% would be better) pronto. Maybe even into a plastic bag with a wet sponge for a few days...........I think you may see the problems disappear.

Yes, David, the gaps close back up, but the question is whether I should do anything to them that would perhaps help them not open.
After all, this guitar is probably going to live in the same 20+ humidity for foreseeable winters. Not much I can do about that - I'm just flattered that it's owner plays it about twice as often as his nice reasonably big name Spanish guitar. But it does consequently sit out on it's stand quite often.

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Jim Kirby
kirby@udel.edu

You can't make a guitar humidity proof, at least not without making it so heavy it will no longer sound like a guitar. If you repair it (I'm thinking splint) at 20% it may tend to buckle some at higher levels.

If the crack is right at the center seam I also suspect a glue, or joinery problem. Most center seam cracks I've seen are actually right next to the joint. A good glue joint should crack the wood, before it cracks.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

The lacquer/joint fractured very slightly after a year or so on my first guitar, made with fish glue. Structurally it is fine but the fracture is visible from close distance and the lacquer roughness can be felt. I blame it on a less than ideal jointing job. I used a wooden No 4 my only plane at that time. After half a day of struggles it probably was still not perfect. The back is fine though, done the same way. All my others are fine so far.

If it is not loose enough to be opened, I would suggest a few strong wet FP sessions. This tends to melt the film and fill issues, however from my experience with similar fracures within rosettes tiles, the issues might show up again pretty soon. So if you have/are willing to buy some extra thin CA, give this a try too...

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Build log

Again, no direct experience, but CA might be a solution. At least it will stick to the glue residue in the crack, if it's right on the join line. If there is already finish there, it will protect the Spruce from staining. Of course you'll have to get the crack to close up first. Humidify. I have a crack in the top of my #4, which I stupidly left sitting on a stand in my office all winter, without humidification. Something else to deal with, however it's not at the seam.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

If you put a puddle of thin CA on a piece of wax paper and pick up small drops with the eye of a sewing needle that has had the end ground off to a fork shape you can apply just a small amount to the seam. I made several sizes of needle from cheap ones from the dollar store so I can control the drop size, if a real small drop is needed use the pointed end of the needle to pick up a droplet. This is a tip from my other hobby ultra light indoor model airplanes, it is surprising how little CA is needed to do the job and hold things together.

Fred

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Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866