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This is the first problem I have had with a top cracking. This is guitar #8. Checked some of the archives and it is probably humidity related. This is the thinnest top I have done, right at .100. It looks like some glue failure but I can't be sure. I had set it in a spare room in a case, and the room was not heated except for the door being opened occasionally. It might have got down to 55 degrees but thats it. The finish is EM 6000so I should be able to repair it ok. Any tips for this?

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Wisdom is justified by her children

The top picture shows that the crack is stepped, so at least it is (partially) a wood crack. You mention the temperature but not the actual Humidity that it was built in or the Humidity in which the Guitar was kept.
Try to re-humidify and see if the crack closes. You can use an empty plastic film canister (or 2 or 3) with a damp sponge inside. Damp but not dripping wet. Drill several holes in the canister top. Place this inside the Guitar, all within a hard case. It may take a week to close the cracks. Keep checking the moisture within the sponge and moisten when it seems to be dry.

Looks to me like it may be on or around the glue seam.

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ey Mark, bummer.
Does that have a reinforcement strip under there?

There is no reinforcement there. I usually don't put any. Next time I think I will. The humidity I build in stays prety stable.(I build in my basement). It is the center seam thats why I was thinking of a glue failure. This is for my daughter so I want to repair not replace the top. Replacement is a big job

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Wisdom is justified by her children

Mark: That crack looks like it is open a fair bit. That makes me think it may be more of a humidity control problem than anything else. I also build in the basement and can only brace and assemble in the winter months. At that time the Rh is 35%-40% or so.Wonder what your RH was when you assembled the box...?
Tom

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what kind of glue?

what does the shape (excessive dome, concave, flat, normal, etc.) of the top look like?

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sweat the small stuff.

Hey Mark, Did this just happen? I'm assuming you guys got that cold front last week even worse on the east side? Even over here, I turned on my humidifier, dumped puddles of water on all the bare spots on the concrete floor, and hung wet towels in the shop just to keep the humidity at 40%. It was dry!

Good luck.

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Kent, Thats what I'm thinking. It was 2 degrees away from record cold over here. The heat was on more so maybe it just got too dry. Its back in the case with a sponge in plastic bag with holes. I will check it daily. I have some hide glue that I can mix up. Should I reinforce the joint in a couple places?

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Wisdom is justified by her children

In my experience, tops become more prone to cracking when you build them thin like this. I'm not sure why, but I'd suggest that maybe they are less able to withstand changes in the box due to changing humidity?

Trev

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I build OM's but rarely build them thicker than 0.100". I have never had one instrument crack or suffer soundboard distortion over the years - so it definitely can be done.

My first thoughts are that the problem is two-fold. With a proper glue-joint, I almost never can break apart the centerseam. It is always to the left or right of the joint (I break the off-cuts to test the joint). My thinking is that the joining was not done properly. I also think the biggest part of the problem is humidity. That joint has separated too much and so it definitely appears to be too dry. I would re-humidfy and the repair but also add reinforcement patches in the lower bout to help secure that joint.

In the future, I would analyze your joining methodology and make certain that it isn't part of the problem.

Best of Luck,
Simon

I've yet to have a top split and I build pretty thin. I got one back last year after that huge cold front hit NYC. The strings were sitting on the fingerboard. No cracks. Re-humidified it and it was right back where it started. I tend to brace my tops at 40% or below. Maybe that helps.

Mark, yes, I would cleat that after you get it back together.

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Looks to me like the crack is crisscrossing the glue line so it probably is due to an improper joining of the top. You can also re-humidify a guitar by placing the guitar on a stand in your bathroom after taking a shower. Don't get it dripping wet of course but nicely humidified. Trace the outline of your guitar lower bouts on some 2x4 and cut it out on a band saw to make clamping cauls, line the cauls with cork. Once the crack is closed work some Titebond in there, message it in really good and reach in through the sound hole to force the crack open and closed to get the glue in really good. Clean the area with a damp cloth then clamp it over night.

Magnets make great clamps for gluing cleats to the underside. Glue cross grained cleats every 1in on that crack I'd say.

I think alot of people miss this point. I've always tried to keep my house ~50% RH, so when I started building I kept the RH in my shop that high. A cracked guitar top and cracked violin top later I figured out the RH needed to be lower in my shop.
If the top was braced/box was closed at 50% RH or higher I'd install a splint instead of humidifying it shut. If it takes alot of moisture to get it to close it will probably just crack again, in RH levels a guitar should survive. You can do an invisible repair with a splint, but some finish touch up will be necessary.

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I've got a guitar that I built 10 years ago with a wide crack on the top glue line from the bridge to the butt end. I wasn't paying attention to humidity factors when I built it. I reglued it a couple of time using the padded 2x4 clamping cauls and a couple of inside cleats as jmmckenna suggesst, but it opens up again. I'm thinking of either just living with it or putting in a splint.
Any tutorials on splinting around? Or good advice from some one who has done it?

I would probably humidify it, splint it and then keep a kyser lifeguard in the soundhole during the dry months...

I've built a number of guitars where that happened. After reading and taking advice, I think I underbuilt them in high humidity, (Portland, Or). I now watch the humidity on the weather before I glue braces. Even here there are some drier times. fwiw.

I will probably do the splint to fix this. I will also pay more attention to humidity when bracing the next top.

Thanks for all the help.

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Wisdom is justified by her children

If you are going to splint it then you still need to humidify the guitar before splinting. IF you don't, and the split is not due to low humidity, then when you splint it and the humidity rises then you will get an ugly hump as the top is trying to push out the splint.

Don't ask me how I know this to be true

Its sitting in its case with a wet sponge in platic with holes and I am practicing on an old top I have. Thanks for the great warnings learned the hard way.

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Wisdom is justified by her children

Mark.. it has been asked a few times above but I have not seen a reply.

What glue did you use to glue-up the top? Cold creep is not your older brother.

chris

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Chris Oliver
Infinity Luthiers
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live every minute...

If the temperature was down to 2 degrees off record this is almost certainly a Humidity issue. Here in the UK the first cold snap has arrived. I'm recording RH figures at 30% indoors. A month ago it was 60%.