Dovetail vs humidity

Dear all together,

I was looking around the other topics but I didn't find the right answer for my question. I hope one of you has a good one for that.

I'm a luthier myself and I got one guitar in for repair. It has a loose neck joint (dovetail). The guitar is about 1 1/2 years old.

The owner came in last year for some checks and I already noticed a sunk in top. So I told him to keep an eye on the humidity to get no damage.

I'm asking myself now if low humidity could cause the dovetail joint to fail? Or if it is more likely that it is a mistake in the joint itself?

It's not a big deal to repair, but I'm wondering what could have caused it.

Thanks a lot for your answer and excuse some mistakes. I'm from Germany and so there could be some.

Jakob

Tags: dovetail, humidity, loose, neck

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Permalink Reply by Andrew on March 11, 2015 at 12:36pm

I don't think low humidity alone can cause the dovetail to fail - there are probably loads of guitars out there with shrinkage cracks all over the place that still have a solid neck joint. However, if the fit of the dovetail wasn't very good in the first place, I could see how a big humidity change could result in a loose neck. It's also possible that the wood wasn't seasoned well enough or that the builder wasn't careful with the humidity in their shop, based on the fact that the top has sunk already at only a year and a half old. Of course its also possible that the guitar was subject to low humidity and also happened to have a questionable neck joint, or a glue failure there, which was unrelated entirely to low humidity.

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Permalink Reply by Carl Mesrobian on March 13, 2015 at 6:53pm

If you have a moisture meter , check the moisture content of the dovetail and moisture content of the neck block after they have had time to acclimate in your shop. If you don't have a moisture meter, hmmm....

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Permalink Reply by Frank Ford on March 13, 2015 at 8:17pm

I agree. We really don't see many loose dovetails on well-made instruments, regardless of humidity. White glue and aliphatic resin glue will soften and stretch in high heat, so if the joint was loosely fitted, it wouldn't be surprising to see it pull away.

Hide and other glues may not loosen so easily with heat alone, but a poorly fitted dovetail set with hide glue can present its own problem. Hide glue has no gap-filling ability, so if it was loosely fitted to begin with, the glue could dry out, pull away, crack and crumble. That's what we see with old Harmony and Kay instruments, but then, they are old by the time we see them.