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I buffed out a couple of giutars the other day and had them looking pretty nice. When I went back down to the shop a few days later they all were showing a line in the finish right where the center join is, on the top and back on one of them, just on the back on the other two.

I can sand it out and rebuff and clear it up. I was just wondering if this was due to lacquer shrinking or some other factor. The heat in my Oklahoma shop gets pretty intense. It is usually 10 degrees or so hotter than the outside air temp. Which means these guitars are sitting around in temps exceeding 100 degrees.

I would have thought that an epoxy pore fill or CA pore fill would have taken care of filling any minute amount of space in the joint. But now I am questioning whether my top and back joins are really as good as I thought they were.

Any help or feedback would be appreciated.

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Dave Rector
Rector Guitars

Dave, Ive had this issue and it has caused me to start joining my plates in advance.
My feelings are that its glue shrinkage, so with my latest batch of guitars I actually joined the plates several months ago, and continue to do this with each commission I take, as soon as the wood is selected, the plates go together, and get shelved until I need them.
Thats usually 8 months or so down the road.

LanceKLanceK38589.4355439815

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Lance@LuthiersForum.com

Interesting theory Lance. I never even considered that the glue might be shrinking. I have one in the shop now that has been glued up for a couple of months. It'll be interesting to see if it has the same problem when finished.

If it doesn't, I will have proved your theory to be correct. Thanks for providing another possible cause for the problem!

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Dave Rector
Rector Guitars

Dave what are you joining your plates with??

-Paul-

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-Paul-

Patriot Guitars

Titebond original is about all I have used since I started building.

I've used a little HHG for some repairs, but all my plates have been joined with the Titebond.

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Dave Rector
Rector Guitars

I'll probably start a firestorm here but it sounds like the top is expanding and contracting and the glue is basically like a plastic and not moving as much and that shows up in your finish.

Another thing that can cause it is if the guitar goes through big humidity or tempurature changes in a short period of time, the wood can swell and the joint can't keep up. Your finish might be sinking into that joint as an effect of that.

And Lance has a good point too, some glues do shrink a little, your lucky if that's the case because leveling the finish will fix the issue.

That being said I only use Hide Glue for my tops and backs and braces, but I use LMI or titebond everywhere else, it's not as hard to work with as people make it out to be and it gives you a far superior joint along the seam (see frank fords site for his hide glue vs titebond tests).

Cheers

-Paul-

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-Paul-

Patriot Guitars

Thanks Paul, I'll keep that in mind as well. I was a little concerned that the extreme heat might be a part of the problem. The temp is often over 11 degrees and it is my understanding that Titebond doesn't like heat too much.

The shop I am having built (along with the new house) will be well insulated, vapor sealed and will have heat and air. I believe having control over your environment makes a big difference with this kind of stuff.

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Dave Rector
Rector Guitars