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#1
08-09-2022, 02:29 PM
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Building, how long can a glued top sit around
Hello all forum members, long time lurking finally getting my feet wet, it a big body of water
I have started my first build and it is slow going, so I was saving photos until I had enough to make a start at a build thread. I have made some jigs and have just glued the top together. My question is how long can a glued up top sit around before being used. It could be a few months before the sides are ready to receive the top. Should I have waited until I was closer to use it. If so I guess this could be a practice one and I could put together another one closer to when it is ready to glue on the top. Also it is summer here and humid is in the %55. I thought by the time I am ready to glue the top on the humidity will be in the %36-%40. Any advice for a beginner would be appreciated, so many factors to consider and I keep thinking of new ones as I go along. I was going to glue up the back as well since I had things set up but I don’t want to pooch the back as well as the top in one go. Cheers Ron 
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#2
08-09-2022, 03:38 PM
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a thought
My answer: Quite a while. Like years. We don't do anything with a top but brace it and glue it in place. The glue joints don't get covered up or protected. It would be nice to store them carefully and keep the dust and dirt off.
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#3
08-09-2022, 04:09 PM
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Take a look at this auction. I'd say these have been together 50 years. I have used some from Martin that sat around about the same amount of time.
Long shelf life if done right. https://www.ebay.com/itm/32529639313...YAAOSw0vti7oRI
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#4
08-09-2022, 04:27 PM
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I was told about some tests that were done on this back in WW 2 at the Forest Products Lab, in relation to getting good glue lines in wooden aircraft structures. They found that working the surface within 15 minutes of applying the glue gave measurably stronger joints.
As the wood sits around it undergoes chemical reactions on the surface that make it harder to glue. The term of art here is 'surface energy', which sounds sort o 'new age' but it's a real thing. You can check it out by misting the wood with a light spray of water: if the drops spread out into a film the surface energy is high, and glue will stick well. If it beads up the surface energy is low, and the joint might not be as good. Usually all you have to do is remove a small amount of wood from the surface to get down to the non-reacted part. You can do this by sanding, scraping, or cutting. The object is not to produce a mechanical 'tooth' on the surface, but to get a better chemical bond with the glue. For this a smooth surface works best. Of course, you have to be careful not to lose the proper fit between parts.
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#5
08-09-2022, 05:53 PM
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Same goes with metals, any surface being bond together with a glue. I took a course about it in relation to aerospace construction (boy I missed that job), and the free electrons sticking out of the matrix makes an covalent bond (the glue and the surface sharing an electron). When the surface is old the electrons that could have been shared gets 'stuck' to other molecules on the surface or ant piece of dirt floating in the air. So as Alan says, a quick cleanup of the surface before gluing helps with the bond.
__________________
Fred
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#6
08-09-2022, 07:07 PM
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The point about surface energy is well taken, but does not apply to the OP's already glued center seam. However, it will come into play whenever the braces are glued and the top is installed on the rim.
I will add that the braces are best glued just prior to installing the top or back. That reduces the chance of the plates going concave or otherwise warping from sitting around.
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#7
08-09-2022, 07:26 PM
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Thanks all for the quick and excellent information. I will proceed with the back glue up.
I used a shooting board to plane the surfaces that received glue. So they are fresh wood. I will not assemble the body until the humidor drops or do the bracing until the humidity drops. I can work on the sides in the mean time. I use to build fishing rods graphite and bamboo and yes proper gluing is a important aspect. This is where I first read about the water drop to see if the surface was correct for a good strong glue adhesion. Thanks again for the guidance this form is concentrated knowledge I appreciate people sharing what took them time to learn and test out Cheers Ron
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#8
08-10-2022, 12:49 AM
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Quote:
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