aarongreen -> RE: Pedro Maldonado / cedar top? (Apr. 15 2004 13:06:41)
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Hey Anders, Hide glue is really the only glue where the joint is either glued or not. My old teacher used to call PVA and to a lesser extent titebond "bubblegum glue". That is to say they aren't really holding but they also aren't letting go. If you have ever seen a creaped joint you will know what I mean. I remember when I was an apprentice that Alan took the top off a Martin that the airlines had their way with. The shoulder brace had moved down towards the soundhole while still being glued to the top. The tension of the strings did that, not the airlines. This is way bad. If that brace had been glued with hide glue, that joint would not have moved, if there was an impact of sufficient force to cause the joint to fail, the brace would have popped off, most likely that would be the least of your worries in that situation though. In reversing a hide glue joint that isn't dessicated you need more than just heat alone, you need either water and heat, which is not always advisable or you need to run a little alcohol into the joint which will reverse the glue nicely. Titebond and PVA don't join the way hideglue does which is one reason why you had better luck taking off that back. Those glues form a bond where the glue is basically a mechanical gasket between the two pieces of wood. We're talking on the molecular level here if it's a good joint. Hide glue penetrates the wood and keys them together. So you can see why it is harder to pry apart. I believe it also makes for a better acoustical response in the guitar as you don't have this gasket as it were between your braces. We're talking small differences here but every little bit helps, believe me. In restorations like I mentioned a hide glue joint is the only one where at any given point down the road, if the joint fails, you can run some new glue in there and the joint will be good as new. (I should mention here that I think the braces unglued from the back because the back, being flat sawn Brazilian rosewood, moved around quite a bit. The braces popped which I am sure kept the back from cracking all over the place) Any other glue you have to get all the old glue out of there and prepare a fresh surface. Not always possible in the case of a partially unglued brace. This is a big part of making your instruments fixable and thereby increasing the potential life span of the guitar. Making life easy for future repair people is always a good idea. One common misconception is that hide glue isn't as strong. It does depend on how you make it but in reality it is incredibly strong. Textured glass like they used in old office buildings is made with hide glue. They take an ordinary piece of glass, coat it with glue and then peel the glue off which takes a lot of glass with it. Very strong indeed. I used titebond for many years and for a number of those years I resisted going to hide glue because it seemed to difficult to use. That was silly, it is easier to use than titebond. You do have to worry abou the glue gelling on you but if it does you heat it up a little and your off and running., When gluing on a top or back I run a little glue in there on a knife, clamp and move to the next section. It is wonderfully easy and stress free. You will not regret making the switch, I promise.
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