By Craig Brougher
There has been an interest in the use of Gorilla Glue in the MMD recently, so I thought I'd just throw in my two cents, here.
The kind of glue used in a player is VERY important. In the first place, hot hide glue is airtight, rock hard, and permanent, as proven in ancient furniture, found in the tombs of Pharaohs and museums around the world. The wood passeth away, but the joints do not pass away. And yet, if you ever need to fix them, they are possible to be soaked loose eventually and repaired.
Such is not the case with Urethane glues, just as it is not the case with yellow or white carpenter glues. Repairing player piano actions with glue that cannot be removed out of the wood signs the eventual end of that player, because the player will keep playing as long as it can be repaired. 50 years isn't a long time to a player piano, even though the repairman may be long dead in the meantime. So my suggestion is to use glues that are strong and also removable.
You are asking yourself though, is there anything else wrong with Gorilla Glue, other than the fact that it's a one-time repair? The answer is, yes-plenty!
Gorilla Glue gets its exceptional strength from PU polymerization with isocyanate reactants, and it's possible to create a wide variety of properties by varying the isocyanates and polyol reactants. But the fact that it also foams when reacting with water is caused by isocyanate moiety which creates CO2, but so also do the alcohols in the polyol formulation, or so I am advised by Paul Harris, a professional chemist kind enough to find this article and correct my first assumption.
When it does that, it swells and fills the spaces of the joint. At the same time, any glue that swells also moves the parts, so you have to clamp each joint (rubber bands won't work). By occupying every bit of the joint area and not requiring moisture loss for drying, this glue will not leave a lacy pattern in the joint, as does every other carpenter glue. So even if it were not also stronger than aliphatic resins per sq.in it would still make a stronger joint by this reason.
In addition, urethanes are solid but flexible joints. They have some give to them. That means they won't transmit sound well. So if you were to use Gorilla Glue to fasten a new cap on a soundboard, you would get only half the tone out of it, than you would by using hot hide glue. Doesn't sound like a good deal, to me! The same reasoning goes for all soundboard and bridge repairs.
Let's suppose you have 100 Ampico valve blocks to glue back together so you run down to your hardware store and buy a small bottle of Gorilla Glue. It seems to work wonderfully, so you jump the gun and write to MMD'ers. "You just gotta try this stuff!" Well let's say you talk 20 of them into doing it. If you did, that's just 20 Ampicos that will soon never play again, probably, without an exceptional amount of work trying to get that junk out of the wood of a valve block. Why?
Because as soon as you clamp those blocks against the channel board with cork in-between, the pouch board begins its slow, insidious slide backwards, away from the clamped joint because of the spring effect of sheet cork gaskets. Within months, the elasticity of Gorilla Glue has double-crossed you again, because the stack will leak like a sieve, completely stopping your player for good. All that trouble for nothing. Plus the fact that now, you can just throw them away, instead of trying to do it right.
When you think of all the other things you have to know to rebuild a player piano, and the times you have to get back into your own work to fix something again that didn't turn out right, why double-cross yourself and negate everything you've done by selecting a glue that nixes you and everyone else from that time forward?
You can easily tell what Gorilla Glue is going to do in a piano by what it does in an opened bottle spout. It solidifies by exposure to air and moisture in a tight space. You will notice, as you are trying to get it out of the spout that it is not brittle, at all. It is aggravatingly tough. Nor is it soluble in anything, so you can forget soaking the spout free. But were you to confine a joint to about 1/3 sq.in. and then stretch a very strong bungee cord against it for awhile, it would hold-for awhile, and then over a few weeks time, it would break, because it stretched apart. Were you to compare that joint with a similar one using hot hide glue, if the hide glue held initially, it would hold forever. That's the kind of glue to use in a piano or a player action-NOT this modern junk by people who are just trying to sell you something, but could care less about the consequences.
After reading the MSDS for this product I would personally only ever use this product if I was convinced that its properties were absolutely required. The product contains a small amount of the monomer diisocyanate called "MDI". This chemical is an extreme respiratory sensitizer for certain individuals. Sensitivity to the chemical builds up after exposure, and eventually only very tiny amounts are required to initiate respiratory distress. I suggest that your article should contain a warning! (Paul Harris)
Spencer Chase had a good point when he mentioned that Dow Corning used to make this kind of glue in the 80's but discontinued it for some unknown reason. I think I know why. As many times as they tried it, they couldn't get gorillas to stick.
Many thanks to Paul Harris who helped me out here. I love to be right, and when somebody as knowledgeable as Paul takes the time to write me, he assures that I'll always look good. Thanks, Paul! :
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