Removing Animal Hide Glue
By Terry Smythe
The process I use to remove old pneumatic fabric I share with caution. I've been doing this for some 30 years and it works for me, but it can be dangerous, not only for the bellows being worked on, but also on self and home. It involves heat, lots of it, but with a measure of discretion and precision.
I agree with steam/hot water for leather removal, but in small amounts. Very easy to overdo it, and possibly warp the lumber or separate the plys. Use water sparingly.
For small pneumatics, I put them into a conventional sandwich toaster that I picked up at a garage sale for $2. It has a thermostat which I can set just a little above lowest possible temperature. I fill it up with about 30 note pneumatics, let soak in the heat for about 20 minutes, then go at it. As I remove one pneumatic, I put in another on the LIFO principle.
Both the fabric and the glue are well softened, and the fabric removal is clean and simple. Entire stack of 80+ pneumatics can be stripped in about 30-45 minutes. The residual animal hide glue is very slight and can be lightly sanded off real quick on a piece of medium sandpaper affixed to some solid scrap lumber. That step might take another 45 minutes. I finish up with a fine file removing all the sharp edges off every pneumatic. I do not want to risk having new fabric cut from the inside by residual sharp edges.
Medium and large pneumatics need a more courageous approach, otherwise known as brute force. Safety precautions are imperative. The technique I use involves the use of a propane torch, with the smallest flame possible. It does not take too much trial error to get a feeling for how much heat to apply against the old fabric. It will get scorched, and will be destroyed, so good idea to take span measurements and write them down before removing the old fabric.
While constantly moving the flame along the glued surfaces, I quickly heat up the panel such the old glue actually breaks down and crystalizes. It will soften quite quickly, and the fabric can be removed fairly easily. At this point, there is still residual animal hide glue left behind on the bare wood. Sanding this is an exercise in futility. Furthermore, the friction of sanding warms the old glue which quickly makes the sandpaper useless.
I hit the residual glue with the moving naked propane flame, watching carefully for crystalization, which is usually real quick. Use extreme caution here for it very easy to overdo it and scorch the wood. The crystalized glue then can be removed super easy with medium sandpaper. It literally falls off in a dust, leaving behind clean wood, ready for fabric replacement.
I would suggest practicing this technique on old scrapped out player piano pneumatics that are headed for the junk box. A certain skill level is needed to get it right, and the eventual process is quite quick and reliable.
I do have a heat gun that I have used from time to time, but this slows down the process enough that I keep going back to the propane torch.
Safety precautions are very important. Do have nearby a shop fire extinguisher, full and certified. Do have nearby a pail of water and a wet rag. From time to time in the process, the old fabric will spontaneously combust into raw flames, upon which the wet rag and pail of water are handy.
And finally, place the old fabric, which is certain to be scorched in many places, into a metal pail, and leave it outdoors overnight. Do not put this fabric into your shop garbage box. There may be hidden glowing embers in some of the fragments.
If the weather is decent, do the entire process outdoors. If you do it indoors, risk of fire is always present; presume the worst and take reasonable precautions. And the smell throughout your entire home is dreadful, certain to provoke domestic disharmony.
I share this technique with caution. I'm aware there are a number of people around who use similar techniques, and so far I'm unaware of serious problems emerging from the process. There may well be others out there who have developed other approaches that achieve the same result. While this process works for me, and is reasonably swift, I'm always receptive to another approach that may be quite different, but equally effective.
What are others doing?
Regards,
Terry
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(Message sent Tue 15 Oct 1996, 03:43:32 GMT, from time zone GMT-0500.) |
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