Written by Craig Brougher
This is a subject that is sorely needed in the field of Player Piano Rebuilding and every other form of furniture building. In it, I will try to answer for you all of the questions you may have about hot animal hide glue from questions I have received myself. So first, I will address the questions dealing with its intrinsic worth as a glue, to begin with. If you have another basic kind of question about hot animal hide glue that we haven't covered, maybe I can add it to this list. It seems to keep growing.
Q: TiteBond, Elmers, and other white and yellow PVA glues seem to work just fine. They are stronger, they apply easier, they are more readily available, and they will glue a broader array of materials than will animal glue.
A: That's wrong on all counts. Stronger? Not hardly. A wood to wood bond, for example, will vary widely with the PVA and modified PVA glues, depending on the porosity, time of clamping, etc. Also, once they have fully dried, their hidden glue joint looks like an old-fashioned lace, because it must lose a percentage of its water content through evaporation or absorption before it can set. Therefore, it must be under pressure the entire time, since moisture loss results in adhesive thickness decrease. That weakens its bond. Hot hide glue isn't under those constraints at all. It sets by gelling momentarily, dependent on temperature and time to set. From that point, no clamping is even required, and it just keeps getting tighter and tighter, a 100%, perfectly conforming airtight joint that will not leverage apart its own bond, as does PVA glue in unexpected instances.
This is why hot hide glue is so vastly superior to PVA glues in strength. Hot hide glue will never set up in one portion of the bond and remain still wet in another section-- as does PVA glue-- which negates the theoretical strength of PVA glues completely. Freshly made animal hide glue is so much stronger than the wood itself that there is no comparison. On the other hand, PVA glue joints are not as strong as the wood, even though they may take wood with them when broken apart (which doesn't mean much). They most certainly are not airtight joints by their very nature because of the way in which they must evaporate and absorb moisture into the wood to allow setting to occur.
I am not denigrating PVA glues, by the way. They are a chemical marvel, when employed in the things they are designed to do. They are called "carpenter glues" and that is not by happenstance. So why not let carpenters buy them for carpenter stuff? And carpenters who also build furniture will themselves decide if they can improve on their own glue or not. On the other hand, artisans who want the best would not even touch a factory sample of modified PVA glue because its bond is "elastic". That means, given a steady pressure, that joint will "creep". When a joint creeps, certain parts of the joint "stretches". As it does that, other joints must "adjust" as well. Pretty soon, the chair or rocker or cabinet starts getting wobbly because its joints are pulling apart. Chairs, for example, which are repaired using PVA glues last about 1-1/2 years, and then become looser than ever. Why? Because the mortise/tenon or dowel joint was never tight to begin with. So, because it continues to shrink about 1-1/2 years, they loosen up. Now, this is only if the chair is never used. If used in that time, it breaks apart much more quickly because the weight on the chair stretches the still loose dowel joint, and if one joint is stretching, the others must, too. One stretched joint puts the pressure on the others.
On the other hand, hot hide glue margins in a loose dowel joint do not move at all. Even when the joint fails, the margins stay as hard as rock. So you have radial support for the dowel, even if you don't have axial support. That may protect the other joints from following suit.
It is a false premise that slightly flexible joints will be stronger than hard ones. Any joint susceptible to "creep" dooms all the other joints in furniture like chairs, or anything else dependent upon the stability of its own wood. So unless each joint is rock hard, no joint can be safe for very long. Hot hide glue and epoxy are the repair glues of choice here, commonly.
Airtightness? This isn't only important in pneumatics. It's important in all quality furniture (You figure it out). But, in player pianos, a lacy pattern in a glue joint, times 88 notes, makes for a weak performance, and an impossible correction. You have ruined it!
They apply easier? No way! When you apply PVA glues, you do so with a squeeze bottle. It instantly begins to evaporate and dry, and so does hot hide glue, even faster. However, in the same circumstance, you can reheat the hot hide glue joint with an iron and restore it. Not so with the PVA glues. So if you like squeeze bottles, put the hide glue in a squeeze bottle. If it wants to set too quickly, add water, heat, or both. You can veneer with hot hide glue. Not so with PVA, because PVA glue has no grip when setting, it doesn't spread well, you cannot successfully thin it and still get much strength when dry, and its need to evaporate to set up, would curl the veneer off the surface anyway, unless you are doing very small inlays and can control wood warpage completely. Remember too, that hot animal glue has what is called a "death grip". That means, once the parts are contacted together, as long as their initial press was solid and not allowed to slip, the glue will act as its own clamp. Conversely, PVA glues require clamping for 24 hrs. to attain their advertised strength. Since small parts invariably slide when clamped unless extreme measures are taken, just the instructions on the bottle itself prove PVA glues to be most difficult to use properly. Hot hide glue doesn't require clamps, and by sizing one or both surfaces first, just dampening a surface and then warming it back up will reactivate the glue momentarily, which seizes its mated surface quickly and acts almost like contact cement. Thus, complex shapes can be followed with success when experienced in its use.
As far as gluing a wider range of materials, this isn't so, either. Hot hide glue is so versatile that certain additives allow it to be used for almost everything. Its bond is molecular. It's a chemical bond primarily, and a mechanical bond, secondarily. PVA glues bond only mechanically. And since they are elastic, PVA glues only work in areas where there are only momentary shear forces at work. If shear forces are continual, PVA glues will creep, slide apart, and break relatively quickly. So in player piano work, if you have been unfortunate enough to own a set of clamped block valves sealed with a cushioned gasket material like cork, glued together with TiteBond or a similar glue, you will discover that the pouch boards will have slid back on each of the block valves, until they begin to leak and disable the player.
Q: I have rebuilt lots of player pianos using PVA carpenter glues, and they all played fine. So what can you say about that?
A: I am constantly stripping down a lot of actions like that and restoring them, too. And I can speak from experience that, without exception, everything that was glued down with PVA leaked excessively, or, it was thickly filleted around with so much glue that the parts had to be re-manufactured, making the original player parts unrestorable, except by using new wood and extra time that should have been completely unnecessary. I also find many parts like pneumatics badly aligned with the piano actions because the pneumatics had to be clamped overnight to make a bond. And even at that, many warped, due to the direct release of moisture into them from that kind of glue. In addition, those actions which were put back with PVA glues were typically mediocre to bad workmanship all the way around. Cheat on one thing it seems, and nothing else really matters that much, either. So I invariably find the cheapest materials, worst quality bellows cloth and covers, valve leather that should have ended up in the trash can, and many necessary but easily hidden or camouflaged things undone. "Faithful in little, faithful in much. Unfaithful in little, unfaithful in much". That saying works every time. There is never an exception to it. To the contrary, rebuilds in the 50's and 60's which used hot hide glue have, without exception, proven to be much more nicely and conscientiously done, neater, more detailed, and show a degree of respect for the instrument and its original maker. And I feel a degree of respect for that rebuilder, who at least tried to do his best work. It makes me feel like there are still honest people in the world. Put yourself in the next rebuilder's shoes before you attempt your next player and ask yourself, "Would I want to know this guy? Or has he just made my life miserable, not caring if the instrument survives his rebuild, or not? Did he just think of himself, or was he conscientious enough to regard his instrument highly, and to pass it on in good shape?"
Q: I bought some hot hide glue, tried to use it, but no matter how I thinned it out, I couldn't get it to stick to anything unless I just piled it on, and that "hinge-bound" the pneumatics. I found I could do a much neater job with PVA glue.
A: Sounds like the problem you had wasn't of your own making. There are grades of hot hide glue that must be specially designed for a very narrow range of applications. These are usually the super-strong hide glues that require special techniques and environments to utilize successfully. The best glues for shop work vary in gram strength from between 130-240gm. But there are hide glues that range all the way from 30 gm to 600 gm strengths, and having vastly different characteristics. Don't buy glue from anyone who can't tell you what grade and gram strength they carry. It may be ok, but you're taking a chance.
Q: I was told that fish glue is just as good as hot hide glue, just as strong, and much easier to apply. What do you think about doing a player with it?
A: Fish glue is a "specialty glue" only. It is not designed to glue player actions together. It is mainly used for emulsions, but the pipe organ industry uses it to get an instant grip between leather and leather, or leather and cloth. It allows soft lambskin to be contoured around corners because of its cold tack properties. On the other hand, fish glue is very hygroscopic (meaning that it draws moisture from the air). Long-term humidity alone can disassemble parts put together with fish glue, whereas hot hide glue, once fully dry, can withstand about any amount of humidity without weakening, and over 400 degrees Fahrenheit without softening.
Q: What do you think about using some of the other glues on the market today, like Weldwood space age miracle adhesive, or PVC-e glues, like Sobo, super glues and epoxies?
A: I think some of these glues are fine for specific jobs. Super glues like Hot Stuff, especially, when you have the mild hardener to go with it, really works wonders with broken action parts. It makes them much stronger than the original parts. It's also good to harden screw holes and do a variety of wonderful jobs in seconds that used to take hours. Sobo and Plastic glues (PVC-e glues) are good to glue things that require an elastic bond, or to materials that hot hide glue in its pure form without additives isn't able to stick to. Devcon 5 minute epoxy is one of the most convenient glues of all, when mixed properly. I love it, and use it often, particularly when I need to fill gaps, or need a bit of an initial tack when I cannot clamp. On the other hand, some of the most highly advertised space-age glues aren't any good, period. So my advice to you is, test it first. Glues also can go bad, like the alpha cyanacrylate super glues. In all, these glues are "specialty" glues, and not to be used for the general rebuilding process.
Q: I used hot hide glue on my first player, and said, "never again". The pneumatics started falling off the shelves about three weeks later. That stuff is terrible.
A: Hot hide glue has what we have called a "death grip". It begins as the glue cools and starts its gelling phase. This setting period is critical, because within this small window of time, the part cannot be slid or bumped without ruining it. The best thing to use is a weight when gluing pneumatics, and if you don't have weights, then size the shelf they glue on, first, and then after the sizing coat is moderately dry, mount the pneumatics without weights. Clamps will slide the pneumatics, and instead of assuring a bond, they will more likely assure disaster.
Another mistake is to use a glue pot that gets the glue too warm; that means, over 150 d. F. This temperature weakens some formulations of glue considerably. Other formulations (such as the chrome-tanned types) it will not hurt. If glue is applied too slowly, or is too thick, it will break easily because a large percentage of it was getting cold while the percentage of water in the glue was too low, so your latitude to tolerate slow application time is greatly shortened.
Whatever the application, remember that hot hide glue is similar to solder. Unless solder flows into a joint and is kept motionless until it sets, it will become a cold solder joint that looks like it's stuck until some weeks later when it suddenly just snaps off. A bad hot hide glue joint does the same thing, and the joint then can be seen to be granular. Whenever you glue anything with hot hide glue, be sure the glue is flowed onto the surface and remains wet while the other piece is contacted and pressed down. People who "paint" glue onto a surface, trying to be meticulous should realize that the trick to a good joint is their accuracy and quickness of application. And if they aren't managing, then to use a bigger brush and add a little water to the glue; just enough that they have the time they need. Otherwise, they must pre-warm the parts they are trying to glue. For example, put pneumatic leaves in a cardboard box in the oven at 150 first.
Q: I wanted to use hot hide glue on this player, but I'm afraid to because the first guy used white glue. I'm afraid it won't stick to it.
A: Got a propane torch? By briskly moving the torch over a solidly clamped part, you can heat it up to just the right temperature with a flat nozzle and then blade off most of the white glue without burning the part. On pneumatics, you can clamp many of them together and do the same thing. Once scraped, resize these edges first with a thin mixture of hot hide glue and allow to fully dry. Once you prove that the glue is sticking and not cracking off, then you can go ahead and use hot hide glue.
Q: I can never seem to get the consistency right. It's either too thick, or too thin, or something's wrong. I just have trouble using a brush, I guess.
A: Begin with a new pot of glue and put a candy thermometer in the pot to check temperature. It shouldn't be over 150, ever. 140 degrees F is about right. Grab some scrap wood and a brush and try some. It's probably going to be too thick. Add water with an ounce cup. Try 2 oz at a time. Notice the difference it makes. Practice just a minute before you start in. If you're too slow, then get a larger brush. A 1" natural bristle brush is great for large bellows, and even works for pneumatics when you're slow. Otherwise, a 2" brush is better. But always use natural bristle. White china bristle is good because it doesn't deform much over time, sitting on its bristles.
If you are covering pneumatics, you'll want fairly thin glue. If you are mounting them, you will want medium weight. If you are gluing felts, you will want thick glue. Gluing heavy bellows requires a double gluing of medium weight glue. That means, you will apply glue to the edge of the bellows, press down the cloth, then pick it back off and reglue. Once covered, you will then wait for it to dry, or at least set for 2-5 hours, and then iron at a low heat. Ironing down bellows covers after double gluing greatly increases the tightness. But if you fry the glue (it turns white and powdery), you will have to do it all over again. So watch for just a few tiny little wet beads of warmed glue appearing at the edge of the joint as you go around the bellows. Take your time. Use your hand as a temperature sensor to prevent getting too hot.
Sizing parts first helps the setting grip. It strengthens it and speeds it up. So when you are sure you will not need to re-position the parts too much, then I recommend sizing first.
Q: Are you sure about the strength of hot hide glue? It doesn't seem very strong, to me.
A: Oh, it's strong all right. Even relatively weak hide glue is stronger than wood. You might have some old glue, there. Glue doesn't have to stink to be old. If your pot is too high a temperature, or you are using an aluminum liner to keep it in, or you keep reheating it every day, or if you leave tin-plated iron throwaway brushes in it, then it loses its strength fast. On the other hand, you don't have to make it fresh every day. That's wasteful. If you make a fresh pot and then don't plan to use it in the next day or two, turn it off. But if you plan on using it steadily for the next few days, just leave it plugged in. Keep it in a glass jar that fits your heating jacket, with a plastic lid over it, about the size of a small yogurt cup lid or tennis ball can lid. If your jar is smaller than the jacket, cut a ring of styrofoam that fits snug around the jar and stands on the rim of the jacket, sealing in the heat.
If you forget to cap it and it drys out, as long as you don't use that glue for wood to wood strength joints, it's still very useful to glue covers, pouches, valves, and what-have-you. But don't use reconstituted hot hide glue for critical work like gluing down pneumatics; just to be safe. Start with a fresh pot of glue for all wood to wood joints.
Q: How do you recommend fixing a broken grand piano lid? Someone said to use a biscuit jointer and PVA glue. It is a clean break right across the center of the lid.
A: start with two strong, heavy and straight runner supports on a table or bench crossing the break at right angles. Don't strip the lid or remove the finish. As long as the break is clean, this is the strongest way to do it. The first thing you must do is to determine that the two halves of the lid are flat and true with each other by shimming the lid to the runners. You are going to just butt glue the lid together with no splines or biscuits, but you have to support it first. It will be just as strong this way as it was originally. Biscuits won't strengthen the joint, They just keep the two halves together if the joint breaks again. Cleat the runners together now so they won't be moving with respect to each other.
By using the runners as clamps, you can push the joint together and keep the two large halves true, just by weighting or gently pressing the halves down at the break. So insert large plate screws into the top edges of the runners where they will meet the front and back of the lid, with two inches or more clearance. Shove the curved rear edge of the lid tight against these two screws to begin with. Your shims can be front rail paper punchings. Start with 4 thick ones placed on each side of the break on top of both runners, and a corresponding thickness slipped under the front and back edges. From there, you will able to get more exact with straight edges and light reflections.
Cut two wedges about 10" long and about 2-1/2" deep at the ends. Then you'll need about 4- 1/4" thick pneumatic leaves or scrap wood to protect the lid edges from clamp pressure denting. You will also need some weight to control the joint. Spread apart the halves and very liberally and quickly, spread new hot hide glue on both halves simultaneously with a large brush, or any way you can do that best. If the shop is cool, pre-warm the joint first with a heat gun or hair dryer by insulating below and forming a tunnel for the hot air to be contained in. Then apply the glue and close up the joint. Use a mallet and tap the bass edges of the lid flush, then immediately drive the front wedges between the plate screws and the wood scrap protectors. This will quickly draw up the joint while still wet. If you think the joint cooled, reheat it now until you see the glue beading and getting nice and wet again, drive in the wedges moderately snug, and place the weight on top of the lid to assure flatness.
Once the glue has set for several hours, remove the wedges, then the weight and with a putty knife, roll off the excess glue on top. The glue on the bottom will stick to the runners, but the old finish will prevent it from fastening itself permanently to them until fully dry. Since the width of the break is almost nothing, the excess glue between the runners and the lid should be immaterial. When fully dry, the glue will easily break off the lid finish. The excess glue along the break underneath will also break off, and whatever is left can be dampened and wiped off, as long as it is still fresh, even though dry. Now the lid may be stripped and refinished if desired, and the break should be repaired so well that it is hard to tell that it was ever broken at all.
Q: What's the best way to glue down pouches? I seem to get glue just under the rim of the hole, and it makes the pouch too stiff.
A: Pouch glue is thinnest of all. Most people use the same weight glue for everything. That isn't good. Pouch glue should be like a very thin sizing mixture. To tell how thin, drill some large through holes in scrap wood with a forstner bit and try laying down pouches on them. Dip them as you go with a home-made dipping tool. That's just basically a washer or disk as large as the pouch circle with another smaller washer or disk glued to it to create the overall dip you want, and a handle to control it with. Do not dip the pouches after they have been placed and dry. Pouch leather does stretch, very true, but it also returns back fairly close to its original dimensions after awhile. That is why pouches appear to "shrink". They were dipped with a stretch.
Q: I seem to make a mess out of pneumatics. They are tight and straight, but I can't keep my sticky fingers off the new covers.
A: I would also doubt then that they are tight and straight. The only correctly covered pneumatic is a clean one. That is the proof that the person covering knew the correct way to cover, and so the chances of those covers being tight and the leaves true are much better than when covers are stippled with gluey fingers.
When glue is too thick, too thin, the brush too large or too small, or the method is clumsy and the lighting poor, then problems occur. Instead of belaboring the subject, let me suggest a covering jig now made by the Player Piano Co in Wichita, KS. It is designed from one I built for them years ago, and allows the greenest novice to start covering pneumatics perfectly after just a few tries. However, do not use their plastic glue for any pneumatic. Pneumatics need good support all the way around. That means, you cannot do it with a hinge, alone. And were you to use their hinge circles, which are simply adhesive tapes, and then cover the pneumatics with plastic glue, you really have no support at all, to speak of. Don't trust shortcuts. They are usually just shortcuts to disaster. If you have to hinge a set of pneumatics, use canvas and hot hide glue, with strips of wax paper in-between.
Q: I have been told that Hot hide glue will not stick to nylon cloth or any synthetic sealant, like polyurethane. But you say that you use nylon cloth and always use hot hide glue. So how do you do it?
A: I can't answer for every form of glue and every nylon material there is to use, so let me say that whenever you buy materials, test them first. They may not work well. But the nylon/ polyurethane pneumatic cloth from American Piano Supply Co is the best there is in my opinion, and it glues perfectly to the sealant side with hot hide glue. I have, in the past, received different brands of nylon cloth, and some did not work well at all with any glue. I have seen a set of pneumatics literally fall open as though they had never been glued, and they had been done with PVC-e glue and a particular brand of bright red pneumatic cloth with a white backing (this was many years ago). If you find that your cloth has a release agent on it that prevents gluing, you could try wiping it down with a solvent like lacquer thinner, first.
The basic principle is always, "Try it first. Don't just blindly trust whatever you buy to work correctly. Check it out."
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