Dear Folks,

I am curious about how our technicians here prepare and use hot-hide-glue. For years I have used the glue for keybushing and hammer replacement...but a recent internet search has made me question my technique. So...how about it? Here's how I prepare and use the product. My preferred source is Pianotek; the glue is consistant and has no odor, or very little. A nice product.

Prep;
1. Soak the nuggets! The glue works best when the granules are allowed to gradually soak for an hour or two in water. Flash heating the glue creates lumps that will not break-up or mix, and trying to hurry just makes things more difficult. Soak it!

2. Generally I start with a baby-food jar with a small amount of glue and just cover that with water...a tick more, but not much. I try not to prepare much more than needed for the project. The glass jars seal well, and the glue can be re-used several times.

Heating;
1. I use an adjustable heat water pot and a candy thermometer for accuracy. The baby-jars fit nicely on the heating coil in the water bath and maintain a nice even temperature.

2. Once it has melted I remove the first 'skim' that forms on the top of the glue. I beleive this removes contamination that might be in the glue or bottle. After that first skim is removed, I just blend the skim back into the mixture after that.

Consistancy;
1. Depends on the job. For keybushing; thin enough to just start soaking into the felt. Too thick does not penetrate and properly glue. Too thin and it wicks through the felt. A sample dab of the glue on the bushing cloth will let you know. For woodjoining, I use a slightly thicker mix, but again it has to be just thin enough to work into the joints. Too thick will not bond correctly.

2. I thin with water, but make SURE it has thoroughly mixed before testing again.

3. Thicken with more glue...but I try to avoid that! Lumps can form. Best to start too thick and just need to thin a little. It will thicken with time sitting in the water bath...but who's that patient? ;>)

Application;
I use brushes, various. They easily clean in the water bath of the glue-pot set-up. At the end of the job, I just warm the brush in the clean hot water and wipe clear.

Temperature?
That's the question I have for you all. I have used 165-degrees as my temperature forever.....but several sites suggest as low as 140 or as high as 180. What's your pleasure? What temperature do you feel is best for working with the hot hide glue?

Salt?
I have never really used salt to extend the setting time. In bushing or hammer replacement, I just work as far as the glue allows me to get. But, some sites and people I've talked with say that a slight amount of regular table-salt can extend the time that glue can be 'worked' without compromising the strength. Up to 3% or so can give you more time....or so I am told. Do any of you extend the setting time with salt?

So, there's my questions! Most importantly; temperature!

What say you?

Respectfully,
I remain,

All of what you said sounds normal. However, I do things a bit differently. I don't use a warm bath but rather a laboratory hot plate, and my container is a glass nail polish container.

The hot plate is set to about 85C to 90C. The glass bottle has a narrow neck and wide body which minimises evaporation to the extent that nuisance skinning does not occur although the mix will still thicken slowly over time. My applicator is a length of piano wire bent to form a handle and little spiral at the application end.

Beside not skinning, another advantage is that the bottle can be temporarily brought close to the job, without messy dripping, and then returned to the hot plate although the mass of the glass bottle keeps its heat and the glue soft for quite a long time off the hot plate.

I use the hold heet g115 or whatever the model is that they all sell. The adjustable thermostat is inside under the heater shell. This is a very robust pot and was originally made for large scale veneering. This is a dry pot no need for water in the container either…..

Always use a clean scalded container or clean out the container you have been using for making a fresh batch.

Use filtered or boiled water that has been chilled back to cold. Always store the unused portions of mixed up glue in the fridge as this is an organic product. At best it will last for a couple of days, just like fresh meat.

Low quality glues have a bad odour; this is one way to tell if the glue used is of poor quality.

All animal glues contain fats. It is the fats that go bad and causes the glue to deteriorate. By adding a pinch of lye the fats are saponified and fall to the bottom, harmless, even when remixed.

Always good to remove the initial skim. Most of the time this contains microscopic bacteria that will infect the glue. Small air bubbles is the clue to bacteria that will destroy the adhesive properties of the glue.……

Soak the beads or kernels overnight. To test the quality of your glue do the weight test. When soaked the beads should retain five times their weight.

Example: 75 grams of dry beads soaked overnight should weight 375 grams in the morning. This shows high quality glue.
A little thinner for the felt jobs. Add some water is ok to a mixture. I don’t encourage adding crystals or beads to an existing pot of glue as this can cause lumps and also the skin that forms will be new skin in the old mix, so contamination becomes a reality. Better to lift the lid and allow some water to evaporate off for thicker consistency.

Check the bloom rate of the glue you use. Ideally it should be around 280-320 for gram strength.

I use a combination of rabbit skin and steer hide. Rabbit skin glue has a high bloom rate of 380-420 and will set on you as soon as you lift the brush out of the pot. Traditionally it was used for oil canvas prep along with certain types of gesso and compo…. Because rabbit skin glue is hydroscopic it has been found to be the major cause of cracking in oil canvases by conservators.

Another thing about rabbit skin glue is while it has good gram strength it does not have high cohesive strength and cannot be used as gap filler so your parts have to fit snugly to begin with.

The steer hide is around the 240 mark for bloom and mixing them together leaves me around the 300 mark. The steer hide does have good cohesive strength.

Alum can be added to the mix or just simple table salt. I don’t use urea because it eventually hydrolyzes the protein structure of the glue and weakens it over time.

One more thing; I don’t recommend using the liquid fish glue for any piano jobs. It is full of urea to keep it flowing.

I never heat over 150F.

Someone else has some other ideas or tips?