Hide glue was the woodworker’s and luthier’s glue of choice for many centuries. Hide glue has several advantages compared to most contemporary aliphatic resin and polyvinyl glues including the following:
- Hide glue soon becomes tacky and keeps parts from slipping while clamping
- As the water in the glue evaporates during drying the joint pulls itself tighter
- Hide glue residue does not show under many finishes
- Joints made with hide glue are easily disassembled for repair with heat and moisture
- Hide glue does not creep under stress or tension like many modern woodworking glues
- Hide glue is non-toxic and is actually edible (You’ll never think of gelatin the same way again)
Hide glue has also been used as grain filler and can be tinted and used to fill small imperfections.
The perceived disadvantage of hide glue is that it must be mixed, heated and properly applied. There is a learning curve involved but it the results are worth the effort.
Hide glue must be heated in a double boiler of some kind. There are many articles on the web showing simple, inexpensive set ups for heating glue. Mine is similar to many of these; a small electric crock pot, a thermometer and a baby food jar.
Hide glue is available in a variety of strengths for different purposes. I use 192 gram strength glue. I fill the baby food jar about 1/3 full with dry glue and add just enough water to cover it. I give the glue some time to absorb the water and then it is time to warm it for use. Once it is warm I usually add a little more water to make sure it flows easily, more like water than syrup.
Most articles recommend keeping the glue at around 140 – 145 degrees Fahrenheit. I set the temperature of the water in the pot to 140 degrees using the thermometer and mark the position of the knob on the pot so that this is easily repeatable.
Overheating the glue ruins it. If the glue gets heated above 160 degrees or so it is best to dump it and start again.
The baby food jar sits on top of another jar lid to keep the bottom of the jar from touching the bottom of the crock pot. I want the glue in the baby food jar to be heated by the water surrounding it and this helps keep the bottom of the jar from overheating.
It is important to keep the glue covered so that it does not produce a skin or become too thick do to evaporation. The lid on the pot does a fine job of this though sometimes I keep the pot open and loosely cover the baby food jar with it’s lid. If the glue does become too thick just ad a little water. If it becomes too thin let it evaporate or add a little more glue. I shoot for a consistency similar to warm honey.
I use a small acid brush to apply the glue. The open time for using hide glue is relatively short. If the glue becomes jelled before the joint is assembled it is too late and you should clean up the joint and start again. Working in a warm room or warming the parts to be glued with a hair dryer can help extend the time you have to assemble the joint after glue has been applied.
If the glue is the consistency of warm honey it should flow off the brush very well. Don’t be afraid of squeeze out. You can clean it up with rag and warm water, a soft tooth brush and warm water, a scraper after it begins to gel or a combination of these techniques.
When not in use I close the jar and keep the glue in the refrigerator. It only takes a few minutes to heat up in the crock pot when needed.
Since hide glue is made of animal protein it will smell very bad when contaminated with bacteria. If the glue smells bad it is ruined. Get rid of it! I have been told that old or spoiled hide glue makes a great fertilizer so I dump it in the garden.
I would strongly suggest practicing using hide glue on scraps or mock ups of the projects you plan on applying it too. I learned this the hard way. I avoided using hide glue after my first failed attempt but practice on some scrap, some additional research and plain old experience has brought me back to using this wonderful stuff.
This article is by no means comprehensive and is intended to give you a general introduction to using hide glue. There are many more detailed articles available but this information should help you get started.
Please feel free to ask questions.