I am interested in hide glue for a number of reasons. The first of which is the “romance” of using a traditional method that has its foundations as far back as Ancient Egypt and the cabinet shops of Colonial America. I also appreciate the pace of using hide glue . . . slow while getting set-up and quick when applying the glue. I also like the reversibility of hide glue and the fact that it accepts stain and finish without leaving telltale glue marks like that pesky spot of PVA that you missed during final clean up. All that said, hide glue is not the main glue in my shop, but I am adding it to my shop armamentarium. You can experiment with this fascinating and historic glue inexpensively. Trust me, you won’t regret the adventure!
A Hide Glue Primer
Properties of HideGglue
1. Hide glue is thermoplastic – softens to a liquid state when warmed and solidifies when cool
2. Hide glue is hydroscopic – in other words, it has an affinity for water which means, for wood working purposes, it responds to some degree with changes in relative humidity just as wood does and more importantly, a hide glue joint can be “reversed” with warm water
3. Hide glue is an animal protein (collagen) – when hide glue cools (dries) the protein structure contracts (on a molecular level) which has the effect of clamping
4. Hide glue grading – hide glue is graded in terms of “gram strength” (GEEK FACTOID: gram strength is a measure of how many grams of force it requires to depress a 1/2” plunger 4mm. into a 12.5% protein solution of the glue at 10° C). Hide glue gram strengths range from 85 to 379. The important point to know is the higher the gram strength, the quicker the set. The general recommendation range for for woodworking applications is 135 – 251 gram strength (192 or 195 is considered the all around glue for most woodworking applications).
Some Work Flow Considerations for Using Hide Glue
1. Mix a large batch of hide glue and pour into a set of ice cube trays. Store the premixed “hide glue cubes” in the freezer. Add the cubes to the glue pot as needed to keep a batch of working hide glue ready at the bench.
2. The general rule of thumb for mixing hide glue is one cup of dry glue to one cup water, vary the amount of water depending on the desired consistency. Add the glue to the water and allow to soak for 30 minutes. Stir occasionally while gently heating to 140 F°. Be careful to not “cook” the glue as this will weaken the glue by breaking down the protein molecular chains.
3. On a day when you are planning on working with hide glue, the second thing to be turned on after the shop lights is the glue pot!
4. Your glue pot can be covered with plastic wrap and stored in the refrigerator overnight. After a week of use (heat-cool-heat) it is best to discard and start with a fresh batch.
Modifications to Hide Glue
1. To make hide glue liquid at room temperature (longer open time / slower drying) add approximately 5 tablespoons of urea for each cup of dry glue.
2. To make hide glue be made waterproof add 1/2-1% aluminum sulfate.
3. To make hide glue flexible add approximately 5% glycerin (based on the weight of glue), with increasing increments of 2-3% to achieve greater flexibility.
4. To increase the ” wetting properties” of hide glue add approximately 1% vinegar.
The Basics of Hammer Veneering with Hot Hide Glue
Both surfaces are brushed with glue and placed together. The top veneer surface is also coated with glue to act as a lubricant. The “hammer” is then pushed across the veneer surface from the center outward to force out the excess glue. The glue will begin to cool and gel immediately and holding the veneer in place. For large work surfaces, make sure the surface is warm. Have a heat source (heat lamp) nearby for a longer working time.
Hide Glue & Veneering References
The definitive hide glue resource and “hide glue guru” is Eugene Thorndahl of Bjorn Industries in North Carolina. Eugene has the most experience with hide glue. Bjorn Industries has the widest variety available of hide glue gram strengths.
Interesting Hide Glue & Veneering Resources from Fine Woodworking.com
Great source for the “gold standard” for glue pots . . . Hold-Heet Glue Pots
Hide Glue Brushes
Don’t want to fuss with a glue pot? Then check this out! Patrick Edwards - Old Brown Glue