In a nutshell, hide glue has been used as an adhesive for as long as humans have been trying to glue things together. As the name suggests, hide glue is made from animal products. Skin and bones, tenon and tissues.
As unappealing (and unappetizing) as that may sound, hide glue is still the choice of glue for many professional designer/makers. Let's take a look at why.
There are many benefits of using hide glue, but the answer I hear most frequently is: reversibility. Hide glue is reversible. By adding steam and heat, the glue bond is able to pull apart without risk of damaging the piece.
Why is this desirable? Imagine you build a fine arm chair using a modern wood glue — Polyvinyl acetate (PVA, PVAc, poly(ethenyl ethanoate). These are the common white, or yellow carpenter glues we find in most hardware stores. Now imagine again in 50 years time, the leg on that fine chair somehow gets broken. Could it be fixed? Not likely, or easily if PVA glues were used. The problem is that the glue is so strong the chair would never come apart. The joinery is more like it's cemented in place, and would only come apart if it was broken apart.
Now that same arm chair made using some form of animal glue would be a different story. Because hide glue was used, the joinery could be pried apart using steam and heat, without damage to the wooden joinery, and the chair could be repaired.
Let's imagine now that you aren't all that concerned about your furniture lasting for generations, why is this reversibility desirable in the modern work shop? Answer this: Have you ever been in the middle of a glue-up, only to realize that you've made an error along the way? Perhaps a back left chair leg should have been a front right, or a cabinet panel was glued in upside down? Inevitably, errors can happen and when they do, you'll be happy to know they can be fixed if you used hide glue.
Besides reversibility, hide glue has many advantages; let's look at a few more.
Hide glue is sold in a dry, granulated state and needs to be mixed with water and heated when used. The advantage of dry, granulated glue is its shelf life. When left unmixed, the granules can last for a very long time. We'll have a closer look at the mixing process, as well as the differences and benefits between traditional hot hide glue and the modern, more user-friendly, liquid hide glue, in a future post.
Another big advantage of hide glue is finishing. Oils and wax, varnish and shellac can all be used over hide glue without any danger or worry of glue lines showing through the final finish. The same cannot be said for modern glues. How many times have you looked at a finished project, only to see visible glue lines showing through the finish? Not with hide glue.
The long and the short of it
Another benefit of using hot hide glue is the open, or working time. (That's the length of time you have before the fresh glue starts to harden.) Depending on how concentrated the glue is, the faster or slower the working time would be.
Instrument and model makers find benefit in a shorter working time, when small parts can be attached to a project without having to create an elaborate clamping system or jig. For example, the bridge on a guitar may simply be held in place while the glue sets in a matter of minutes. No fussing around with special purpose clamps, just spread a little glue and hold the parts in place by hand.
On the flip side, a cabinet maker trying to glue-up an elaborate, dovetailed drawer may want a long working time so he/she can spread the glue through all of the areas of the joint, assemble the parts and if needed, attach some clamps. This can be a challenge when using modern glues.
And finally, a personal note on why I like using hide glue in my own wood shop is that it's a completely natural product. There are no chemicals added, or unfriendly additives to worry about. A damp cloth is all it takes to clean up, and knowing that any errors made during an assembly can easily be fixed making glue-ups much less stressful.
A modern choice
As mentioned, next time I'll show you how to mix hot hide glue, the gear you'll need, and some more applications that make this a truly versatile glue for furniture makers, hobbyists and crafters. The one drawback most modern shops have is with the glue pot. Hide glue has to be "cooked" daily in a hot glue pot or a makeshift double boiler type appliance. The good news is that modern hide glue manufacturers have come up with a way to have all the same benefits of traditional hide glue, without the hassle of a hot glue pot. The answer is liquid hide glue and we'll look at that next time.
Thanks for reading. If you have any questions, comments or concerns, don't hesitate to contact me.
If you'd like to read and see more of my work, check out my website at www.theUnpluggedWoodshop.com .