Under the Choko Tree By Nevin Sweeney

Sustainable Sticking #1 Animal Glue

The majority of glues in use today – epoxies, cyanoacrylate “super glues” and even the humble PVA white wood glue are all made from petrochemicals using industrial processes that would be impossible, or at least very dangerous, to try and replicate in the home. If you are looking to be more sustainable in your choice of glues there are a number of options that are still available to you that can be made using “kitchen table” technology and from reasonably local raw materials. This is the first of those choices –
Animal glue.

Animal glue can be made from animal (usually cow) hide, bones, hooves and horns, glue can even be made from fish skins although that is generally referred to imaginatively enough as “fish glue”. The bit we are after is collagen which is also sometimes referred to as gelatine. In general terms the collagen is extracted by boiling in water and then concentrating by boiling off the excess water and casting the glue into sheets, which are then cut up for future use.

The Raw Material

As the raw material you could see if you can hold of the more traditional hooves and horns or even perhaps a cow hide from somewhere but for a first time it is easiest to work with rawhide and rawhide is easily available to us urban dwellers in the form of rawhide dog bones. These tasty (I assume) dog treats can be had from pet stores, some supermarkets and even your local butcher may come up with them. The whiter the colour of the rawhide, the paler the glue that comes out in the end. You can also use just about any raw animal skin so you could use rabbit or roo of you can get hold of it freshly killed.

The Raw Material - I used doggie treats!

The Process

Find a decent sized pot that will hold the rawhide, with some allowance for swelling as it absorbs the water. The rawhide bones will unravel as they soak up the water too so a bit bigger is better than a bit smaller. To get the water into the rawhide it is best to cut it up but dried rawhide is pretty tough stuff so the easiest thing is to do is to boil it for half an hour then cut up the softened rawhide with scissors.

In the water and starting to cook

We have a wood burning so I set it going and put the pot on to simmer while Linda was out one day. As it turned out, this was a good thing! The boiling rawhide gives off an aroma redolent of very old, very dead, socks. The smell starts off light but after a half hour or so it graduated to gag-worthy and permeated the whole house. Needless to say this is one job that should be done outside; although in my case I was able to get most of the cooking done, get the stuff transferred to the garage and the house aired out before she got home. This prevented any body odour and flatulence jokes at my expense.

Well and truly cooking, and very fragrant!

The rawhide needs to simmer for a good long time, 3-4 hours to extract all the goodies so a low grade heat source is good, like a wood stove, but most of us don’t have one so whatever you have would do. If you were going to use a rocket stove the high heat they develop might be a problem so it would be best to use a double boiler, especially near the end of the process. You will probably need to top the pot up with water as it boils off anyway, so keep an eye on the level and how thick it is getting. The mix gets very thick towards the end anyway and you have to be careful not to burn the bottom, stuffing the glue and making it very dark.

The boiled down glue, with solids removed

Once I had boiled the stuff enough I used a pair of tongs to pick out the remaining solid rawhide for composting, and then poured the liquid glue into a steel pan. I lined the pan with baking paper first to ensure it released easily but I suspect that it would have come away easily enough as it was and the baking paper was not necessary.

poured into the tray to cool and solidify

I left it until the next morning, at which it was a floppy brown mass and I removed it from the container, cut it up into squares about 1 to 2 cm on a side and left it sitting on the bench to finish drying. Once completely dried the glue was quite hard and would probably have lasted quite a long time if stored in a cool, dry dark space. Remember that it is a form of animal protein and may attract mice or cockroaches etc so put it in a sealed container.

The glue cut up and dried, ready for storage or use

Using the Glue

To remelt the glue it is best to use a double boiler for a couple of reasons, it stops the glue burning onto the bottom of the pot but also the heat in the water keeps the glue molten and ready for use. That is why here was glue boiler in the old wood working shops, so it was ready for use when required. I put all of the glue into the inner pot of my old cast iron glue boiler and then added just enough water to cover the glue squares. I put the whole thing on the heat and it only took about 30 minutes to get to a usable consistency although I did give it a stir every 5 or 10 minutes or so.

The (semi) antique double boiler glue pot, inner and outer

Once the glue is properly dissolved, to use it all you need to do is get the pieces of timber to be joined, paint both mating surfaces with a good layer of glue, and then apply pressure with a wood vice or cramps. Leave the glue to set over night and you should have a good solid bond in the morning. This type of glue is not waterproof and so should be kept for indoor applications only.

The glue pot assembled, plus glue!

Keeping a lid on the inner pot prevents too much water evaporating when it is hot, when finished gluing just remove the pot from the heat and the glue will solidify again. To reuse it just put it on the heat again and if the consistency is too thick and gluggy* add a bit more water and give it a stir.

(*technical term)

These two boards were joined with the glue and I could stand on the join

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