Saturday, February 24, 2007

Hide Glue 1-2-3

I guess the first question is where to get it! I like to know the gram strength of my glue, which tells me about the amount of water to add, the set time and the strength. Gram strength is a measurement taken when squeezing the glue in its gelled form. The higher the gram strength, the stronger the glue, the more water necessary to get the right consistency. I buy my glue from Eugene Thordhal at Bjorn Industries. He is an amazing expert and kind enough to give solid advice. He is also the only person that sells reasonable amounts (5lbs and up) of various gram strengths. The glue arrives in a granular form that will last indefinitely in an airtight bag.
I prefer 192 and 251 gram strength. These are in the middle range and appropriate for woodworking. When I want more open time I use 192 and when I am concerned about strength I use the 251. To extend the open working time of both glues I add 20% urea, by weight. The urea is availible as fertilizer at your local nursery. I have been told all sorts of ways to mix the glue. Now I simply add cold water to the glue and urea and wait about an hour or more. Then I put the mixture, in a plastic cup, in my Sunshine water pot (about $15, no expensive pot needed) set on the lowest setting and wait for the glue to go liquid. Never heat the glue above 140 degrees, it degrades the strength. The measurements that I use for enough glue to make a chair are
1 Tbs. glue
2 Tbs. water
1/4 tsp. urea
This makes a consistency like paint and should have a long open working time (3-4 minutes at 68 degrees air temp). I keep the glue warm when I need it and let it cool to a gel when I'm done. During winter, my shop is cool enough to leave it unrefrigerated when not in use. It is like food, it can spoil, so the fridge is a good place to store it once mixed.
Obviously, speed during glue up and the air temperature will affect open time. If the glue starts to gel up on the wood before you put it together, simply heat it with a heat gun and apply some fresh glue. It takes a little getting used to and gluing the undercarraige, where one joint can be glued at a time, is a good place to start. The joint must be assembled before the glue gels and then left to cure. Like sweating a copper joint, any stress after the joint is assembled can disturb the bond. A good introduction to hide glue is to use Old Brown Glue from Patrick Edwards. It is a liquid hide glue and comes bottled. Because of the shelf life, I recommend getting a small bottle. This is a basic introduction, like any tool, I believe that there is always more to learn to get better results. There is a lot of good info on hide glue if you google it. Always make a sample joint or two before relying on any glue or new mixing process. Good luck


Jean-Francois said...

Finally! "Hide glues for dummies". Thank you very much! I've read on the subject but have not found a lot of information on gram strength.
How long can you keep your prepared hide glue?

Greg said...

I have used hide glue on my chairs for the past year or so. Up until then I used Elmer's white glue because the Windsor Institute recommended it for it's long open time. A long open time is essential for me, because the way I was taught to assemble a chair. I don't dry fit the undercarriage, for example. I drill a joint, glue it, and move on to the next. The advantage to this is that when you assemble the legs into the seat (assuming the glue is still open in the first joints you made) the joints can all give a little so that the glue will set with the parts in their optimal final positions relative to each other. Obviously 5 - 10 minutes is not enough open time for this.

With Old Brown Glue from Patrick Edwards ( also sells it) you get the best of both worlds- all of hide glue's advantages, plus a long open time. The down side is that it's relatively expensive and as you say, has only about a year shelf life.

I know it might be too ambitious to try to do in a blog entry, but it would be wonderful to have you explain how you assemble your chairs to accomodate the relatively short open time of hide glue. I may just have to schedule taking a class with you to find out!

Peter Galbert said...

Mixed hide glue will keep for a month or more in the fridge, but I like to mix it fresh for each chair. It only takes a minute and then I know that the glue is at its best.

Peter Galbert said...

I drill all of my holes at once and then glue and assemble them one at a time. My joints are what I call hammer tight. I size them to be within 1/1000th or so of an inch. Once the joint is driven home with a hammer and glue, there is no play at all, I can make no further adjustments. I will be going into more about assembly on the blog soon. During the gluing of the stretchers and stretcher to leg joints, I can do one at a time and the 2 minute open time I get with the 251 hide glue with 20% urea works great. For longer open times use the 192 gram strength and make sure the air temperature is above 70 degrees and preheat the tenons with a heat gun. Above 70 degrees, the 192 mix should act like a liquid hide glue and stay open longer.

Anonymous said...

What is the 'Sunshine water pot ' to which you refer? I've never heard of it. Is that a brand name, or is it some sort of electric kettle?



Peter Galbert said...

My mistake, the pot I use is the Rival model 471. When set on the lowest setting, it keeps the glue just below 140 degrees. As you can see in the photo, I cut a couple of notches in the side for a rubberband which holds a plasic cup (for the glue) in the water, no tipping over! Later, when the glue is almost gone and I'm through with it, I let it harden and pull it out of the cup in one piece! Easy clean up.

Anonymous said...

Ah, the wonders of knowledge beyond the common SUCKAS!!!

Krijoga said...

As an antique restorer, I have long loved rabbit skin glue but recently have been tasked with a job in making cutting boards. I worry about the cleaning of the boards, glue getting soft and board coming apart not to mention the how sanitary it would be. Any advice?


Peter Galbert said...

Hide glue is not appropriate for cutting boards because it is most certainly affected by moisture. As far as sanitary reasons, hide glue is actually harmless to consume but repeated wettings may cause some sort of mold to form. I would contact glue manufacturers to ask whether they consider their glue waterproof and foodsafe. Some glues, toxic while in the bottle, become inert in their dried form.