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. http://www.bjorn.net/. 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