Friday, February 23, 2007
Why Hide Glue?
The first question has to be "What are you gluing?" I make my chairs to hold tight without glue. Using bone dry tenons and air dried mortises, as well as tight joints ensure that the glue that I choose is a backup. No glue can glue a loose joint, except epoxy, and I'll touch on its limitations.
The next question has to be "why hide glue?". I use hot hide glue for a number of reasons.
The main reason that I use hide glue is that it is infinitely repairable. I give a lifetime structural guarantee on all of my work. Imagine one loose joint amidst the 20 or so joints in the top of a chair. Hide glue is the only glue that can reglue a joint (made with hide glue). Simply add a little steam or hot water to the joint and then some fresh glue. Any other glue would require disassembling the joint, and chair, scraping all the glue off, dealing with a now too small tenon and regluing, the entire chair! Perhaps epoxy could work but it doesn't have the 2000 year track record of hide glue and the only way to repair epoxy is to stuff more epoxy in the joint. And adding epoxy doesn't redesolve the old epoxy so I am not comfortable calling it repairable. All of those revered antiques were made with hide glue, and have been maintained with it through the ages.
Reason 2 is that I use hide glue is the strength. Unlike bottled glues, I can use various strengths of hide glue and never have to worry about cold creep (when white or yellow glued joints shift in time because they never fully harden). The different gram strengths availible can offer longer open times or greater holding strength. I have done many samples and have been amazed to see a 3/4" thick piece of white oak, edge glued, shatter, not on the glue line, or near the glue line but 1/4" from the glue line.
Reason 3 is that dry hide glue that I mix myself (a lot easier that you think) has an infinite shelf life. Bottles of premade glues degrade during their life. Is the last chair from a bottled glued as well as the first?
Reason 4 that I use hide glue is that it allows very tight joints to slide together without seizing. Yellow glue takes an instant bond in a tight joint and can sieze it before it is driven home. Hide glue acts almost like a lubricant until it gels.
Reason 5 that I use hide glue is that it has doesn't require the clamping pressure that white or yellow glues do. Instrument makers often use it to glue braces to the inside of violins etc... Just put glue on the brace and hold it in place until the glue cools.
Reason 6 that I use hide glue is the hot water clean up and interaction with finishes. Even dried hide glue can be dissolved with hot water, making scraping and sanding unnecessary.
There are many things that should be glued with other glues. I have found that hide glue is the simplest and best way for me to make a chair. I know that this is a contentious issue and that my opinions are my own. It is through much experimentation that I have settled on my current method. I will give details about mixing and using hot hide glue tomorrow.