We have a bureau that is 50 to 100 years old and its joints are coming apart. The glue is still attached to the wood; the breaks are in the glue itself, which has become very brittle.
What kind of glue could this be? It is shiny, hard, and almost translucent–like light-colored toffee. It burns but doesn’t melt.
I’m asking out of curiosity only; the joints will be repaired with PVA adhesive.
Janetf
Replies
Janet,
The glue is most likely hot hide glue, which is easily renewed by removing any loose flaking glue and applying more of the same stuff, or liquid hide glue by Franklin's. Hide glue is not a good gap filler, so in re assembling old joints, if there is evidence that they are sloppy loose, you ought to add shims of veneer or similar to make a tight join. Even strips of bed sheet can be used to tighten up things like a chair round.
If it is hide glue, hot water is the solvent. If you are re-gluing with pva, you ought to remove as much of the hide glue as you can. The water in the pva partially melts the hide glue and the hide glue then contaminates the pva, making for a weak glue job.
Casein glue, popular shortly after WWII, is sort of cream/ light tan/khaki colored, but more opaque rather than translucent, and usually presents a slick-looking surface-- as opposed to hide glue's translucent, often granular appearance( rather like brown sugar). Hot water will soften but not dissolve it. The softened glue is best carefully scraped/picked away from the wood with a sharp instrument, chisel, xacto blade or the like. Sometimes a bronze bristled brush helps to gently abrade the old glue away.
Ray
It looks like your description of casein glue. I looked up "translucent" in the dictionary and now think it was the wrong word to use here. The glue is light because of its color value, not because of any light coming through. And it definitely looks slick, not granular.
Well, casein is certainly versatile. I knew there were knitting needles made of casein, but didn't know it could also be turned into wood glue, guitar picks, buttons, etc. (gotta love Google). My husband is going to dread the next couple of days.
Janet
It's worth a hot water test to see if the glue might be hide glue, being actually dissolved instead of just softened. If it is hide glue, then there are advantages in using hide glue again in the repair. While you still need to have snug joints you don't need to be nearly as thorough in removing the old glue as you would with PVA. Hide glue, even the liquid variety, is as strong as PVA, and as your piece demonstrated had at least a 50 year life expectancy.
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