Q: Years ago, in school shop, we used to work with something called Plastic Resin glue, made by Weldwood® and others, that was a urea-formaldehyde formulation (brown powder) you mixed with water to produce amazingly strong joints. I’ve been searching for it lately, and it seems to have disappeared from the shelves. Has it been pulled because of new regulations or simply replaced with something that’s significantly better?
Also, I read more and more about the usage of epoxies for bonding wood, yet I also remember reading that experts agree that epoxy is not the best glue for wood because it depends on surface adhesion, rather than actual penetration, and it tends to produce a joint that is not as strong as one might think. Can you comment on this, too?
A: I know the product you are talking about and have used it from time to time. I did a Google search and found that Weldwood, made by DAP, is still around and it is still for sale. As to the question about epoxy as a less-than-desirable bonding agent: I have never personally seen a well-made joint fail when it was bonded with epoxy. For me, its main drawbacks as a day-to-day wood glue are many: it’s expensive, it’s putzy to use, it’s messy, it leaves very visible glue lines, and it’s kinda stinky. But I have no argument with its capabilities to bond two pieces of wood together. With that said, I recommend using an epoxy with a long open time in wood-to-wood operations, because those formulations are slightly more elastic when they cure.
Of course, epoxy’s primary benefit is its durable waterproof nature. Boat makers have used it for years and in a type of construction where glue joint failure is not acceptable.
Image #1: Applying epoxy
Image #1 Original Caption: Epoxy is available in formulations with open times ranging from 5 minutes to overnight. If you are planning to use epoxy for wood-to-wood joinery, use a product with as long an open time as is practical.