What applications do you use different glue types for? Glues such as PVA, epoxy, Unibond, polyurethanes, etc. Is it acceptable to use a combination?—Anon
Mike Korsak replies: While I can’t speak to all of the different types of adhesive available to those of us who work with wood, I can say that I have lately become a fan of using two part epoxy over PVA glue for certain situations. If I’m dealing with a large or complex glue-up that involves a lot of parts, and very precise clamping setups, I like epoxy over PVA because of the longer assembly time. Using epoxy allows me to get everything in place, clamped, checked for accuracy and adjusted as needed before the adhesive begins to harden. I also appreciate the fact that epoxy acts as a lubricant, allowing parts to be slid together and their fit adjusted, whereas PVA begins to grab pretty quickly after assembly. For me, the choice comes down to the specifics of the task at hand—are there multiple joints that must be glued at the same time, is the clamping setup complex, etc. And sometimes it just boils down to what I have on hand.
Bruce Wedlock replies: Use polyvinyl acetate (PVA) glues for most woodworking. Titebond Original is for interior work. It is not water resistant, but dried glue lines sand easily. Titebond II is water resistant so can be used outdoors with a quick grab and five minute open time. Titebond III is waterproof, but not for marine or underwater use. Open time is about ten minutes. Unibond 100 is a one-part PVA glue that has a hard glue line and is used for veneering and laminating to reduce cold creep. It is also suitable for interior furniture assembly. Open time is 15 minutes.
Polyurethane glues like Gorilla Glue are water activated and expand into materials to form an incredibly strong bond to virtually anything. It is good for end-grain applications, and will fill small gaps, up to a 1/16˝.
Two-part epoxies are probably the ultimate glue. They are incredibly strong, bond a variety of different surfaces, and will fill gaps of any size. They are excellent for chair repair where dowel joints have come loose. Depending on the mixture, open times of 30 minutes or more are available. Vinegar is a solvent for liquid epoxy resin.
Cyanoacrylates are strong, fast acting adhesives, known as instant glues, Super Glue, Krazy Glue or just CA glue. They are great for quick repairs, but have a short shelf life—a year unopened, a month after opening. Care must be taken not to bond fingers to materials or other skin. They are most effective in thin layers; they do not effectively fill gaps.
Hot hide glue has been around for thousands of years. It is found in the pyramid tombs. Today it is available both hot and room temperature. It is the only reversible glue, yielding to heat or water. It is used particularly in reproduction furniture and for inlays and veneers as it can be moved and adjusted with the application of a hot iron.
Unibond 800 is a two-part urea resin gap-filling glue used for vacuum veneering. It dries extremely hard and resists spring back. It is primarily used for veneering curved surfaces and bent laminations, eliminating cold creep. Open time is 45 minutes.
Pick a glue for your purpose. Combining different glues is likely to reduce the performance of both.