How To Choose And Use Wood Glue
When you grew up using Elmer’s all throughout grade school, the vast selection of woodworking glues can seem intimidating come first glance. Yet, it’s not as complicated as you’d think, and there’s remarkable overlap in utility of the various adhesives. In many scenarios, one glue will work nearly as well as another.
In despite the overall similar nature and shared functionality purpose, there are nuances between each that take your projects to professionalism. From PVA glue and epoxy to polyurethane glue – do you know already the differences between these common woodworking glues?
As a practising woodworker, you owe it to yourself to learn all about these tiny differences. Here is a brief breakdown to the most common woodworking glues and their applications.
PVA glue is the most easily accessible glue out on the market and includes white glue, yellow glue, school glue, Elmer’s glue, and many types of carpenter’s glue. Its made with polyvinyl acetate so it doesn’t emit toxic fumes and is harmless on exposed skin. PVA glue is a well-reputed bonding agent for its easy application and intense adhesiveness.
Main Uses: Great on most woodworking projects, especially for bonding joints. It even works on “fake” woods like plywood and medium-density fiberboards(MDFs). White glue is ideal for indoor use, but yellow glue is superior for weathering outside conditions.
How To Apply: Spread a thin layer to each surface you’ll be gluing together. Clamps are highly recommended. It hardens in 5-10 minutes so use a damp cloth to dab away excess glue immediately after application.
When purchasing an epoxy adhesive, you’ll typically find that it’s sold in two components; a resin and a hardener. The hardener in it makes the epoxy resistant to moisture and extreme temperatures. Meanwhile, the resin is an incredibly effective bonding agent. So strong, in fact, that its industrial form is used to mend airplane hulls. But a brand made for household use should be sufficient for any woodworking project.
Main Uses: It’s the best glue for filling gaps between surfaces or joints. Great elemental resistances make it ideal for outdoor projects. Creates very strong bonds. As a rule of thumb: The quicker it dries, the weaker it is. A lengthier dry time means a stronger bond.
How To Apply: Don a mask, gloves, and safety goggles to protect against toxic fumes. Miniature measuring pumps are usually sold with each component of the epoxy to guarantee an exact mixture. Use a plastic tub to stir it up just before application. A stiff brush works great for rubbing the epoxy on each piece, or for reaching into gaps. Also, refrain from using clamps. They may actually weaken the bond.
Polyurethane glue holds just about any material together; from wood, rubber, and metal to concrete, plastics, and even epoxy. Most polyurethane glues are thermosetting polymers which means they don’t melt. Only a few brands are sold to melt, which means you won’t normally apply it with glue guns.
Main Uses: It’s waterproof so it can be set even with moisture on the piece or in heavy humidity. This makes it preferable for woodworking in damp environments. Take note though that it doesn’t fill gaps as well as epoxy.
How To Apply: Due to expansion while curing, only apply the polyurethane to one of the two surfaces you’ll be gluing together. Moisten the unglued surface with a damp rag to improve the bond. After clamping the pieces together, wait until excess squeeze out dries before scraping it off, otherwise it will be too sticky.
Hide glue, as the name implies, is made from animal hides. Actually, it’s more accurate to say hide glue is derived from boiled connective tissues since fish can be used to make it in addition to horses and rabbits. Generally sold in packets of grains to be heated up for use as an adhesive, you can also buy hide glue in liquid form. But if you’re looking for optimal strength, hot hide glue is your best bet. It’s stronger and more heat-resistant than liquid hide glue.
Main Uses: Aside from reliable adhesiveness when modding joints together, hide glue is unique in that it’s “recyclable”. Moderate warming of a hide glued wood joint is enough to take it apart. Then you can warm the leftover glue on the joint and reuse it.
How To Apply: Liquid hide glue is used identically to PVA glue with the advantage of easier to clean runoff once it cures. The non-liquid version must be prepared first though. The entire process spans 48 hours. You can learn about it here. Only set it in cooler temperatures.
CA glue, informally known as superglue or instant glue, is a formidably fast-acting adhesive and bonds within minutes of setting. If that doesn’t sound quick enough to you, apply a canned accelerator for a speedier process. Moisture is required for the CA glue’s chemical reaction to activate and bond with other surfaces. Thus, make certain to prevent moisture from contaminating your bottle, otherwise large swathes of it will harden and become unusable.
Main Uses: While CA glue is the home-body’s go-to for quick mends, the bonds it makes are weak and brittle. This makes projects susceptible to breakage through blunt trauma, and even long-term decay via vibrations. CA glue is an adequate finisher substance, though it doesn’t sport any advantages over other finishes. It’s main advantage in woodworking is usage as a wood hardener.
How To Use: Only one side needs to be set before clamping together. It should set rapidly, so move swiftly. If it doesn’t, you’ll need to provide a thin layer of water to activate the bond. When applying an accelerator, take caution not to use too much, otherwise the glue will foam up and become particularly brittle.
As mentioned before, there isn’t always a single best type of woodworking glue for each situation. The main variances concern the time a glue takes to cure, its resistance to moisture and extreme temps, as well as proficiency in gap filling. There’s also factors of toxicity and preparation time to take into consideration as seen with the epoxy and hide glues respectively. Armed with the knowledge above—and some firsthand experimentation—you’ll soon be choosing the optimal woodworking glue for each project with confidence, just like the pros.