Jul / 2642
When shopping for adhesive, you’ll see pretty quickly that there’s not just one type of wood glue—rather, there are five main varieties. Most wood glues are synthetic polymers or resins that are stronger than the wood itself, one exception being hide glue, which is made of animal collagen. In addition to makeup, these glues also differ in terms of bond durability, flexibility, toxicity, and waterproofness (some may even affect your wood’s finish more than others).
This wood glue is non-toxic (except when ingested), water-soluble (thinned by stirring in small amounts of pure water), and ideal for a wide range of projects, especially for non-structural wood-to-wood bonds. White varieties of PVA are designed for indoor use, while yellow varieties (also called “carpenter’s glue”) are formulated for outdoor use. If you need a water-resistant glue, always check for “waterproof” on the label.
PVA will leave a residue, affecting your wood’s finish—especially oak. Another drawback is that PVA does not accept wood stain very well. If you try to stain the dried glue, it will look patchy. Make sure you wipe away any excess glue with a Q-tip or sponge before it is dry. For best results, press the pieces of wood together with a clamp until the glue is dry. If clamping is not possible—for example, if you want to glue a wood plug into a screw hole—add pressure by hand for a few minutes. Then allow air circulation (from an open window or fan) to create a strong bond. Know that PVA glues are basically permanent; once dry, the glue cannot be reversed or removed for repairs.
Used for everything from paint to wood floor finishes, polyurethane is also a major ingredient in many wood glues. These wood glues excel when joining wood grain end-to-end—for example, if you need to connect two pieces of crown molding—forming flexible, durable joints. Polyurethane is moisture-activated, meaning it relies on the moisture in the air to set to set, so it bonds very well in humid conditions unlike other wood glues and doesn’t dry out sensitive wood fibers.
This toxic chemical needs to be handled with care. Always work in a room with good ventilation, and wear a face mask and goggles to avoid inhaling glue fumes. If you intend to stain your wood, know that polyurethane goes on more easily than PVA. Still, remove any excess glue with mineral spirits—water is not strong enough.
Once cured, these bonds are very hard and rigid, which is helpful if you only need to create a temporary bond—a couple taps of a hammer or mallet will break it. CA glue can be used to apply glue blocks, or short strips of wood designed for reinforcement, to the back of a fresh furniture joint for as long as they’re needed. It also comes in handy for filling cracks when mixed with sawdust.
Unlike other wood glues, CA glue will not bond to a dry wood surface and requires the wood be slightly damp before application. It does, however, bond almost instantly at room temperatures, so it should be handled with care and precision. Wear a mask and protective gloves when working with the runny, water-like glue; if any glue touches your skin, remove the superglue with acetone (nail polish remover). Acetone can also be used to remove excess super glue from your work surface, but this chemical solvent can also damage your wood finish if not used carefully. Its short shelf life means that CA glue will only work on near-term projects, good for about a year when sealed but as little as a month after opening.
Basically boiled animal collagen, hide glue comes in two forms: liquid and solid crystals that are melted in a hot water bath and applied with a brush. The liquid (room-temperature) hide glue utilizes urea crystal additives to keep it fluid and allow more time to work. Hot glue, in contrast, will cure as it cools soon after application. Today, woodworkers choose both forms of hide glue primarily for the leeway (i.e. reversibility) it offers as it dries and its natural, lubricating properties. It creates lasting, yet flexible joints—which is why many antiques are still repaired with hide glue. Using this adhesive preserves the quality of antiques and honors traditional craftsmanship.
In liquid form, hide glue gives you more time to perfectly fit two pieces of wood. When fully set and dried, it is an excellent choice for furniture construction and other tight, lasting bonds. Both types of hide glue are often used in guitar and stringed instrument construction. Best of all, it won’t harm your wood’s finish.
Unlike the liquid texture of other wood glues, epoxies thicken to a putty-like consistency. This wood glue is a two-part formula, consisting of a resin and a hardener that interact right at the time of application. Once cured, epoxy’s durability and waterproofness make it favored by woodworking experts. For example, epoxies are often the go-to wood glues for joining wood in boats and sailing vessels.
Epoxy glue works best with clean, dry, and sanded surfaces. First, wipe your wood with an appropriate cleaner to remove any dust, waxy build-up, or other residues. Next, gently buff the surfaces with paper towels and air-dry fully. Finally, make sure your wood is sanded and ready to join. Then you can mix your two-part epoxy and apply according to package directions. Have a wood clamp handy if you are joining two surfaces. While epoxies are considered non-toxic, they are irritants and can cause rashes and burns. Wear gloves and keep your hands away from your face and eyes.
