What's your go-to glue? Know the difference between wood glues.
PVA glue In the woodshop you probably know Polyvinyl Acetate (PVA) by several names: wood glue, PVA glue, white glue, carpenter's glue and many others. Bottom line, PVA glue is used for gluing together porous materials such as wood (cloth and paper, too). This water-based glue literally wets the wood fibers causing them to expand. As the water evaporates, the wood fibers contract and intertwine. The glue’s chemical polymers harden, trapping the boards tightly together.
While dry times for PVA glues vary by brand, as a blanket statement, PVA glues dry quickly. PVA is often dry to the touch in as little as 30 minutes.
PVA glue and cutting boards: Several brands tout FDA approval on their products for indirect food contact (ie, cutting boards), including Elmer’s wood glue, Titebond II and Titebond III. In our shop, we use Titebond III for anything with moisture exposure.
Real-life shop tip: Neither yellow or white PVA glue will accept stain, and any glue that gets into the grain of your boards will likely reveal itself during the finishing process.
Need a longer working time with your adhesive? Keep reading…
Long before epoxy river tables were a thing, epoxy enjoyed a distinguished reputation as an adhesive. Simply put, epoxy was engineered to create a long-lasting, permanent bond. It’s ideal for gluing up wood destined for moist environments or marine activities. It’s even recommended for gluing up teak, whose oily content may disrupt the adhesion of more traditional wood glues.
Epoxy is a two-part product of resin mixed with a hardener. The resulting mixture transforms from a thick liquid, into a putty and eventually a fully cured and hardened material.
The real win with using epoxy in the shop is when we need a longer working time (open time) with our adhesive, such as when laminating strips together to mold into an arch or curve. We can choose an epoxy with a slow hardener (we use West Systems). This gives us the additional minutes needed to finesse the boards into position and still get a permanent bond.
Real-life Shop Tip: Epoxy gives off some serious fumes, so be sure to work in a well-ventilated area.
Epoxy is also known for creating a tough protective coating that dries clear. So, it’s a popular choice for table tops and even charcuterie boards. While some epoxies promote themselves as being food safe, never, cut on an epoxy cutting board. Ingesting epoxy fragments is harmful.
This glue option's existence can be traced as far back as 2000 BC, and it’s still used today for repairing antiques and for building musical instruments—(hot) hide glue.
Also known as protein glue or animal glue, hide glue is formed from animal protein much like gelatin. It is eco-friendly and FDA approved for indirect food contact. You’ll often find hide glue used in the manufacturing of candy boxes and paper towel rolls.
What’s so special about hide glue for woodworking? Even when fully cured, hide glue maintains an elastic quality. This natural flex allows for the expansion and contraction of the wood, without creep. Hide glue can be reactivated with heat and will stick to itself, unlike PVA glues and epoxy, which must be cleaned away before regluing. Hide glue dries strong and clear (though not water resistant).
The challenge that comes with using hot hide glue is that it must be prepared. Granules are mixed with water, left to sit, and then heated to 145° using a double boiler technique. The resulting mixture is similar to a thinned honey. Hide glue has an odor, though it goes away once the glue dries.
One other interesting note about hide glue is that it does not cause the wood fibers to swell, so, it’s great for tightly fitted joints. By comparison, PVA glue will cause wood fibers to swell and joints may become difficult to assemble.
Finally, hide glue is measured in gram strength. The higher the number, the less open time and the stronger the bond. 192 is a good general-purpose strength for many woodworkers.