Epoxy: Still Gluing Strong After All These Years

Containers of Epoxy.

Before dazzling rivers and bar-top coatings, epoxy simply served as a humble, high-performance adhesive and repair resin. Epoxy manufacturers catered primarily to boat builders, providing a product that withstands the harsh conditions of a marine environment. You’ve seen epoxy at center stage; now learn how this versatile adhesive can play an important supporting role in your woodworking.

Good bonding moments

Epoxy bonds to a wide range of surfaces, making it the adhesive of choice for joining dissimilar materials. And cured epoxy forms a waterproof bond, so it’s also a good option for outdoor projects, especially those consistently exposed to moisture. Because it requires a surface with “tooth” for bonding, when gluing plastic, metal, or other smooth, non-porous materials, scuff up the glue surface for best adhesion [Photo below].

Showing a coarse sandpaper with screw.
Use a coarse- to medium-grit sandpaper to scuff up smooth or polished parts, providing a better bonding surface for the epoxy.

Choose your cure speed

Epoxy consists of two parts: a liquid resin, and a hardener that must be mixed in a precise ratio. Hardeners, available in fast and slow offerings, give you open times ranging from 10 minutes to 60 minutes or more.

If you need only small quantities, squeeze bottles or syringes work well for eyeballing the proper amounts of resin and hardener. But for mixing quantities larger than 12 oz. at a time, some manufacturers sell metered amounts with a single push [Photo below]. Or, in lieu of pumps, use a kitchen scale and measure the parts by weight.

Five different types of epoxy.
From syringes to pumps, you have lots of options for an epoxy-dispensing system. Consider how often you use epoxy in the workshop and how much you mix up at a given time.

The temperature of the work environment can influence your choice of hardener. Epoxy gives off heat as it cures (known as an exothermic reaction), and the ambient temperature either accelerates or slows down the reaction. A fast hardener produces more heat, good for cool ambient temperatures, and a slow hardener gives you more working time in a hot environment. Always refer to the manufacturer’s instructions for the appropriate working temperature range of your epoxy.

Mix it and stick it

It might seem like a small detail, but choose your mixing container carefully. Mixing epoxy in a tall, narrow container reduces surface area, concentrating heat buildup and speeding cure time. The built-up heat can also melt plastic containers, or even combust. A metal tray, or the hollow on the bottom of a soda can make good mixing containers.

Using a paint stick to mix ingredients in a foil dish container.
Mix the resin and hardener thoroughly until no visible streaks remain. For a small amount, a few strips of masking tape directly on your workbench provide a good mixing palette.

After accurately measuring your resin and hardener, mix the two using a disposable spatula [Photo above]. Avoid the temptation to add more or less hardener to adjust your working time, as it decreases bond strength.

Long screw with an acorn nut. Nut has epoxy on it and is being placed into a hole in end of a dowel.
For a small part, such as this acorn nut, use the accompanying bolt as a handle and dip the nut into the epoxy. The bolt also serves as a visual guide that the nut is placed squarely into the workpiece.

Spread epoxy with your spatula, brush it on with a stiff-bristle disposable brush, pour it where you need it, or even dip parts into the mix container [Photo above]. Freshly mixed thin adhesive will flow into cracks and crannies. For jobs requiring a thicker viscosity, let the epoxy set up partially before applying [Photo below].

Using pain brush to spread epoxy on end of board.
For vertical surfaces or areas requiring a more controlled application, use a slower-setting mix and allow it to thicken slightly before applying.

If you drip epoxy where you don’t want it, wipe it off before it cures, using denatured alcohol. Otherwise, wait for the epoxy to fully cure and carefully remove the excess using a scraper, chisel, or sandpaper. Spread leftover epoxy in a thin film so the heat generated dissipates quickly as it cures. Once cured, you can cut, sand, and shape epoxy using the same cutters you use on wood.

Containers of Epoxy.
Read more about

Tip of the Day

Center Counterbores Over Existing Holes Precisely

When I need a counterbored hole, I normally drill the counterbore first, then the hole. But... read more