Epoxy for Wood Repair
Learn about the products and their best use, get tips from the experts, and see a DIY project.
Contrary to popular usage, “epoxy” is not one thing, nor is it a verb that means “to glue.” The word refers to a class of synthetic thermosetting polymers used in adhesives, consolidants, plastics, fillers, molding compounds, and coatings. Different formulations make epoxy compounds compatible with wood, glass, stone, concrete, and more. This article is about those epoxy products used to reinforce and fill wood elements.
Epoxies are two-part systems. The product typically comes in cans or tubes labeled as A and B. These are mixed (thoroughly) immediately before application. As thermosetting compounds, they cure through a heat reaction. The epoxies used in rehabilitating wood are made up of a resin and a hardener. When they are mixed together, a chemical reaction changes the resin into a gel and then a solid.
Chemists formulate epoxies with a wide range of pre-cure and post-cure characteristics. The product may be watery to penetrate porous materials, or thick and viscous for use on a vertical surface. The cured epoxy can be hard and brittle or soft and rubbery. Chemists can adjust the rate at which the epoxy cures. Additives may make them more flexible or spreadable. It’s important to use epoxy products specifically formulated for your application.
Epoxy technology
dates to the 1940s; like plywood and Plexiglas, it was an innovation of the war effort. Epoxy was used as an alternative to metal fasteners in the production of aircraft. By the 1960s, strong epoxy adhesives were on hardware-store shelves.
Epoxy: Yes or No?
Epoxies have grown in versatility and thus popularity, but they are not always the right answer. Traditional repair methods (such as a wood dutchman, scarf, or splice) or replacement of a part may be better options. Some architectural conservators believe that epoxies do more harm than good, both because an epoxy repair can backfire if preparation is poor, and because epoxy repairs are virtually irreversible and permanent. Historic windows, for example, typically need maintenance that requires disassembling one or more joints, so you should use epoxy only on non-jointed window elements. (More upcoming in OHJ’s Sept. 2019 issue.) Reversibility is a key preservation tenet, and thus required for some work on landmarked buildings and antiques.
“And you don’t need $150 worth of epoxy when you can splice in a $10 piece of wood,” says conservator Ray Tschoepe. By volume, epoxy fillers are more expensive than most woods, so consider the value of making repairs with epoxy versus new wood. Sure, a repair project can resort to both epoxy use and traditional patching in kind. But a large epoxy repair is unnecessary for a common building component. Spend the money on an item that is difficult or costly to replace, such as a carved column capital.