Having had a bit of experience with it, I've learned that you CAN work with epoxy in an unheated shop. All it takes is a bit of experience.

Epoxy, being highly temperature-sensitive, behaves differently as the temperature varies. When it's very warm, epoxy can cure with frightening speed. Too much in your container can become so hot, it will literally begin to bubble and smoke!

In the cold, one effect is that the epoxy becomes thick and therefore hard to mix. To beat this problem, I constructed an epoxy 'oven'. It's just a crude plywood box, lined on the inside with 1" of pink styrofoam obtained from the local home center, and heated with a 25 or 40 watt light bulb in a socket inside. This 'oven' will keep the epoxy at least 20-30 degrees Fahrenheit warmer than the ambient temperature. When I need to mix some up, I remove the containers, meter out the appropriate amount, and return the containers to the oven.

The epoxy 'oven' (click to see a high resolution image)

Cold temperatures inhibit curing, but I've never had an outright 'failure' due to allowing an epoxied joint cure in the cold. It just takes a lot longer, and the epoxy will remain in a 'semi-cured' state for a day or two, or possibly longer. Once the joint has been allowed to warm up for a while, the cure will be complete.

If you need to speed the cure, one solution is to use small heat lamps to direct radiant heat onto the joint or surface. I have a pair of these, and use them often. Another solution is a small electric space heater, positioned so that the warm air will rise up and gently warm the joint or surface to be cured. It is obviously important to insure that neither a heat lamp nor a space heater get too close to a combustible surface, in the interests of fire safety.

Another problem with curing epoxy in cold conditions is the 'amine blush'. When epoxy cures in the cold, the surface will have a greasy film from the amines in the hardener. This film rapidly clogs sandpaper. The solution is really simple, though; if there's any trace of amine blush (i.e., if the cured epoxy surface feels greasy), just wash it with warm water, to which a tiny bit of dishwashing detergent has been added. The amines are water soluble, and will wash away easily.

I've always used West System epoxy. Supposedly, the other manufacturers have epoxy formulations that don't produce an amine blush... but I've never tried them. Regardless, it's an easy problem to solve.

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