Shop Tips » Working With Epoxy and Fiberglass

Epoxy in Cold Weather

In many parts of the country there comes a time in the Fall when there aren't enough layers of neoprene and fleece in the world to make the local waters attractive for boating. At this point we wax our skis and clean up the garage for the next boatbuilding project.

Even in many parts of the South, your basement or garage can get chilly enough to make it hard for glue and paint to cure. Epoxy is especially sensitive to temperature---too hot, and it starts smoking in the mixing cup before you can get it on the boat. Too cold, and it can take the duration of the football playoffs to cure. Indeed, the epoxy on your boat should really be at 70 degrees F or better to permit 24-hour cures.

I can count the number of amateur boatbuilders I know with heated shops on one hand, so providing Winter heat in your workspace is a challenge that has to be confronted. Fortunately, it's a lot easier than sealing the garage door, stapling up insulation, and running another duct from your heating plant.

The Heat Is On

Let's say you're building your boat in a single car garage. In all likelihood, your garage has a concrete floor that retains the cold like the bottom of an icebox. Then there's the usual garage door, with cracks through which the Winter winds whistle menacingly. Now, the first approach to heating this space is what I call the Brute Force Method, which acknowledges the tendency of Americans to confront problems by pouring out gallons of fossil fuels. We speak of the kerosene-fired heater, and we've been guilty of this approach ourselves, when building a Chesapeake 17 in a small garage measuring 16'8" (but that's another story). A single kerosene heater was placed in the corner and set to Full Military Power, where it guzzled kerosene and put out thousands of BTUs. This was enough to heat the space to a sultry 80 degrees even though it was 40 outside and daylight could be seen around the edges of the old garage door. The epoxy cured.

Aside from the need to make almost daily trips to the service station to fill the kerosene tank, this method has some drawbacks. First, although marine epoxies don't give off flammable fumes or vapors, an open flame in the shop can be an invitation for a visit from the local volunteer fire department. Fido, for example, might knock that box of wrapping paper onto the heater. For this reason, I never leave kerosene heaters unattended. During the aforementioned Chesapeake 17 project, we would turn the kerosene heater off at 11at night when we left the shop. The concrete floor in the garage would hold the heat for most of the night, and it wouldn't start getting down into the 40's again until the next morning, when we'd switch the heater back on.

Also keep in mind that kerosene heaters in disrepair, besides being dangerous, can give off soot that settles on your project, creating "fisheyes" in the epoxy. Most kerosene heaters of my acquaintance have been relatively new and have neatly trimmed wicks, so this isn't a problem, but keep it in mind.

Also bear in mind that the fumes given off by paint or varnish, and the solvents used to clean the boat between coats, are quite flammable and the kerosene heater's open flame is a big no-no when these products are in use. You'll want to wait for an Indian Summer day to bring out the solvents.

Resistance Heaters

Electric "space heaters" are inexpensive and easy to use. Plug them in, they start to glow, and soon enough the garage is warmer. Some of them even have fans, which make it easy to direct a stream of heat onto the part of the boat you want to dry overnight. One problem is that electric heaters pull a lot of amps, and if you keep them on all the time you might find yourself upgraded by the electric company to Gold Preferred Customer status along with the guy who out-does everyone in the Christmas light competition. Another problem is that we've almost never seen an electric heater that we trusted enough to leave unattended. If we have to leave one on overnight, our goal is always to ensure that the electric heater can melt into a puddle on the concrete floor without setting anything alight.

Let There Be Light

 So, kerosene and electric heaters have their drawbacks. How do we heat gently and safely? The answer is surprisingly cheap and simple: work lights. A string of work lights (also known as drop lights, and by a few other names) can provide even, controllable heat with little fire risk. We just use 75 watt bulbs. Heat lamp bulbs are a bad idea, as the inexpensive work lamps aren't built for the kind of heat they can generate, and if they get knocked over they can set things on fire very quickly.

Gluing scarfs in your hull panels? You're probably doing it on that cold concrete floor. Clip a pair of lights so that they shine on each scarf. The gentle heat will cure the scarfs in less that 24 hours even if the rest of the garage is 38 degrees. 

Once the boat is assembled, you can string the lights out along its length to speed the cure of a coat of epoxy. It becomes instinct to clip a light next to anything with curing glue, such as a deckbeam or a pair of hatch covers.

If you're having trouble getting epoxy to cure over the entire length of a kayak or small boat, make up a tent using cheap polyethylene plastic. The tent can be simple or elaborate; just make sure the lights under the tent aren't touching the plastic anywhere. With the tent even loosely sealed the boat cures in a gentle heat overnight while the garage drops towards freezing.

And Don't Forget the Glue

Nearly as important as keeping what you're gluing warm is keeping the glue itself warm. Many brands of epoxy can "crystallize" if they get too cold, not a terminal problem but annoying all the same. Cold, viscous epoxy can make the pumps "cough," messing up the vital ratio. And if the resin is warm, it'll go off more quickly when dispensed onto the boat.