Epoxy & Fibreglass in Winter

It's still winter up here in the great frozen wilds of Ontario. That doesn't mean that boatbuilding has to come to a complete stop. We can, with a few tricks, turn ice-cold epoxy into something usable.

Step one is simply to get the stuff warm enough to flow. We're using Tri-Tex for this boat; the hardener stays nice and fluid down to -10°C or so, but the resin is hopelessly viscous below about +7° to +10°C. That's easy enough to solve with a little walled platform, holding the epoxy cans right at the outlet vent of a portable heater. (We're using a cool-touch infrared heater here, with no exposed hot parts; I'd be a bit nervous about doing this with the cheap nichrome-wire space heater.)

The mixed epoxy's fairly easy to spread, but cools before it can soak into the tape.

Our solution is to wet out the fibreglass tape on a flat cardboard sheet, which results in a film of gelatinous epoxy on top of a piece of tape whose back is still dry. We'll press this tape into place, wet side down, on the joint. Then we break out the heat gun (basically an industrial-style 1.5 kW hair dryer).

A few seconds with the heat gun warms up the glass, which then warms up the resin in contact with it. The heat causes the viscosity of the epoxy to plummet, and it is quickly wicked up by the glass.

A little bit of pressure helps to speed the process along. Because the wetting-out is happening from the bottom up, air bubbles are few and far between.

Once we've worked out the air bubbles, the filleted seam can be left to cool. Within a few minutes, the viscosity is once again too high for the resin to flow, and while the joint does not yet have any strength, the tape won't move under its own weight.

The epoxy curing reaction slows dramatically as the temperature falls. In summer, I'm comfortable applying load to the Tri-Tex epoxy after 24 hours, but at this time of year, I wait at least three days before moving the completed parts.

This technique isn't much good below -5° to -10°C. If it really is cold, the epoxy just won't cure; the reaction will simply come to a halt until things warm up again, and there isn't much good data on the cured properties of room-temperature epoxies mixed at such cold temperatures. (Chilling to stop the reaction, by the way, is the idea behind factory-prepared prepreg materials. Keep 'em frozen, lay up the part with the temperature in the teens, then bake it when you're satisifed that all the fabrics are where they should be.) For March, April, November & December, though, a resin warming station and a heat gun are just the ticket to get a bit of boat work done up here in the Great White North.



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