Hi,

I'm also building outside with a tent and heat lamps (Seattle area so it's not quite as cold, but we did have some pretty cold weather in December). I'd say leave the lights on for an hour or so to get the temperature equalized before you start to epoxy.  I leave the lights on at least overnight after I epoxy.  I asked the people at MAS how low I could go on temperature and they said:  "As far as the temp it will be OK at night, it will just slow down the curing process a little bit during the night and take a  little bit longer.  It can go down to around 30 degrees.  The strength will not change."  I have a thermometer under the tent and try to keep it in the 50-60 degree range overnight and the cures have been fine; usually hard by next morning.  I'm a bit more finicky about really warming up the temperature and then letting it slowly drop when I'm laying glass in an area that will be seen by everyone (e.g., outside of kayak).  

 (Note:  I did get a small space heater for when I'm doing whole boat epoxying and didn't want spot heat in just a few places - it works great, I put it under the tent and turn it on.  Leave it on for an hour or so after I'm done then switch on the lights.  I don't leave it on when I'm not home or overnight.)

Kathy

Thanks Kathy,  I did my fillets yesterday and kept the heat lamps on all day.  They were hard to the touch by night, so I shut off the lamps.  You mentioned this will not effect the strength, however, if I turn the lamps back on, will that again speed up the process or is that a waste of electricity?  Do you know if there is a way to determine if they are cured properly before I cut the stitches?  Thanks in advance for your replies.

Epoxy cure times are a function of temperature.  I'm not an expert, but I believe I read somewhere that it takes 2 week to reach full curing/strength, but after 24 hours you're well on the way there.  I generally would leave my lights on overnight, but I really don't know if it is a waste of energy or not (figured for the relatively small amount of electricity it was worth it if my seams didn't pop open). 

I've found that for epoxy applications requiring strenght (tack welds, using thickened epoxy for glue on the hatch covers, coaming, etc.) 24 hours has been fine for a cure time at cooler temperatures with the slow hardener. 

For epoxy applications where you're not using it as glue (putting down the fiberglass cloth, fill coats) you actually want to re-coat within 8-24 hours so that you don't have to sand, and the epoxy bonds chemically with the coat underneath.  

Hope this helps.

Kathy

Thanks Kathy, I appreciate the feedback. 

Kiz,

This is my first boat build, but I have done quite a bit epoxy work on aircraft...  "my general rule of thumb-nail"  I don't disturb the assembly until the epoxy is hard enough to withstand being dented when I push on it with a fingernail.    I just cut all the stitches off of my Ches 17 after having allowed the "tack-welds" cure to the above spec. (took about 24hrs)  If you don't know what "tack-welds" refers to, do a search on this forum (lots of info about it, they are smaller than full fillets and are placed between the stitches) and the boat didn't spring apart anywhere.