That's tough to answer. My understanding is that epoxy dries gradually over quite a long time -- days to weeks. However, when the temperature is high (80's+), it can "go off," or harden, quite rapidly. Sometimes in minutes with dramatic heat and melting of associated plastics.

I think it's fine to work with it in the 50's to 70's, especially if you can set up some heat lamps after you spread the epoxy. It should then get tacky or firm to touch in a matter of hours. If the ambient temperature is too cold, the chemical reactions will slow down, but they should pick back up again when the temperature rises.

Start out mixing and spreading small batches and you will soon get a feel for how the stuff responds to the conditions you have.

I think you'll be fine. 

I envy you RJ62, as much because you’re a’building (my Waterlust kit’s still in its shipping box) as because where I am it’s winter too w/outdoor temps anywhere from maybe 40F (seldom now but welcome!) to - 20F for the next three months.

Important points:

- Epoxy components should be stored at 50-70F, or brought up to temp before use. Cold can cause crystallization, which is reversed by warming & stirring before mixing for use;

- Materials being covered/glued together should be at 60-70F so as to avoid pulling heat from applied, mixed epoxy and to keep it more workable during application. Once applied, temps can be allowed to drop while keeping in mind that lower temps mean longer cure times.

- Some brands of epoxy have hardeners that are for use under unusually cold or warm conditions but application temps still affect workability. Supplemental heat (space heater, heat lamp, even standard incandescent lamp in suitable socket placed appropriately) will facilitate proper curing in reasonable time frames.

- The epoxies we commonly use reach 90% of their fully-cured strength in 24-48 hours when hardeners are matched for conditions under which they’re used. Full cure strength often take up to a month unless ambient temps are maintained at 60F or above.

   For specifics, I did most of the epoxy work on my skerry in my unheated garage in Maryland in the winter.  I had a small 1200 W space heater and a halogen work lamp that threw some heat, so I could keep it above 50F except in the cold snaps.  I used the Mas epoxy that came with the kit, with the slow hardener.  It generally took an extra 12-24 hours to get the cure to the point of being sandable beyond what the instructions suggested.  For steps where sanding wasn't needed, I sometimes moved to the next step with it a bit "green".  It never stopped me though.  Once it was to the point of finish sanding, it was early spring, so I could get the garage a bit warmer.  Plus, I wasn't rushing so I gave it a week or so at the end. I never had the Mas fail to cure or kick off prematurely (that's happened to me w/ West Systems before, I think because the ratios were more critical).  And with no blush, cleaning between coats wasn't needed.  

   MAS has a chart of different hardeners and when it cures. It is under the resources tab, Frequently Asked Question. It is the 5th one.

I have been working on a kayak the last month in Indiana. Temps have been getting up to around 40-50. I epoxied what I needed, tented it off and put a small heater in it. No probelms with sanding the next day.

Thanks for that post crpntr133!

I knew of WEST hardeners for different temps but not of MAS’s ‘till I read that. Good to know too the different hardeners can be blended (within brands!) for finicky stuff, likely not something I’d need to mess with often.

Looking at that chart you refer to, I note the absence of info for below 40F; availability of slow/medium/fast extends the working range quite nicely but won’t overcome limitations imposed by physical & chemical conditions for proper curing.

It’s easy enough to provide for supplemental heat as needed as long as one is prepared for the need ahead of time.

Northern California where the temps will be between 70-40 for the next few months. .......you've just described North Florida weather.   Of course we also get some low 30s.    But it will be in the 70s or 80s by noon. 

I place epoxy in the morning when the temps are rising. Then place my quartz flood lights on the stand, a foot or two away, shinning on the area to keep it warmer at night. As long as I keep the area reasonably small and the temps don't fall too fast things have been OK.  Cure time will often take longer in cooler temps.