Guessing we are talking EC. Epoxy - if so I use the same resin and suffered the same problem in cooler weather, especially with their slow setting catalyst mix.
I called Easy Composites and was told it's Anhydrous (absorbs water) while setting?, which seemed really odd to me !
and to leave my model next to a hot radiator to warm it up.
Tried this with little change after 3-4 days, still tacky, spoke to a pal with knowledge of the moulding industry, here parts are autoclaved to high temperatures, I spent an afternoon blasting the model with a hair dryer to get the surface very hot and this eventually sets it off - it seems to go almost glossy when cooked.
Last week I skinned another model with EC. slow set and used the hair dryer straight away, spent the evening heating up it up eventually it cured to a hard gloss.
Seems a great shame this happens, I like the 90 minutes working time allowing plenty of time to skin a hull in one session,
but clearly something needs addressing by the manufactures, hair dryer to the rescue - it can take hours of on and off heating,
but does eventually go off. regards Paul