Chris wrote:
Are you sure about that? 16-21C? All epoxy would harden in the can.

Epoxy cannot harden if it's not mixed. The resin may crystalize over
time, but it can be "rejuvenated" by heating it until it turns back to a
clear liquid.

Polyester resin WILL eventually cure without being mixed with hardener,
which is actually a catalyst, not a structural/chemical component of the
final product.