I have been using the EL2 resin and hardener for a number of yeas now to repair damaged fishing pole sections for myself and also for other team members while we are away at major competitions.  One of the problems when away at International events is the time it takes to effect repairs due to the tacking up and then curing time of the the EL2 resin..

What size batches are you mixing?  ideally it needs to be within 1%.  It could be quite easy to be a few % out.

Adding extra hardener will never work with epoxies as the chemistry is such that there needs to be a precise amount of each part to react with each other.  As such adding extra hardener will make things worse almost gauranteeing a tacky finish.

The rapid repair at a constand 25C should be hard within a couple hours at most. It is possible that your environment is still quite humid and that would effect the cure.  However normally you see excessive humidity as a slight milkyness in the resin.

It is normal for an epoxy to soften on first application of heat. This is because at room temperature it does not fully cure initially so the application of heat softens it.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant