Too fast?

I just did it again - mixed up about an ounce of 30 minute epoxy-- equal parts. And BAM - in abuout 5 minutes it started to set.
I very nearly lost major parts of a 1/4 scale extral.

The first time it happened with Hangar 9 epoxy, I though I might have a bad batch. -- Called 'em they said it couldn't happen - must have mixed it too much. (the label says mix well).

This batch was from Tower Hobbies. Same problem.

The room temperature was 70.

The slower epoxy cures, the stronger it is. Will these two parts come apart?

How can I slow down 30 minuted epoxy enuff to have 30 minutes to get it right.

Less hardner?

Put it in the fridge prior to mixing?

Thanks for your help