Am i reading this correctly total epoxy required 600ml ? had a look @ my measuring jug and 150ml is a really insignificant amount. the larger the quantity the bigger the exothermic reaction but i would have thought with the slow setting hardener exotherm would be reduced. i would drop West an email and see if you could do the 600ml in one mix, will make life a lot easier.
Good luck on your next attempt.
Regards
Mike