Yup hardener will do that if you add to much, the excess hardener made the normal warm sensation of an exothermic reaction during curing into a rapid reaction and in turn causes the reaction to heat up violently.
Always be carful with your mix. I’ve seen resins burst into flame during curing when improperly measured.
Clearly this was an accident but you got lucky that you only boiled water off with the heat, if that was left to do it’s thing it would have started smoking and any items it’s attached too may have caught light or melted.
I think this is a good warning to people to just be carful when using resin products especially quick setting resins.
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