Possible problem has been noted by George and after Iread his comment, I have noticed it also. Epoxy has what may be termed two curing cycles. The first 'sets' it and, if heated to 100 - 130 F will go through a softening and then hardening stage for the final cure.

I live in Michigan and have been using my workshop in my garage which means I heat it with a woodstove. I had a couple of joints come loose when I got the stove kind of hot which heated the room up pretty good. Once I noticed it when it was warm. The epoxy was soft and before the area was heated it was hard.

this may not be your problem, but it could be.

> Using MAS epoxy

> From time to time I have used some fast hardener for small jobs, cheek
> plates ect. The problem I'm having is the stuff is not getting hard enough
> to sand. I have had no problems with the slow hardener, in fact it is
> sandable before the fast. Also I am using a container graduated in CC's
> for mixing and am mixing for 2-3 min.. so that is probably not the issue.

> Has anyone experienced this problem. Do you think the hardener is bad ?