I am been having trouble with epoxy recently (for the last year, actually). I mix the two parts 50/50, and stir it thoroughly. Yet although it says "20 minute cure" on the label, it's been taking more like 20-40 hours
to harden. At least ten just to get to the point where I can touch it without it sticking to my finger! And yes, I know it's winter now and it's cold, that's why I have been bringing my projects inside the house where it's a constant 70-75 degrees F. And it was taking a long time to cure last summer as well.
At first I though I just had a bad batch, but this has been the case for the last three
packages I've had over the last year, which is why I'm thinking it's me.