The trouble with West Epoxy is that, unless you can accurately proportion the resin and the hardener you invariably have to mix the whole lot and then use it pretty quickly. I also made the mistake of leaving it in the plastic bottle after mixing, not realising that the generated heat was enough to melt it. That was a mess that took some cleaning up.
I tend to use Isopon products now as you can measure out a smaller amount of resin and then add the relevant amount of hardener from the small tube.