Thanks to both Scustom and routercnc, think you have both nailed it, the combination of waiting for bubbles, and mixing in a tall narrow container allowed the exothermic reaction to spiral out of control.

I've got a new set of Epoxy on order, I've spent the evening clearing off the crap pour and the mountain of silicone, and will try again soon. Thankfully the frame hasn't suffered and can be used again with a fresh set of silicone. Expensive mistake but hey, we all screw stuff up every now and again!

This time, I'm going to make the amount in three mixes rather than 6, and in a wider tub. I'll then transfer to another jug with a taped up hole in the bottom, and immediately pour onto the rails.

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