What thickness of backing plate should I use?

[Scotty_Tradewind]

Yes, good point, about 4 inches diameter and I think about half an inch thick. Maybe best done in stages

I did some glass work a few years ago and left the pot of resin mixture too long in a large quantity. Got extremely hot and hard in seconds,
Possibly consider that you spread mixture out in/on a flat tray/surface so that hexotherm less likely to take place to any extent.

S.

 

[Scotty_Tradewind]

She's a big girl is our Kipper.

A tank, just like my Ambler!