[petruscad]

you have re-bar in the casting right?

Right, there is re-bar in it, not a lot that it should bend the whole structure though.

What does a 20 degree rise equate to in linear per inch? remember that for each cross- section of the casting epoxy is spaced apart with rock which has a different expansion rate so the overall change in length should be reduced wouldn't it?

Yes, stone has a much lower expansion coefficient, about half of that of steel so overall the expansion is reduced from that of epoxy. I still feel that EG expands more than steel though. Concrete on the other hand expands at the same rate as steel - one lucky accident of nature!

Expansion of steel is about 1.3 tenth per inch per 20 F. Pure epoxy is 7 tenth and natural granite is 0.9 tenth (1 tenth = 0.0001").

Where in Cali are you? I'm in 1000 oaks

San Francisco Bay area