How flat is a granite worktop?

[Tenson]

Update!

I got 30mm thick quartz, 1m x 0.6m and 2m x 0.6m

I created a steel support frame with screws around the top that I can adjust to support the quartz nicely.



I got myself a nice straight edge and I'm glad I did!

So far I only mounted the 1m piece, but the results are that it is pretty flat on the longer axis but cupped on the shorter axis. Damn, it's almost 1mm!

I expect it was flat when created as it comes in a far larger sheet, but I'm not sure if this cupping is due to storage or internal stress released when cut. Being cast, I expect the former.





Now I'm wondering how much I can help the situation by supporting it only at the middle points and clamping down on the outside edges. It has helped flatten it while the clamps are there.

I know quartz can sag if not well supported, but I don't know how long this might take?? Days, months? Any ideas?