has any one used calcium silicate board

[berryst]

looks like chalk, rated to 1100 degrees
Will this hold up under the weight of the oven ...
I was thinking of using it under the firebrick floor for insulation
$4 per sq ft. (2"thick)

berryst

[dmun]

Cal-sil board is the generic name for the super-isol board sold by FB. It's the best under oven insulation.

[dbhansen]

Berryst, lots of people here are using the boards, but there are several types and thicknesses. Do a search here for cal-sil, super-isol, Kaowool, Insblok, and tried-and-true FB Board, to name the most common, and you'll find lots of discussions. I think some people calculated that the oven exerts about 2 psi on the hearth, so that shouldn't be an issue in most cases. Getting them wet is a concern for some (like the kaowool - see this post (Kaowool Refractory Ceramic Fiber Insulating Board)).

[berryst]

I have given up on calcium silicate board. My oven will be underground in the pacific Northwest. Rain is a daily affair all winter. I drove 70 miles and bought perlite. The seller says that the call for perlite is down as consumers are not building fire places. Thanks to all who replied