Insulating so my granite slab does not crack/explode

[RoscoeWilson]

Hello. This isn't a question about a pizza oven, but about a grill. This seems like exactly the right place to ask it, though.

I purchased a grill. It looks like this:




It doesn't come with a bottom - they tell you to line the bottom with fire bricks, which I will do, but there are no instructions regarding what would make an appropriate table / counter / base.

So ... I have a big 2" thick granite slab that I want to use as a kind of tabletop for the grill to sit on. I was hoping I could place the firebrick pad directly on the granite slab, and build a fire right on that firebrick. But after reading some horror stories about how granite will crack or even explode when exposed to high heat, it's become clear that I need some insulation between firebrick and granite. Perhaps quite a lot.

(Unlike with a pizza oven, I don't need the fire bricks to retain heat for any reason.)

Is this workable? Could I use the 2" ceramic fiber boards that Forno Bravo sells, put them between the firebricks and the granite? Or should I completely scrap the granite and come up with a different slab solution?

Any advice is much appreciated.

[MarkJerling]

Welcome Roscoe.
The ceramic fibre boards should work. Note, "should". Granite can handle quite a bit of heat but what it does not like is differences in temperature. So, if I was you I'd double up with the ceramic fibre board and hopefully that will be fine.
We have a granite mantlepiece over our living room fire and it regularly gets to around 80C in the centre, while being cold at the ends. It's still in one piece, so who knows!

[RoscoeWilson]

Hey Mark, thanks so much. Would I need to build a water-tightish wall around the ceramic fiber to encase it? Or can it just sit there with the edges exposed to the elements?

[UtahBeehiver]

CaSi board is very water absorbent and when if gets wet if gets mushy and loses all of the insulation properties. So you need to mitigate water ingress and exposure. Some of the newer CaSi boards are water "resistant" but same precautions apply. FoamGlas is a possible option, it does not absorb water but needs some abrasion protection and notoriously hard to find.

[MarkJerling]

Hey Mark, thanks so much. Would I need to build a water-tightish wall around the ceramic fiber to encase it? Or can it just sit there with the edges exposed to the elements?

Hi Roscoe.
As Russell has said, you need to keep it dry.
Kind regards,
Mark