Thin, Fireproof Board/Insulation/heat shield for fire table?

[bedn0009]

Hi. We have a gas fire pit/table with a 125k BTU burner. The top of the fire table is made of reinforced concrete. It was made by a local guy with a lot of experience making concrete structures, counters, fire pits, etc... But ours cracked... He believes because of the heat (which I don't agree with because the concrete itself stays amazingly cool)

In the attached picture, I was wondering if I could put something around the inside perimeter of the burner recess to further protect the concrete from any heat. It would need to be dark (blend in) and thin (maybe 1/4" or less?) and weatherproof (outdoors)

Any ideas? Some fireproof rigid board? Some pieces of aluminum set in there just as a barrier?

Thanks

 

[Dumber than lumber]

Just spitballing here: That fireplace and chimney mortar? I think someone makes a version that comes in a caulk tube.
Aluminum angle could be mitered, and maybe fastened with a few anchors. My guess is that you will continue to get cracks. Fireboard is a good idea. Glass block of some type?
Stay away from asbestos.

 

[bedn0009]

I wondered about a thick layer of high temp silicone and some aluminum pieces

 

[rlitman]

The crack could be heat related. As the center of the concrete heats first, it expands faster than the perimeter, putting the perimeter in tension, which is why the crack started on the outside edge. The perimeter should have been reinforced to make up for this, but now that's too late.

How high does that fire feature get? A thin stainless "liner" that reflects heat, with a small air gap (could be paper thin) from the concrete would help a lot more than any silicone or mortar that would conduct heat.

 

[bedn0009]

What about some 4" aluminum or stainless angle iron that was kept a few millimeters away from the concrete? It'd stay put because I could rest the burner and fire rocks on it

 

[engineer2]

I agree with a metal liner around the pit with an air gap. Stainless would be better than aluminum, but aluminum is much cheaper and easier to work with. Just make sure no one touches the hot metal.

Once the heat is isolated from the concrete perimeter, you might be able to tile it with stone to make it look pretty. Gray slate would be about the same color, but with texture.

 

[bedn0009]

Thanks as always for the advice from GJ members. Here's what I came up with. I do woodworking, not metal fab, so I'm not set up for metal band or chop saws. This could be cleaner, but all of my rough cuts sit beneath 3 inches of lava rock anyway.

Some quarter inch aluminum angle with 1/8" nomex tape on the back. High temp silicone will seal up any small gaps. Should keep the heat totally away from the concrete.

Thanks