I have normal cement between the brick tiles in my braai and where the fire was in direct contact it has degraded. Everywhere else it is still fine.
50/50 below the fire imho. Think you might be fine.
You can also mix it with vermiculite/pearlite to make it more heat resistant and lighter.
PS...
Anyone that can make and sell me something like this:
Without the complexity of the lifting mechanism.
Just a simple solid frame and I can lift the bike onto it.
280 Is groot. Dan is daai 'n man size steak daar.
Lyk my die 410a is maar omtrent soortgelyk 250 x 300. Dis so 1/2 tot 3/4 van 'n gewone rooster.
As jy kan weld en nie 'n deksel soek nie kan mens dit seker in 'n 250 x 500 braai verander.
PS Daai silinders is gebou om iets soos 30bar te kan...