i have just been given some insulative firebrick from an old kiln. they are around 100m square and they are not enough of them to make a complete burn chamber so i was wondering about slicing them up and using them to line a red brick burn chamber, keeping the correct dimensions of course. there are a couple of larger ones i was thinking of using for the top of the burn chamber. i know they are soft so could be damaged ,but they were the right price! i am going to use concrete blocks to sit the RHM on so maybe i should use them to protect the concrete?