OT:Gas Open Fires - Reinstating Coal

2.5 inches of air gap (this is a terrible description I know).

Anyway, spoke to vendor, and asked if this would do (was a pain to get it delivered you see), and they were adamant that it would only last 6-12 months and would eventually crack as it wasn't meant to withstand the heat of a coal fire. So vendor took it back and sent the correct "coal one" (vendor paid carriage). The correct one was same size, but was made of 3 pieces of tile instead of one long continuous one and there as no air gap underneath, it was filled in with mortar.

The bit behind your fake gas coals, is that really likely to be suitable for a coal fire ? (ie fireproof brick things and cement) ? Although you might still get away with simply scraping that bit out and putting in the right stuff.

Do you have a local builder who knows about fires who could take a look at it ?

Ours came round, looked up the chimney and said "looks ok". But, we did know the fire had been used in the recent past as a coal fire (it was us that bricked it up).

Cheers.