Originally Posted by seriph1
OOOOOPS!
I made a huge assumption that if you intended placing cement sheet inside the hearth that you would NOT be lighting a fire in it - that it would be for display only, due to other forms of heating being employed. If you intend to have a fire inside it, it is a no-no to have cement sheet. If as has been suggested sensibly, that you wish to put a slow-combustion heater in there, get maker's specs and their data sheet on what's required as a priority! What material will you be laying onto?