Just about to start construction and have a queary on the hearth. I thought about building the stand 5 blocks high and using the top row of blocks as the formwork for the structual and insulating hearth. I would lay 4 courses, put down a fibre cement sheet then put the last course on top. The reo bar would tie it all together and keep it stable. Could i then just use reo mesh in the 2 slabs for strength???