We bought a reproduction cast-iron fireplace ,one with a tiled insert and a wooden surround along with a slate hearth. I'm now about to fit the fireplace but have a slight concern. There is a recess of approx. 4 cm on the inside of the wooden surround. If I fit both the cast iron insert and the surround flush against the wall I will be left with a gap of 3cm between them as the insert is approx 1cm thick. The 'easy' way around this would be to keep the insert 3cm off the wall. However as we want to use the fire occasionally to burn solid fuel I'd need to seal this space with something but I'm not sure what with? Does anybody have any suggestions?