How do I seal around fireplace surround

Hello

I'm in the process of fitting a cast iron fireplace surround and have a question on how do I create a good seal to prevent any smoke entering the room.

You'll see from the pictures the cast iron surround mounts onto the wall but that leaves a void between the wall and the back of the surround which some smoke could enter and then enter the room. How should I seal this to prevent? I've considered just using mortar or potential even using fire rated expandable foam but i'm not sure it would cope with the heat from the fire.

Any advice would be gratefully received.

Thanks in advance!

just cut out the plaster so the edge of the fireplace sits against the bricks. Screw into plugs with washers under the screw heads if required. re plaster around the edge. When a fire is operating correctly, it actually sucks air from the room (and smoke ) so there is not a big problem.
Frank

In my humble option your missing a piece that sits on the top forming the mantle.

Did you buy this off someone?

Graeme

Thanks for your advice Frank. Only challenge I have with bedding it into the wall now is I've already cut the grooves into the hearth so moving the surround back would leave these grooves exposed Any ideas to seal it as is or to you point around the suction is it necessary?

Graeme - you're quite right it is missing the mantel. Just in the process of making this one, then it'll be mounted on the top.

Cheers
Sam

fire proof glass rope, (used to be called asbestos rope) and a tub of fire cement