I have a brick-o-lator fireplace with the air passages on the sides that circulate the air around the firebox. There is missing mortar bewteen the firebrick on the floor of the fireplace where the wood would go (for the fire) and I can see through to the structure underneath. it looks like concrete blocks are underneath but it also looks like theres some open areas under there that might go to the air circulating passages for the brick-o-lator (I can smell burnt wood if I sniff the air vents when its being used so Im assuming the smoke is getting in there from the missing mortar) I was thinking of pulling up the brick where the mortar is missing and cleaning it up before reinstalling them. Then I thought about adding a fresh air intake under there. Is that possible or does that need to hapen when the fireplace is build? There is also an ash dump in the back of the fireplace that goes to a passage outside. I'll try and post some pictures if I can. Oh ya, what kind of mortar should I used to put the brick back in.

I have a standard brick fireplace that has a hearth that extends out on to the floor. The layer on the floor is one brick high. I am refacing my firplace in Marble tile and I'm removing the layer on the floor to add a tile layer that is flush with the carpet. I've found that the bricks on the floor appear to be mounted on some sort of morter/concrete slab. I was expecting to find wood under the bricks an I'm not sure how to repair/level this mortar/concrete mixture that's left behind after I've removed the brick(the surface is very jagged and uneven after removing the brick) Any suggestions on how to level/prepare this suface for the tiles? Thank you