I have an existing fireplace (insert) w/ a brick chimney. It is fairly old, but in decent shape except for the back wall of the insert itself. It appears to be nothing more than concrete or mortar of some type over top of the back metal wall of the fireplace. It is cracked and has several plugs taken out of it. My question is this: Is it safe to use? And if not, can I chip all of it out and replace it with fire bricks. And if I do, what kind of mortar mix or mastic should I adhere it with? Any and all help is appreciated. DT

I have an existing fireplace (insert) w/ a brick chimney. It is fairly old, but in decent shape except for the back wall of the insert itself. It appears to be nothing more than concrete or mortar of some type over top of the back metal wall of the fireplace. It is cracked and has several plugs taken out of it. My question is this: Is it safe to use? And if not, can I chip all of it out and replace it with fire bricks. And if I do, what kind of mortar mix or mastic should I adhere it with? Any and all help is appreciated. DT
The integrity of your fireplace is very compromised. Go to a local fireplace dealer where they should be able to fix you up with the appropriate filler material such as pyro-seal.