We have a fireplace that has what looks like a concrete layer around the walls and on the floor of the fireplace. There are a couple of hairline cracks in the floor of the fireplace which appear to only be in the concrete. What should we use to repair these cracks?

JR

Is this a real fireplace or a prefab?

It is a prefab. The house is about 25 years old.

Probably best just left alone. Its for looks more than anything else. The real thing is the metal liner behind it. You could patch with mortar mix if you would like. If its disintegrating you may be able to replace but be hard to find being that old.