We recently purchased a 1940's home. In cleaning the fireplace thoroughly, I discovered the floor of our otherwise real brick fireplace was square terra cotta tiles. These were badly cracked in the firebox and no longer attached to the cement below. Needless to say, we need to replace them. The issue for us is that in order to have them be the same height as the hearth, we only have 3/4" of an inch depth. So far, I have been unable to find fire bricks in this depth. Is there something this depth that would work for us? Are thin bricks okay to use in the firebox if there is cement below?