I posted in another thread that I discovered that the construction of my fireplace seems a little odd. The floor had a few bricks that were sinking. Upon removing a couple of them, I discovered that beneath the floor bricks there was a layer of concrete or similar material about an inch thick. It was cracked and sinking in places (obviously) so I removed some chunks of it to find that beneath it was a seemingly random jumble of bricks and chunks of rock, with sand in between them. Some bricks in the inside wall of my fireplace were a little loose so I removed one of them and found the same thing: a random pile of bricks in the space between the interior and exterior walls of the fireplace. My most recent discovery is that the hearth on the left side of my fireplace wobbles a bit. Obviously, I need to do some work and so I have some questions, but first, here's a picture of my fireplace: The hearth is about a foot high. The wall to the left of the fireplace is an exterior wall, with brick on the outside. The wall to the right is an interior wall. Our house sits on a concrete foundation, and it was built in 1975. I should also mention that I see no signs of the foundation shifting - no cracks in any walls, and the door immediately on the other side of the wall to the right if the fireplace opens and closes fine. My first thought is to take the floor out of the fireplace and try to investigate the cause of the sinking material beneath the floor. Assuming it's just some kind of expected settling, then I would guess that I should fill the space with a loose concrete. My big question is this: given the year it was built as well as what I've been able to discover so far, what do you think I'm likely to find regarding the construction of the fireplace as I remove more flooring bricks? Specifically, I'm wondering where the structural support for the interior walls of the fireplace is likely to be. For clarity, when I refer to the interior walls of the fireplace, I mean the black-bricked part of the fireplace. From what I can tell, the interior walls of the fireplace do not continue down to the foundation of the house. It seems that the interior walls sit on the floor of the fireplace. I need to remove and rebuild the structure below the floor bricks, but I'm concerned that if the interior walls sit on the fireplace floor, then as I remove more of the floor, the whole interior of the fireplace may come caving in. Second, is there a way that I can put some kind of support beneath the interior walls as I fix the problem with the floor? Third, given that the fireplace shares part of an exterior wall (exterior of the house) which is also brick, how likely is it that the brick of the exterior part of the fireplace on the inside of the house is connected to the exterior brick wall of the house? Fourth, is the fact that the space behind the interior walls is filled with a random pile of bricks a cause for concern? Was that a common practice at one time? Is there anything I can or should do to fill in the gaps? The bricks behind the walls don't move, by the way. There seems to also be random blobs of mortar which are holding them in place. Thanks for reading through this rather long post, and thanks for any advice you can offer!