Sinking masonry in fireplace floor

[Crobran]

Our house was built in 1975. The large brick fireplace is one of our favorite features of the house. Unfortunately, some of the masonry in the floor is sagging. Some of the bricks in the back wall also seem to be shifting either in or out. Our house is a single story on a concrete foundation, with no basement. I have no idea what kind of structure is under the fireplace and hearth. Can anyone shed some light on what might be going on and how it can be repaired?



You can see some bricks on the left wall of the fireplace have masonry breaking loose around them. The top one is loose and I think I could probably pull it out. You can also see that some of the bricks on the back wall, especially toward the bottom right, are not all flush with each other.


Here's a closeup of one of the sagging bricks, with a quarter for reference. There is some masonry inside the front left corner of that particular brick. A previous owner apparently tried to do some kind of patching.

 

[bholler]

The bricks need pulled up and you need to see what is under them. It is possible only a few bricks need pulled and some cement put under them. It is also possible the whole firebox needs relaid. Further investigation is needed

 

[Crobran]

Do you have any idea what the structure might be like, given when it was built? Specifically, I’m wondering if the fireplace and hearth could be sitting on wood framing that is rotting and that’s what’s causing the sagging, or if it’s more likely to be concrete under the firebox and hearth. Also, is the fireplace most likely a metal box lined with masonry? Thanks for your input.

 

[bholler]

Do you have any idea what the structure might be like, given when it was built? Specifically, I’m wondering if the fireplace and hearth could be sitting on wood framing that is rotting and that’s what’s causing the sagging, or if it’s more likely to be concrete under the firebox and hearth. Also, is the fireplace most likely a metal box lined with masonry? Thanks for your input.

It should absolutely not be on wood. That would not be good structurally of from a safety standpoint. It should be on masonry

 

[begreen]

Is the house built on a cement slab or cement foundation walls with a crawlspace. If the former, it could be they did not properly reinforce the slab with rebar. If the latter, can you go in the crawlspace with a camera and take some pics of the underside of the hearth and fireplace foundation?

 

[Crobran]

Is the house built on a cement slab or cement foundation walls with a crawlspace. If the former, it could be they did not properly reinforce the slab with rebar. If the latter, can you go in the crawlspace with a camera and take some pics of the underside of the hearth and fireplace foundation?

It's a cement slab - no crawlspaces. I dug some of the loose bricks out and what I found seems alarming, but maybe it's totally normal. Removing a (loose) brick from the side wall, I found what seems to be a random pile of bricks behind it. There are bits of mortar which seem molded to the random configuration, which suggests that they were this way when the fireplace was built, and that they weren't in some other arrangement but then fell apart. The bricks don't seem loose though I didn't try very hard to move them.



Removing some bricks from the floor uncovers something that looks more like mortar than concrete, and as you can see, it seems to have sagged below where I had sagging bricks in the fireplace floor. What I don't understand is how solid concrete could have sagged like this, as there are no corresponding cracks in our walls to suggest that the foundation is sinking. Unless my fireplace was built on top of some kind of frame with hollow space inside of it, what is the cement sinking into?

 

[Crobran]

More updates: I removed a few more bricks from the floor of my fireplace to get a better look at the concrete like material beneath it. Since it was cracked, I removed a piece and discovered that it is only about an inch thick. Beneath that seems to be more randomly piled chunks of concrete or brick and sand. Is this normal?

 

[bholler]

More updates: I removed a few more bricks from the floor of my fireplace to get a better look at the concrete like material beneath it. Since it was cracked, I removed a piece and discovered that it is only about an inch thick. Beneath that seems to be more randomly piled chunks of concrete or brick and sand. Is this normal?
View attachment 246136

No it should be a slab

 

[xman23]

It looks like the the base was dirt filled. And now has compacted. The floor is hanging in the air, held up only by the brick next to it. Hopefully the fireplace perimeter is masonry and solid. If it is I would pull the floor out and remove as much dirt as possible, and refill with concrete. Then lay a new fire brick floor.

 

[begreen]

I would probe a bit beyond just the floor of the fireplace. If the structure of the chimney doesn't have a proper foundation this could be a can-o-worms.

 

[Abekech]

It's a cement slab - no crawlspaces. I dug some of the loose bricks out and what I found seems alarming, but maybe it's totally normal. Removing a (loose) brick from the side wall, I found what seems to be a random pile of bricks behind it. There are bits of mortar which seem molded to the random configuration, which suggests that they were this way when the fireplace was built, and that they weren't in some other arrangement but then fell apart. The bricks don't seem loose though I didn't try very hard to move them.

Back in the 70's we would use a piece of decking meaning subflooring to hold the concrete until it cured but other then the reinforcing mesh that was it. Practice was still preformed into the 90's. We never went back and stripped the ply off the bottom.
If your dropping heavy logs down yearly its possibly been broken down. Especially if a previous owner liked to split his kindle there..

 

[bholler]

Back in the 70's we would use a piece of decking meaning subflooring to hold the concrete until it cured but other then the reinforcing mesh that was it. Practice was still preformed into the 90's. We never went back and stripped the ply off the bottom.
If your dropping heavy logs down yearly its possibly been broken down. Especially if a previous owner liked to split his kindle there..

The hearth floor slab should be thick enough to handle any ammout of firewood being thrown in. That will break down the firebrick over time but shouldnt effect the slab.

And yes i know masons rarely remove the wood forms. And it is a real pita for us to do it after the fact to bring it up to code.

 

[bholler]

This fireplace clearly does not have a proper slab under the hearth. The floor will need pulled up and a slab poured. Hoefully the rest of the box can be saved

 

[PaulOinMA]

Looks similar to our brick front steps in the house we are in now. House was built in 1990 and we are third owner in 2003.

Some bricks were previously replaces, and I replaced some when we moved in. Finally called the company that I saw did some really nice stone work in the neighborhood. They ripped out the entire front steps and replaced them.

He writes stonework articles for Fine Homebuilding magazine.

(broken link removed)

He said that my front steps were of the type where the builder told the person, "here's your budget for the front steps. Put something in."

 

[Ctwoodtick]

This fireplace clearly does not have a proper slab under the hearth. The floor will need pulled up and a slab poured. Hoefully the rest of the box can be saved

I had my chimney sweep remove the plywood from bottom of our hearth extension. I can attest that it was difficult for it to be removed and of course cost me in labor fee. Lack of concern to code really stinks.