Patch

How to patch a concrete slab floor that has cracked and slopes 3" in 10 feet?

The floor floats from the footings and walls, which show no sign of movement, but the slab has cracked across the middle of the room and one half now slopes down with a pitch of about 3" in 10'. This has occurred over a number of years and there has been no sign of worsening in the last couple of years. How do I patch the floor to return it to a level condition? It now has old vinyl or asphalt tile on it, When level, I will refloor it with tile or laminate. Will I have to remove the old tile before patching? Is there some sort of self leveling cement I can use, or something that is strong enough to feather to a fine edge? Of course it worries me that I don't know the cause of the settling, but don't know how to investigate short of taking up the slab. Any ideas or suggestions will be appreciated. Further information on the slab- it was poured in 1945 and the original cracking began about 12 years ago. As I said, It hasn't seemed to worsen in the last 2 years

Public Comments

1. The floor is sinking because the earth and stone beneath the slab were not properly compacted and/or the slab was not poured properly. I presume this is a ground level slab? In your living room or something? The correct way to pour this type of slab is as follows: Let's say the foundation walls (whether cement was poured into a mold or whether it was built up with cement blocks) are 8 inchs deep. The top course of blocks would only be 6 inches deep. The 2 inch difference would be on the inner perimeter of the foundation forming a ledge all around. The gravel that the slab cement is to be poured onto would be brought up to about 2 inches below the ledge I just described. Then, when the cement is poured (usually 4 inches deep), it goes up and over the ledge by about 2 inches. So you wind up with the slab having a kind of rim that sits on the 2 inch ledge to prevent it from dropping in the event the ground below shifts downward. Floating slabs were popular with builders about 20 years ago in an attempt to prevent basement floors from cracking. Cracking tended to occur over time when a slab was poured up against the foundation walls due to settling, water pressure, etc. Floating slabs in my experience are nothing but trouble though. They allow water to creep in as well as bugs, etc. You could pour cement on top of the existing slab BUT since the slab has already moved, it will move again. So your fix will only be temporary. But for the time being, you could try just pouring a new layer of concrete on top. Get the slab down to bare concrete and just use regular portland cement to pour on top of it.
2. I would assume there are a couple issues here. 1. Water infiltration has caused the ground under the concrete to settle. Patching is not a solution 2. Improper gravel base under slab. still patching is no solution Your probably gonna have to either call someone in for an estimate. Estimates are ussually free and you can learn a lot from one. or core a hole near the middle of the depression to see what you find under the concrete. Either way, your probably gonna have to remove all the concrete and correct the problem before you pour more concrete. Adding more concrete will not solve your problem, that is a huge slump.
3. I agree with the answers given, somehow the base material has been removed/moved and is causing a gap under the slab- apparently the slab isnt all that thick either or very little rebar inside it ( if any) - since theres no support for the concrete, its weakening and cracking. Its possible to cut a couple holes into the concrete floor and inspect the damage - it also could be possible to fill in the gap with more concrete, i would consult an engineer tho. Compacting as much of the underlaying base material /adding more and supporting/raising then filling with concrete would permently fix the situation . I imagine the correct way to fix it would be to totally break up the floor and put new base material/concrete in - both options wont be cheep.