Fixing very uneven concrete floors in existing houses?

December 15, 2010 12:13 PM

Builders and contractors: is there anything that can be done, after-the-fact, about very uneven, sloped concrete floors?

I'm starting to look at houses, and a number of them have bedrooms or offices on the ground level with very uneven floors, generally sloping severely from one side to the other. Though they have tile or carpet, it is evident that this is laid on top of the poured concrete of the foundation, which is what's actually sloping. Basically, it appears that rooms which would previously have been extra storage beneath the main living space are (sloppily) converted into more living space.

My question is: can anything be done about this, in an existing house, to make the floors approximately level? Assume that knocking out a wall and backing up a cement mixer is not a viable option.

To some people, I'm sure it seems ridiculous to even consider a house with properties like this, but property values are VERY high around here...

posted by rkent to home & garden (17 answers total)

Funny you should ask, I'm installing a new, level, bathroom floor at the moment. I'm doing it the way my father, a building contractor, had me do it in the past.

I've cut 3" by 8' strips of 1/4" plywood, primed and sealed them. Starting at the highest point in the room I lay the strip down square. using a level, I proceed along the strip raising it with wooden shim wedges, or pieces of the 1/4" plywood. I'm moving along at 1 foot increments.

When this strip is in place it will itself be level. Then I snap chalk lines, parallel to that at one foot increments, and I snap chalk lines the other way, to make a grid. I lay down more strips and level them with wedges and shims. I'm nailing to a wood floor, you could put some decking adhesive underneath, and tack the shims under the strips with small nails or brads.

The level strips will come to the door at whatever level they are at, there might be a slight up or down at that point. Now the floor is crossed with strips, one foot apart, and each is level, to itself and it's neighbors. Put down a 3/4 or 1/2 inch sheet of plywood, primed and sealed on both sides, and screw it to the strips. More decking adhesive is applied underneath.

Now you have a level floor. The toilet can be either worked around, by cutting a hole in the plywood where it is, or raising it up by various methods.
posted by StickyCarpet at 12:27 PM on December 15, 2010 [1 favorite]

These people make all sorts of stuff to level and resurface floors.
posted by hortense at 12:27 PM on December 15, 2010 [1 favorite]

For what it's worth...I'm an architect (and former general contractor). There are self-leveling concrete resurfacers available at most home centers. It's a a mix that you add water to and it forms a thin, pourable concrete that levels itself without troweling or additional work. It is meant to do exactly what you are asking.

Different brands feather to different max. and min. thicknesses, so you have to be mindful to get the one that suits the amount of slope you want to correct. You can use it room by room. No concrete truck, although mixing it is like mixing a combination of sacrete and paint. Once you start an area, you have to do the entire zone (a room, for example) because one wet area needs to be poured to merge with the previous wet area.

It works well, is pretty sturdy and pretty fast when you compare it to other possible solutions. It also happens to have a very nice, warm, "leathery" look to it when dry. I have used it as a finished floor on a number of occasions. Seal it, apply several coats of paste wax, and you are finished.
posted by nickjadlowe at 12:33 PM on December 15, 2010 [3 favorites]

Last fall my husband and I had this same problem. We used a self-leveling concrete like nickjadlowe mentions above and it worked like a charm. It was hard work but we saved ourselves thousands dong it ourselves. I think it was $10-15/bag and we used 14 bags for our 12ft x 37ft kitchen/den area. Quotes we had gotten started around $3K and went up to $8K.

We had to make an assembly line b/c the stuff set up very quickly. I mixed it up outside (yay power tools!) and one of our dear, strong friends carried each bucket in the house where my husband was waiting and then he poured it onto the floor. It took a couple hours and made installing new floors a breeze when the time came.

Good luck!
posted by ACN09 at 12:46 PM on December 15, 2010

Are these slab on grade foundations or do these houses have basements?
posted by electroboy at 1:06 PM on December 15, 2010

I am a electrician. I agree with nickjadlowe above, use self-leveling concrete resurfacers - I have seen it done many time, and done it a few times myself on my own rental units. It works well.
posted by Flood at 3:31 PM on December 15, 2010

I think you need to clarify how out of level the slopes are in each room. Or are the floors bumpy with high and low spots in each room. If you have a 4' (or longer) level you can lay it on the floor and lift one end up until you get the bubbles level. Measure how far it is above the floor you will have an idea how far out of level it is within the length of the level. Hopefully it is under 3/4 inch out of level, otherwise you have to get a good amount of self leveling cement. I seen a lot of floor guys use he 'Mapei' brand. It is easier to mix than the concrete and still has high compression strength.

One thing to note is that all building settle.

Good luck.
posted by MiggySawdust at 4:14 PM on December 15, 2010

Thanks for all the answers so far.

Are these slab on grade foundations or do these houses have basements?

Essentially, the houses are set a little bit into a hill; which one is that? It's kind of like a basement toward the front, but then it opens into a backyard.

I think you need to clarify how out of level the slopes are in each room.

Yeah, I think that might be an issue. In one of the rooms in particular, the slope is visually perceptible from the other side of the room, it's not a minor dip or anything. I would estimate the floor at one side is at least 4" higher than the other. Like, it seems like the initial batch of auto-leveling stuff would run out the door before you could add batch #2. Although I don't know exactly how the stuff works.
posted by rkent at 4:46 PM on December 15, 2010

Essentially, the houses are set a little bit into a hill; which one is that? It's kind of like a basement toward the front, but then it opens into a backyard.

This sounds like a walkout basement.
posted by thomas j wise at 4:51 PM on December 15, 2010

I also have a cement basement floor that needs to be surfaced, and I'll probably use that self-leveling stuff mentioned above. It's worth noting that the method I described, with the shimmed wood, results in what's called a "sprung" floor, like the ones used in dance theaters. It's more comfortable to walk on, and if children are playing there, they won't crack their heads open horsing around on it.
posted by StickyCarpet at 5:10 PM on December 15, 2010

Concrete can be ground down or topped off with self-leveling [stuff]. (Forget what it is called.)

But I would be more than slightly worried that the house wasn't settling in a troublesome way. That seems like a pretty big mistake for the builder to have made. (Unless it is sloping toward a drain or something.) I would check the squareness of the room(s). Are the walls all plumb, or do they tilt with the tilt of the floor? (The first case would mean that a more-or-less plumb house was built onto a tilting slab. The second would mean that the house and slab were straight, and it now sliding down the hill.)

(For future viewers: If it is a wood frame floor and it is doing that sloping, you need to contact an engineer asap. They aren't supposed to do that. You could have a poorly engineered structure, or something has spread out that shouldn't, or someone cut something they shouldn't have somewhere along the line.)
posted by gjc at 5:13 PM on December 15, 2010

4" is a lot. I'd start wondering about more serious structural issues. How old is the house?

Concrete is not forgiving, it doesn't bend. There must be some cracks elsewhere, and where there are cracks there's potential for all sorts of trouble. Water leaks being one, but loss of structural support is another.

If I were considering a property such as this I'd get it looked at by a structural engineer, not just the usual 'inspection'. At the very least, talk with other neighbors that have the same model house and see what problems they've had.

There's lots of ways to deal with a bad concrete floor or foundation. I've seen situations where the whole floor was dug out, the foundation shored up and a new floor poured at a lower height (to make more headroom in the space).

But you'd want to address why the floor sloped in the first place. It'd be pointless to spend money trying to fix it only to have it do it again, or get worse.
posted by wkearney99 at 5:17 PM on December 15, 2010

To some people, I'm sure it seems ridiculous to even consider a house with properties like this...

To the contrary, I'd look for those kinds of properties. It's not all that hard to fix (assuming you have enough ceiling height to work under,) and it scares off the other buyers.
posted by StickyCarpet at 5:20 PM on December 15, 2010

But I would be more than slightly worried that the house wasn't settling in a troublesome way.

If the house was indeed shifting, that would be troubling. I'm assuming that it was a somewhat sloppy trowel-job, with the assumption that it would be a storage space or be finished better later. If it was once level, and moved, that would indeed be troubling. And if it moved four inches, there should be a lot of tell-tale cracks and gaps. (Look for fillers and patches.)
posted by StickyCarpet at 5:26 PM on December 15, 2010

Essentially, the houses are set a little bit into a hill...

The ground beneath you is shifting over time. This is normal, many houses do this, some more than others.

This is a structural problem if the shift is rapid or potentially unstable. If "set a little bit into a hill" means "a stunning valley view cantilevered over an eroding escarpment", then you would have a problem.

I wouldn't be in a big rush to knock out any walls.
posted by ovvl at 8:29 PM on December 15, 2010

4" is a lot. I'd start wondering about more serious structural issues.
Unless the house is designed to have a slow grade for drainage and the walkout basement wasn't intended for living space, but was later converted sloppily.

My basement is MUCH taller on the front (street side) than the back (hill/underground side). My closet and rumpus room, however, were built with raised floors, angled to compensate and actually be flat. Without doing that (which loses you lots of headroom and thus wouldn't be to code) or serious excavation, I don't think you've got any quick fix options if that's the situation you're looking at in these houses.

It looks like your Silicon Valley-ish and I'm in SF, so I don't know if that's what you're seeing or not, but just a counter to the "OMFG the house is sinking into the ocean".
posted by Gucky at 10:19 PM on December 15, 2010

You really need to consult a structural engineer before making an offer on a house like this. There's a few possibilities:

1. If they're older houses, the basement may have originally had a dirt floor that had concrete poured over it. This could account for the general unevenness. My current house had a dirt floor basement which wasn't levelled off properly before pouring concrete. This isn't really an issue because, in a house with a traditional foundation, the floor slab isn't structural.

2. The house could be settling, which is ok within certain tolerances, but you should worry about differential settlement, which is where different areas of the structure are settling at different rates. This can have serious structual implications, because most structures aren't designed to resist the forces created during this kind of settlement.

Any idea how old the house is? Are there any surrounding structures like retaining walls? Are there any drainage or erosion issues?

There's certainly ways to mitigate settlement issues, but they can get very expensive, very quickly, to the point where it might erase any of the savings from buying the cheaper house.
posted by electroboy at 8:22 AM on December 16, 2010