Straightening Tilted Slab Floor

Big E

I'm not even sure if this is the right forum, since it's more a masonry-ish question, but here goes.

I am in the process of refinishing my walkout basement, and I have a major "challenge" that I am at a loss as to how to solve. The foundation at one corner of the house has sunken quite a bit, enough that somewhere under the 1st layer of ugly tile, there is a crack in the slab and a noticeable slope to the floor. This, per se, isn't really the big problem. The house is roughly 40 years old, and I have been in the house for just over 5 years, and the foundation movement occurred well before I moved in. It was noted on the home inspection I had done (hard not to notice the slope), and he had concluded (I'm not sure exactly how/why) that it had probably been that way for a long time. Now that I've ripped off the old wall paneling and drop ceiling and am down to the actual block foundation and studs, etc., you can see that when the walkout door was put in - the basement was not originally a walkout, but was made a walkout probably close to 20 years ago - they compensated for this and the basement door is framed in such a way that over the 30" of its width, there is a change in distance to the rafters of close to an inch! The door, however, is perfectly level, so this tells me that the foundation movement happened prior to the installation of the walkout. I have also not noticed any significant new cracks in the drywall/paint upstairs at that corner since I've been there.

On top of the slope from the foundation movement, it also appears that when the house was built they just plain poured the slab off of level.
If I swing the walkout door from closed to fully open, the gap between the bottom of the door and the floor goes from about 1" or more to 0.
It actually will start to bind on the floor when opened near 180 degrees. And the floor keeps going up from there. How on earth do I level it out over such a large area, and with such a dramatic change in height? And then, even if I get that level, I'd have to blend that into the rest of the floor, which is still level and smooth? Wow, this doesn't sound pleasant.

Any advice is appreciated!

PipeGuy

If raising the slab to its original position is something you want to accomplish, search the yellow pages or internet for "mudjacking". This is a process by which grout is forced beneath a slab by use of a pressure pump. Slabs can frequently be raised to their original heights with this process.

TAKE NOTE! The main danger that the mudjacking process poses is to plumbing under the foundation. As the back pressure increases, the foundation begins to raise and the possibility of plumbing lines separating increases. The moment a sewer line breaks, the grout starts entering the line and the cement can set before a plumber can clean it out. Once the grout sets, the plumbing line has to be broken out and replaced.

__________________
Fortunately I keep my feathers numbered for...for just such an emergency. -Foghorn Leghorn

Mike Finley

I guess this depends on how much money you want to light on fire to get the floor acceptable.

First I really am skeptical that the floor was poured out of level. If you have foundation wall movement it is logical to assume the slab floor would not be immune from the same forces at work on the foundation.

The slab has expansion joints right? Is there different levels to these different slabs or is the entire floor slab moved as a unit?

Mud jacking as stated is an option.

Floor leveling is an option.

Another cement pour on top of the slab is an option.

All of these options involve raising the low sections to the level of the high sections so no matter what you do you are going to have to tear out the door and reframe and reset it.

The other option is to jack hammer the existing slab out and start over.

I don't know of any easy or cheap option, other than laying carpet and living with it.

PipeGuy

floor leveling


My favorite

__________________
Fortunately I keep my feathers numbered for...for just such an emergency. -Foghorn Leghorn

Big E

Thanks for the replies.

I'm not certain that the slab has expansion joints. The original layer of tile was the old, thick linoleum-type stuff, similar to what is still used commercially today, and this stuff seems to be stuck pretty well, so I can't see the actual slab for most of the floor. In one area away from where the uneveness is, I am down to the slab, and the area is somewhere around 10x10 w/o any joints (I'll freely admit I don't know how often the expansion joints should be).

The reason I say that I think it wasn't poured level is that, ignoring the part where I know it has cracked/sunken, the rest of the uneven part of the floor is essentially concave. Somewhere along the way it tapers to a nice, flat, even slab. But, there isn't any corresponding convex portion that would occur had it moved/settled/cracked.

I guess just leveling it out is going to be the simplest and least expensive method, I'm just concerned about how much "height" I'm going to lose, since it's a basement and doesn't have 8' ceilings to begin with. I probably need to just take some semi-precise measurements and figure out what makes sense. Any reason I couldn't just jack hammer the corner where it's extra high?

Mike Finley

In regard to jack hammering the high corner - I was under the impression that you were dealing with the opposite, which was a small area of low point, not a small high area. If getting rid of the high point means working with a much smaller area of your floor, by all means work on that portion only.

Expansion joints - should be roughly every 8-15 feet. So if you have a 30 foot wide basement there should be at least one in the middle, or 2 evenly spaced ever 10 feet.

Cheating the level - keep in mind that hardwood floors and tile floors with their visual lines formed by grout and the spaces between the boards will allow the eye to see unlevel floors pretty easily. A carpeted floor will hide a good degree of unlevelness from the naked eye.

So you might want to compromise and fix what you can within a reasonable budget and then cover with carpet to create an acceptable finished appearance.

There are lots of tricks to finishing work and choosing the final finish materials can often dictate how much time, materials and labor have to be expended to allow the choosen finish to appear correct.

An example of this is paint sheen. Choosing a flat sheen in paint can let you get away with poorly finished drywall and textures as opposed to choosing a gloss finish paint, where the surface needs to be prepped perfectly.

The point is that it is always cheaper to choose the finish materials for a project based on the existing conditions rather then the other way around.

jdlong

You don't say how much headroom you actually have but if you have roughly 7 feet at the high point, you might consider building up a wood subfloor with treated tapered joists that are cut to match the contour of the slab starting with 1 1/2" wide at the high point. If you have water seeping through the walls or floor, consider water drainage by cutting weep holes in the joists where the joists meet the slab and find a place for the water to leave via gravity or install a sump. You can install 1 1/2" foam insulation between the joists and cover them with 3/4" OSB. You will loose roughly 2 1/2" of headroom so it's best to jackhamer out the high point and refill. This will make a good base for hardwood or carpet. The advantage is you will have an insulated floor for winter that will stay dry. It sounds like the door is at the low point so you may have to either cut it back or reframe and raise it.

If you plan to tile, your best bet may be pouring a floor leveler compound.