mrken

I am planning to install laminate flooring in a room the main level of a concrete slab. After peeling off the original carpet, there appears to be a few inches of uneven concrete that runs along the drywall covering the exterior walls (but not the interior walls). (Please see attached photograph.)

There is around an inch or two of blue polystyrene with a plastic moisture barrier between the "outer" concrete and "inner" concrete. The "inner" concrete appears to have been levelled (1/8-inch maximum imperfections), but approximately 1/2 inch lower than the "outer" concrete.

What should I do to raise the "inner" concrete floor to achieve a constant level throughout the room? Would I need to use levelling compound on the few inches of "outer" concrete?

Unrelated to the topic of flooring: Is the protruding "outer" concrete part of the concrete slab foundation?

Thank you in advance!

samfloor

Looks like a converted garage. That outer concrete is footing. It was poured, the walls put up and the floor was poured later. They always pour the footing wider than the wall they are going to build on it. In a garage, it really isn't going to matter. When it's converted to living space, it can be a hassle.

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mrken

Sadly, it is a 2100 square feet home in expensive west-side Vancouver that cannot possibly be a converted garage... I had just bought the home at 15 years old and do not have a history of the builder.

Would using 1/2 inch extruded polystyrene be okay to raise the "inner" level?

nealtw

I have seen this before, actually so this happenin my area last year and I would bet that you are on a hill and part of your foundation is full height front or back. The builder is a jerk. After fixing one screw up with another and then didn't compact the fill so the slab sank right away and he used the foam to fix that screw up. I would l level as best you can and install your floor. If I am right about the high wall I can tell you all the mistakes he made.

mrken

The concrete slab is on a very flat piece of land...

Please share his mistakes regardless.

nealtw

When you say level ground, does that mean you don't have any part of the concrete wall that is full height as in 8 ft.
At minimum he should have put the slab on top of the footing and may have been to cheep to put in the backfill. You can be sure it was level when the slab was pored so it sank before the carpet was put in.

joecaption

What a horrable job they did. Should be ashamed of thereself.
Impossible to tell over the web just what to do on this one.
I think I would start by getting some contact info from my local concrete suppyer on some of there customers that do what's called flat work or finishers. There the people that do nothing but work with things like pads and sidewalks.
They can tell you if the pad sunk, what to do about it, and how they can fix that mess.
It looks to me like someone shorted the load of concrete and ran out before the whole thing got covered.

nealtw

So what have you done with this?