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How do I level a concrete floor? Answered

I removed a wall down the middle of my basement.  It had a concrete footing which came out with the curb when it was removed, but the concrete floor on one side of this area is one inch higher than one the other side.  How do I level this so I can install a floating laminate flooring?


Burf has it correct, gyp-crete is way easier than chipping 50 yr old concrete.   Just cut the bottom edge of your drywall, waterproof/mask it off or learn to repair drywall (a very useful home owner skill!)

An inch is a hell of a lot of screeding isn't it ? 

You need to see where the discrepancy is over a good long length, say 8 feet or so. Are the floors actually flat, or do they slope in some way. Take a look at the laminate you want to use, and see if there is a surface flatness specification.

The discrepancy is over at least an 8-10 foot length.  The rest of the concrete is actually pretty level except for this ledge.  I'm actually using a vinyl plank flooring which is floating (adheres to itself on the edges).  I wondered about breaking out some of the concrete on the high side back aobut 3' from the edge and trying to level it after that?

Yes, but it's not very much thickness of concrete either? You could fill the gap with a lot of things I suppose.


Yes, it was a load bearing wall but I installed a steel beam and support post to take the load according to the engineers specs.


8 years ago

The are two basic ways. The first is to use a flowable concrete mix, sometimes called flow-crete or gyp-crete. These are special mix concretes that when pumped onto an existing floor, the mix flows as a liquid and is self- leveling. It makes a permanet bond to the subfloor and you can apply whatever floor covering to it you choose.
The second way is to build a wooden sub-floor. Lumber is cut lengthwise (called sleepers) so the bottom side is flush to the existing unlevel floor and the top side is level. Basically, a long wedge shape. A plywood or chipboard surface is nailed or screwed to the sleepers and then you can install your flooring on that.

Unfortunately the levelling compound would climb my drywall 1", so maybe not a good option.
And I don't have enough height to do a subfloor since the house is >50 years old.
Any other ideas??


8 years ago

I was a general contractor (and a carpenter before that) for better than 20 years. I have encountered this situation many, many times.  On a concrete floor I nearly always used the flowable concrete.  On a wood floor, it depended on the dead weight I wanted on the existing floor structure.

Hm. My own basement floor is an uneven mess, since it started as a rather lumpy layer of concrete-over-dirt and then suffered some subsidence over the past century. I keep trying to decide whether I really want to know whether there's really anything under the cracked sections... and/or whether the right thing to do is open it up just  enough to pour lots of concrete in to stabilize it and level it out again.

Should ask the contractors next time they're here, I suppose.

I would do a few core tests to see what's under the concrete. If the concrete was poured over plain soil, chances are very good that the only lasting remedy is to replace it completely.
My  guess would be that the existing floor should be broken out and removed. The soil excavated down 8" to 12" and new ABC (aggregate base course, a mixture of crushed stone and coarse sand) fill put in to replace the excavated soil and a wire mesh, reinforced concrete floor poured on the fill.
Short of that, you will probably never get a permanent fix.

Hm. I'm willing to bet that's what I've got, and I see your point re giving it proper support.. Feels like it might be tricky to do that without disturbing the fieldstone foundation., though. Or the lally columns, though one _hopes_ they've got substantial footings under 'em.

I've got a contractor signed up to do some other renovation; may ask for advice on this, since he's shown himself to be relatively handyman-friendly. (One of the alternatives we looked at would have put another column right in the middle of this space, and since neither he nor the engineer seemed particularly bothered by the subsidence I'm assuming it doesn't pose any immediate structural risk. Of course, you know what they say about assUme.)

Remodelers do this all the time.  I design lots of gamerooms that start out as double or triple car garages.  Nice big open room except the floor has a 2-3 inch fall from from to back.

If the concrete is stable enough -

What we do is clean the floor then wash it with muriatic acid.  Block off the low portion then fill it level with "pea" gravel conc. that has an additive like elmers glue.  Not really elmers glue but something like that.  Right now I can't think of the name but the conc. co. will know the name.  Pea gravel is 1/4" or less sized aggregate.

Where the conc. is getting thin at the higher place we block it off where it gets to be 1/2" thick.  Then when the conc has cured, we fill the rest that is 1/2" or less with "water rock putty".  It's very hard, sticks very well and is non shrinking.  Home depot used to carry it.  Might be called "floor fill" or something like that.

When that's dry we put down the floor as chosen by the owner.  No need for wire in the conc. unless the base is unstable.

When pouring the conc. all of the existing wood should be kept out of the pour or changed for treated wood. 

A vapor barrier should go down over the conc. if the new floor is wood or carpet.

If the conc. is not very stable I would pour a 4" layer with wire mesh over the existing conc. instead of removing what is there.  If you remove what is there there is not telling how much you will disturb the walls and outer load bearing foundation.