How do I level a basement floor but not the slab underneath?

Question

I'd like to install laminate floor on top of Delta FL in my basement.

The basement slab is not level, it slopes (from all directions) towards a floor drain (that, via a pipe, leads to a sump pump) near the exterior door. I wouldn't like to level the slab, because drainage is a good thing.

How do I level my floor. And should I? I think I should, because otherwise the laminate won't be stable.

I came up with two ideas:

1) Somehow level below the Delta FL layer, for example with some sort of small pebbles (allowing water to go through them but large enough not to go in the drain). Or other material, I'm open to ideas!

2) Level above Delta FL but below the laminate by using dry sand.

Edit: My basemen is dry, but since I have a drain and a slope why would I give that up? Turns out that using sand, while uncommon, is something people do (google it!) and the only downside I read was that the sand can move over time unless you somehow contain it.

Answer 1

I can't imagine the sand idea working. I'd probably scratch that one off the list.

Is the basement dry? If you feel that you still need a sloped floor to deal with water issues, I think you want to tackle those first before thinking about finishing the floor.

Otherwise, your shimming idea makes the most sense. I don't think pebbles will work but some form of furring strips may work. Get treated 2x2s or 2x4s and scribe them to match the slope. Then cut them and affix them to the slab (adhesive may be enough...otherwise you can nail them with a power-actuated hammer).

You could apply the shims radially from the drain to accomodate any eventual water flowing to the drain.

For what it's worth, we have an old house and when we finished the basement I decide to be lazy and we stained the concrete floor. If you like the look, it's easy, cheap, and never any fear of a water-damaged carpet or subfloor.

While the floor can be a tad cool in the winter, once the space is heated it's quite comfortable--especially if you put a rug down.

Answer 2

If you look at comparable products like DriCore, they sell leveling kits (aka - shims) specifically for use with their product in uneven spots in your concrete - basically they're extra heavy duty shims designed to go under the subfloor.

However, if your uneven spots are particularly large, you will need to build those areas up to be true (if not level) and for that you can use a light weight concrete or even a pre-mixed floor leveling compound like you can find in the tile area at Lowe's or Home Depot.

Answer 3

The floor does not have to be perfectly level. Just flat enough so the flooring lays flat. I use a 4' level or 2x4 and check the area. You dont want the level to teader or have a gap under it more than 1/4"-3/8". Small trouble areas you can fix with doubling up on the underlayment.

If you need to level the floor more use floor leveler let it set up then drag drainage grooves towards the drain. Using a screwdriver will be the best width. Thicker would be better but it will mess up the surrounding concrete. You will want to remove the old floor drain set it at the height you want the new concrete to be. Once the concrete sets up you can drill or cut some notches where you put the drain grooves. Doing it any other way may cause you to fill your drain with concrete.

You can also cut drainage grooves once the concrete has dried. I would use a circular saw or grinder with a mason blade. But this will not leave a thick groove and trying to make it wider would be time consuming. If you were to do this i would would suggest cutting 2 lines about 1/2- 1" apart. then take a chisel and break out the area in between.

Answer 4

I would use underfloor leveling blocks. Readily available, they are screw adjustable designed to carry a joist and relatively inexpensive. You would lose some head space maybe 5" if you used 2x4 pressure treated for the joist and spaced the leveler every 4ft. It is time consuming fastening to concrete and adjusting. The benefit is I like the small air space if there ever was a water problem.