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

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.

• What is the slope of the floor? Eg: 1/8" over 6' is a lot easier to shim than say, 2" over 4'. See diy.stackexchange.com/questions/9297/… for how to do this Commented Oct 4, 2011 at 7:24
• The slope along the length of the basement is not much. Starting six feet from the drain the slope from either side to the center of the floor is 1" over 2'. So that's the worst: 1"/2'. Commented Oct 4, 2011 at 13:49
• Wow - just noticed your answer - 1" over 2' is somewhat steep for a floor. Generally in plumbing you only look for 1/4" over 1'. How about true - how true is your floor? Commented Oct 4, 2011 at 17:40
• How "true"? What do you mean by "true"? Regarding slope, only the last few feet are like extreme like that. Commented Oct 4, 2011 at 21:07
• True = flat and even, where Level = perfectly perpendicular to the pull of gravity and Plum = perfectly parallel to the pull of gravity. Commented Oct 5, 2011 at 16:00

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.

• Funny, I just came back to DIY post a follow-up question in which I was going to ask this exact thing: self leveling concrete + grooves. Please see my question: diy.stackexchange.com/questions/9516/… Commented Oct 14, 2011 at 1:31

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.

• Shims and such may not work under a laminate floor, since laminate (depending on thickness) is fairly flexible. Once the floor was laid over the pebbles/furring strips, it would likely sag between the strips and be wavy. Commented Oct 4, 2011 at 12:21
• @tester101 he's using a sub floor. Granted, I have no idea how stiff that Delta product is, so you may have a point.
– DA01
Commented Oct 4, 2011 at 13:10
• I don't know how stiff that product is either, that's why I added the comment. Commented Oct 4, 2011 at 13:14
• Delta FL is not soft like rubber; it is stiff but flexible. Commented Oct 4, 2011 at 13:25
• sand is heavy and acts like a sponge...so it will only trap any moisture. Plus you'd need a TON of it.
– DA01
Commented Oct 4, 2011 at 13:59

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.

• I like the idea of using DriCore and their specially designed shims, but the OP likely can't use floor leveler or concrete as they want to maintain the slope (under the new floor) for drainage. Commented Oct 4, 2011 at 12:23
• Pre-mixed floor leveling compound is thick enough that it will hold a slope once applied. It is not like self-leveling concrete (which I agree should not be used). It's more like a paste. A thick concrete mix would work too but probably not as well, I agree. Commented Oct 4, 2011 at 12:43
• I already bought the Delta FL and I can't return it. I didn't like DriCore for a number of reasons (price, too thick, squares rather than a whole piece, etc.) Commented Oct 4, 2011 at 13:27
• Point wasn't to sell you on DriCore but to show you how they do it. If you pick up a bunch of composite shims (waterproof) and your subfloor tiles are strong enough to handle being shimmed, that will work. :) Commented Oct 4, 2011 at 13:50