Levelling Uneven Cement Floor

How easy are self-leveling cement compounds to use?
September 24, 2009 11:00 AM   

Q: How easy are self-leveling cement compounds to use?

In remodeling our basement, we have decided to put in some engineered hardwood floors. I have removed a couple of walls, all of the carpet and pad, and scraped the glue residue off of the concrete slab. The installation instructions say the floor must be flat to within 3/16 of an inch over 8 feet. Our floor is not this level, with some areas dipping down by about 3/8 of an inch.

The suggestion to me has been to use some "self-leveling" compound on the slab, to even things out enough for the floors to be installed. I have a feeling this is going to be one of those things which sounds easier than it actually is. I have been told to either pour the leveler into the low spots and use a level to even it out into a thin layer, and then the compound will even itself out. Another person told me to do the whole room, starting furthest away from the doorway, and ending at the door, so that I can just walk out and leave it to dry.

Should I just be filling in the lower dips (assuming that evens it out enough), or do I need to do the entire floor? I would prefer to not do the entire thing, but if that is required for some reason than I will just bite the bullet and cover the whole floor.

Do I need to worry about preparing or priming the slab ahead of time (some of it is painted currently, and some of it is bare cement), if I am going to not be walking directly on it (I will put down an underlayment/ moisture barrier between the floor and the slab)?

Is this something that I can do myself, or will it require more than one person?

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A.1 I did 20 bags of it in the basement in my old house. It was pretty easy.

What made it easier were a five gallon bucket and a whisk-like thing that attached to my drill. I'd pour the water in the bucket, add the compound, and then use the drill/whisk to mix it up. Then I'd pour it all on the floor, starting at the lowest point. I used a spreader to help it settle but you could probably use a hoe or rake for that.

They make a primer/cleaner thing that you mop onto the floor beforehand. I think this helps the cement adhere to the floor. You're also supposed to clean the floor really well.

I did this to level the floor before putting a plywood subfloor and carpet on top.

If I were you I would just pour it into the low spots. It should make it level enough.

It was hard physically, in that I had to lift and mix a lot of cement, but it was easy in terms of skill required and difficult to really screw up.
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A.2 I'd just like to echo what bondcliff said, self leveling cement is basically just a more water-y mix that will find the low points and harden. I definitely recommend the 5 gallon bucket + stirring drill attachment. Also, use your level to go see for yourself the general slopes of the basement to find the spots that are most needed to be filled.
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A.3 I've only used a bit of it, to level a bathroom floor for tiling. It behaves more like pancake batter than water - it doesn't flow perfectly level by itself. Getting it reasonably flat over a large area could be challenging. I would opt to fill in low areas rather than flooding the whole basement.

Tangentially, is your basement dry enough for wood flooring?
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A.3 We haven't had any moisture issues in the basement, and we are using an engineered wood flooring with moisture barrier, which is what I have been told is the only way to do it without problems later on.
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A.4 I leveled the floor in my bathroom using LevelQuick (I think?) from Home Depot. I used one bag the first time out and probably mixed it a little on the stiff side and it didn't flow everywhere I wanted. The second time I mixed it looser, used three bags for better coverage and it did the job.

One way to tell where it's going to go is to pour a bucket of water on the floor. Draw circles around where the water puddles and that's about where your levelling cement is going to go.
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A.5 Nth'ing the recommendation to use a 5 gal bucket and a drill stirrer. At the watery consistency needed to be self-leveling, the coarser particles will come out of suspension if you leave it too long. You need to get it on the floor right after mixing it.

If you're only dealing with one part of the floor that dips, you are better off covering that part of it and smoothing out the edge with a trowel, so there isn't a lip. If the whole floor is uneven, I would recommend just covering the entire floor. I've tried the alternative with a really bad subfloor, which just led to doing the whole floor later anyway.

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A.6 One way to avoid the levelling and a recommended way of doing it these days (that I found out about just after we did our basement floor) is to lay down thin sheets of pink foam insulation, tuck tape the joints and then lay 4X8 plywood over that and secure it all with concrete screws. The insulation keeps the floor from being cold in the winter and reduces the tendancy of a cool floor to sweat in humid weather.
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A.7 Adding plywood isn't going to work for us, plus we already have an underlayment with built in insulation and moisture barrier, so right now I just need to get the slab flat enough for the new flooring to not start to squeak and fall apart after 6 months.
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A.8 Get some golf shoes with spikes for walking around in the gypsum puddles.
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A.9 Oh right, use a 1/2" drill minimum. I burned out my brother's 3/8" drill trying to mix with the paddle mixer.

Also, I haven't tried it, but supposedly asphalt roofing shingles make good levelling shims.

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Materials needed:

· Latex bonding agent
· Self-leveling compound
· Water
· Sand
· Cement

Here's what to do:

1. Fill any cracks with epoxy. Widen any small cracks, if necessary. Clean the concrete floor as thoroughly as possible with detergent, removing any grease or oil [source: edisoncoatings]. The floor must be dry and free of dust before proceeding.

2. Apply latex bonding compound over all the concrete when the floor is absolutely dry. (This will enable the self-leveling compound to adhere properly.) Use a cheap paint brush to get into the corners and edges. You can use a regular mop to spread the bonding compound over the rest of the floor. Allow the latex bonding compound to dry.

3. Mix the self-leveling compound with water, according to the manufacturer's instructions. It needs to be quite smooth, so mix it thoroughly in a bucket.

4. Pour the self-leveling compound immediately, because it can dry very quickly. Start at one corner of the floor, and pour the self-leveling compound mixture over the whole concrete floor. Be sure to start in the corner furthest away from the door so that you don't get boxed in!

5. Smooth out any irregularities you see with a long-handled garden rake, which will give you a long reach.

6. Allow the floor to dry for several day