I was going to install a laminate floor over the cement slab in my home but can't get the slab to the required levelness of 1/8 inch ove a 6 foot radius. I tried it and now have hired and paid for 2 contractors who have been unsuccessful with using the self leveler product. Do you have any tips at all? Now I am also concerned about the moisture that the self leveler product is going to add. HELP!!

Self leveling products are too viscous to "self" level to this standard without feathering the edges and is not without other issues when used for this purpose. It is great when filling deep depressions over a larger area.

For this problem, I prefer to use a "flex" tile thinset. This is more workable than a traditional finishing compound and can be screeded using a screeds made for leveling floors for a tile installation. As a matter of fact I believe the standards for installing a marble floor are near the same as those for the laminate floor installs. I learned this method from my brother who was an accomplished tile setter.

Map your floor out. Lay a straight edge over your floor with the length then width and on each diagonal to find you highs and lows. Once you understand how your floor rises and falls. Make you plan. Grind your high spots and then pull thinset over your low spots to fill them with thinset.

Boy, that was an eye-opener. Will give it a try. Thanks so much.

As an amateur... here's what I did in the same situation.

I got the longest straight edge I could find at the hardware store, which at the time was a ~7' level.

On the bare floor, after all the little dots of paint and plaster and mortar were cleaned off, I went around with a sharpie and slid the straight edge across the floor in various patterns (east-west, north-south, sweeping out a circle) and mapped out on the concrete how much space there was between the straight edge and the floor. Everywhere there was a gap, I marked on the concrete at that spot what the gap was.

This gives a rough map of the high and low spots. Then I got the self-leveling cement stuff and mixed it up.

I poured it on the lowest low spots and used the straight edge to skim it flat over as wide an area as was necessary. I just swept the straight edge across it like you're skimming concrete. I had to work the leveling compound at the edges - took some wrist force to mash the product flat as when it starts to cure, it doesn't want to level anymore. After it cured I had to knock down the edges a bit as they tend to dry with a little surface tension to them.

At that point the floor was pretty level, but you can repeat the process as required, and the leveling cement is easy to grind down if it hasn't cured for too long, so if you make a mistake and end up with a hump you can scrape it off without much work.

My advice: make it as level as you possibly can. Don't give up and leave some bad spots - they will come back to haunt you. A perfectly flat subfloor makes for a very nice finished product but if you're like me, a few bad spots can haunt you forever!

I have found that trowelling a filling cement compound for fast cure or more thinset to feather out the edges will create the smooth finish you desire. Thinset is also easily knocked down the day after it is spread.