Before you decide on the flooring you'll want to do a moisture test. Vinyl floor will not allow any water vapor to escape the slab, so as moisture wicks up through the slab it will become wet below the vinyl. This can lead to mold issues and a breakdown of glues and patching compounds. There are plenty of effective ways to deal with a moisture in a slab, but without a test you won't know which to choose.
Now to the question of leveling the concrete, first step is to map out the slab to determine high and low spots. The easiest way to do this is to set up a rotating laser in the middle of the room, be sure it's sitting level and turn it on projecting a level line around the room (the height you set it at doesn't matter). Next take a straight stick, pole, broom handle, whatever as long as its straight, set it next to the laser and place a mark on it where the laser hits it. Then make your way around the room taking note where the laser is hitting the stick in relation to the first mark. Plot several points around the room (the more the better). Marks above the control line means the floor is low, below means high.
High spot are best ground down, low spots are best filled. Most jobs I've done require both grinding and filling. If you find more low spots than high the more leveler you need, more high then low the less you need. Remember to respect all control and expansion joints, and follow the manufacturer's instructions to the tee to insure a proper job.
Answer from user81381 on Stack ExchangeVideos
Hey I have some quick questions regarding putting in this kind of flooring. So I have a basement that aside from having a concrete floor, is finished. I do want to redo the trim and repaint and such but it's in pretty good shape.
I'd like to turn this into a big playroom for the kids as well as a sewing corner for my wife(her desk and stuff is down there already) and we do have a bunch of pretty decent exercise equipment donated by the previous owner that we may or may not keep. That all is I guess not super relevant but just saying it's a pretty big area total, not sure on the exact square footage but pretty good sized.
My questions are as follows. One, how important is the floor being like exactly level? It seems pretty good but I'm sure there are slight variations throughout and there are very minor bumps and imperfections in places.
Second, I would like for this floor to not be super hard and freezing cold or anything, what would be good to use to prevent this? Do I need a full sub floor material or is that the kind of thing where I can buy the flooring padded enough where this won't be an issue?
Third, there is one small corner of the basement that occasionally gets a very small amount of water in it if it pours. I'm talking seriously a small puddle but it does happen and usually the crappy looking rubber trim in that one spot falls over as well. I think this is because there is a negative grade(may be using that incorrectly) in the front of the house in a flower bed. It slopes towards the house a little bit. I plan on fixing this but not sure exactly how to go about it right now.
Any advice here would be super helpful. Also any estimates on what I can expect price wise per square foot? Thank you!
The back half of our basement is partially underground. When we had the house inspected, our inspector told us it was one of the dryest basements he had seen in a while, yet despite this, the old bag test (placing a grocery bag in the back) did have very small traces of moisture in it if you looked closely.
At the hardware store they told us vinyl with underlayment attached would be good enough but do I need to also buy a vapor barrier? Is that overkill?
We bought a small dehumidifier as well for the back area where it's wetter so hopefully that helps.