You need to do a calcium chloride test. And check for flatness. No humps or bird baths.

I guess I will do the test, but I'm still wondering what would happen if I put down the heavy plastic. How would it fail? (just curious...)

Problem with the plastic alone is the seams. You wont have one solid piece. Unless its a small room. You can tape the seams all you want but if you have excessive moisture in the slab eventually it will penetrate.

Doing the test will help identify if you have an issue with the slab. Last thing anybody wants to do is spend thousands on a floor and then have to rip it up shortly after. Fyi if your slab does have an issue with moisture no warranty on any product will cover it.

I pulled up the rug and pad. A little moist to the touch. I want to clean the slab and let it dry out. I think it will. Can anyone suggest a way to clean the slab. There is a little bit of latex paint overspray plus some small amount of glue from previously having linoleum. Can I do a light sanding? With a drum sander, or? It's only about 300 square feet, and the layer that I want to remove is very thin. Whatever I decide to apply, I want to put it on a clean surface.

thx,
rob

If the area to be cleaned is only spots and doesnt emcompass the entire floor then id look into a floor scrapper. Its a bit more elbow grease but cheaper.

But renting a drum sander seems over kill. You can rent a floor buffer with a concrete grinding attachment and that will remove glue paint and anything else with better control.

Curious ... wouldn't a product like Red Guard work to seal out the moisture?

Just wanted to report back about cleaning the slab. I tried various methods with little success. Then I rented the diama-brush coating removal tool from home depot. It runs on a standard buffer. It wasn't easy, but all-in-all it worked great. I had a vac connected, but I used a fair amount of water, sprinkling from a drinking water bottle. Every now and then, I would scrape up the "slurry" of glue and mastic and put into a garbage can, put down some fresh water and go over it again. Came out very nice. Worth the 100+ dollars to rent that thing. With the water, there was no issue with dust - that was nice!

If you do it, watch the video on youTube first. The main tip that helped me is that you always want to work into the coating from an uncoated area as much as possible.

What is your next step, gwald? Are you going to use a moisture barrier? Which one?

This is for glue-down, but still relevant:

Here is a link that might be useful: gluing