Flooring and Carpeting/Install floor over basement concrete
We moved into our house this past summer. It was build in 1976. We're in Ohio. The walk-out basement of this bi-level has 1 finished main room. It was pointed out that this room has been "waterproofed" in the past. This is the only room below grade also. It appears that a sump-pump has been recently installed, drainage pipes in front of the garage doors, and there is newer concrete that goes around the boarder of this finished room - like a pipe was installed in the floor. The walls look like drywall but they are vinyl sheets that look like drywall. Lastly, there there was a fan/vent that sucked air out to the outside. Similar to this http://www.wavehomesolutions.com/ventilation/
. The house did not have AC but we installed that ASAP. With AC we were told we didn't need that Vent. We took it out and added a dehumidifier. We removed the carpeting and I replaced it with those foam gym flooring squares that fit together like a puzzle. For months we had plastic laid down on top of this flooring and now we are lifting the plastic up, we are smelling a mildew smell. It was very strong at first. I'm asking if there is something I should have put down under the foam? The old carpet pad had a plastic bottom. Should I have put plastic down first? Or paint/epoxy the floor to seal it? I thought the foam floor would have been enough. Is this just because we had the plastic covering the entire floor for so long? What do you think?
You obviously have a moisture problem, that is why you are smelling the mildew odor and apparently even with all the work that was done to negate it such as the possible drainage pipe installed around the rooms perimeter. I wonder of the outside concrete wall was sealed? This would be visible as a black tar looking substance on the concrete wall below ground level.
Laying down plastic does not allow the concrete floor to breathe, so mo moisture will accumulate underneath. This will be true if you lay plastic directly over the concrete or over the carpet.
A quick test you can do to prove moisture this is to lay a small square plastic sheet down on the concrete, (ex: 2' x 2')or even a plastic or solid rubber floor entry or door mat mat and leave it there for a day or two. If moisture has accumulated then you know you have a moisture problem.
In order to cover the floor with a flooring product you need to find out how much moisture the concrete floor is giving off. We refer to it as vapor emission. One such test is the calcium chloride vapor emissions test. Once you find that out you can determine which type of flooring product you can use on the floor. There are do it yourself kits such as http://www.humboldtmfg.com/vapor_emission_test_kit.html
or you can hire someone to do it. You must do a minimum of 3 tests, one each in a different area. You must do more if you are over a certain amount of square feet (Usually it is 1000 sq ft, but check you directions in your particular kit).
When you have these results then you can research different flooring products and find what their vapor emissions specifications are. If your readings are at or below those then you can install that flooring.
As far as paint/epoxy, I do not deal with that type of product so I cannot answer that question in terms of their effectiveness or restrictions. You may find helpful instructions on their products or at their websites.