I agree with Ben, as usual. First, test your slab - put a sheet of plastic over it, at least 3 feet square, taped down to the slab all around - leave for 3 days. If the slab darkens with moisture, or there is any condensation drops on the underside of the plastic, you have a damp slab. If you have visible moisture or moisture discoloration at any time during the course of the seasons with exposed concrete slab, then you have a wet slab. Even just a damp slab can put several quarts of moisture passingfrom the ground through the concrete into the air per day, and a wet basement slab in contact with wster at its base can generate as much as 10 gallons a day of air moisture - which means that pretty much anything placed on it WILL get damp enough to mildew or mold.For a wet slab, a polished concrete or epoxy/polyurea surface is your best bet. Any other surfacing you put over it is likely to mold. Ceramic tile with waterproofing additives in the mortar mix can work if the surface is properly prepared for good bonding, and you use "plastic" thinset and grout rather than cement based grout.
Basically has to be done the same way as for a gymnasium shower floor or pool deck to work right.For a damp slab, assuming it NEVER actually gets wet either from high water table under it in wet season, or from surface flooding from foundation leakage, then you have several options:1) As Ben says, Pergo and others make totally plastic flooring material in a variety of surfaces that can be put down on a smooth slab over a vapor barrier and totally inorganic plastic padding - looks like bubble wrap commonly. Does not guarantee mold will not form between the vapor barrier and the concrete. IF you use a snap flooring version, can be taken up if it gets saturated and dried, then put back in. Not so with glued or nailed versions. Some people also use snap or interlock together rubber or foam flooring over a vapor barrier, particularly in rec rooms, which can be taken up easily in event of flood. 2) A vapor barrier under an inorganic pad as above, overlain with an open-weave backing synthetic fiber (nylon, rayon) carpet with NO natural materials in it, which has lots of breathing space in the weave can work.
I have used open-weave backing short-pile 100% nylon carpet from Armstrong in my basement for about 30 years, with vapor-barrier floor paint but no plastic sheet vapor barrier or padding and never a mildew problem, even though the plastic sheet test did show a minor amount of condensation. The key is a breathable carpet and decent airflow in the basement.3) Any other type of flooring - laminate, vinyl, hardwood, etc will act to xxxx vapor evaporation, so risk mildew/mold under them. You can put down a sealer on the concrete and a vapor barrier and frequently get satisfactory service in a low moisture slab - generally only ones that are at or above surrounding ground level, but you always have the risk of mildew, and if ever flooded are pretty much trash. If you use a sheet product, use plastic, not organic - so vinyl, not linoleum, for instance. I have successfully done asphaltic based vinyl tiles and vinyl sheet using asphalt adhesive - the 1970's method - on damp flooring without trouble, but you have to make sure the concrete is VERY well sealed first with multiple penetrating coats of sealant placed on ground concrete surface so there is open voids for the sealant to penetrate, then let sit a week or more untouched and unwalked on before putting down the asphaltic-bonded tiles or sheet.
The key is to make sure the concrete is less permeable to moisture than the overlying material. If you use a non-asphaltic adhesive (because of smell issues or allergies), then I would recommend full-adhesion waterproof mastic, not spot-adhered or glueless, so there are no air gaps under the sheet to accumualte moisture and mildew.4) Of course, in new construction, if a full edge-bonded heavy duty plastic liner is put in the bedding sand layer UNDER the slab, that can turn a potentially wet or damp situation into a basically dry one, allowing almost any type of flooring to be used, though I NEVER recommend hardwood over below- or on-grade slabs. Of course, in a basement, one should probably assume that at some point it will get at least partially flooded from foundstion leak or pipe failure, so polished or stained or coated concrete, tile, or removeable flooring is the most likely to survive that.5) Another option, in pretty much either case if your ventilation system removes the vapor as fast as the concrete can supply it
, is padless thick open-weave area rug with a "Miller Weave", "Open Back", "Berber" or "Rag Rug" construction - which have lots of air holes in the rug and backing to let the moisture through. Then if getting damp or floods, just roll up and take out to garage and drape over some elevated 2x4's across sawhorses to dry out. Again, start with good concrete sealing first - preferably deep sealant with compatible epoxy surface coat to minimize water transmission.It’s all right to install virtually any type of flooring in your basement. Although hardwood should be avoided, homeowners have a plethora of other choices. Vinyl, ceramic tile, carpeting, linoleum, cork, laminate—all of these materials, and even some less common ones, can be successfully used as basement flooring. If the good news is that you have a wide range of options, the bad news is that basements are the most challenging part of a house in which to install flooring. To complete your project, you may have to overcome an out-of-level subfloor, ceiling height issues, or, most likely of all, problematic moisture.
Moisture and high humidity The vast majority of basements in America are constructed using concrete, one of the most durable materials available to home builders. One of concrete’s few weaknesses, however, is porousness, which means that it allows water vapor to enter the basement through the slab floor and foundation walls. Particularly in older homes, moisture can also enter the basement through cracks in the foundation or at the joint between the foundation and exterior walls. The effect of water or water vapor is to raise the moisture content of flooring materials that are sensitive to humidity—hardwood and fiberboard above all. This moisture can cause wood flooring to swell or buckle over time. Worse, the flooring can develop mold or fungus before starting to rot and deteriorate. How does one keep water vapor at bay? The conventional approach is to install a vapor barrier over the slab. Manufacturers offer a bevy of options, such as roll-down plastic or felt sheets, paint-on coatings, and moisture-inhibiting adhesives.
Different products are appropriate for different flooring materials, so the best vapor barrier for your basement will largely be determined by the type of flooring you are planning to install. An alternate means of managing water vapor is to raise your floor off the slab. The air gap between the installed flooring and foundation slab encourages moisture to dissipate. Various companies sell waterproofing membranes that work on this principle; dimpled plastic matting is a popular design. Also available are basement flooring tiles with a built-in vapor barrier. Topped by decorative vinyl squares or carpeting, these tiles feature molded plastic bases that enable the concrete slab to breathe. Plus, because the tiles are modular and interlocking, they can be removed, washed, and reinstalled after a flood. Despite the best efforts of contractors everywhere, basements still flood and probably always will. If your basement has chronic flooding issues, it’s imperative that you take steps to address them.
That means keeping water away from your foundation through proper site grading and installing a sound drainage system. Consider, in addition, a sump pump (and a back-up sump pump). Finally, be realistic in your choice of basement flooring, as standing water simply dooms some materials to the Dumpster. In short, choose something that can get wet. If your basement is out of level, you can use a self-leveling cement to create an even subfloor. Follow the instructions closely: It is important to prepare the old concrete surface and apply a bonding agent. Basements rarely boast extra headroom, especially if the ceiling accommodates HVAC air ducts. Even if a floor adds just a couple of inches, this slight increase can spell the difference between meeting or falling short of the minimum ceiling height prescribed by your local building codes. Identify a low-profile basement flooring solution, if necessary. As elsewhere in the home, the basement affords homeowners many flooring options.
But if you don’t like to take chances, you can’t go wrong with ceramic tile, the Cadillac of basement flooring. Unaffected by water or water vapor, ceramic tile may be installed directly over a concrete slab, helping to conserve precious inches in a low-ceilinged space. Another great option is glue-down vinyl tiles or planks, which emerge none the worse for wear even after repeated flooding. Bear in mind that this isn’t your parents’ vinyl; today’s products can emulate the look of wood, ceramic, or stone rather convincingly. Engineered wood is yet another option, although you can expect swelling or buckling should the material be submerged. Typically, engineered wood flooring comes in tongue-and-groove planks, the top layer of which is a laminated veneer. Some are glued down, while others “float” unattached to the underlayment. Floating floors offer easy, adhesive-free installation, but note that basement moisture can affect any product that contains fiberboard (for example, engineered cork).