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Concrete flooring is a great choice in homes and commercial buildings because it’s both versatile and durable. But, these floors can be vulnerable to moisture, and that can cause a lot of issues within a building, from excess humidity or mold problems to things like tile lifting from floors or damaged hardwoods and carpets. Laminate floors can suffer delamination, and resinous floor coverings may crack or bubble. All in all, moisture can do a lot of damage—and it’s also something that can be remedied when installing the slab. Read on to learn more!

What Causes Excess Moisture in Concrete Flooring?

There are lots of things that can cause moisture on concrete floors. Leaks are one example, usually stemming from nearby plumbing. When leaks are present in walls, you may find a puddle on the floor. If there is plumbing embedded within the concrete, moisture may seep to the surface.

Another reason moisture may be present is humidity, which can cause concrete floors to sweat in warmer environments. If this problem is present, dehumidification may be necessary.

Wet floors without an apparent cause could be due to a faulty or missing vapor barrier. This can happen with slabs that are in ground contact. Because concrete is porous, a moisture barrier is needed to keep water out. With a missing or damaged barrier, soil moisture can seep into the concrete and up through the material’s surface.

Protecting Concrete from Moisture

There are quite a few ways to protect concrete from excess moisture—like using a dehumidifier in humid climates, as mentioned above. One of the primary ways to prevent a moisture problem is with a moisture barrier, also sometimes called a vapor barrier, that is installed when the concrete is installed.

A vapor barrier can be any material that prevents water vapor from seeping up through the slab, but in most cases, these barriers are plastic sheets that offer different permeability ratings. You’ll see these as permeance ratings, which are usually presented as a decimal. Permeance less than 0.3 is recommended for most jobs, but higher ratings can be used in residential construction. In general, the moisture barrier should be at least 10 mils thick—or thicker if the barrier will be in contact with sharp edges. The thickness is to ensure they don’t puncture, which will compromise the barrier.

Usually these barriers are placed between the base—sand, gravel or whatever you are using beneath the slab—and the concrete itself. This prevents water from absorbing into the concrete later on. While some opt not to install these moisture barriers, they can be a valuable addition to the project because damp concrete absorbing ground water can cause adhesives to fail, tiles to lift, or wood flooring to mildew and rot.

Other options include acrylic sealers that can be applied after the concrete has been installed—though these are typically somewhat permeable, which allows water to pool on them before absorbing into the concrete so that you can mop up the moisture. Less permeable sealants include things like polyurethane and epoxy coatings, which can help prevent moisture seeping into concrete.

Vapor barriers are usually the best route for poured slabs because these work best to keep moisture from the ground outside where it belongs. However, if there are other issues present—like leaky plumbing or high indoor humidity—then there are other measures, like repair, dehumidification and sealants—that can help remedy the problem.