Al’s Column: Water vapor is invisible, but the problems are not

HomeColumnsAl's ColumnAl's Column: Water vapor is invisible, but the problems are not

July 6/13; Volume 30/Number 2

By Peter Craig

Your customer just picked out her new floor covering and can’t wait to have it installed to see how it will complete—or improve—the look of her home or office. But the subfloor over which the new floor will be installed is concrete and the product installation instructions indicate that there are limits to the amount of moisture that can be present. Why is it important to know the slab moisture levels and how does one determine the amount of moisture in a concrete subfloor?

Among many common construction and renovation problems, moisture-related flooring issues have been some of the most costly for years; cost estimates in the U.S. range from $300 million to $1 billion each year. In fact, not only are the larger commercial projects having problems, but residential projects are experiencing their share of moisture-related issues as well.

Moisture coming from, or through, a concrete subfloor can lead to numerous complications during or after installation, including the breakdown of adhesives, flooring disbondment, distortion, bubbling, blistering, odor and mold. The source of moisture can be the concrete itself or water vapor transmission from the ground that enters an unprotected concrete slab. The potential effects of moisture should not be taken lightly.

Regardless of where one lives or where a project is being built or renovated, the relative humidity beneath the structure will reach a very high level once the structure prevents the free evaporation of the moisture into the atmosphere above. This is as true in Arizona as it is in Florida. Having an effective, low-permeance vapor retarder directly below a concrete slab on the ground prevents this moisture from entering the subfloor and is the most certain means of preventing the future increase of moisture in the floor slab. A below-slab vapor retarder is also a requirement of many building codes, concrete and flooring guides, and flooring manufacturers.

But how can you fix moisture-related flooring issues in a home or structure that was built without a below-slab vapor retarder? All hope is not lost as today there are several topically applied slab treatments that can provide a similar level of moisture protection to the flooring materials when moisture within the concrete is too high, or an effective vapor retarder is not present directly below the slab. If certain moisture protection is necessary, retailers should help direct customers to the type of moisture mitigation system that is recommended for the particular flooring materials they have selected.

Unfortunately, reliably testing the moisture levels in a concrete subfloor is not quite as easy as one might think and, unless you are willing to invest the time, effort and money it takes to obtain several types of moisture testing equipment (as well as proper training), your interests are most often far better served by having International Concrete Repair Institute (ICRI) Certificated Concrete Moisture Testing Technicians (CCMTT) perform the moisture tests. There are currently more than 800 ICRI CCMTTs all around the country and a state-by-state listing can be found by visiting and clicking on “Find a CCMTT.”

The ICRI certification program is held each year in Baltimore, Chicago and at The International Surface Event in Las Vegas for those interested in becoming qualified moisture testing technicians.

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