Excess Moisture in Concrete? Avoid Flooring Problems with Accurate Testing

This article was originally published in Building Services Management (November 2018 issue).

Water Soaked Carpet Pad

Moisture-related flooring failures can be avoided by testing for moisture beforehand.

It’s a well-known fact. Excessive concrete moisture is the leading cause of flooring failures in modern buildings in the United States.

All the components of a floor covering system are sensitive to excessive moisture in some way. It’s not just the finished floor covering that can fail. Moisture can impact the adhesives, primer, patch/leveling compounds, concrete vapor retarder, subbase, and subgrade soil too.

When floor components get wet, they expand. When they’re drier, they contract. This invariably causes dimensional problems in floor systems.

Other problems also occur from unwanted moisture:

  • Discolored floor coverings and coatings
  • Debonding and break down of floor coverings, adhesives, primers, and patch/leveling compounds
  • Microbial growth
  • Deterioration of walls and wall coverings
  • Accumulation of moisture on working surfaces creating a safety hazard
Recording Results at Job Site

In situ relative humidity testing is the most reliable method for assessing the moisture condition of concrete slabs.

Test Concrete for Moisture

To avoid or greatly minimize the breakdown of adhesives, primers, and other floor system components, it’s critical to know how much moisture is present in a concrete floor slab.

The best way to do this is by assessing the moisture condition within the flooring system – that is, deep inside the concrete slab, and not at the surface.

Surface testing should not be relied upon to evaluate the moisture condition of a concrete slab. An accurate assessment is best done using the in situ relative humidity (RH) method.

According to Howard Kanare, who is recognized worldwide for his contributions to the understanding of concrete and moisture, RH gives a useful picture of the overall moisture condition within a slab.

Free Download – 4 Reasons Why Your Concrete Is Taking Forever to Dry

In fact, Kanare has described RH testing as “the most useful predictive tool [emphasis added] for floor coverings and adhesives because it reveals the true moisture condition within the concrete, which is what the floor covering will see after it’s installed.”

Kanare adds that with RH measurements, “we can actually determine the bond strength of adhesives or coatings to a concrete floor under different moisture conditions.”

The RH method provides several additional advantages over other test methods. The cost to conduct the test in terms of labor, and the time needed to obtain useful test results, are lower than with many surface-based tests. So not only is the RH method extremely accurate, it’s easier, faster, and cost-effective too.

When measuring moisture in concrete, Kanare cautions against using tests that measure only surface moisture, such as the calcium chloride (CaCl), or moisture vapor emission rate (MVER) test. His own research found that the test is fundamentally inaccurate and has no scientific pedigree. Moreover, Kanare found that the test can give both false positive and false negative results, and can yield different results depending on the weather, the temperature, and the particular day the test is conducted.

Unfortunately, many builders and flooring contractors mistakenly believe that the surface moisture level reflects the moisture condition of the whole slab when, in fact, it doesn’t.

RapidRH pH meter

Using a kit to test for pH is advisable to make sure the pH of the concrete is in the recommended range.

Check Concrete Slabs for High pH

Along with excess moisture is another problem – high alkalinity.

Alkalinity is a natural occurrence in all concrete and helps prevent reinforcing steel from rusting. But when alkalinity is too high (above 9 or 10 on a pH scale), it destroys the bond between the adhesive and floor covering. So excess moisture at a high pH creates a double whammy for floor installations.

Freshly mixed concrete is extremely alkaline and caustic – exceeding a pH of 10. Fortunately, this highly alkaline condition changes over time. As the concrete cures and reacts with carbon dioxide in the air, the surface pH of concrete declines.

Ideally, concrete should have a pH in the range of 7 to 9 before installing a floor covering. ASTM International states that a pH test should be performed along with every moisture test. Many flooring manufacturers specify pH testing before installing the finished floor.

So for a flooring system that will last for the long haul, don’t leave things to chance. The best way to minimize the risk of a flooring failure is to make sure that the concrete slab is tested for both moisture and pH before the application of adhesives, primers, coatings, and floor coverings.

To learn more about this and other topics related to moisture in concrete floors, be sure to check out the highly informative one-hour webinar, Moisture Testing of Concrete Floor Slabs, hosted by Howard Kanare. This free webinar includes a live Q&A session with Jason Spangler, Rapid RH® sales manager for Wagner Meters.

Last updated on June 1st, 2021

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