MEASURES n how accurate RH Testing will help to ensure the efficacy of safety flooring.

When the flooring is installed over the slab, the surface is sealed so that moisture can no longer escape. Once sealed, the slab’s moisture condition will tend to equalize and create a ‘moisture equilibrium.’ This point of equilibrium is important to keep in mind because if we obtain a quantitative measure of it, we have gained a valuable indicator of the long-term moisture condition of the slab after the floor installation.


CONCRETE MOISTURE The only reliable way to measure this moisture equilibrium is to use the in-situ relative humidity (RH) test, standardised as ASTM F2170, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes. The results of this test are numeric and can be used to predict the long-term performance of the finished floor, given the moisture condition of the subfloor.

Other popular methods of measuring moisture in concrete exist, such as the calcium chloride (CaCl) test. However, they do not assess the all-important point of moisture equilibrium. Historically, though, the CaCl test was widely accepted. Although the origins of the test date back to 1941, this method has evolved over the years to become a quantitative test that measures the rate of moisture vapor emission from the concrete’s surface. Today it is standardised as ASTM F1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.

The ASTM F1869 (CaCl) test does not give reliably accurate results. This is because it is based on the faulty premise that testing moisture at the surface gives an accurate picture of the overall moisture condition of the slab. Now we know that the moisture level tends to be lower at the surface than deeper down in the concrete. We also know that once the slab is effectively sealed after a flooring installation, the moisture gradient in the slab will tend to even out. This brings more moisture to the surface and into contact with the finished floor.

These key facts reveal why surface-based methods, including the CaCl test and the use of handheld concrete moisture meters, often yield misleading results.


MANY ADVANTAGES Unlike surface-based methods, the in-situ RH test measures the moisture within a concrete slab. RH sensors are placed at a specified depth in the slab. Scientific research at Lund University in Sweden demonstrated that measurements taken at 40% overall depth for a slab drying from one side (or 20% for a slab drying from two sides) correlate closely to the point of moisture equilibrium. These depth-specific measurements give a reliable indication of how much moisture a floorcovering or adhesive product will actually ‘see’ after installation.

A second advantage of measuring moisture within the slab is that the test results are not heavily influenced by changing

ambient conditions. Compare this with surface-based measurements, which—by their very nature—are inherently affected by ambient conditions. When the air is humid, the CaCl test may give a ‘false positive’ reading suggesting that the slab is too wet for a successful installation when, in fact, this may not be the case at all.

Yet another advantage of the RH test method is that it can be readily used with electronic devices capable of recording changes in RH within the slab over time. Monitoring these changes can help predict how long it might take a concrete slab to reach an acceptable moisture level.

The leading in-situ RH test kit (the Rapid RH L6) is extremely fast and easy to set up. This test kit can give accurate results in just 24 hours — plus it utilises advanced technology to transfer a digital stream of data wirelessly to a convenient ‘DataMaster’ smartphone app. This app can be used to quickly analyse the RH moisture data and generate reports for clients. It is no wonder that RH testing and the use of test kits such as the Rapid RH L6 have become so popular in recent years.


NOTHING TO CHANCE Years of scientific testing, along with extensive use in the field, all point to the in-situ RH test. It is the only test to provide the type of reliability needed for avoiding moisture- related flooring problems and the significant risk of accident or injury that often accompany such problems.

For more information about concrete moisture measurement or how to use the industry-leading Rapid RH L6 test kit, call the Rapid RH team toll-free at 800-574-0228, or visit Wagner Meters’ extensive online learning library.

In-situ RH testing provides a reliable, depth-specific measurement of the overall moisture condition of a concrete slab.


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