February 17/24, 2020: Volume 35, Issue 17
By Ron Loffredo- 
Excess moisture is the No. 1 culprit of catastrophic flooring failures in North America. This is often due to condensed construction schedules, fast-tracked projects on land with poor drainage, increased environmental regulations and new flooring materials. What’s more, failure to use proper moisture mitigation solutions can be costly and time consuming.
Typically, moisture affects flooring installations through excess moisture vapor transmission (MVT). This excess MVT becomes trapped between the impervious floor coverings and the concrete slab as it moves upward toward the atmosphere. Moisture can be present as rain or groundwater before the slab is first poured. In addition, the new slab contains water, which is needed for the chemical cure. The time to cure can take up to 30 days, which is unrealistic for today’s construction schedules.
Moisture can also be present in older concrete if the slab was never properly protected. It is always best to test for moisture levels; it should not be assumed an adequate vapor barrier is in place. In a remodel, for example, it’s not always apparent that there may be a moisture problem by looking at the existing flooring.
Elevated moisture levels can also lead to the development of mold and mildew. This can compromise air quality in the building and could break down the adhesives, causing warping and buckling. Excessive moisture vapor can also cause debonding, peaking and other issues.
Testing for moisture by following ASTM F2170 is always recommended. Because moisture typically migrates upward from within the slab, measuring moisture at its surface will not accurately portray the subfloor’s RH. Probes placed at specified depths inside the slab more exactly measure its RH levels and more reliably measure the risk moisture poses to an installation. Be sure to follow the instructions supplied with your RH equipment, the ASTM test method and always refer to the flooring manufacturer’s guidelines for their recommended RH levels.
Also keep in mind that moisture test results will indicate the moisture condition of the slab only at the time of the test. To that end, it is important to measure the moisture as close to the flooring installation date as possible. In addition, the building should represent the actual service condition of the finished floor during testing.
If testing proves excess moisture vapor is present, the next step is to select the right solution. When it comes to preventing moisture, it is important to remember not all moisture mitigation products are created equal. There are many types of products on the market, such as: epoxies, which can be effective up to 100% RH and MVER from 25 lbs; single-component polymers, which can be effective up to 100% RH and MVER 25 lbs; moisture vapor retarders, which are either semi-permeable or semi-impermeable; and plastic membranes, rolled moisture barrier systems that can be effective in 95%–99.5% RH.
Ron Loffredo is a senior technical advisor for H.B. Fuller Construction Products. A 35-year industry veteran, he specializes in training and consulting for challenging flooring installation projects.