Installation: Study clarifies moisture myths

May 17, 2016

May 9/16, 2016; Volume 30, Number 23

By Jason Spangler

Screen Shot 2016-05-17 at 11.19.33 AMIt is well known that water—too much of it, anyway—can wreak havoc on a construction project. No flooring installer or builder wants excess water to be present when the finished floor is installed over a concrete slab. Too much water inevitably leads to a catastrophic flooring failure, which can translate into costly repairs and a damaged reputation. So it is essential that the moisture condition of the concrete slab be evaluated before installing the finished floor.

Scientific studies in recent decades have consistently shown that relative humidity (RH) testing is the most accurate and reliable method for assessing the true moisture condition of a concrete slab. But what about the time needed for ensuring a reliable, accurate test? A soon-to-be-released ASTM Precision and Bias inter-laboratory study that focuses on the ASTM F2170 Standard may prove extremely important for flooring installers and others in the flooring industry. The ASTM F2170 Standard addresses this issue and sets forth other important guidelines that people in the concrete and flooring industry rely on for highly accurate RH testing of concrete moisture. Adherence to the ASTM Standard is important because it greatly reduces the risk of significant moisture-related flooring problems.

The current standard requires that in-situ probes must acclimate in the hole drilled in the concrete for at least 72 hours prior to taking and recording a RH measurement. Until now, it had been assumed that 72 hours was the time needed to allow the air inside the probe to be in moisture equilibrium with the surrounding concrete.

However, the ASTM Precision and Bias study has provided data that indicate otherwise. No appreciable difference was found in RH readings taken at 24 hours when compared to readings taken at 72 hours. Based on a statistical analysis of the data, the new ASTM study shows that when using in-situ probes to measure relative humidity, moisture equilibrium is achieved within 24 hours. This breakthrough finding suggests that changes to the ASTM F2170 Standard may be in order.

In ASTM’s Precision and Bias study, the laboratory tested several manufacturers’ RH products, taking temperature and RH readings at various times from one hour to 72 hours. The results of the study indicated that the 24-hour readings for the tested RH sensors were essentially identical with the 72-hour readings. Some slight variation occurred but it fell well within the acceptable range as laid out by the ASTM Standard.

In other words, the test showed that when installers conduct RH testing properly in the field, they can confidently and soundly know what the RH measurement will be at 72 hours. This is due to the fact that the 24-hour measurement is essentially the same. Of course, installers still need to take measurements at 72 hours to fulfill the ASTM Standard’s requirements. But there is no longer a doubt about how long you must wait to get the necessary data to help you move forward on your project.

The ASTM Precision and Bias study’s significant finding about RH readings provides strong evidence that may support a change in the ASTM F2170 Standard from 72 hours to 24 hours. Based on the study’s findings, this should in no way sacrifice the accuracy and reliability of the RH test. Yet such a change would be beneficial to flooring professionals and their clients as it would help people in the concrete and flooring industry accelerate their projects as needed. This would allow installers and contractors to make important business decisions related to concrete moisture earlier in the sales process.

About the author: Jason Spangler, sales manager for the flooring division of Wagner Meters, has 17 years experience in product developing, including concrete moisture testing equipment.

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