Leapfrogging: A Not-So-Best Practice for Concrete Moisture Testing

If you’re like most of us, you look for shortcuts when faced with an important task. Sometimes the shortcut works; sometimes it backfires terribly.

Ever take a shortcut across the mountains that ended up costing you a lot of time because of the road’s painfully slow curves?

It’s no different with the in-situ relative humidity (RH) test for concrete moisture.

Sometimes people who use reusable RH sensors for their testing instead of single-use sensors are tempted to “leapfrog” the sensors from one test hole to the next. This practice is NOT recommended because it runs counter to the guidelines spelled out in the ASTM F2170 standard for RH testing. Even so, some people are convinced that leapfrogging gives them a sensible shortcut that will save time and money when assessing the moisture condition of a concrete slab.

The problem is, leapfrogging RH sensors won’t really save time and money at all.

hardwood floor moisture issues

Inaccurate test results from leapfrogging could lead to bad decisions about when to install, and that could mean a costly flooring failure.

In fact, people who try leapfrogging run the risk of getting inaccurate test results. And that could lead to a bad decision about when to install the finished floor, which could mean a costly, catastrophic flooring failure—one such as buckling, crowning, cupping, cracking, discoloration, mold, delamination or mildew.

What is Leapfrogging?

In a nutshell, leapfrogging happens when reusable RH sensors are moved from one hole to another, typically without allowing sufficient time for the air within the hole to acclimate to the conditions in the concrete. It is generally done when the person performing the test has fewer RH sensors than they really need to conduct the test correctly.

Acclimation can take many hours. And waiting that long is sure to test one’s patience. Much easier to just take the RH reading and move the sensor to the next hole in the slab.

What could be the harm in that, right?

Well, if you don’t allow enough time for acclimation of the air in the hole to occur, you run the risk of getting RH readings that are too low, which will suggest that the concrete is drier than it really is.

Of course, inaccurate or misleading test results defeat the entire purpose of doing RH testing!

You want to use a concrete moisture test that’s scientifically proven for accuracy and reliability, and that means going with RH testing. Studies at Lund University in Sweden and elsewhere have clearly shown that taking RH measurements at 40% depth (for a slab drying from one side) will reliably indicate the amount of concrete moisture the finished floor product will “see” after it is installed.

Leapfrogging: Does it Adhere to ASTM F2170 Guidelines?

The ASTM F2170 standard was developed to ensure that people follow a consistent method for RH testing so they will get accurate test results. Please realize that leapfrogging without waiting the necessary amount of time goes against ASTM F2170 guidelines.

The guidelines specify that you drill the test hole, drop in the sleeve, and cap off the hole for 24 hours. This allows for acclimation to occur. After the 24-hour wait, you come back, remove the cap, and drop in the sensor.

When you do this, you are bringing the sensor from an unacclimated environment, and the sensor is pushing out the acclimated air into the environment. So, after placing the sensor, you need to cap off the hole again and let the air re-acclimate before taking true RH readings.

This will generally take many hours—assuming your goal is to obtain an accurate RH reading. Then, and only then, should you remove the sensor and place it into another test hole to start the process all over.

You can see that if you don’t have enough sensors, and the slab is large enough that you’re conducting a lot of tests (for example, 12 tests needed for a 10,000 square-foot slab), then this could take a lot of time.

Kind of a catch-22—when you have fewer reusable sensors than you really need for the test. If you conduct your test using reusable sensors per F2170 guidelines, you can expect the testing to eat up a lot of your time. But resort to leapfrogging and you risk inaccurate numbers that you shouldn’t be relying on.

Fortunately, there is an easy solution!

When Leapfrogging is Not a Problem

rapid rh single use sensor

Leapfrogging is never a problem when using single-use RH sensors because they don’t get removed and transferred to another test hole.

Leapfrogging is never a problem when using single-use sensors. These sensors are extremely fast and easy to use. They are installed once and left in the hole for the entire time of the test. Because they are never removed and transferred to another hole, there’s no temptation to leapfrog single-use sensors.

Even better, once you’ve waited the required 24 hours for acclimation to occur, you can come back to take your initial reading and as many repeat readings as you want without additional wait time. That’s because the single-use RH sensor is always there, always acclimated, always ready.

Now you know why most people who do RH testing go with single-use sensors. Leapfrogging reusable sensors sounds great—until you know the risks. And why take chances on ruining your flooring project?

For more information about concrete moisture testing and the advantages of using a single-use RH sensor, visit WagnerMeters.com.

Previously published in the Commercial Flooring Report

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