Avoid These 5 Common Mistakes When Testing Relative Humidity in Concrete Slabs

It is truly insane to think you can hack your way into a beautiful flooring installation without disastrous results unless you read up on and adhere to the ASTM F2170 standard. However, it’s not very hard to follow and the technology has made it easier than before. That being said, here are some “honest” mistakes we’d like to warn you about in advance:

  1. Not performing RH testing – This is bad. Don’t forget this really vital step in the flooring installation process.
  2. Assuming that one RH sensor will do the job. – You know what happens when you assume, right?
  3. Installing the RH sensor upside down. – No really, it’s happened.
  4. Trying to recover and reuse an RH sensor. – Going “Green” here is going too far. Besides, we have “reusable” sensors for that.
  5. Waiting 72 hours after installing RH sensors to take readings. The new rule is “24 hours” Read up on ASTM F2170. Don’t be old school.

Mistakes when testing RH in concrete slabs

If you are installing nearly any type of flooring material over a concrete slab, it’s going to be absolutely necessary that you have accurate concrete moisture test data that show relative humidity (RH) readings within the specifications laid out by the flooring material manufacturer. F2170 in situ probe testing has been proven to be the most reliable test method to determine the moisture condition of a concrete slab. But just like anything else, you need to be skilled in the proper use of the tools and know the procedures. The better prepared and the more experienced you are, the better your results will be.

But even with best-laid plans, mistakes still happen. Here are five cautionary tips that have come directly from Wagner Meters call center logs:

Mistake #1: Not Performing RH Testing

This is probably the worst mistake you can make. It just doesn’t make sense to skip RH testing for concrete. Just like neglecting any other diagnostic or measurement tool, the potential cost to your bottom line and to your reputation can be very high if things go south.

flooring damage due to not testing RH

The consequences of overlooking or neglecting to test for concrete RH can be significant damage to the flooring installation and more importantly, your reputation.

Wagner Meters takes great pride in providing personalized customer service to assist flooring professionals and help them be successful with concrete RH testing—sometimes even when they’re not using our well-known Rapid RH in situ testing system. We keep records of our more significant support calls. Here’s a cautionary tale from our files: A general contractor (GC), in charge of construction and renovation for a large school district, was making a 2,000 sq. ft. addition to his own home. Once the HVAC was up and running, the wood flooring was delivered. Because of the GC’s busy schedule, his home addition was a low priority, so the wood flooring had nine months to acclimate.

The GC subcontracted out the flooring installation, but the flooring contractor didn’t perform any RH testing on the concrete slab. Apparently, the GC didn’t fully understand at the time the importance of RH testing because the school district always hired inspection companies to do all the testing. So when the flooring contractor told him that the adhesive would act as a moisture barrier against any problem moisture, the GC gave the go-ahead for the installation. Two months later, the floor failed throughout the entire 2,000 sq. ft. of the addition. Lesson learned: do your own test to be sure. Even if another test has been done, two sets of results are better than one.

Mistake #2: Assuming That One RH Sensor Will Do the Job

We sometimes get calls from customers asking if one Rapid RH® Smart Sensor in a slab will do the job. The answer is no. ASTM F2170 10.1.1 states that you must perform three tests for the first 1,000 sq. ft. and at least one additional test per additional 1,000 sq. ft. The reason for this is that a concrete slab can exhibit a wide variation in moisture conditions due to things like staggered pouring times, irregular aggregate concentration and even exposure to sunlight. You don’t want that one untested section of the slab that was in the shade to ruin your entire flooring installation.

Mistake #3: Installing the RH Sensor Upside Down

Wagner Meters, a leading innovator in wood and concrete moisture detection systems since 1965, produces an in situ probe testing system that is compliant with ASTM F2170. Wagner’s Rapid RH L6 Smart Sensor is a cylindrical sleeve with a closed bottom. Although you might think the closed end should be at the top to enclose the test hole, it doesn’t work that way. The closed end goes in first, and traps a very small volume of air between the bottom of the sleeve and the bottom of the hole inside what is called an “isolation gasket.” That volume of air is where the RH reading is taken by the onboard electronic sensor. Follow the instructions carefully. Once you’ve installed the sensor in the hole, you can’t remove it without damaging it, so make sure you get it right the first time.

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

Mistake #4: Trying to Recover and Reuse an RH Sensor

The Rapid RH L6 Smart Sensors are designed for single use. You can’t remove them without damaging them. Even if you manage to remove them with the sleeve intact, the sensors are very sensitive and they can’t be guaranteed to be calibrated accurately after that kind of handling. The Rapid RH 5.0 Smart Sensors are reusable and have the ability to be verified for correct calibration. Calibration for all sensors is essential for accurate testing and the requirements for calibration are detailed in the ASTM F2170 standard.

Mistake #5: Waiting 72 Hours After Installing RH Sensors to Take Readings

72 hours is a long time, especially if it’s not necessary. The original ASTM standard called for an equilibration period of 72 hours, but in 2018 it was slashed to 24 hours. Big difference! It pays to stay up on things, and one way you can do that is to subscribe to the Wagner Meters concrete flooring newsletter at www.rapidrh.com. If there’s ever a disagreement, don’t argue about it. Instead, consult the document, ASTM F2170 Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes, which you should always have with you while you’re on site.

How to Avoid These Common Mistakes

Training and certification available at icri.org

Training and certification opportunities are available at icri.org

Here are some simple and easy ways to avoid these common mistakes with your concrete RH testing.

You can increase your understanding and skill in concrete moisture testing with training and certification from ICRI, through their Certified Concrete Slab Moisture Testing Technician (CCSMTT) Certification Program. You can find them at www.icri.org.

Another way to avoid mistakes is to always carry a copy of ASTM F2170 Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes with you whenever you’re on the job.

Keep wagnermeters.com bookmarked to access an extensive library of RH testing articles and reference materials.

When in doubt, give us a call at (541) 291-5123. Our courteous and professional support staff would love to help you avoid a disaster beforehand rather than help you pick up the pieces afterward.

Last updated on February 11th, 2022


  1. Robert Swank says:

    Have a building that is 5 year only and about 10,000 sqft approx. The air handlers have been off the entire time since this project has started.
    They have replaced them and just know after the inside of the building has be built out. We are know at the point of needing to install the LVT, sheet vinyl and Cove base. I did a test with Rapid RH with two unit on either side of the building back in December of 2022. I did a dry test and both read at Low 90 RH. The ceiling tiles are not in yet and the roof top unit are firing up on 5-5,6 2023 this week. How long should the air handlers run to climatized the space. Is there any document reinforcing the requirement to honor the manuf. warranty and installation of this product.

    Commercial Flooring Solution
    Robert Swank

    • Jason Spangler says:


      Thanks for the question. To have a valid RH% test per the ASTM F2170 standard the environment must be at service conditions 48 hours prior to the test and for the entire 24 hours of the test. Hope this helps.

Leave a Reply

Your email address will not be published. Required fields are marked *