24 or 72 Hours: Which Number for Rapid RH® Testing?

Wouldn’t it be great if you didn’t have to wait the full 72 hours, as specified in the ASTM F2170 Standard, to know confidently what your relative humidity (RH) measurement was going to be?

NOW, you don’t have to wait until 72 hours have elapsed. You can take your Rapid RH® measurement at 24 hours—a full 48 hours ahead of the 72-hour mark—and be certain that this is the same number you will see at 72 hours.

That is one of the key findings of a Precision and Bias (P&B) study that was conducted by an independent laboratory under the direction of an ASTM task group.

ASTM’s P&B Study

In the study, the laboratory tested six manufacturers’ RH products, taking temperature and RH readings at periods of 1, 2, and 4 hours, as well as 24, 48, and 72 hours.

The results? The 24-hour readings for the Rapid RH® are essentially identical with the 72-hour readings. There was some slight variation, but it fell well within the acceptable range as laid out by the Standard.

In other words, the test showed that when you conduct Rapid RH® testing properly in the field, you can confidently and soundly predict what the Rapid RH® measurement at 72 hours will be, based on the 24-hour measurement.

Of course, you still need to take measurements at 72 hours to fulfill the Standard’s requirements. But there is no longer a doubt about how long you must wait to get the data you need to move forward on your project. With the P&B study’s results, it’s official: with Rapid RH® testing conducted in accordance with ASTM standards, there is no functional difference between the reading you get at 72 hours and the one you get at 24 hours.

Accuracy and Speed…In the Real World

These results are great news for those utilizing Rapid RH® measurement testing to ensure their flooring projects are not compromised by moisture-related problems.
Basically, it means that flooring contractors have a scientifically valid way to help accelerate their project workflow. If the readings for their finished flooring products are acceptable, they can take steps a full 48 hours before testing is “complete” to ensure that everything is in place and ready to move forward in terms of flooring installation. On the other hand, if the readings are not acceptable, they possess this information well in advance of the 72-hour threshold and can begin immediately addressing mitigation issues.

Either way, Rapid RH® testing yields this valuable information almost immediately, avoiding costly delays and potentially enhancing project profitability.

The results also further demonstrate the superiority of Rapid RH® testing over MVER via Calcium Chloride (CaCl) testing. Not only does Rapid RH® testing generate scientifically sound data that is essential to successful flooring project outcomes in a way that the CaCl test cannot, but it gives these fully accurate and usable results in a fraction of the time.

Finally, here at Wagner Meters, we are excited about the release of these results, but we aren’t altogether surprised. As many of you know, we have long designed our Rapid RH® system to give you very close readings, generally within ± 3-5% of the final 72-hour reading, within the first hour.

While it has always been possible to predict your final reading almost immediately with our product, these results from the new P&B study can help you fine-tune your initial prediction by the 24-hour mark, adding confidence to your decision and streamlining your project workflow.

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Jason Spangler

Jason has 20+ years' experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.


  1. Evan Adams says:

    So what I have been telling customers is +/- true, that if your test is high even after 1 hour, you are going to be high at 24hrs or 72hrs. I wonder why they settled on 24hrs? Probably because the concern is false lows not false highs.

    • Jason Spangler says:

      Thanks for the comment Evan. They, the ASTM committee, really hasn’t settled on anything yet. The 24-hour mark looks to be the best that the aggregate RH equipment manufacturer’s can accomplish at this point. There may be continued debate on this though. You are correct, the fear would be false lows.



  2. Todd says:

    Jason, After my first time using the product, have a question. The process seems simple enough, but need clarification.

    After 1 hour, we were pushing the 70% mark. I didn’t bother to check at 24 hours as I assumed we would be exceeding 75% and needing to address moisture concerns for our resinous system. Our start date was postponed by a day and I got back to take reading at the 96 hour mark. One sensor read 94% and the other 5 read 99% RH. Why do you suppose we saw such an increase after the initial reading? Leaving longer than 72 hours shouldn’t have an affect, right?

    • Jason Spangler says:


      Thanks for the question. Leaving the sensor longer like that will not have that type of impact on the reading. It’s hard to say specifically what the culprit could be, but some possibilities could be drastic temperature changes, hole depth other than 40%/20%, etc. I will say, this isn’t what we typically see, but it is why we always state NOT to make installation decisions on the 1 hour reading because situations like this can happen.



  3. Andy Zmoda says:

    1) ASTM F2170 -16b indicates to calibrate probes annually. Does the RH 4.0 probe need to be recalibrated?

    2) I have unused single-use sensors with a NIST calibration that expired in 2013. Do I need to trash these and buy more?

    • Jason Spangler says:


      Due to the fact that you are only using the Rapid RH 4.0 once (in one hole), it doesn’t need to be recalibrated. The NIST traceable certificate you receive with each package of sensors either gives you a two-year date range for expiration or it gives you a calibration date and the sensors are good for two years past that. Regarding your sensors that expired in 2013, you need to dispose of them.



  4. L. Martin says:


    I am needing specific information as to what the job site conditions should be when reading our Rh meters, please.

    In the Astm F2170 – 11, under “Conditioning” – Concrete floor slabs shall be at service temperature and the occupied air space above the floor slab shall be at service temperature and the service relatively humidity for at least 48 h before making relative humidity measurements in the concrete slab.

    What does this mean in regards to getting accurate measurements readings of the concrete?

    I am trying to install vct & carpet tiles. the say the air is on? Temp in the building seams to be @ 75-79?? Can I get accurate readings at these temps??

    • Jason Spangler says:


      Thanks for the question. Service conditions are the conditions that the building/concrete will be at when it is occupied and in use. So, for example, if your job was a retail store, you could walk onto your job, measure the ambient (air) RH% and temperature. Then walk into a retail store that was open for business and do the same thing. If the readings in both environments are comparable, then your job is at service conditions. Based on ASTM F2170, this service condition must be maintained for 48 hours prior to the test and for the entire 72 hour test period. If you have other questions, please contact me at (800) 634-9961 X235.


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