ASTM F2170 Change Authorizes Official RH Test Results after Just 24 Hours

Remember when relative humidity (RH) test readings under the ASTM F2170 standard required a 72-hour waiting period?

Not anymore. The 72-hour wait is history.

The standard’s been updated. Beginning this year, RH test readings are now documentable after just 24 hours.

Doing away with two extra days of waiting comes about because of an ASTM-commissioned Precision and Bias (P&B) study conducted by an independent laboratory. The ASTM committee voted in favor of the change in late 2017.

The P&B study found that test holes were completely equilibrated after 24 hours, such that the RH readings taken at that time were essentially the same as the readings taken after 72 hours.

This change means you don’t have to wait until 72 hours have passed. You can take your 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.

How This Change Benefits You

What will this change to the ASTM F2170 standard mean to your business?

If you’re a general contractor, you now have an extra 48 hours of wiggle room that you can use to full advantage in meeting project deadlines.

If you’re an inspector, you can save money on out-of-town jobs because you can get your test results in faster.

If you’re a flooring contractor, your GC will love the fact you can give him scientifically valid RH readings two days faster. This, of course, can help accelerate the project workflow.

If the readings are within the manufacturer’s specifications for the finished flooring products being used, the ASTM update allows you to take steps a full 48 hours earlier and move forward with the flooring installation.

On the other hand, if the readings are not within manufacturer specs, you possess this information after just 24 hours and can begin immediately addressing options for keeping the project moving forward.

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 RH testing 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 F2170 standard.

In other words, the test showed that when you conduct RH testing properly in the field, you can enjoy complete confidence that readings taken at 24 hours are complete, accurate and official. They reflect the same moisture conditions that you would have recorded under the former 72-hour threshold—except now you can officially record them 48 hours sooner.

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.

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 ASTM F1869, the standard for what is often called the calcium chloride (CaCl) test. 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.

Think of all the time you’ll save using the Rapid RH® test versus the CaCl test. While the RH test results can now be obtained in just 24 hours, the CaCl test under the ASTM F1869 standard still requires a full 72-hour wait period.

CaCl testing also requires that the floor is cleaned, scraped and ground to make a clean surface that will test equally from site to site. Kits must be opened, desiccant weighed and data recorded, then a dish of the pre-weighed CaCl is placed on the floor and covered with a plastic “dome” during the 72-hour test period. Once the test is complete, the desiccant must be weighed again, data recorded and the test sites cleaned and test materials disposed of.

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Streamline Your Project Workflow

Undoubtedly, we at Wagner Meters are excited about the study’s findings and the changes to the F2170 standard, 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, the new change in the ASTM F2170 standard means you can now have official test results within one day, adding confidence to your decisions and streamlining your project workflow.

Last updated on June 1st, 2021


  1. 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.


  2. 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.



  3. 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.



  4. 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.



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