ASTM F2170 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. As of 2018, RH test readings are documentable after 24 hours.
The change came out 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 fully equilibrated after 24 hours, and that readings taken then were essentially the same as readings taken at 72 hours. You can take your RH measurement at 24 hours, a full two days earlier, and record it as official.
How This Change Benefits You
What does the change to the ASTM F2170 standard mean for your business?
If you’re a general contractor, you have an extra 48 hours of room to work with in meeting project deadlines.
If you’re an inspector, you can save money on out-of-town jobs by getting test results faster.
If you’re a flooring contractor, you can give the GC valid RH readings two days sooner, which helps the project workflow.
If the readings are within the manufacturer’s specifications for the flooring products being used, you can move forward with installation 48 hours earlier. If they aren’t, you have that information after 24 hours and can start addressing options immediately.
ASTM’s P&B Study
The laboratory tested six manufacturers’ RH products, taking temperature and RH readings at 1, 2, and 4 hours, as well as 24, 48, and 72 hours.
The 24-hour readings were essentially identical to the 72-hour readings. There was slight variation, but it fell well within the range the F2170 standard allows.
In other words, when RH testing is conducted properly in the field, readings taken at 24 hours reflect the same moisture conditions you would have recorded at 72 hours, and they can now be officially recorded two days sooner.
Accuracy and Speed in the Real World
These results matter for anyone using Rapid RH® testing to keep flooring projects from being compromised by moisture.
They also point to a practical difference between RH testing and ASTM F1869, the calcium chloride (CaCl) test. RH results can now be obtained in 24 hours, while the CaCl test under F1869 still requires a full 72 hours.
CaCl testing also requires the floor to be cleaned, scraped, and ground to a surface that tests consistently from site to site. Kits must be opened, desiccant weighed and data recorded, then a dish of pre-weighed CaCl is placed on the floor and covered with a plastic dome for the 72-hour test period. Once the test is complete, the desiccant must be weighed again, data recorded, and the test sites cleaned and materials disposed of.
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The findings didn’t surprise us. The Rapid RH system is designed to give readings generally within ±3–5% of the final 72-hour reading within the first hour.
Predicting the final reading early has always been possible with the system. The change to ASTM F2170 means you can now have official test results within one day.
Download the Rapid RH ASTM F2170 Checklist.
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.
Last updated on August 18th, 2026
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Jason,
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??
L.Martin:
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.
Jason
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?
Andy:
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.
Thanks,
Jason
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?
Todd:
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.
Thanks,
Jason
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.
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.
Thanks,
Jason