The Concrete Slab RH Test – So Easy Your Whole Team Can (and Should) Do It

Every year North Americans spend an eye-watering hundreds of millions of dollars on fixing moisture-related flooring failures. This may be happening in part because they see slab RH testing as an obstacle rather than an obvious and necessary procedural step.

There are a few reasons why RH testing is sometimes missed:

  • There’s a misperception that it’s a complex procedure with many moving parts.
  • There’s a fear of performing the test incorrectly and getting unreliable results.
  • Finally, there’s the simple fear of trying something new.

So, let’s address these stumbling blocks one by one, starting with…

Isn’t RH testing a complex procedure?

concrete slab rh test - rapid rh l6Not at all. The Rapid RH test system from Wagner Meters is easy to use. Here’s how it works.

Drill a hole to the required depth, insert the probe, wait 24 hours, and then take a reading.

That’s it.

The Rapid RH L6 then allows you to either document the results on paper or send your sensor readings (including ambient temperature and relative humidity (RH)) to our DataMaster app on your smart device.

The Rapid RH L6 also provides you with a way to automate the process of collecting the readings. This is especially helpful if you don’t have the time to continually take readings at regular intervals.

What if the test results I get are wrong?

They won’t be if you perform the test properly.

To make sure you perform the test correctly, get a copy of the ASTM F2170, and make sure your RH testing system complies with the standard. If you follow it, the ASTM F2170 standard will protect you against liability and finger-pointing. We also have a downloadable F2170 checklist to help you.

The Wagner Meters Rapid RH L6 complies with ASTM F2170. If you correctly follow the instructions for fast and easy installation, your test results will be useful.

“But we’ve always done the calcium chloride test”

While the name of the test may sound scientific, no documented science or laboratory pedigree supports the reliability of this test. In fact, concrete slabs certified by F1869 were plagued with so many moisture-related problems that industry professionals began to have serious doubts about the integrity of the calcium chloride test. Here’s why…

The calcium chloride test only measures the top ½-¾ inch of the slab. This is a problem because the wettest part of the slab is deeper than three-quarters of an inch. When this deep moisture eventually makes its way up to the surface, it can’t evaporate if the concrete has been covered. This can easily result in flooring failure. The calcium chloride test also tends to “pull” moisture from the slab. This can lead to overestimated moisture vapor emission rates.

Free Download – Which Rapid RH Sensor is Right For You?

The ASTM F2170 is more reliable than the calcium chloride test

The ASTM F2170 (in situ probe testing) has been scientifically proven to provide more accurate results about the moisture content in concrete slabs over which flooring will be placed. For more information, see Drying of Construction Water in Concrete by Göran Hedenblad and Concrete, hardened: relative humidity measured in drilled holes which can be obtained from

RH testing is easy, inexpensive, and can save your reputation

rapid rh concrete test with mobile appRH testing will definitely save you money. However, it will also save your team from red-faced finger-pointing as well as your professional reputation. Best of all, RH testing is easy. Your entire team can and should be doing it.

For more information on RH testing, visit You’ll find an entire library of videos, articles, and educational content. There’s even a webinar about concrete moisture testing that will take you from zero to hero in about an hour.

Once again, because we can’t stress it enough, RH testing is easy. Very easy. It’s a simple procedure that, if performed properly, will protect your floor against expensive moisture-related failures.

Last updated on June 11th, 2021

1 Comment

  1. Brian Benford says:

    Hi Jason. My company is a retail store that does a lot of commercial jobs. We are currently doing a project in a school here. This is our 1st fairly big installation using the Wagner Rapid RH6 test method. The concrete was poured in the early summer, but because of ground conditions the architect called for 9 inch slab. I’m assuming that this slab will take longer to dry than a thinner slab. The tests so far have ranged from 87% to 98%. The adhesive we are using for vct is the Mapei 373 which has the highest RH tolerance I could find. On the Mapei 373 technical page, it reads acceptable readings for installation – no higher than 99%. This seems high to me because I’m assuming that 100% RH would be the highest RH can go. Maybe you can help me understand how RH in concrete works! Also what is the number of test holes that I should do readings on. The areas are 2 new wings off an existing school. The areas are aprox. 6500 sq ft each.
    Brian at Bob Dionisi Flooring- Sault Ste. Marie Ontario

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