Top 10 Concrete Moisture Questions

The Top 10

At Wagner Meters, we do all we can to provide information and resources to answer all questions from the field. We work to supply concrete and flooring professionals both the answers and the tools they need to ensure their installations and reputations survive the tests of time.

Jason Spangler, our Rapid RH® product and flooring division sales manager, shares some of the top questions people ask about relative humidity (RH) testing and the Rapid RH:

1. What is the connection between RH and MVER?Nothing

Not to put it too bluntly, but there isn’t one. MVER refers to Moisture Vapor Emission Rate and is determined by calcium chloride testing. A traditional “moisture test”, MVER is regulated by ASTM F1869 and has proven to be an unscientific and problematic test method, primarily because it tests only the surface conditions of a slab. In fact, calcium chloride testing has been specifically disallowed for lightweight concrete applications.

RH testing for concrete determines internal moisture levels of a concrete slab at 40% of its depth, as is covered in ASTM F2170. Because of the natural drying process of concrete, only accurate RH testing can determine the final moisture conditions of a slab if it were sealed (i.e., a floor covering installed) at that point in time. Our Rapid RH L6 is the latest in field-tested, scientifically-backed, industry-proven RH testing for concrete and flooring professionals.

You can learn more about the differences between RH testing and MVER at

2. Do flooring industry manufacturers specify the RH test method?

Currently, many of them do. We’re working hard to educate the industry, and many manufacturers understand the benefits of RH testing in improving the longevity of their flooring products and in preventing moisture-related flooring failure. We’ve assembled a list of the floor covering and flooring adhesive manufacturers that provide RH specifications for their products at, along with some helpful articles and resources to help provide best practices for installing and testing concrete slabs.

3. What type of documentation do you recommend for flooring contractors to maintain as proof of proper moisture testing?

ASTM F2170 describes the job site and testing information necessary to meet its industry standard. We provide everything possible to make the documentation easier for you:

  • Each Rapid RH Smart Sensor comes with NIST-traceable certification for immediate calibration compliance verification.
  • Each pack of Rapid RH Smart Sensors comes with an ASTM F2170 test results sheet to provide simple documentation of the required data, including a floor map of the sensor location, sensor recording, depth, and dates and times of RH readings. This form can also be downloaded here. A longer version of the form, including an ASTM F2170 checklist, can be found here.
  • If manual paperwork is not your style, Wagner Meters also developed the Rapid RH DataMaster™ L6 app. The app’s many convenient Read, Record, and Report features make it easier than ever to use your Rapid RH® L6 system for measuring moisture in concrete. The DataMaster L6 app is designed to be used only with Rapid RH L6 Smart Sensors and the Rapid RH L6 Total Reader®.

4. Does my HVAC need to be on for RH testing to be accurate? Do I need to document these ambient conditions and why?

Industrial HVAC PipesIn order to meet the ASTM F2170 standard, the concrete slab and the occupied air space above the slab must be at service conditions for a minimum of 48 hours prior to testing and for the entire 24 hours while the test is conducted. However, even not considering the ASTM standard, it’s a best business practice to have the slab at service conditions before testing. Ambient conditions play a key role in the drying time of a concrete slab, and any change to those conditions will affect the moisture movement through the slab and will change the internal RH. Testing at non-service conditions can become a pointless exercise if drastic changes to the environment will ultimately skew the test results and, ultimately, slow the drying process.

5. This 6” concrete slab was poured 9 months ago and is reading 95% RH. How can it be that high after all this time?

There are a number of reasons why RH can remain high in a concrete slab:

If the initial mix ratio (water, cement, admixtures) was high in water, the drying schedule will take much longer to allow that initial moisture content to dissipate.

If ambient conditions do not allow adequate air movement or include low temperatures or high RH levels in the surrounding air, the evaporation process necessary for drying the concrete may be inadequate.

If an adequate moisture barrier has not been installed under the slab, moisture may be accessing the slab from subsurface sources, including groundwater, defective plumbing or inadequate drainage around the slab.

If the slab surface was hard troweled too aggressively, burnishing the concrete surface and the natural capillary pathways that allow moisture to move to the surface and evaporate may have been obstructed, severely limiting the surface’s ability to release moisture from the slab.

Obviously, identifying the cause of the high RH will determine the correct remedial action. Alternate drying methods may be necessary, the slab surface may need grinding, or alternate floor or sealant options should be chosen based on products with a high moisture tolerance. RH testing with the Rapid RH is the best way to get the correct information in order to make an informed decision regarding the situation.

6. How can I get the concrete to dry faster?

If all the pouring procedures were done accurately (see #5 for some possible problems) and you’re just looking to hurry the drying schedule, a number of possibilities are available:

  • Reduce the water in the initial concrete mix. Your ability to do this will be limited by the admixtures specified.
  • Incorporate a desiccant during batching. During the hydration process, some available materials, like silica fume, will absorb and retain initial mix water. Be sure to understand the risks and directions provided by the manufacturer.
  • Don’t rush troweling. If a slab is hard troweled too quickly or too aggressively, it can lose its capacity to dry efficiently.
  • Dehumidification relies on a number of different methods (desiccant-based, heat-based, condensation) to change ambient conditions and allow moisture to leave the slab more efficiently. In conjunction with dehumidification, air movement in the environment is critical.

The best option really is to plan the entire project to facilitate a faster drying schedule. As part of that, the Rapid RH can help monitor the actual results for informed decisions at every step.

7. Can Smart Sensors be recovered and reused?

One of the unique features of both the Rapid RH L6 and the Rapid RH 5.0 Smart Sensors is the innovative design that sets the sensor directly into the concrete slab. This allows the sensor to have a “one-time” equilibration period that allows accurate readings without a constant re-equilibration period. The unique redundancy isolation ring system on each Smart Sensor seals it from ambient air in the drilled hole to ensure accurate readings every time.

The Rapid RH 5.0 Smart Sensor has been specifically designed to be reusable. This means that each 5.0 sensor that you install can be recovered and reused many times without damage to the sensor. Keep in mind that in order to ensure compliance with the ASTM F2170 standard, calibration must be checked within 30 days prior to use. Calibration checks require additional time and attention to perform, although the included EasyCare Calcheck device makes calibration checks as quick and easy as possible. The 5.0 reusable sensor is a good choice for building inspectors or others who do a lot of RH testing.

In the case of the L6 Smart Sensor, however, it is not reusable. It is a convenient single-use sensor and is a great choice for most contractors, installers, and others who may not do a lot of RH testing. No calibration check is required when using the L6 sensor. Keep in mind that once the L6 Smart Sensor has been installed inside a concrete slab, removing it from the test hole increases the risk of damaging the sensor or the first stage ring system. The reality is that the L6 sensor is not designed for re-use and trying to do so would require recalibration of each L6 sensor before it could be used again.

Fortunately, the cost per test of the Rapid RH L6 system is so reasonable that reuse or recovery is simply not cost-effective.

8. Does the application of a moisture remediation product resolve, alleviate, or mitigate the effects of RH in concrete slabs that are in excess of recommended maximums?

A mitigation product MIGHT help to limit the effects of high RH in concrete slabs BUT there are a number of important factors that will determine the ultimate outcome:

  • The cause of the high RH levels
    If additional moisture is being drawn into the concrete slab from any external source (groundwater, leaking plumbing, etc.), the internal RH levels will continue to rise even after a surface encapsulant is applied. A rising RH level may eventually exceed the moisture tolerance of the product and still cause moisture-related problems.
  • The mitigation product’s specific moisture tolerance
    If the product’s moisture tolerance ratings are insufficient for the actual slab moisture content, then the high RH of the slab will likely cause encapsulant failure, along with the failure of all the flooring or finish products applied over it.
  • Ambient conditions around the slab
    If the ambient conditions around the slab (air humidity, temperatures) are prone to significant changes or seasonal shifts, the high initial RH levels of the slab may be the result of poor drying conditions. Best practices would suggest ensuring drying conditions are optimized before applying any sealant or product to the concrete slab. If RH testing continues to show high RH levels, be sure that any products are chosen with appropriately high moisture tolerances, and always consult these manufacturers directly to discuss your specific situation. For a list of manufacturers that provide RH specifications for their products, visit

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

9. I just tore up a floor that had no issues and was adhered to the concrete fine. Now I am getting ready to install a new floor and the concrete is testing high RH%. How is this possible?

Again, there are a number of factors that might be at play here:

  • Moisture intrusion that has not yet impacted the flooring
    If moisture has begun to impinge on the slab from a new source, it’s possible that the slab RH has been on the rise but that it has not yet reached critical levels. Moisture seepage through a vapor retarder with an insufficient perm rating, leaking plumbing, new groundwater sources, and other possible moisture intrusions can impact a concrete slab over time and will require remedial steps to correct before installing a new floor over the slab. Testing with the Rapid RH can help spot potential problems before a new floor system is adversely affected.
  • The moisture tolerance of the original adhesive
    With the move to newer, “greener” products in the building industry, moisture tolerances are not always as predictable as they once were. Products heavy in petroleum-based components, for example, are inherently less susceptible to moisture. When re-installing the floor, however, it’s important to either take remedial steps to bring the RH levels down or to be sure that all the new materials specified meet the current RH levels of the slab. The Rapid RH system makes sure that the slab moisture readings inform those decisions for the best results over time.

We saved the best for last (Yes, this has been asked.):

10. Does Jason REALLY wear green shirts every day?

Yep, pretty much!

And with pride too.

For more information, resources and quality concrete moisture measurement products, including the Rapid RH L6, visit us here or give us a call at (541) 291-5123.

Last updated on June 1st, 2021


  1. Brian Benford says:

    I just purchased a Wagner RH 4.0 and have done my 1st test on a on grade concrete slab in a local school.
    The slab was at 75 F and the two RH readings were 22 and 23 in the two areas at opposite ends of the school.
    No where in the instructions does it tell me what acceptable RH levels are.
    The slab is 50 years old and we are installing Armstrong Excelon VCT.
    Regards Brian

  2. Thanks for helping me understand more about concrete moisture. I didn’t know that you can help the concrete dry faster by not rushing the troweling process. It definitely sounds like, in general, you need to have patience for this, especially if it can help the concrete slab stay in good condition.

  3. Laura says:

    We used Rapid RH to test the slab of a condo. It reads HI or 97%. The condo is suffering from humidity, is this the reason? What RH% should a slab be in order to be safe to build?

    • Jason Spangler says:


      Thanks for the comment. Different flooring finishes have different RH% thresholds. I would check with the flooring product manufacturer’s you intend to use and see their acceptable RH% levels. I hope this helps.



  4. Kris shipley says:

    Is there a required moisture level needed before remediation can performed?

    • Jason Spangler says:


      Thanks for the question. There are various remediation products on the market that function at different maximum RH% levels. In other words, there are some that are only effective up to 85%, while there are others that are guaranteed effective up to 100% RH. I hope this helps.


  5. Dan Haeseker says:

    Recently had concrete Bocce court tested and wonder what results mean?

    • Jason Spangler says:


      Thanks for the question. I have to say, I am not a Bocce court expert, so I had to do some research. From what I can see, Bocce courts are not made of concrete, correct? That being the case, I am not sure what you had tested or how to interpret the results. Sorry I can’t be of more help.


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