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ASTM F2170 Explained

Concrete slab moisture is a major cause of concrete flooring failure. When concrete is mixed and poured, water vapor migrates from the bottom of the slab to the surface to evaporate. This process requires time and quantifiable concrete moisture measurements to verify.  ASTM F2170 formally recognizes the use of in situ probes as a means of conducting relative humidity testing. In fact, ASTM F2170 represents a fundamental change in moisture measurement.

The Standard

The Problem (as defined in ASTM F2170):

“Excessive moisture permeating from floor slabs after installation can cause floor covering system failures such as debonding and deterioration of finish flooring and coatings and microbial growth.”

In lay terms, the American Society for Testing and Materials recognizes that floor coverings often fail due to unsuitable concrete moisture levels beneath them. In that case, builders did not allow the slab sufficient time for concrete moisture levels to equilibrate (reach equilibrium moisture content) according to relative humidity (RH). Concrete slab moisture problems can cause floor covering delamination, peeling, blistering, staining and sweating.

The In-Situ Method

In-situ probes deepen concrete moisture measurement. For decades, builders used (and some still do) the anhydrous calcium chloride test for concrete moisture vapor emissions rate (MVER). The MVER is defined as the rate of water vapor emissions from the surface of concrete and is determined with the use of a desiccant material sealed to the slab surface for a specified time period, then measured. It has been believed that the change in the desiccant weight could be translated into a moisture ratio for the concrete beneath.

In-situ concrete moisture testing places sensors, or probes, inside the slab itself. As concrete dries, moisture migrates from the bottom of the slab to the surface where it can evaporate away. Logically then, moisture levels at the bottom of a slab will read higher from those at the surface. In-situ probes provide relative humidity (RH) measurements at 40% of the slab’s depth*, a position proven to more accurately portray the final RH levels of the slab if it were to be sealed at that point in time and the slab moisture allowed to fully equilibrate. In this way, in situ measurement provides a composite picture of overall slab moisture levels, and provides the data necessary to make business decisions regarding flooring installations.

The Wild Cards

Relative humidity (RH) in a concrete slab can fluctuate with environmental changes. Concrete absorbs water vapor from the air under high ambient humidity; concrete releases more water vapor when the humidity of the surrounding air is low.  Surface-based test results will fluctuate, even more, under these changes in environmental conditions.  General contractors must bear in mind two interactive processes when they are looking at construction schedules: concrete slab drying, and internal changes in relative humidity.

Ground moisture can also impact relative humidity in a concrete slab. Foundations are poured over, and underneath, ground level (also known as “grade”). Sub-grade water vapor can permeate even well-mixed and applied slabs. Many contractors use vapor barriers directly under the slab to slow moisture permeation. And moisture can still be an issue at grade so concrete foundations must be designed to include proper moisture drainage. Without it, even a well-dried and functioning foundation can end up with concrete slab moisture problems.

In situ moisture measurement systems are evolving rapidly as a result of ATSM F2170 and reflect the industry realities of the concrete installation business. For example, Wagner Meters Rapid RH system includes probes which remain in the slab for faster readings because re-equilibration time is not needed. Flooring associations like the Maple Flooring Manufacturer’s Association are recommending RH testing as giving greater success with flooring installations. And installers are finding results are more accurate and more dependable with RH testing.

It’s a sure sign of advances in the industry of concrete moisture management.

*This depth is for slab’s drying from one surface only. For slabs drying from two sides ASTM F2170 specifies RH probes be placed at 20% of the slab’s total depth.

Article by F2170.org Staff

Timothy Duncan holds a degree in Physics from UC Berkeley, and has been working on product development in RH testing technologies for the past 4 years. He most recently designed the latest version of RapidRH® products for Wagner Meters with ease of use, accuracy, and dependability foremost in mind. This latest revolutionary state of the art technology in RH in-situ testing is currently patent pending under license by Concrete Testing Laboratories, a subsidiary of the Portland Cement Association.

3 Responses

  • Dr. John Sudick says:

    I am using a Tramex Concrete Moisture Encounter which uses electrical impedance measurement with 8 co-planar electrodes with spring loaded contacts on the base of the instrument. During the operation, a low frequency signal is transmitted into the concrete to measure the change in impedance caused by the presence of moisture. This meter reads out as %H2O from 1-6%. I am having difficulty finding how this correlates to a Percent Relative Humidity or RH that Armstrong Flooring recommends prior to laying linoleum. We get readings that vary from 3.5% to 5.5% depending are where we are in the building. Current Air Humidity has been between 14%-20% in past few days but we had rain just a week ago. Chapter 3 page 13 on subfloors and Underlayments says
    10. Moisture Testing
    Moisture testing is an essential part of determining the suitability of a concrete slab to receive a resilient floor covering. Moisture testing must be performed on all concrete slabs, regardless of their age or grade
    level, including areas where resilient flooring has already been installed. Moisture testing should be conducted with the area or building at service conditions, (i.e., fully enclosed, weather-tight, and with the permanent
    or temporary HVAC in operation). In general, moisture testing should be conducted on concrete surfaces that exhibit the final prepared stage before the installation of the flooring material and before installation of smoothing or leveling compounds. Armstrong recommends the following test methods:
    a. Percent Relative Humidity (RH) in Concrete Slabs – Preferred Method
    Testing for internal relative humidity of concrete slabs must be
    conducted in strict accordance with the latest edition of ASTM F2170
    “Standard Test Method for Determining Relative Humidity in Concrete
    Floor Slabs Using in situ Probes.” So how does our Tramex tester relate to this??
    Pls respond to sudickdds@aol.com
    God Bless,
    Dr John Sudick

    • Dear Dr. Sudick,
      Thank you for your inquiry about concrete moisture testing. A handheld electrical impedance meter, such as the Tramex device that you have been using, is not considered to be an industry accepted method for testing concrete moisture prior to installation of finished flooring products. A handheld meter can be used for obtaining relative surface moisture readings, which may be helpful in selecting locations for further accepted testing methods, or for quickly surveying a floor with a known moisture problem.

      The readings you have been getting with the handheld device do not correlate with relative humidity measurements. One significant reason is that a handheld meter for concrete is primarily a surface measurement device, and does not measure moisture deeper within the slab.

      As such, a handheld devices should not used for stand-alone concrete moisture testing. They do not provide a reliable indication of the overall moisture condition of the concrete floor slab and should not be used to assess a slab’s readiness for a flooring installation.

      Before the finished floor is installed, a moisture gradient exists within the slab (typically drier at the surface, wetter deeper within the slab). To ensure a successful flooring installation, it is extremely important to use a testing method that provides results that reflect this overall moisture gradient, and relative humidity (RH) testing has been scientifically proven for doing just that.

      This is undoubtedly why the Armstrong recommendation that you cited lists in situ RH testing as the preferred method. This test uses RH probes that measure relative humidity at 40 percent of the depth of the slab (when the slab is drying from one side, which is typically the case). Extensive testing has shown that at this precise depth, relative humidity testing will give an accurate picture of the overall moisture condition of the slab.

      Thanks again for your inquiry. I hope this answers your questions.

  • Duncan Mbugua says:

    Dear Sir,

    I have benefited from your information about floors. Specifically, the articles by Jason.

    I am now dealing with moisture problems in several projects. Wood parquet flooring has failed due to high moisture contents in the sub floor concrete that may have arose from poor moisture management.

    I hope to use your tools in my future work and get the installations right the first time.

    Regards



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