How to Measure Concrete RH (Relative Humidity) in Compliance with ASTM F2170

Referenced products:
Image of the PosiTector CMM IS depicting in situ measurement with a smart phone

The PosiTector CMM IS In Situ Concrete Moisture Meter by DeFelsko is the simple, durable, and accurate way to perform concrete moisture (RH) testing in accordance with ASTM F2170, "Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes". This article compares different methods used for measuring concrete relative humidity in floor slabs, details the innovative concrete moisture measurement system offered by DeFelsko, and explains how the test is performed.


Concrete is a composite material composed of fine and coarse aggregate bonded together with cement (calcium oxide).  When mixed with water, cement powders undergo a chemical reaction that binds the aggregate materials together into a durable, stone-like building material. However, after hardening (curing), much of this water remains as moisture within the porous concrete structure. Over the following months, this moisture is slowly emitted from the concrete until it eventually equalizes with ambient moisture levels.

How to Measure Concrete Moisture—Common Methods

Before applying a protective coating or other flooring materials to a concrete slab, it is critical to ensure that the moisture level inside the concrete has decreased to acceptable levels. If not, moisture can accumulate below the coating or flooring causing discoloration, cupping, buckling, blistering, adhesive failure, and/or mold growth.

Photo collage and caption showing several types of flooring and coating damage due concrete moisture.

There are various methods used for concrete moisture measurement. The three most-common methods utilize anhydrous calcium chloride, non-destructive electronic meters, or in situ relative humidity (RH) probes.

Anhydrous Calcium Chloride Tests

Illustration of a anhydrous calcium chloride test measuring concrete moisture

The anhydrous calcium chloride test involves measuring the increase in weight of salt as it collects moisture from an encapsulated area on the concrete surface. However, significant doubts concerning the accuracy of this test have arisen:

  • There is no practical way to calibrate these kits with traceability to national standards.
  • They measure moisture only on the surface of the concrete.
  • They are heavily influenced by ambient conditions.

Non-destructive Electronic Concrete Moisture Meters

Non-destructive electronic concrete moisture meters, such as the PosiTest CMM, measure the electrical impedance of concrete—which is related to concrete moisture. Offering near-instantaneous measurement of the top ¾” of a slab. But, owing to their design, these meters can be affected by other slab conditions. Variations in the concrete composition and the presence of reinforcing materials like rebar can cause erroneous readings. ASTM recommends that this type of concrete moisture meter be used as a comparator, or a companion to in-situ RH probes, and not for determining quantitative moisture content.

Watch this video to learn more about non-destructive concrete moisture meters.

In Situ Relative Humidity (RH) Probes

The new industry standard for measuring concrete RH is the in situ concrete relative humidity test as described in the ASTM F2170 standard test method. It involves drilling a hole into the concrete and using an electronic relative humidity probe to directly measure the moisture in the slab.

The in situ RH test has a number of advantages over other methods:

  • In-situ probes directly measure the actual moisture conditions within the concrete, regardless of mix, aggregate types, floor slab thickness, or surface conditions.
  • In-situ tests tend to provide a significant saving in testing time and labor versus calcium chloride tests.
  • In-situ probes can be calibrated with traceability to national standards.

DeFelsko's Solution for Measuring Concrete RH

The PosiTector CMM IS In Situ Concrete Moisture Meter is the simple, durable and accurate way to measure concrete relative humidity in accordance with ASTM F2170. Each reusable NIST-traceable probe includes a calibration check salt and chamber for conditioning and storage. Probes feature auto-pairing Bluetooth Low Energy (BLE) wireless technology and transmit concrete moisture measurements to a smartphone operating the free PosiTector App (iOS and Android compatible) or to a PosiTector Advanced gage (serial numbers 784,000 and greater).

Each PosiTector CMM IS probe operates for up to three weeks on a single coin cell alkaline battery and features an innovative combined sleeve and probe design providing the same function as a separate sleeve without the expense or hassle of consumables. Also included is a reusable, bright yellow cap to seal the probe within the test hole.

The free PosiTector App allows users to easily capture and report probe data in accordance with ASTM F2170. Using a compatible smartphone or tablet, overlay each probe on a floorplan and add metadata and notes as required by ASTM F2170. When testing is complete, quickly print a professional PDF report that includes all data required by the standard.

Select from three PosiTector CMM IS kit configurationsBasic, Complete, and Pro.

Image of the 3 PosiTector CMM IS kits as well as probe packs and probe extension sleeves
  • The Basic Kit is ideal for measuring concrete moisture in areas up to 1,000 square feet (100 square meters) and includes 3 probes, calibration certificates, check salts, calibration chambers, a measuring tape, and an extraction tool.
  • The Complete Kit includes 2 additional probes, calibration certificates, check salts, and calibration chambers (5 total) and is ideal for measuring concrete RH in areas up to 3,000 square feet (300 square meters). Includes all items in the Basic Kit plus a hard shell carrying case and vacuum tool for cleaning the hole after drilling.
  • The Pro Kit includes all items from the Complete Kit in addition to a PosiTector DPM Advanced gage for measuring ambient temperature and humidity above the drilled hole. It can wirelessly receive and record in-situ humidity and temperature measurements, displaying them alongside the ambient measurements. The PosiTector DPM also includes a surface temperature sensor ideal for concrete temperature measurement.

Expansion Packs and additional Stackable Probe Extensions are available for any jobsite.

PosiTector CMM IS Concrete RH Measurement Process in Accordance with ASTM F2170

The PosiTector CMM IS greatly simplifies the process of performing a concrete moisture test in accordance with ASTM F2170.

Step 1: Determine the number of RH probes required.

ASTM F2170 requires 3 probes for the first 1,000 square feet (100 square meters) and another probe for each additional 1,000 square feet (100 square meters). One test must be performed within 3 feet (1 meter) of each exterior wall.

Use the PosiTector App to map and overlay probe locations by taking a photo of the test area floor plan with your smartphone. Ensure that the slab and the ambient conditions are at service conditions for a minimum of 48 hours before testing begins.

Photo of the PosiTector App being used to select RH test locations against blueprints. Caption—Use the PosiTector App to map and overlay test locations.
Use the PosiTector App to map and overlay test locations.

Step 2: Verify RH probe calibration.

PosiTector CMM IS RH probe with calibration check chamber

The reusable PosiTector CMM IS probes include a long-form certificate of calibration traceable to NIST. ASTM F2170 requires that each probe be calibrated within one year after initial use. ASTM F2170 also requires probe calibration to be verified within 30 days of use with a saturated salt solution.

To make verification easy, each PosiTector CMM IS probe arrives conveniently pre-packaged in a calibration chamber complete with a saturated salt solution. Simply turn on the probe and insert it back into the chamber, ensuring that the probe reading matches the label on the chamber. Refer to the Verification of Accuracy section of the instruction manual for further details.

Step 3: Drill the test holes in Accordance with ASTM F2170.

Photo collage depicts the process of drilling a probe hole in accordance with ASTM F2170.

Using a hammer drill and ¾” drill bit, drill to the required depth—40% of the slab thickness if it is drying from one side only (i.e. slab-on-grade) or 20% of the slab thickness if it is drying from two sides (i.e. suspended slab). Remove any debris from the hole and use the PosiTector App to note the time the hole was drilled.

Step 4: Insert the PosiTector CMM IS RH probe.

Place the PosiTector CMM IS probe in the hole (sensor end first) and gently push it to the bottom. Use the supplied yellow cap to seal the probe in the hole. Note the time the probe was inserted using the PosiTector App.

Photo shows the PosiTector CMM is in-situ with the companion PosiTector App

Step 5: Collect in-situ RH readings.

The probe begins measuring immediately and readings can be displayed at any time using the PosiTector App or PosiTector Advanced gage body. However, ASTM F2170 requires waiting 24 hours for conditions in the hole to equilibrate before measurements are recorded. After that time has elapsed, use the PosiTector App or PosiTector Advanced gage body to wirelessly record the in-situ temperature and humidity along with the time and date without opening the hole or removing the probe.

Image shows both the PosiTector App and PosiTector DPM Advanced colleting readings from the PosiTector CMM IS RH probes

Step 6: Withdraw the PosiTector CMM IS probe.

Use the supplied extraction tool to remove the reusable PosiTector CMM IS probe from the hole when RH testing is complete. Fill the hole with a suitable patching compound. ASTM F2170 also requires that the ambient temperature and humidity above the hole be measured. If using the PosiTector App, lay a CMM IS probe on its side next to the hole and record the ambient conditions. If using a PosiTector DPM Advanced gage, ambient conditions are automatically recorded alongside in-situ measurements.

Step 7: Report test results in Compliance with ASTM F2170.

With all probe data required by ASTM F2170 collected, the test is now complete. Use PosiSoft software to download stored readings from your PosiTector Advanced gage body, or press the “report” button in the PosiTector App to view a PDF inspection report. This report contains all information required by ASTM F2170 and can be e-mailed or saved.

Image shows the PosiTector App on a smart device as well as a sample ASTM F2170 compliant report


Photo of a concrete parking garage with protective coatings on the floor

The innovative, reusable PosiTector CMM IS Concrete Moisture Meter In Situ makes the process of concrete moisture measurement and reporting faster, simpler and more accurate. The certified, reusable probes are an ideal solution for measuring in situ concrete RH in accordance with ASTM F2170.

PosiTector CMM IS cutsheet PDF thumbnail
Click the image above to view a downloadable PDF

Featured DeFelsko Products:

PosiTector CMM IS — Concrete Moisture Meter In Situ

PosiTest CMM — Concrete Moisture Meter

PosiTector DPM — Dew Point Meter

PosiTector App — Companion app for the PosiTector CMM IS RH probes

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