Relative humidity (RH) testing is an in-situ method for measuring the moisture condition inside a concrete slab by inserting probes into drilled holes and reading the humidity at a specific depth, per ASTM F2170.
Understanding RH Testing in Concrete Moisture Analysis
Relative humidity testing, or RH testing, is an in-situ method for measuring the moisture condition inside a concrete slab. Small holes are drilled to a specified depth, sensors are inserted and sealed, and the probes are left in place to equilibrate before taking a reading, following the ASTM F2170 standard.
How Relative Humidity Testing Works
The test measures humidity at roughly 40% of the slab’s depth for a slab drying from one side, which is where moisture problems tend to originate. Probes need time to equilibrate with the surrounding concrete, usually at least 24 hours, before a reading is considered valid. The result is reported as a percentage relative humidity, which coating manufacturers compare against their own maximum threshold for a safe installation.
RH Testing vs. Calcium Chloride Testing
Calcium chloride testing measures moisture vapor emission at the surface only over a set period, typically 60 to 72 hours, and can be thrown off by recent weather or surface conditions. RH testing reads conditions deeper in the slab, which most in the industry consider a more reliable predictor of how the slab will behave over time, and it has largely become the preferred test for coating and flooring warranties.
Practical Tips for Accurate RH Test Results
Condition the space to the temperature and humidity it will see once occupied for at least 48 hours before testing, since ambient conditions affect the reading. Follow the minimum number of test locations required by ASTM F2170 based on the size of the space, rather than testing just one spot. Keep the manufacturer’s maximum RH threshold on hand before testing so you know immediately whether the slab passes or needs mitigation.
Also Called
In-situ probe testing, ASTM F2170 testing
