Concrete moisture testing before flooring installation is not optional — it is the quality control step that prevents flooring failures that are expensive to remediate and frequently disputed between contractors, installers, and flooring manufacturers. Understanding the three primary testing methods, their limitations, and when each is appropriate helps flooring contractors, specifiers, and building owners make informed decisions about their testing protocols.
The Calcium Chloride Test (ASTM F1869)
The calcium chloride test is one of the oldest and most widely recognized concrete moisture tests in the flooring industry. The test exposes a known quantity of anhydrous calcium chloride to the concrete surface in a sealed chamber for 60 to 72 hours, then weighs the calcium chloride to calculate the moisture vapor emission rate (MVER) in pounds per 1,000 square feet per 24 hours. Most flooring manufacturers specify maximum MVER limits in their installation instructions. The test is relatively inexpensive and widely accepted, but it measures only surface moisture, not the moisture condition at depth.
Relative Humidity Probe Testing (ASTM F2170)
Relative humidity probe testing is now the more technically robust standard and is increasingly required by flooring manufacturers and specified in project documents. The test involves drilling holes to specific depths (typically 40 percent of slab thickness for slabs drying from one side), inserting relative humidity probes, allowing equilibration (minimum 24 hours), and reading the RH level at depth. This method characterizes the moisture condition within the slab rather than just at the surface, providing a more accurate prediction of long-term performance for moisture-sensitive flooring systems.
Surface Moisture Meters: Screening Tool, Not Acceptance Test
Handheld surface moisture meters are useful screening tools for identifying areas that warrant more formal testing, but they are not acceptance tests and should not be used as the sole basis for flooring installation go-ahead decisions. Their readings are affected by surface contamination, surface temperature, and the specific concrete mix, making them unreliable for absolute moisture content determination.
Frequently Asked Questions
How many tests are required per 1,000 square feet?
ASTM F2170 requires a minimum of 3 RH test sites for the first 1,000 square feet plus 1 additional site per 1,000 square feet beyond that. ASTM F1869 calcium chloride tests require a minimum of 3 tests for the first 1,000 square feet plus 1 per additional 1,000 square feet. More tests are appropriate when moisture conditions are variable across the slab.
