Among many safeguards, ASTM International (formerly the American Society for Testing and Materials) has established standard ATSM F2170 for the use of in situ probes to measure concrete moisture content. However, F2170 recognizes relative humidity (RH) measurement as the standard for determining concrete moisture content in slabs.
When concrete moisture appears, the age-old building conundrum emerges: “where did that come from?”
The answer is complex. Water is a natural ingredient in healthy soil, concrete itself and the earth beneath your building foundation. Water vapor can leak from plumbing pipes, it can permeate a slab from below grade (ground level), it can result from concrete moisture that could not evaporate after the foundation was poured. Builders often install vapor barriers beneath slabs to “stop” water vapor from entering concrete. Most vapor barriers are not-so-aptly named, though, because they seldom stop the moisture wicking effect that can produce concrete moisture problems.
Concrete moisture problems may originate from hidden view. If grade is below a water table, hydrostatic pressure can build and eventually cause water to invade. Vapor barriers may slow moisture permeation, but they also slow concrete drying times. Uninformed contractors may not wait long enough for concrete water vapor to naturally move from the bottom of the slab to evaporation point at its surface. These are all possibilities which may not be detectable at first.
This is another prime reason that ASTM established standard F2170: to protect against the unseen.
Why in situ?
Concrete moisture measurement has changed. For decades, the anhydrous calcium chloride test (a.k.a. MVER) was the norm. When ASTM established standard F2170 after researching the science behind the RH test method, it legitimized RH as a key measurement of slab moisture content.
One key reason was the integrity of in situ probes. As F2170 states, “This test method covers the quantitative determination of percent relative humidity in concrete slabs” (1.1). By placing probes inside concrete, builders can measure relative humidity at 40% depth in a slab, the depth shown to present the most accurate final RH if the slab were to be sealed and equilibrate at the time of the reading. In situ probes feed data to a hand-held concrete moisture meter, which represents the data as a percentage.
In situ testing provides diverse measurement as well. Contractors can conduct multiple tests in multiple locations in the slab to build a more detailed, composite picture of concrete moisture status. And as results for in situ probes and relative humidity measurement became better tested and documented, ASTM International created standard ASTM F2170 as an accepted industry method.
Reading the Invisible
In-situ probes go where humans cannot in order to measure concrete moisture.
Wagner Meters has developed its Rapid RH in situ concrete measurement tool to meet the invisible challenges of concrete moisture content measurement. The Rapid RH features Smart Sensor technology. Builders insert sensor-housing sleeves into drilled holes in concrete. Unlike other such probes, the Rapid RH system reaches equilibration in approximately one hour, allowing you to get a reading within 3%RH on the low side of where it will end up in the required 72 hours per ASTM F2170 standards.
Given the many potential external influences, concrete slabs dry at varying rates in different locations and making business decisions without RH assessment can be tricky at best, and costly at worst. The Wagner Rapid RH provides a cost-effective, immediate picture of a slab’s RH and how successful builders can safely proceed with top-quality flooring installation. The Rapid RH can also help identify areas of higher, unexplained moisture sources that may be putting your flooring in jeopardy.
Tap into the unseen with the Rapid RH in situ moisture measurement and eliminate the moisture problems that can spoil your concrete floor.