The in situ probe test is a testing method to quantify the relative humidity (RH) of a concrete slab. The in situ probe test, when following ASTM F2170, is a widely accepted moisture test and arguably the most accurate. As implied by the term in situ (which means "in the natural place"), a probe or sensor is placed into the concrete to gather internal readings. The test gives current conditions and does not indicated future conditions.
For each probe or sensor, a hole is drilled measuring 3/4" in diameter and at a depth equaling 40% of the slab's thickness for slabs that are drying from one side or at 20% depth for a slab drying from two sides. (For example, 40% depth is 1.6" in a 4" slab and 2.4" in a 6" slab.) The dust and loose particles are vacuumed from each hole. The in situ probe or moisture sensor is inserted. The probe or sensor is left in the hole for the full equilibration time of 24 hours. WagnerMeters.com writes: "In most cases, one hour after installation, the Smart Sensor will generally give a reading within 3% RH of the reading you would see after the ASTM-required" 24-hour mark. For each plot location, we document the date, time, relative humidity percentage, concrete temperature, ambient air temperature, and more. Afterward, each hole is filled with a concrete floor patching compound. Proper testing requires three (3) testing probes or sensors in the first 1,000 square feet. An additional testing probe or sensor is added for each additional 1,000 square feet.
The in situ probe test gives current conditions and does not indicated future conditions because concrete's RH is influenced by the air's current relative humidity and the ground's current moisture vapor. The HVAC system must be operating at normal conditions of temperature and humidity at the time of testing and for a period of no less than 48 hours prior to testing. If the building has been without climate control (e.g., new construction), prior to testing, the building envelope should be sealed and the HVAC system should operate at normal conditions for a period of two or more weeks. These tests require two site visits separated by 24 hours or more.
Moisture is more likely a risk if the substrate is below grade, but on grade and above grade substrates can also have moisture problems. The State of Florida is known for subterranean moisture issues. Moisture damage can ruin your new flooring.
Wolfe Flooring provides both the in situ probe test and the calcium chloride moisture test.