Testing concrete subfloors for moisture before installing new flooring is crucial to prevent installation failure, such as adhesive breakdown, material warping, or mold growth. Two common and reliable methods are the Calcium Chloride Test (ASTM F1869) and the In-Situ Relative Humidity (RH) Test (ASTM F2170). **Calcium Chloride Test:** This is a field test where a specific amount of anhydrous calcium chloride is placed in a sealed dome on the concrete surface. After a set period (usually 24-72 hours), the weight of the desiccant is measured to determine the amount of moisture vapor that has accumulated. The results are reported in pounds per 1,000 sq ft per 24 hours. **In-Situ Relative Humidity Test:** This method involves drilling holes into the concrete slab and inserting probes that measure the relative humidity within the slab at a specific depth. This is considered a more accurate test because it measures moisture within the concrete matrix, rather than just surface emissions. Results are typically reported as a percentage of relative humidity. Both tests require specific testing kits and adherence to manufacturer instructions. Flooring manufacturers will specify the maximum allowable moisture levels for their products, and it is imperative to meet these requirements before proceeding with installation.

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