A moisture meter is excellent for finding patterns, but a number displayed on stucco, drywall or concrete is not automatically an exact percentage of water in that material. Different meter modes and building materials use different scales, and metal, salts, density and concrete composition can distort readings.
The Most Useful Skill: Mapping a Pattern
Take repeated readings across a suspected area and compare them with a nearby area of the same material that appears unaffected. A gradient that increases toward a window corner, baseboard or roof intersection can be more informative than a single “high” number.
Pin vs. Pinless Readings
Protimeter describes pinless/search-mode readings as relative readings used to locate higher-than-normal moisture. Pin meters are calibrated to wood; on many other building materials the displayed value is a wood-moisture-equivalent or reference reading, not literal percent moisture by weight.
Why Concrete Is Special
Concrete’s electrical properties vary with aggregate, salts and composition, and handheld meters mainly evaluate the near-surface zone. Protimeter recommends in-situ relative-humidity testing when the decision requires a reliable assessment of moisture inside a concrete slab.
False Positives and Misleading Comparisons
Metal behind a wall, conductive salts and material-density changes can all alter meter response. Comparing drywall to stucco or concrete using the same number can therefore be misleading. Compare like material with like material and use the correct scale for the instrument.
What a Homeowner Can Reasonably Do
Use a meter to locate and track a moisture pattern, document whether the area is drying after a repair, and identify where professional testing should concentrate. Do not use one unexplained reading as proof that a roof, window, stucco wall or slab is the source.