Moisture meters detect the presence of moisture in walls by measuring electrical resistance. When moisture is present, the resistance decreases, allowing more current to flow through the meter. The higher the moisture content, the lower the resistance and the higher the reading on the meter.
Understanding Moisture Meter Readings
Moisture meter readings are typically expressed in one of three units:
- Percent moisture content (% MC): The amount of moisture present in the wall relative to the total weight of the material.
- Relative humidity (RH): The amount of moisture in the air relative to the maximum amount of moisture the air can hold.
- Wood moisture equivalent (WME): The moisture content of the wall compared to the moisture content of a specified type of wood.
Factors Affecting Moisture Meter Readings
**1. Type of Material:** Different materials have different electrical properties, so the same moisture content can produce different readings on different meters.
**2. Temperature:** Temperature affects the electrical resistance of materials, so readings should be taken at the same temperature for accurate comparisons.
**3. Depth of Penetration:** Moisture meters measure moisture at different depths, so the depth of the probe should be consistent for accurate readings.
**4. Surface Conditions:** Surface moisture or dirt can affect the accuracy of the reading. It’s best to clean the surface before taking a reading.
Interpreting Readings
Readings should be compared to reference values for the specific material being tested. For example, a moisture content of 10-15% in drywall is generally considered acceptable, while readings above 15% indicate potential moisture problems.
Detecting Dampness in Walls
If you suspect dampness in a wall, use a moisture meter to confirm:
- Insert the probe into the wall at a depth of 1-2 inches.
- Take multiple readings at different locations to get an average reading.
- Compare the readings to reference values for the material.
If the readings indicate excessive moisture, further investigation is needed to determine the source of the dampness.