What is a moisture meter?
A moisture meter is an instrument used to determine the moisture content of a building material, such as wood, masonry, plaster or a screed. You use it to check whether material is dry enough to finish, and to track down moisture problems.
Types of moisture meter
- Pin meter (resistance meter): two pins go into the material and the meter measures the electrical resistance. Wet material conducts better. Suitable for wood, often with a setting per wood species.
- Non-contact or capacitive meter: pressed against the surface, it measures without damage to a depth of a few centimetres. Handy for quickly scanning a surface and finding wet spots.
- CM test (carbide method): a sample from the screed is shaken with calcium carbide in a pressure bottle. The gas pressure gives the moisture content in CM percent. This is the usual, reliable method before parquet, vinyl or linoleum is laid on a screed.
- Hygrometer: measures the relative humidity in the room, not the moisture in the material itself.
| Pin meter (resistance meter) | Measures electrical resistance between two pins; suitable for wood, often with a setting per wood species |
|---|---|
| Non-contact or capacitive meter | Measures without damage to a depth of a few centimetres; handy for quickly scanning a surface and finding wet spots |
| CM test (carbide method) | Screed sample shaken with calcium carbide; the usual, reliable method before parquet, vinyl or linoleum is laid on a screed |
| Hygrometer | Measures the relative humidity in the room, not the moisture in the material itself |
Applications
- Screeds: before laying a floor finish. Commonly used guide values are about 2 CM-% for a cement screed and about 0.5 CM-% for an anhydrite screed, lower with underfloor heating. The flooring supplier’s instructions always take precedence.
- Wood: checking whether wood is dry enough to paint, glue or work. Use the limit given in the technical data sheet of the paint or adhesive.
- Walls: mapping damp spots, for example with rising or penetrating damp.
Tips and pitfalls
- Electronic meters on masonry are indicative. Salts in masonry also conduct and give too high a reading. Use the result for comparison, not as an absolute value.
- Measure a pattern: take readings on a grid and from bottom to top. This shows whether moisture is rising from below or coming in from outside.
- Reference: also measure at a spot that is certainly dry, so you have a value for comparison.
- Surface condensation can give a wet reading while the wall itself is dry. Measure the air humidity too.
Related terms
- Construction moisture
- Relative humidity
- Equilibrium moisture content
- Condensation
- Screed
- Anhydrite floor
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