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Damp Survey Calculator — Interpret Moisture Meter Readings
Interpret resistance moisture-meter readings on the Wood Moisture Equivalent (WME) scale — dry below 18%, borderline 18–20%, wet above 20% — for plaster, brick, timber, concrete and stone.
Height from floor level - map readings to spot a rising-damp profile
Rough manual allowance only - not a calibrated correction
Salts cause variable false highs - confirm by carbide test (BS 6576), not a fixed offset
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How We Calculate This
This calculator averages your resistance moisture-meter readings and places them on the Wood Moisture Equivalent (WME) scale. A resistance meter reads every material on this one scale, so the dry / borderline / wet bands are the same for plaster, brick, timber, concrete and stone.
WME zones (Protimeter green / amber / red)
- Dry (green): ≤18% WME — the safe condition for an ordinary indoor environment (16–18% moisture content in wood ≈ 75% RH)
- Borderline (amber): 18–20% WME — monitor and re-check
- Wet (red): >20% WME — action needed; in any material a reading above 20% is a damp condition, and persistent timber above 20% MC allows wet-rot decay
Reading masonry vs timber
- Timber: on wood the meter reads actual % moisture content; 20% is the recognised decay threshold.
- Masonry & plaster: WME is qualitative (BS 6576) — it shows the surface is behaving electrically like wood at that moisture, not its real water content, and salts give falsely high readings. Treat as low / moderate / high and confirm with a carbide (calcium-carbide) test.
- Do not use the screed-drying single-digit limits (plaster 5%, brick 3%, concrete 6%) as a meter dry/damp boundary — those are gravimetric moisture-by-weight figures, not meter WME.
Frequently Asked Questions
WME is the standard unit for resistance-type moisture meters. The meter measures electrical resistance and displays a percentage calibrated against wood. For non-timber materials, conversion tables are needed because brick, plaster and concrete conduct differently. A reading of 17% WME on plaster does not mean 17% water content.
A resistance meter reads every material on the same WME (Wood Moisture Equivalent) scale, so the green/amber/red zones are the same whatever the surface. Per Protimeter (which defines the scale): below about 18% WME is the safe dry (green) zone, 18–20% is borderline (amber) and any reading above 20% WME — in timber or masonry — is the wet (red) zone that needs investigating. The often-quoted single-digit figures (plaster 5%, brick 3%, concrete 6%) are gravimetric moisture-by-weight limits for floor screeds, not meter WME readings, so they are not the dry/damp boundary on a meter. On masonry a WME reading is only a relative guide (BS 6576) — quote it as low, moderate or high.
Push the pins firmly into the material surface. Take readings at consistent heights — typically at 150mm intervals from floor level upward. Take multiple readings across the wall to identify patterns. Avoid readings near metal (radiator pipes, DPC trays) as they give false highs. Note the temperature and any salt contamination.
Salts from rising damp, de-icing or chimney deposits can give falsely high readings because salts increase conductivity. Temperature extremes also affect readings. Foil-backed plasterboard, metallic paint, carbonation in plaster and proximity to metal pipes all cause inaccurate readings.
A damp survey is recommended when you see visible signs: staining, peeling wallpaper, white salt deposits (efflorescence), musty smell, condensation, or deteriorating plaster. A survey identifies the type of damp (rising, penetrating, condensation) and its cause, guiding the correct treatment.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.