Short answer: A non-invasive damp meter can help map comparative readings across a plaster wall without making pin holes, but it cannot diagnose the cause of damp or prove that plaster is dry. The MT-28 product page describes pinless surface-moisture checking on wood and building materials, a colour screen and a listed 5–75% range. The manufacturer does not specify plaster calibration, sensing depth, accuracy or diagnostic thresholds. Use repeated readings to identify patterns for further investigation, then assess ventilation, leaks, condensation and building defects separately rather than treating one displayed percentage as a diagnosis.
What the MT-28 can show on plaster
The current listing supports non-invasive surface scanning on building materials. That makes the meter suitable for building a comparative map: scan a visibly unaffected area, then compare nearby points using the same orientation and contact method.
A higher or lower display at one point is an observation, not a diagnosis. Metal, services, salts, surface finishes and different underlying materials may affect comparative readings, while the manufacturer does not specify how the MT-28 responds to those conditions.
| Question | What is documented | What remains unknown |
|---|---|---|
| Does it pierce the finish? | The meter is described as pinless | Whether every delicate finish tolerates contact |
| What range is shown? | A listed 5–75% range | Plaster calibration and diagnostic thresholds |
| How deep does it read? | Manufacturer does not specify | Sensing depth and influence of hidden materials |
Make a repeatable wall map
Comparative scanning is most useful when each reading is taken consistently. Mark a simple grid, keep the meter in the same orientation and record the location rather than relying on memory. Repeat an unexpected result before changing the investigation plan.
- Inspect the wall for visible staining, mould, damaged finishes and nearby plumbing before scanning.
- Choose a reference area of the same wall construction that appears unaffected.
- Scan a labelled grid with consistent contact, orientation and spacing.
- Repeat unusual readings and note nearby corners, windows, pipes or external walls.
- Use the pattern to decide where a competent survey or defect investigation is needed.
Separate moisture screening from damp diagnosis
GOV.UK guidance explains that damp and mould can have several causes, including building defects, inadequate ventilation, condensation and leaks. A meter reading cannot distinguish those causes or assess the associated health risk.
Do not use the MT-28 result to dismiss visible mould or symptoms. Address visible damp and mould promptly and seek appropriate housing, building or health advice where the problem persists.
Limitations before buying
The manufacturer does not specify plaster accuracy, sensing depth, resolution, repeatability, calibration modes, operating humidity or a plaster-specific interpretation chart. The 5–75% listing should therefore remain a displayed range, not a claim of absolute plaster moisture content.
Buy this model only if comparative surface screening is the intended task. Work needing traceable measurements, material-specific calibration or a formal damp diagnosis requires documented specialist equipment and competent interpretation.
Related guides and product details
Choose the MT-28 for non-invasive comparative mapping, then keep decisions about cause, remediation and building safety with a properly evidenced investigation. Read Pinless Moisture Meter for Walls: UK Buying Guide for related guidance. Read Wall Moisture Scanner for an Old House: Reading Guide for related guidance. Review the documented specification on the MT-28 pinless moisture meter with colour screen product page before ordering.
Sources and safety context
- Supports the pinless format, listed materials, colour screen, 5–75% range and approximate dimensions. Current Andinstrument MT-28 product page.
- Supports the need to investigate and address causes of damp and mould rather than relying on one reading. Understanding and addressing the health risks of damp and mould in the home.