Short answer: A wall moisture scanner can help map suspicious areas in an old house, but mixed materials make cautious interpretation essential. The MT-28 product page describes a pinless meter for surface-moisture checks on wood and building materials, with a colour screen and listed 5–75% range. The manufacturer does not specify sensing depth, accuracy or calibrations for lime plaster, gypsum, masonry, timber lath, salts or foil-backed finishes. Compare only similar construction areas, record patterns and investigate visible defects separately. Do not use one percentage to declare an old wall dry or to identify rising damp, condensation or water ingress.
Why old-house readings need context
An older wall may change from masonry to timber, contain repairs, salts, metalwork or several finish layers. A pinless scanner can react differently across those changes, while the current MT-28 page provides no old-building calibration or material-response chart.
Start by identifying the wall construction as far as practical. Compare readings within the same apparent build-up rather than ranking unrelated rooms or materials on one scale.
| Old-house feature | Possible interpretation problem | Practical response |
|---|---|---|
| Mixed plaster or repairs | Different materials may display differently | Map construction changes and compare like areas |
| Hidden metal or services | May influence a pinless reading | Repeat nearby and corroborate before drawing conclusions |
| Visible salts or staining | A reading does not identify the cause | Record the evidence and investigate the defect |
| Unknown wall build-up | Depth and calibration are unspecified | Seek a competent building assessment |
Create a defensible survey record
A grid and notes make the scan more useful than isolated numbers. Record room, wall, height, visible condition, finish and nearby features. Repeat the same points later only when conditions and the purpose of monitoring are clear.
- Photograph and describe visible staining, mould, decay or damaged finishes.
- Mark areas of apparently similar wall construction.
- Take consistent grid readings and repeat unexpected values.
- Note windows, chimneys, plumbing, external ground levels and previous repairs.
- Refer persistent or complex patterns for competent diagnosis and remediation advice.
Do not let the scanner name the defect
GOV.UK guidance identifies multiple routes to damp and mould, including condensation, leaks and building defects. The MT-28 display cannot distinguish among them, date the moisture or show whether hidden structural material is affected.
Use the scan to refine questions: where should the building be inspected, does a pattern repeat, and what visible evidence needs attention? Keep the diagnosis separate.
MT-28 limitations in historic fabric
The manufacturer does not specify accuracy, sensing depth, lime-plaster calibration, masonry calibration, salt compensation, response to metal or suitability for heritage surveys. Its listed 5–75% range is not evidence of absolute moisture content across old-house materials.
Where intrusive work, conservation decisions or remedial treatment are being considered, use an appropriately qualified surveyor and methods suited to the building fabric. A handheld screening meter should not decide those interventions alone.
Related guides and product details
Use the MT-28 to build a cautious comparative map in an old house, then combine that record with visible evidence and competent investigation before deciding on repairs. Read Non-Invasive Damp Meter for Plaster Walls: Limits for related guidance. Read Pinless Moisture Meter for Walls: UK Buying 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, stated material scope, colour screen, listed range and dimensions. Current Andinstrument MT-28 product page.
- Supports investigation of varied damp and mould causes and prompt remedial attention. Understanding and addressing the health risks of damp and mould in the home.