Sign of damp
Black mould spots
Clusters of black, dark green or grey dots that spread into blotches, usually in corners, behind wardrobes, above windows, on bathroom ceilings or along the line where wall meets ceiling. It may smear when wiped and tends to come back in the same place.
What it might mean in a flat
Dark speckles and patches on walls and ceilings.
Mould needs a surface that stays damp, so it tells you where moisture sits for long periods. The key question is whether that moisture comes from inside the room as condensation or from a leak or rain entry. Condensation mould tends to sit on the coldest surfaces and corners with low readings inside the wall; mould from a leak sits on plaster that reads wet through its depth.
Common causes
- Surfaces staying damp for long periods, whether from a leak, rain entry or condensation
- Condensation in bathrooms and bedrooms with little ventilation, especially on cool external walls and corners
- Wardrobes or beds pushed against an external wall, stopping air from drying the surface
- A slow leak from a concealed pipe or the floor above keeping one patch wet
- High indoor humidity through the monsoon with windows kept shut
What an inspection checks
How we confirm it.
- Meter readings on and around the mould: pin readings show whether the plaster is wet below the surface, pinless readings show the wider area, both against the dry reference wall
- Room temperature and relative humidity with a hygrometer, to judge how likely condensation is
- Thermal scan to find cold corners and thermal bridges where condensation forms, and any cool patch that could be a leak, confirmed with the meter
- Ventilation: exhaust fans, window openings, and furniture against external walls
- Whether the mould lines up with a bathroom above, a pipe route or a window head
When to worry
Signals that it's active.
- Mould returns within days or weeks of cleaning
- The plaster under the mould reads wet with the pin meter, which points to a leak rather than surface condensation
- Mould is spreading inside wardrobes, behind panelling or on a ceiling under a bathroom
- Anyone in the home has health concerns: WHO's 2009 guidelines on dampness and mould link damp homes with respiratory symptoms; speak to a doctor about health concerns
Where it usually comes from
Questions buyers ask
Is black mould dangerous?
Megahedge does not give medical advice. WHO's 2009 guidelines on dampness and mould link damp homes with respiratory symptoms; speak to a doctor about health concerns. What we can tell you is where the moisture is and where it is likely coming from.
Does mould always mean there is a leak?
No. Much bathroom and bedroom mould comes from condensation: warm, humid air meeting a cooler surface. A meter reading into the plaster, a humidity reading and a look at ventilation usually separate condensation from a leak.
Will anti-fungal paint fix it?
It can slow regrowth on the surface, but if the wall stays damp the mould usually comes back. Fix the moisture first: the leak, the rain entry, or the ventilation.
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