Black mould on walls

Black Mould on Walls

Spots in corners or around windows are usually condensation, not damp from outside.

OxfordshireDamp · Remedy · Restore

Field note

Category: Wall symptoms
Likely cause: Condensation
Guarantee: 10-year written

CSRT-accredited survey

Schematic · Plate 03

AP/DAMP

Spots in corners or around windows are usually condensation, not damp from outside.

The cause

What causes it

Black spots that appear in corners, behind furniture, or around window reveals are almost always condensation mould rather than rising damp. It grows where warm, moist indoor air meets a colder surface and deposits its moisture there — the same way water beads on a cold drink. Modern living habits produce a lot of moisture: showering, cooking, drying laundry indoors, and breathing all add litres of water to the air every day. Without enough ventilation and background heat, that moisture finds the coldest spot in the room and feeds mould growth.

Presentation

What to look for

The mould looks like clusters of small black or dark green spots, sometimes merging into larger patches. It favours the cold side of north-facing rooms, the upper corners of external walls, the strip of wall behind a wardrobe, and the silicone seals around windows. The wall itself usually feels cold but not soaking wet. You may also notice misted-up windows in the morning and a faintly musty smell in the affected room, even after wiping the visible mould away.

Why it matters

If it is left alone

Condensation mould is a health concern as well as a cosmetic one. The spores it releases can trigger asthma, allergies, and respiratory irritation, and the problem typically worsens through autumn and winter as heating patterns and ventilation drop off. Bleaching the visible mould without changing the underlying conditions only works for a few weeks before it returns. Persistent condensation can also damage soft furnishings, books, and clothing stored against affected walls, and over time it deteriorates plaster and decoration.

The remedy

How we treat it

Successful treatment focuses on the cause, not the symptom. We carry out a moisture and ventilation survey to identify why the air in the property is staying damp — which often points to inadequate extraction in the kitchen and bathroom, blocked or sealed-up vents, or insufficient background heat. Solutions can include positive input ventilation units, upgraded extractor fans on humidistats, trickle vents, and targeted insulation of cold spots. Affected areas are treated to remove existing mould safely, then redecorated with a moisture-tolerant system. The work is guaranteed and tailored to your property.

Recommended treatment

Condensation Control

Every treatment begins with a CSRT-accredited on-site survey, is delivered to a written specification, and is backed by a 10-year guarantee against recurrence.

Written specification 10-year guarantee

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