Topic
Most mould in UK homes is surface mould caused by condensation. It is not a sign that the building is failing. It is a sign that warm, moist air is meeting a cold surface and staying damp long enough for mould to grow.
The fix is almost always the same combination: reduce the moisture in the air, improve airflow, and deal with any cold surfaces that keep attracting condensation. Surface mould can be cleaned safely. What you cannot do is clean your way out of a moisture problem — if the wall keeps getting damp, mould will keep coming back.
If you have mould and want to understand why it keeps returning, start with Why Does Mould Keep Coming Back After Cleaning? — it covers diagnosis and points you to the right fix based on what you find.
If you have a patch to clean right now, go to How To Remove Mould From Painted Walls first, then come back to diagnosis once the surface is dealt with.
If your bedroom windows are wet inside most mornings, that moisture is also affecting your walls. How To Stop Condensation On Bedroom Windows covers the overnight condensation cycle and how to break it.
Surface mould on painted plaster is usually a DIY job. Get advice if:
Ventilate the room, wear gloves and eye protection, and clean the patch with a mould remover labelled as suitable for painted surfaces. Wipe it down as directed and dry the wall fully. Do not repaint until the mould is gone and the wall is completely dry.
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The fix is usually about moisture and airflow, not the window itself. Open trickle vents if you have them, avoid drying clothes in the bedroom, keep curtains away from the glass overnight, wipe water off each morning, and use a dehumidifier if humidity stays high.
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Mould usually comes back after cleaning because the surface has been treated but the cause has not. In UK homes, the usual causes are condensation, poor ventilation, cold external walls, furniture pushed tight against walls, leaks, or damp materials that never fully dry.
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