Clean mould safely and fix the moisture source before repainting
Wear suitable protection, avoid dry brushing large areas and stop if the mould is extensive, linked to sewage or flooding, or affecting vulnerable occupants.
MOST LIKELY CAUSES
Start with moisture, airflow and cold surfaces
Symptom variations Match the exact location, smell and recurrence pattern. ⌄
- Mould returns within weeks
- Same patch reappears
- Musty smell persists
- Paint bubbles or peels
- Area stays cold or damp
Quick checks Simple checks before cleaning or redecorating. ⌄
- Check whether the surface is cold or visibly damp.
- Look for blocked airflow and furniture against walls.
- Measure humidity if possible.
- Check extractors, vents and recent water leaks.
- Identify whether porous materials are badly contaminated.
Step 1 — Stop treating only the surface Clean safely, dry fully and fix the moisture source before redecorating. ⌄
Map when and where the mould returns.
Step 2 — Identify the moisture pattern Clean safely, dry fully and fix the moisture source before redecorating. ⌄
Compare weather, occupancy, cooking, bathing and heating.
Step 3 — Repair the cause before redecorating Clean safely, dry fully and fix the moisture source before redecorating. ⌄
Ventilation, insulation or leak repairs come first.
Why mould grows here How this mould pattern develops. ⌄
Recurring mould means the surface is still becoming damp. Cleaning removes visible growth, but not the condensation, leak, poor ventilation or cold bridge behind it.
Advanced checks Further diagnosis for recurring or hidden mould. ⌄
- Monitor humidity over several days.
- Compare surface and room temperature.
- Check roof, plumbing and external walls.
- Inspect behind furniture and finishes.
- Replace badly contaminated porous materials where necessary.
Tools and information needed Useful items for safe diagnosis and cleaning. ⌄
- Digital humidity meter
- Suitable mould cleaner
- Protective gloves, mask and eye protection
- Surface-temperature checks
- Inspection of ventilation, insulation and leaks
Parts or improvements that may help Common items linked to this problem. ⌄
- Humidity meter
- Moisture investigation tools
- Ventilation upgrade
- Insulation materials
- Replacement plaster, sealant or damaged furnishings
When to call a professional Conditions that should end basic DIY treatment. ⌄
- The affected area is large or keeps spreading.
- There is hidden water ingress, sewage or flood contamination.
- Timber, plaster or insulation is badly damaged.
- Occupants have asthma, allergies or other vulnerabilities.
- The source appears structural or inside a wall or roof.
- The smell or mould returns despite ventilation and drying.
Frequently asked questions Common mould questions. ⌄
Can mould-resistant paint solve the problem?
Only after the moisture source is controlled. Paint alone will not stop mould on a surface that keeps getting damp.
Should mould be painted over?
No. The area should be cleaned, dried and the cause fixed before redecorating.
Is bleach always suitable?
No. Product suitability depends on the surface and contamination. Use a cleaner intended for the material and follow its instructions.