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MOULD GROWTH

Mould Around Windows

Mould around windows usually develops where condensation repeatedly wets cold frames, reveals and sealant. Poor airflow, high indoor humidity and failed seals can make the problem worse.

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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

Repeated condensation Moisture on cold glass and frames feeds mould growth.
Restricted airflow Curtains, blinds and furniture trap damp air around the window.
Failed sealant or frame seal Water can sit in gaps and porous finishes.
Cold reveal or frame Thermal bridging creates a colder surface around the opening.
◫ Symptom variations Match the exact location, smell and recurrence pattern. ⌄
  • Black mould on silicone
  • Mould on window reveals
  • Musty smell near frame
  • Wet sill each morning
  • Paint peeling around window
✓ Quick checks Simple checks before cleaning or redecorating. ⌄
  1. Check whether the surface is cold or visibly damp.
  2. Look for blocked airflow and furniture against walls.
  3. Measure humidity if possible.
  4. Check extractors, vents and recent water leaks.
  5. Identify whether porous materials are badly contaminated.
Important: Mould returning after cleaning means the moisture problem is still active.
1 Step 1 — Clean the visible mould safely Clean safely, dry fully and fix the moisture source before redecorating. ⌄

Use suitable protective equipment and a product intended for the surface.

2 Step 2 — Dry the area completely Clean safely, dry fully and fix the moisture source before redecorating. ⌄

Remove standing water and allow the frame, sealant and reveal to dry.

3 Step 3 — Fix the moisture cause Clean safely, dry fully and fix the moisture source before redecorating. ⌄

Improve ventilation, airflow and seals before redecorating.

⌁ Why mould grows here How this mould pattern develops. ⌄

Mould around windows usually develops where condensation repeatedly wets cold frames, reveals and sealant. Poor airflow, high indoor humidity and failed seals can make the problem worse.

⌘ Advanced checks Further diagnosis for recurring or hidden mould. ⌄
  1. Check whether moisture is room-side condensation or external leakage.
  2. Inspect glazing seals and frame drainage.
  3. Measure indoor humidity.
  4. Check trickle vents and extractor performance.
  5. Assess insulation around the reveal.
◇ 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. ⌄
  • Mould cleaner
  • Protective gloves and mask
  • Replacement silicone
  • Window seals or gaskets
  • Mould-resistant paint after drying
! 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.