Damp and Mould on Exterior Walls: How to Prevent and Fix It
Exterior walls are constantly exposed to the elements, and when damp and mould appear on the façade, it’s not only unsightly—it can also damage your property and reduce its value.
Here’s what you need to know about preventing and treating mould and moisture on your home’s external render.
🧪 Why Does Mould Appear on Exterior Walls?
Mould and algae thrive in humid, shaded areas—especially on north-facing walls. The most common causes include:
- Poor water drainage or splashback from the ground
- Blocked or broken gutters and downpipes
- Leaky roofs or windows
- Cracked or porous render
- Lack of ventilation
These factors create an ideal environment for algae, moss, and black mould growth.
🧼 How to Remove Mould and Moisture Stains
If mould has already formed, take these steps:
- Clean the surface: Use a pressure washer or stiff brush to remove visible growth.
- Apply anti-fungal treatment: Special biocide or anti-mould solutions kill spores at the root.
- Rinse thoroughly: Let the surface dry completely after cleaning.
- Inspect render: Cracks or damaged render should be repaired before mould can return.
- Paint with breathable coatings: Use a high-quality, mould-resistant exterior paint that allows walls to breathe.
🧱 How to Prevent Mould on Your Façade
Prevention is key to long-term protection. Here’s how to reduce the risk:
- Improve drainage: Ensure water drains away from walls and the ground slopes away from the building.
- Fix leaks fast: Repair damaged gutters, downpipes, and roof tiles.
- Increase airflow: Trim nearby vegetation and trees that block sunlight and airflow.
- Maintain your render: Inspect and repair cracks, chips, or damaged areas annually.
- Apply protective coatings: Use breathable, water-repellent products that reduce water absorption while allowing moisture to escape.
🔧 When to Call a Professional
If mould keeps returning or the wall shows signs of structural damage, it’s time to consult an expert. Persistent damp could indicate hidden leaks or insulation issues that need proper investigation.
A professional render specialist can:
- Identify the root cause
- Clean and treat the façade properly
- Repair and reseal damaged render
- Repaint with protective coatings