You've cleaned it.
You've sprayed mould remover.
You've even repainted the wall.
Yet a few weeks later, those familiar black spots begin appearing around the window again.
Across Stoke-on-Trent, this is one of the most common concerns we investigate during damp surveys.
Homeowners regularly ask:
👉 "Why is the mould always around the windows?"
👉 "I've cleaned it several times—why does it keep coming back?"
👉 "Is the window leaking?"
In many cases, the answer isn't a leaking window at all.
Window reveals are often one of the coldest parts of a home, making them a prime location for condensation and black mould.
Understanding why mould forms here can help you solve the underlying problem rather than repeatedly treating the symptoms.
🪟 What Is A Window Reveal?
A window reveal is the section of wall between the window frame and the internal room.
Although it appears to be just another part of the wall, it's actually one of the most complex areas of the building.
Around every window there are several different materials coming together, including:
- Brickwork
- Window frames
- Lintels
- Plaster
- Insulation
- Sealants
Because these materials conduct heat differently, window reveals often remain colder than the surrounding wall.
🌡️ Thermal Bridging Makes Reveals Colder
One of the biggest reasons mould appears around window reveals is thermal bridging.
Thermal bridges occur where heat escapes more quickly through part of the building fabric.
Around windows this may be caused by:
- Concrete lintels
- Older cavity construction
- Limited insulation around openings
- Structural changes in the wall
As a result, the reveal often has a much lower surface temperature than nearby plaster.
💧 Condensation Forms On Cold Surfaces
Warm air naturally contains water vapour.
As this warm, moisture-filled air touches the colder reveal, it cools rapidly.
Once the surface temperature falls below the dew point, condensation forms.
Initially, this moisture may not even be visible.
Repeated condensation allows the surface to remain damp for extended periods.
This creates ideal conditions for mould growth.
🍄 Why Black Mould Always Returns
Many homeowners successfully remove the visible mould.
Unfortunately, if the underlying conditions remain unchanged, it simply returns.
This happens because:
✔ The reveal remains cold.
✔ Humidity inside the room remains high.
✔ Condensation continues forming.
Cleaning removes the mould.
It doesn't remove the moisture causing it.
🌬️ Poor Ventilation Makes The Problem Worse
Homes produce moisture every day through:
- Showering
- Cooking
- Drying washing indoors
- Breathing
- Everyday living
Without effective ventilation, humidity gradually increases.
The moisture then settles on the coldest surfaces.
Window reveals are often first in line.
This is why mould frequently appears around windows before anywhere else in the room.
🏠 Modern Windows Don't Always Eliminate Condensation
Many people believe installing new double glazing will solve mould around windows.
While modern glazing improves thermal performance, it doesn't remove the moisture created inside the property.
In fact, because modern windows are more airtight, natural background ventilation can actually reduce if trickle vents remain closed or extractor fans aren't used effectively.
Without adequate ventilation, humidity levels continue to rise.
🛋️ Curtains And Blinds Can Restrict Airflow
Window reveals often receive less airflow than the rest of the room.
Heavy curtains, fitted blinds and furniture placed beneath windows can reduce warm air circulation.
This allows the reveal to remain cooler for longer.
The longer the surface stays cold, the greater the opportunity for condensation to develop.
🌧️ Could Rainwater Also Be Contributing?
Sometimes.
Although condensation is by far the most common cause, external defects should never be ruled out.
Potential issues include:
- Failed window sealants
- Cracked render
- Defective pointing
- Damaged brickwork
- Faulty window cills
If mould worsens after heavy rainfall or damp patches appear beneath the window, further investigation may be needed.
⚠️ Signs Your Window Reveals Need Attention
Watch for:
✔ Black mould around window frames
✔ Condensation every morning
✔ Peeling paint
✔ Bubbling plaster
✔ Damp patches below the window
✔ Musty smells
These symptoms often indicate that moisture is repeatedly collecting around the reveal.
🔍 How We Diagnose Mould Around Windows
At Weather Wise Solutions Limited, we assess:
- Relative humidity
- Ventilation performance
- Thermal bridging
- Window detailing
- External wall condition
- Moisture patterns
Because the important question isn't:
👉 "How do we clean the mould?"
It's:
👉 "Why is moisture collecting around the window reveal?"
🛠️ How We Resolve Recurring Window Mould
The correct solution depends on the cause.
Recommendations may include:
- Improving ventilation
- Installing Positive Input Ventilation (PIV)
- Upgrading extractor fans
- Repairing failed sealants
- Repairing defective render or pointing
- Managing indoor humidity
- Installing insulation plaster systems where appropriate
Our objective is always to eliminate the moisture source rather than repeatedly treating the mould itself.
👨🔧 Preventing Black Mould Around Window Reveals
Simple changes can significantly reduce the likelihood of mould returning:
✔ Keep trickle vents open where fitted.
✔ Use extractor fans during cooking and showering.
✔ Avoid drying clothes indoors where possible.
✔ Leave a small gap between curtains and the wall.
✔ Maintain a steady indoor temperature.
✔ Repair external defects promptly.
These measures help keep reveals warmer and drier throughout the year.
📞 Need Help in Stoke-on-Trent?
If black mould keeps returning around your window reveals, it's worth identifying the underlying cause before it spreads further.
At Weather Wise Solutions Limited, we're a family-run damp company specialising in:
- Damp proofing
- Mould and condensation control
- Ventilation solutions
- Penetrating damp diagnosis
- External wall repairs
We're also proud members of the Damp Proofing Association and the Federation of Damp, with surveyors holding the City & Guilds-recognised Federation of Damp Certified Surveyor (FODCS) qualification.
👉 Book your free quote here: https://weatherwiseuk.co.uk/pages/contact
👉 Contact us today: https://weatherwiseuk.co.uk/pages/contact