Black Mould on Cold Solid Brick Walls Treated With Isotherm
A small room with two cold external walls, solid brickwork and recurring black mould. We treated the mould, fitted the Isotherm thin thermal lining and skimmed over it, leaving the wall surface around 8°C warmer and far less likely to form condensation.
Cold solid walls, condensation and black mould
We were called out to a small room with solid brick walls. Two of the walls are external, one with a window, so the room has cold masonry on two sides.
Solid brick walls have no cavity and no insulation, so in colder weather the inside face of the wall gets very cold. Warm, moist air from everyday living hits that cold surface and turns into condensation, and black mould soon follows. Wiping it off or painting over it does not last: while the wall stays cold, the mould keeps coming back. Getting the right fix starts with a proper damp survey to confirm the cause.
Treat the mould, then warm the wall
We began by thoroughly cleaning the affected walls with a specialist fungicidal wash containing benzalkonium chloride, a biocide that kills the mould rather than just bleaching the staining. The walls were then prepared and keyed so the new system would bond to a sound, clean surface.
- Mould killed with a benzalkonium chloride fungicidal wash
- Walls prepared and keyed ready for the thermal lining
- Isotherm thin thermal lining bedded in its own adhesive
- Taken right into the window reveals, often the coldest spot
- Skimmed over to leave a smooth finish ready to decorate
A thin thermal lining that loses no space
The Isotherm thermal lining is a thin thermal liner bedded in its own adhesive across both external walls. We took it right into the window reveals as well, often the coldest spot in the room.
It is thin, with a finished build-up of only around 10mm, so the room loses no noticeable space. Once fitted, the walls were skimmed directly over the lining to leave a smooth, clean surface ready for decorating.
Why it works
Condensation forms when warm, moist air touches a surface colder than its dew point, the temperature at which moisture in the air turns back into water. Cold solid walls often sit below that point in winter.
By putting a thermal layer between the cold brick and the room, the inside face of the wall stays warmer and above the dew point, so moisture stays in the air instead of settling on the wall. No damp surface, no mould. Good ventilation and steady heating still help, and we are always happy to advise on both as part of our condensation and mould control work.
Warmer walls, no sign of the mould
The room now has smooth, freshly skimmed walls with no sign of the black mould. The Isotherm lining warms the wall surface by around 8°C, so the walls are far less likely to drop to the point where condensation forms.
Once the plaster has fully dried out, the walls can be decorated, ideally with a breathable paint. The result is a clean, usable room with the underlying cause of the mould addressed, not just the staining hidden. If you have similar cold, mouldy walls, get in touch for honest advice.
The job, step by step
From mould treatment and wall prep, through fitting the Isotherm lining into the window reveals, to the finished skimmed walls.
Got black mould or cold walls?
If you have black mould or condensation on cold walls anywhere in Barnsley, Sheffield, Rotherham, Doncaster or across Yorkshire, our qualified CSRT and CSSW surveyors will find the real cause and recommend the right fix, with no pushy sales. We are PCA certified and TrustMark endorsed, with insurance-backed guarantees available.
01226 287181Request a damp survey