Mould and Groundwater Ingress in a Flat on Girdwood Road, Wandsworth SW18
A flat on Girdwood Road in Wandsworth had mould in the back bedroom despite a dehumidifier running with the windows open. The survey found two problems feeding each other: condensation and groundwater coming through the wall.
Project at a Glance
The Brief
The occupants were fighting mould around the bedroom windows and at low level on the walls.
The Survey
On arrival a dehumidifier was running in the bedroom with the windows open, yet mould was still present around the window frames, ledges and low on the walls. The front bedroom, which already had Type A and Type C waterproofing, read 55.5 percent humidity, a level at which mould spores can activate.
The back bedroom was also believed to have groundwater tracking from the surrounding earth into the cavity wall and saturating the render and skim, adding more moisture to the room. There was no mechanical extract in the bathroom and only a cooker hood in the kitchen.
The Solution
A combined plan:
- Install a Type C cavity drain system to the back bedroom walls, except the internal wall to the kitchen.
- Fit smart extract fans to the kitchen and bathroom.
- Replace the battery in the existing high level sump alarm.
- Apply a mould treatment wash before redecoration.
The Work
The waterproofing, mould clean, electrics and passive vent work was carried out on 21 July 2026.
The Result
Managing the water behind the wall and the moisture in the air together gives the bedroom a real chance to stay mould free. See our page on damp proofing in Wandsworth, or read about mould removal.
Frequently Asked Questions
Why is there mould even with a dehumidifier?
If water is also coming through the wall, or rooms lack extraction, a dehumidifier alone cannot keep up.
What is a Type C waterproofing system?
A cavity drain membrane that collects water coming through a wall and directs it to drainage, rather than trying to block it.
Do extract fans really help?
Yes. Humidity controlled fans remove moisture at source in kitchens and bathrooms before it spreads.
Mould that keeps coming back?
Our CSSW and CSRT trained surveyors find the real cause before recommending any work. Non-invasive survey with a clear written report. No obligation.
Project completed by Advanced Damp in Wandsworth, SW18.
Sam Fitzgerald is the founder of Advanced Damp and a working damp and structural waterproofing surveyor diagnosing and treating moisture problems in residential and commercial properties across London and the South East. He is FODCS certified (a Federation of Damp Certified Surveyor) and a member of the Federation of Damp. His hands-on work covers rising damp, penetrating damp, condensation, basement waterproofing to BS 8102, and thermal imaging surveys, and he has personally completed over 400 damp surveys across properties of every type and age. Everything he writes draws directly from jobs he has carried out. He does not write about treatments, products or causes he has not dealt with first-hand in the field.
