Removing a stain is not the same as solving a damp problem. Water can reach a building through leaks, defective external details or condensation, and several causes can operate together. Start by recording what is happening before choosing a treatment.
Record symptoms without assuming a diagnosis
Photograph affected areas and note the date, weather and any recent plumbing or building work. Record whether marks change after rain, appear beside a bathroom or recur behind furniture. A cold wall, a musty smell or a reading from a handheld meter does not, on its own, establish the cause.
Make a simple room plan marking the affected surfaces. This gives an inspector a useful starting point and makes it easier to compare conditions after repairs.
Arrange an investigation that considers the whole building
Ask an appropriately qualified surveyor or building professional to explain the likely sources of moisture, the evidence supporting their conclusions and any areas they could not inspect. Request a written account of recommended repairs and further investigations. Be cautious about committing to a proprietary treatment before the source has been established.
Deal with mould and the underlying defect
The government’s damp and mould guidance for England stresses the health risks and the need to address underlying causes. Surface cleaning alone will not stop recurrence. Larger affected areas may require professional removal; people with health concerns should seek medical advice.
Do not paint over active mould or use a dehumidifier as a substitute for repairing a leak. Follow product safety instructions for any cleaning and never mix cleaning chemicals.
For tenants and landlords
Tenants should report the problem promptly in writing and keep a record of reports and responses. Landlords should investigate sensitively, assess urgency and avoid assuming that the occupant’s behaviour explains a building defect. Ventilation and heating advice must sit alongside proper investigation and repairs.
Check that the work has succeeded
Agree what will be repaired, how drying will be assessed and when the property will be revisited. Compare dated photographs and observations over time rather than judging success from a freshly decorated wall. If the symptoms return, reopen the investigation.
For wider work, use our renovation budgeting guide to distinguish investigation, repairs and decoration costs.
Revised and sources checked on 21 October 2026.














