If mould returns after cleaning or painting, the moisture problem hasn't been resolved. Better ventilation may help condensation, but a leaking pipe or rain entering the building needs a different repair. Before paying for another coating or treatment, ask how the source of the damp will be established.
Notice when it gets worse
Photograph the same area over time. Note rain, wind, cooking, bathing, drying clothes and periods when the home is closed up. Check whether it follows a pipe or fixture, appears after storms or gathers on cold surfaces.
These patterns help the investigation, but similar-looking stains can have different causes. Be cautious about anyone who chooses a universal treatment before asking how the moisture behaves.
Ventilation matters, but it cannot fix a leak
Check that vents and extraction are present and working. Normal indoor activities produce moisture; Spain's Building Code treats ventilation as part of managing it.
A dehumidifier may help drying and condensation. It won't repair a pipe or failed façade. Neither will leaving the window open indefinitely. Ask for an explanation of the likely source and how it will be tested.
Agree a repair that addresses the cause
Shared roofs, façades and pipes can need community involvement, so notify the administrator when those are suspected. Have the source dealt with, allow drying and restore the wall with suitable materials.
Where cold surfaces drive condensation, insulation or thermal-bridge work may be part of the answer. IDAE recommends dealing with moisture defects before thermal rehabilitation. Ask the contractor to explain how the proposed treatment addresses the cause and what would need reviewing if the damp returns.
Before you go ahead
- Pattern and weather recorded
- Plumbing and exterior sources considered
- Ventilation checked
- Community notified if common element suspected
- Cause repaired before repainting
Common questions
Is black mould always caused by poor ventilation?
No. Ventilation can be involved, but leaks, rain penetration, thermal bridges and other moisture sources can create similar visible growth.
Will a dehumidifier solve it?
It can reduce indoor humidity and help drying, but it does not repair a leaking pipe, failed façade or missing ventilation system.
Sources and further reading
Official information checked on 12 October 2026. Rules and procedures can change; verify the live source for your exact circumstances.