Damp is the most common defect in Madeira's houses. The mild but humid climate, the nearby sea and homes built into slopes all favour it. The most common mistake is to paint or re-plaster without knowing where the water comes from, and the problem comes back the following winter.
1. The three types of damp
- Condensation: water vapour from inside condenses on cold surfaces. It appears in corners, behind furniture, around windows and on bathroom ceilings, often with black mould.
- Rising damp: groundwater rises through the walls by capillary action. It leaves a damp band near the floor, up to about 1 metre, with white salts and crumbling plaster.
- Water ingress: rainwater gets in through roofs, terraces, windows, cracks or buried walls. Stains grow after rain and usually have irregular edges.
2. How to tell them apart on site
Watch when and where it appears. If it gets worse in the cold with the house closed up, think condensation. If it is always at the base of the walls, even in summer, think rising damp. If it appears or grows after rain, look for water ingress. Hygrometer readings and thermal imaging help confirm it, but do not replace observation over time.
3. On a slope, look behind the wall
In houses built against the hillside, many stains come from buried walls without waterproofing or drainage. Water builds up behind the wall and passes through it. In these cases the fix is on the outside: drainage, waterproofing and sometimes a ventilated cavity.
4. Repair in the right order
- Remove the cause: ventilation, roof repair, drainage or a barrier against rising water.
- Let the wall dry, which can take weeks.
- Remove damaged plaster and salts.
- Redo it with compatible materials: on old stone walls, lime mortars and mineral paints that let the wall breathe.
5. Mistakes to avoid
- Cement renders and plastic paints on old masonry.
- Anti-mould paint as a permanent fix.
- Sealing every air gap when replacing windows without planning ventilation.
Quick checklist before asking for a quote
- Dated photos of the stains, before and after rain
- Rooms and walls affected
- History of work on the roof and windows
- Technical diagnosis with the cause identified
A repair is only done well when the cause has been solved. If the expert cannot explain where the water comes from, it is too early to price the work.