Why damp is an island subject
Relative humidity in Funchal stays close to seventy per cent for most of the year. The air almost always carries a lot of water vapour, and that vapour is where most wall staining comes from.
The mild climate has a side effect: homes here are rarely heated. Without heating, external walls stay cold, and cold surfaces are exactly where vapour turns back into liquid water.
The island is not uniform. The north side is wetter and cloudier, the south is drier and sunnier, and near the coast salt air attacks window frames and fittings. Homes cut into the hillside have the additional problem of ground water behind the rear wall.
Condensation and ingress are not the same
Condensation is moisture produced inside the home: vapour from showers, cooking, drying laundry and breathing, which cools on a cold surface and settles there as water. It is a problem of ventilation and surface temperature.
Water ingress, or infiltration, is water entering from outside through a defect: the roof, a terrace, a blocked gutter, a crack in the facade, a poorly sealed window or a leaking pipe inside a wall. It is a problem of weathertightness.
There is also rising damp, which travels up from the ground through the wall and shows near the floor, mostly in older buildings built without a damp barrier. Each has a different remedy, which is why identifying the source always comes before repairing anything.
How to tell them apart
Condensation spreads out: corners, the junctions of external walls, behind furniture, inside wardrobes, on window glass in the morning, on the bathroom ceiling. It shows as speckled black patches and gets worse in the cooler months.
Ingress is local and has a history. It stays in one place, has a defined edge and often a yellowish halo, and it worsens with rain or with wind from a particular direction. If the patch grows on wet days, it is not condensation.
Try the plastic test: tape a piece of clear plastic tightly over the patch and wait a day or two. Droplets on the room side mean condensation. Moisture underneath, against the wall, means the water is coming through the wall.
- Water on the inside of windows in the morning: condensation
- One fixed patch that grows when it rains: ingress
- A damp band at the base of a wall with white salt deposits: rising damp
- Mould across several rooms at once: not enough ventilation
- A bulging ceiling or paint lifting in sheets: water from above
What you can fix yourself
Almost all mild condensation improves with habits. Opening windows fully two or three times a day, even for a few minutes and even in winter, replaces saturated air far faster than leaving one window ajar all day.
Dry laundry outside whenever the weather allows. A full load hung indoors releases litres of water into the air of a closed room, and that water reappears on the walls.
Pull furniture away from external walls so air can move, use the extractor when cooking, and leave the bathroom door open after a shower. A dehumidifier helps in a closed-up flat, but it treats the symptom rather than the cause.
- Ventilate in the morning and again in the evening
- Do not block the ventilation grilles the building already has
- Dry laundry outdoors or in a ventilated room
- Keep furniture a few centimetres off cold walls
- Clean small patches with a proper product, gloves and the window open
What needs a professional
All water ingress does. The source is rarely where the stain is: water enters at one point of the roof or facade and travels through the structure before appearing somewhere else, sometimes several metres lower.
Call a roofer when the stain is on a top floor ceiling, when gutters overflow, or when tiles are missing after strong wind. Call a window specialist when water comes in around the frame, or when single glazing is the coldest surface in the room.
Once the source is fixed, the wall itself needs work: cut out the affected render, replaster and repaint with a suitable product. Painting before the wall has dried is money wasted, because the paint lifts again.
- Roof, terrace and blocked or broken gutters
- Cracks in the facade and failed window seals
- Plumbing leaks inside walls or under floors
- Render or plaster breaking up over a large area
- Installing ventilation or mechanical extraction
- Insulating cold walls as part of a renovation
Mistakes that make it worse
The most common mistake is painting over it. Paint hides the stain for one winter and then lifts, while the damp has carried on working underneath.
The second is sealing everything. Blocking ventilation grilles and sealing old windows to keep the warmth in leaves the vapour with no way out, and simply moves the mould into wardrobes and behind furniture.
The third is waiting. A roof with one broken tile is a small summer repair and a full ceiling, plaster and paint job after a whole winter of rain.
When to deal with what
Summer is the season for anything outside: check tiles, clear gutters, seal cracks and redo window seals while it is dry and the wall can dry out after the work.
The wet months are for observing. Note which days the patches appear, with which wind and which rain, and photograph them with the date attached. That information is valuable to whoever diagnoses the problem.
If you rent, report ingress to the landlord in writing and keep your photos. If you run a holiday let, check the closed rooms between guests, because an empty home with no ventilation grows mould within weeks.