Do I have damp or condensation on my wall?

What is each one?

Condensation happens when water vapour in the air of your home meets a cold surface and settles on it. The water comes from inside the house: showers, cooking, washing drying indoors.

Water ingress is water that gets in from outside or from a pipe and soaks the wall from within. It comes from rain, a cracked façade, a pipe or a roof.

Likely causes

Condensation tends to show up with poor ventilation, cold windows and walls, and a lot of vapour produced indoors. This is very common in Portugal: homes are often poorly insulated, many have no central heating, and a portable gas (butane) heater adds a lot of moisture to the air. Water ingress usually comes from faulty tiles, flashing or gutters, cracks in the façade, badly sealed windows or leaking pipes. You can have both at once, and then the picture is harder to read.

How to tell them apart: 5 signs

1. Where it appears. Condensation: cold corners, behind furniture, around windows. Ingress: near the roof, pipes or the outside wall.
2. When it appears. Condensation gets worse on cold days, in the morning and after showers and cooking. Ingress gets worse after rain.
3. What the mark looks like. Condensation: scattered black dots. Ingress: a yellowish or brownish stain with an edge and rings, and the paint may blister.
4. The window glass. Drops on the inside of the glass in the morning show the air in your home holds too much moisture.
5. The foil test. Tape a square of aluminium foil to the wall, sealed all round with tape, and leave it for 48 hours. Drops on the outside of the foil point to condensation. Moisture on the wall side points to water coming from inside the wall itself.

No single sign decides it. If three or four point the same way, the hypothesis gets stronger.

What to do now

• If it looks like condensation: ventilate every day, even in winter, with the windows open for a few minutes. Use the extractor fans in the kitchen and bathroom, avoid drying washing indoors without ventilation, and pull furniture away from cold walls. A dehumidifier helps, and a gas heater without a flue is best avoided.
• If it looks like water getting in: photograph it, see whether it worsens with rain, check gutters and drains, and find the source of the water before treating the wall.
• Either way: clean surface mould carefully, with gloves and a mask, but do not treat the problem as solved because of it.

If you rent, send your landlord (senhorio) the photos and dates. It helps to show what you saw and when.

When to call a professional

Call for help if the stain has an edge and is growing, if the wall is wet to the touch, if the paint is blistering, if it gets worse with rain, or if it came back after ventilating. For ingress from outside or from a pipe, look for a builder (pedreiro), a roofer (telhador) or a plumber (canalizador), depending on the source. For persistent condensation, a damp-proofing and ventilation specialist (técnico de isolamentos e ventilação) can assess the home.