Damp Patches: the Cause Comes First

A damp patch is the spot where water travelling through a wall or ceiling becomes visible. The most common repair that doesn't last is painting over it before the water has been dealt with.

Where it comes from

• From above. A roof terraceFlat roof (roof terrace)The flat concrete roof on top of a building. It is the most common kind of roof in Greece and the part that takes the most sun and rain., a balcony or the bathroom upstairs. A ceiling stain that grows after rain points first to the roof or the balcony.
• From a pipe. A patch that stays wet whatever the weather, near a bathroom or kitchen, may be a dripping pipe. That needs a plumber first.
• From the ground. Rising dampRising dampMoisture from the ground that climbs up inside walls through the pores of the materials. It shows as stains, blown render and salts at the foot of walls. shows low on the walls, above the skirting, often with white saltsEfflorescence (salt deposits)A white, powdery or crystalline crust on the surface of a wall. It is salts carried by water through the masonry, left behind when the water evaporates.. In one apartment the paint above the skirting boards had bubbled and peeledPeeling paintWhen paint loses its grip and lifts off in flakes or sheets. It is almost always a sign of a problem underneath, usually damp or poor preparation. for this reason.
• From the air. CondensationCondensationMoisture in the air turning to water on cold surfaces such as windows, outside corners and ceilings. It is the most common cause of mould indoors. appears in cold corners, behind furniture, in bathrooms and kitchens, usually with black spots of mouldMouldFungi that grow on damp surfaces, leaving black or greenish spots and a musty smell. It is a symptom of damp, not a problem with the paint..

Stains around windows can have more than one explanation: water getting in at the frame, or condensation on the cold wall around it. In the home where the ceiling had come down, there were stains and blistered paint between two windows. These areas were scraped and filled before painting. Which cause applies in a given home is something only an inspection on site can tell.

The order of the work

1. The cause is found and stopped: waterproofingWaterproofingThe work and materials that stop water getting through on flat roofs, balconies, bathrooms, basements, planters and tanks., a plumber, better ventilation, depending on the case. Often this is another tradesman's job.
2. The wall is left to dry. FillerFillerA fine paste or powder that fills holes, fine cracks and dents so a wall, ceiling or piece of wood is smooth before it is painted. and paint don't grip well on damp plasterRender (plaster)A layer of mortar (sand, cement or lime, and water) spread over brick or concrete to give a wall a straight, sound surface ready for paint or tiles..
3. Anything blistered or loose is scraped back to a sound surface.
4. Mould is cleaned off, otherwise it comes back through the new paint.
5. Filling and sandingSandingSmoothing a surface with sandpaper or a power sander to remove bumps, loose old paint or gloss, so the new paint or varnish grips well and comes out smooth..
6. A primerPrimerThe thin first coat that goes on before the main material. It binds dust, seals the pores and helps paint or waterproofing stick firmly. suited to the stain. Without it, the mark often shows through the new paint.
7. Painting, preferably the whole surface.

What to watch out for

• No paint can stop water that is still coming in. It may hide the stain for a while, but it won't solve the problem.
• If the stain comes back in the same place, the cause hasn't been fixed.
• If, along with the stain, the ceiling sags, sounds hollow or shows rusty steel, the job is bigger than a coat of paint.