Condensation damp: how to tell what it is and which paint to use
Guide to condensation damp.
Es la humedad más común en casa y se trata sin obra: el vapor de dentro se posa en la pared más fría. Te contamos cómo reconocerla, por qué vuelve si la tapas y qué necesitas.
If you see two or more at home, it's most likely condensation. The good news: it's treated at the surface, with anti-condensation paint and ventilation.
Drops on the glass in the morning and a darkened window frame. It's the vapour in your home settling on the coldest surface.
Black or greenish spots where air doesn't circulate: ceiling corners, behind headboards, wardrobes against outside walls.
It appears with the cold and the heating on, and almost disappears in summer. The wall isn't wet: it's cold.
Towels that never dry, a damp smell when you open the wardrobe, cold sheets. A sign the air is loaded with vapour.
Condensation doesn't come from outside. A family of four produces 10 to 15 litres of water vapour a day from showers, cooking, breathing and drying clothes indoors. That vapour seeks out the coldest surfaces in the house: corners of outside walls, pillars, roller-shutter boxes and lintels, where the wall is several degrees colder than elsewhere. There the air reaches its dew point and releases water.
If you cover the stain with a closed-film paint, you create a sealed layer. The vapour that used to escape through the wall can't any more; it gets trapped behind the coat and within a few months the paint blisters, flakes and the mould reappears in the same spot. The paint didn't fail: the approach did.
What works is the opposite: a breathable, anti-condensation mineral paint that doesn't form a closed film, plus ten minutes of cross-ventilation a day.
Dos productos, en este orden, con el −10 % en el MATE5000 ya aplicado en el carrito. Eliges el color en el siguiente paso.
Por separado 28,59 €26,69 €
Household fungicide or 10% bleach, rinse and scrape off anything loose. Let it dry for a day with the window open.
Short-pile roller, undiluted, from ceiling to floor. Water-based and low odour; ventilate while you paint.
At right angles to the first so the corners are well covered.
It doesn't remove the vapour. Condensation happens because humid indoor air touches a cold surface and releases water. MATE5000 is a breathable, anti-condensation mineral paint that works on the surface of the wall. Combined with 10 minutes of cross-ventilation a day, it's what we recommend for condensation.
Condensation comes from inside and follows the cold: ceiling corners, outside walls, behind furniture, and it gets worse with the heating on. A leak comes from outside and follows the rain: ringed stains that grow after it rains, usually on the ceiling or under windows. If the stain is low on the wall, less than a metre from the floor, read the salt damp guide. If you're unsure, send us a photo on WhatsApp and we'll tell you.
No. First clean it with a household fungicide or bleach diluted to 10%, leave it to work, rinse and let it dry for 24 hours. If the wall is badly affected or flaking, apply a coat of Sellador Total L44 before MATE5000: it regulates absorption and helps prevent algae and fungi growth. Painting over uncleaned mould only hides it for a few weeks.
A 4 L tin of MATE5000 covers around 10–14 m² with two coats (the manufacturer states 5–7 m²/L per coat). A 3 × 3 m room with a 2.5 m ceiling has about 30 m² of wall before taking off the door and window: a 15 L tin is more than enough. On the product page you enter your m² and it calculates the order.
For condensation, usually not. If the wall is sound, clean and dry, MATE5000 bonds directly to plaster, well-adhered old emulsion or cement. You only need Sellador L44 if the wall is flaking, has very absorbent new plaster or you've had recurring mould in that area.
The paint works on the surface of the wall, but the moisture in the air comes from how the home is used: drying clothes indoors, cooking without an extractor or sleeping with the window shut all load the air. Ventilate for 10 minutes a day and keep furniture away from outside walls. If the stain comes back, send us a photo and we'll take a look for free.
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