If your walls darken in a corner, it’s no coincidence: find out what it really means (and how to fix it) | April 23, 2025

Annonce:

Did you spot a little black spot in a corner of the wall? At first, we think it’s probably a little dust or a forgotten trace… and then the days pass, and this area widens, darkens, and sometimes a smell of mouldy begins to be felt. There’s nothing anodial about it. These marks are often a sign that something is happening behind the walls. But don’t panic: with a few good reflexes, you can act, limit the damage and find a healthy interior.

Why do these black spots appear? (It’s not just a household issue)

A wall that blackens, especially in a corner, is rarely just a matter of cleanliness. More often than not, it is an excess of humidity that is involved.

In poorly ventilated rooms – a bathroom where steam remains wedged, a kitchen that heats up without opening, or even a room that is rarely arranged – the humid air does not escape. He ends up condensing on the cold walls … and that’s where the mould finds their favorite playing field.

It may also be infiltrations from outside. An overflowing gutter, a damaged roof, a porous wall or even a rising water from the foundations… all of this can lead to these famous spots.

And sometimes it’s isolation that plays against you. A “thermal bridge” – a place where the temperature varies greatly between the inside and the outside – can create a cold spot where humidity is easily deposited.

A little detail that we don’t always think about: furniture glued too close to the wall. Without space for air to circulate, moisture stagnates and moulds are separated discreetly behind the sofa or chest of drawers.

According to ANAH, every fifth dwelling in France shows signs of persistent humidity. In other words, you are far from alone in this case.

A golden piece of advice: don’t underestimate these discreet corners. It is often they who “talk” the first when something goes wrong.