Mold on a wall

Mold on the wall

If there are dark stains on the wall and there's a musty smell, there's probably mold. Mold comes in various forms: A black stain, a white coating or a greasy spot. Most of the time, but not always, it appears on outer walls. Not every mold stain is a catastrophy, but it should be taken seriously: If left untreated, it can easily spread and become a big problem and can even require restoration works on the building.

Humidity is the most probably cause for mold

There is no one single reason for mold on the wall. It's always multiple factors playing together when mildew emerges on a wall.

Mildew likes it moist and somewhat warm. Heat won't kill it though, and neither will cold. Mold is quite resistant and can survive under non-optimal conditions. It is completely independent of light. It just needs a little oxygen to survive, and a nutrient medium. That can be wood, wall paint, wallpaper, many synthetic materials, but also house dust.

If you detect mold on your walls, that indicates that the wall is at least somewhat moist. That usually is a result of condensing water due to too high air humidity.

When it's cold outside and warm inside, the difference in temperature can cause water to condense on the walls. After cooking and showering, the air humidity increases and enables mold to grow in the kitchen, in the bathroom or other connected rooms. Warm air can hold more water than cold water. Walls tend to be cooler than the air inside, and so is the air in immediate proximity to the wall. That'S when water starts to condense, moistening the walls as a result. That doesn't have to be visible, the water can soak into the walls, and not dry for a long time. Perfect breeding ground for mold, unfortunately.

Mold under a magnifying glass Mold next to a window

Too high air humidity?

Air humidity can be measured with a hygrometer and should remain below 60%.

When airing does not suffice, a dehumidifier can reliably reduce the air humidity and thus help prevent mold.

Other possible reasons than condensed water

Humidity could also enter through cracks in the outer walls. Basements are often prone to mold growth for this reason. Leaking roofs, insufficient drying time during the construction and floods also enables water to enter the walls, promoting mold growth. So condensed water is not always at fault, even if landlords like to claim that it is. Wrong airing not always the sole reason for mold in an apartment.

Hygrometer Water drops

The spores are everywhere

Mold spores are everywhere. They permanently float in the air, cling to furniture and carpets and even to the human skin. As long as there's just a small amount of them, that is not a problem. Not the mold itself, but its metabolites is what's harmful for humans. They can cause cancer, allergies and other serious illnesses. If the spores find a wet wall, they have an ideal breeding ground and spread quickly.

What appears to be dark spots or greenish-white coating on the wall is just the smallest part of the mold, the tip of the iceberg. The actual mold is invisible from the outside, it's within the wall, below wallpapers, paints and isolation layers. There, it can even grow if the building has been isolated. Inner isolations are ineffective in regard to mold prevention.

Mold grows slow, but steady

Since mold starts to grow on the surface, it can be easily removed if detected early. Small round black or green dots appear first. They slowly spread and can merge into a single, larger stain. Then it spreads below the surface, penetrating the walls, building mycelium, an entire network of threads. That's the actual mildew, not even visible.

Mold spores Woman looking at a wall covered in mold

Different kinds of mildew come in different colors

There's a myth circulating, claiming that green mold is not harmful, and that only black mold is. In fact, the color doesn't say much about a mildews toxicity. It should be removed from living spaces no matter what. If it is left untreated, it is a potential health hazard. Let's take a look at different molds and their colors nonetheless.

Black mold

There are around 40 different kinds of mold that can appear as black spots on the wall. It can grow on wallpapers, food, furniture and even on concrete walls. If ingested, black mold is a serious health hazard; The excreted mycotoxin can acuse red eyes, a runny nose, trouble breathing and allergic reactions.

Red mold (neurospora sitophila)

Not long ago, red mold was suspected to cause respiratory diseases in bakers. It preferrably affects grain, but also wood, paper and cardboard. It can also often be found on walls.

Green mold (aspergillus fumigatus and others)

There are many different kinds of mold that look greenish. One of them is aspergillus fumigatus. It's color range can also extend to grey. It can cause allergies and harm the lung tissue. Green mold is often found on walls. It prefers warmth and often emerges near heaters. It can also be found in potting earth.

Yellow mold (aspergillus flavus)

This mildew emits aflatoxin which has proven deadly to many archeologists. It has been common in excavations in egypt, but also grows in food. Food products get recalled on a regular basis whenever aflatoxis are found in products or processing factories. Yellow mold, or rather its aflatoxins, is believed to cause liver cancer and heart failure.

Mold on a wall next to a window Mold in different colors

Problem areas

Whenever water condenses on a wall, it happens because that wall is cooler than the surrounding air. That tends to be around windows, near doors and on outer walls.

Moist window

Removing mold from walls

If the mold has just spread on the surface and there are only some small spots, it can be removed rather easily. A commercial chloride spray or mold removal spray works well. We recommend a mold removal set.

Vinegar water is often not aggressive enough and just removes the dark stains while leaving the mildew alive. The same goes for lemon juice. Concentrated alcohol can help keep the mold in check. You can also try:

  • propyl alcohol
  • hydrogen peroxide
  • baking soda (preferrably for floor tile joints)
  • denaturated alcohol

If the mildew has already penetrated wallpapers, the affected areas should be removed entirely. If it's enough to just apply new wallpaper has to be decided on a case to case basis. If the wall below the wallpaper is also affected, just applying new wallpaper will not suffice because the mold will regrow rather quickly. In such cases, having a professional take a look at it is recommended.

If wooden sufaces are moldy, the affected areas can be grinded down. The so-called blue-stain mostly just affects the surface. Often, cleaning it with a cleaning agend can suffice. When grinding it down, make sure to use breathing protection, because neither wood dust nor mold particles should be inhaled. We recommend wearing a protection set.

Wiping mold off while wearing gloves Spray bottle

Preventing mold on the wall: Proper airing

Shock-ventilating multiple times a day prevents mold growth. Regularly check the air humidity inside with a hygrometer. If it's too high, you risk mold growth. Make sure to leave a small gap between furniture and outer walls to enable air circulation. Cloth should be dried outside. Houses should be isolated from the outside, and energy efficient windows help prevent mold too.

If airing does not suffice to keep the air humidity down, use a dehumidifier.