Growths on the basement walls

Hello everyone,

I hope someone can help me regarding the growths on our basement walls and tell me what this is in the photo?
The house was built in 1960 and, except for the basement, has been completely renovated. We haven't really done anything in the basement.

Best regards

Oh my God .... straight out of the house, close the doors and call the police ... it’s an alien!

.... the alien is called efflorescence and is common in buildings of this construction age.
It can have two causes, both of which are not critical - but also difficult to fix.

1. Basements of this construction age are neither thermally insulated nor do they have a permanently waterproof coating on the outside towards the soil. The bitumen thick coating applied 60 years ago is now only a dark gray shadow, but with sufficiently moist soil the basement wall will also become damp. This moisture slowly migrates through the wall and evaporates on the inside. Salts from the concrete are washed to the surface. When evaporating, they remain behind and form these crystalline efflorescences.

2. The basement walls are, especially in summer, colder than the outside air. Warm humid air enters the basement and condenses there on and inside the basement walls. In colder seasons, or with drier indoor air, the moisture evaporates from the wall again. Over time, these structures also remain.

Usually, both processes occur.

Is this bad?
No, not really. You should not store baby clothes or similar outside the warm boiler room (and here only if there is no oil heating). They will get musty and possibly develop mold spots, depending on how damp the basement really is. The boiler room is usually warmer. This is not mold; mold in the basement is usually black.

What can you do?
1. Excavate the outside basement wall, apply a new sealing, apply insulation, replace basement windows and light wells, replace basement entrance door. Then everything will be warmer and drier. Then seal the floor from the inside, possibly insulate inside. Quite expensive for the added benefit.
2. Brush off and if necessary apply new lime paint - no sealing layer or similar, only lime or silicate paint. Otherwise, you trap moisture and it will find another way out — either upwards or the layer will eventually detach.

You will also frequently find this phenomenon under the name saltpeter. But this is factually wrong because it is not true saltpeter. That only occurs if someone has long and extensively urinated on the wall before - for example in cow barns. Otherwise, it is simply various salts.

Forgot to write earlier... I assume or hope these are salt efflorescences. However, I would like to get another opinion here. If that is the case, does anyone have any tips?

Oh my God .... straight out of the house, close the doors and call the police ... it's an alien!

.... the alien is called salt efflorescence and is commonly found in buildings of this construction age.
It can have two causes, both of which are not critical - but also difficult to fix.

1. Cellars of this construction age are neither thermally insulated nor do they have a permanently waterproof coating on the outside facing the ground. The bitumen thick coating applied 60 years ago is now only a dark gray shadow, but with adequately moist soil, the cellar wall will also become damp. This moisture slowly migrates through the wall and evaporates on the inside. Salts from the concrete are flushed to the surface. During evaporation, they remain and form these crystalline efflorescences.

2. The cellar walls are, especially in summer, colder than the outside air. Warm moist air enters the cellar and condenses on and in the cellar walls. In the colder season, or with drier indoor air, the moisture evaporates from the wall again. These structures also remain over time.

Usually, both processes are present.

Is this bad?
No, not really. You should not store baby clothes or similar outside of the warm heating cellar (and there only if there is no oil heating). They will become musty, possibly develop mold spots, depending on how damp the cellar really is. The heating room is usually warmer. This is not mold; mold in the cellar is usually black.

What can you do?
1. Excavate the cellar wall outside, apply new sealing, apply insulation, replace cellar windows and light shafts, replace cellar entrance door. Then everything will be warmer and drier. Then seal the floor from the inside, possibly insulate from the inside. Quite expensive for the added benefit.
2. Brush off and if necessary apply new lime paint - no sealing layer or similar, only lime or silicate paint. Otherwise, you trap the moisture and it will look for another way, either upwards or the layer will peel off over time.

1000 thanks! Didn’t plan on moving out ;) Just wanted confirmation. Many thanks for the detailed post!! I’m now calmer and of course will tackle solution 2.

Since you can only edit your post for 4 minutes, one more addition: In the case of localized strong occurrences of efflorescence or moisture, a defective rainwater pipe / downspout in front of the wall can also be the cause or intensify the effect, making the efflorescence stronger.

Yep, salt efflorescence. The rest has already been explained. We also have that everywhere in the basement where the basement is in the ground. We replastered these walls with renovation plaster and painted them with silicate paint. The efflorescence naturally comes through again, but the plaster can absorb quite a bit and this protects the masonry a little (also called sacrificial plaster; it doesn't last forever and has to be renewed eventually). I just sweep it off occasionally. Our house is from 1921.

Be careful with old houses and digging outside. If you dig too deep, it can endanger the structural stability (for example, if the house doesn't have a slab foundation). No idea if that was still the case in the 60s, I just wanted to mention it.