Rising damp on basement wall after prolonged rain

Hello,

our inherited house was built in the mid-1980s and presumably does not have moisture barriers in the basement. After the recent rains a few weeks ago, there was quite a bit of moisture and efflorescence visible on the plaster.

The basement wall consists of concrete hollow blocks, above which, according to information, there is a cement plaster and above that a lime plaster as the final layer.

We were able to borrow a moisture meter from an acquaintance and found very high moisture (80-100) in the first and second plaster layers. Less moisture (device shows about 30-50) in the concrete hollow block.

In addition, “masonry efflorescence” — presumably some kind of salts — can be seen on the last lime plaster layer.

Is this rising moisture somehow concerning with regard to structural stability/building fabric, or is it “only” a matter of the plaster falling off and needing to be renewed?

Thank you in advance,

Rising moisture + efflorescence – about 20-40 cm high – here the most extreme spot after several days of continuous rain:

Is this rising damp somehow concerning in terms of statics/building fabric or is it "just" about the plaster falling off and then having to be renewed?

Statics won’t be affected that quickly.
Building fabric is a bit of a vague term... And yes, with damage like this I would definitely say that it damages the building fabric. From the moisture, there will be more moisture (it moves upwards and in the worst case eventually ends up in your bedroom or living room) and it becomes increasingly difficult and especially expensive to get rid of.
In addition, efflorescence often turns into mold. Also with mineral plaster. And then you might as well renew everything down to the foundations.

So: monitor the damage. If it really only occurs exclusively during heavy rain and then COMPLETELY disappears afterwards, then you can (if you want) live with it. If it gets worse each time or the wall no longer dries out, you’ll have to call in a professional. Possibly dig out the exterior walls and waterproof them anew. If that’s the chance, then insulate (newly) at the same time.

Statics don’t get affected that quickly.
Building fabric is just a term... And yes, with such a damage pattern I would clearly say it harms the building fabric. The moisture will become more moisture (moving upwards and, in the worst case, eventually be in your bedroom or living room) and it gets increasingly difficult and especially more expensive to get rid of it.
Besides, efflorescence often turns into mold. Even with mineral plaster. And then you can go ahead and redo everything except for the foundation walls.

So: monitor the damage. If it really only occurs during heavy rain and then COMPLETELY disappears afterwards, you can (if you want) live with that. If it worsens every time or the wall no longer dries out, you’ll probably have to call in a professional. Possibly dig up the outer walls and seal them again. If that happens to be the chance, insulate (or re-insulate) directly.

Hi Karsten,

thank you very much for the reply.
By "building fabric" I meant the hollow concrete blocks, so the load-bearing elements—so probably the statics. I am not an expert. :)

Above the 20-40 cm visible moisture everything was dry—the device showed 20-30. The plaster was completely hard as well.

Meanwhile, everything is dry again. We had the windows open and also used a fan and heater to be safe. It rained less a few times now. There was no sign of new moisture.

For now, I would knock off the loose plaster first. Then, to be safe, spray anti-mold spray and let it dry. Keep measuring the moisture regularly after rain, especially.

What kind of plaster could I use to replace the fallen areas?

They had the windows open

Please keep in mind that warm air outside contains more (absolute) moisture than cold cellar air. That is the difference between absolute and relative humidity. Ventilating a cold cellar with hot summer air leads to water condensation on the walls/floors.
Just a note, if the cellar is nicely cool.

I would then use a mineral cement plaster or renovation plaster again if you want to replace it.

I would always install a fan with a differential humidity controller and then first see whether the moisture really comes from outside or rather from inside. I was once in an old building where there was a large bucket in the heating cellar into which water was dripping, and it was not little. The source was initially alarming, namely the main water tap. Then it quickly became clear that it was simply condensation water condensing on the ice-cold water pipe – thanks to the huge and soaking wet cellar with actual streams.

As well as a differential humidity controller regulates, basically no human can do that. That’s why I find the statement "you just have to ventilate!" only 1/10 of the truth. Sensible fresh air flap, good fan with exhaust flap, and of course a properly set differential humidity control.

Sure, sometimes it simply comes from outside, then you have to dig up and seal it. Been there, done that.