ᐅ Mold in the Basement: Moisture From Below or Condensation Issue

Created on: 9 Aug 2021 11:40
T
Tassimat
Hello everyone,

Yesterday, I discovered a mold issue in my basement, as shown in the attached photo.

The wall is an exterior wall in a heated basement room that I use daily. The area around the baseboard is about 1.5m (5 feet) below ground level. In front of the baseboard, there was a cabinet and moving boxes placed very close to the wall, so there was almost no air circulation, although the room has large windows (mostly kept closed).

I haven’t had time yet to expose the area further, but I am wondering whether the problem is caused more by water coming from below or by water condensing on the cold exterior wall? It seems like water from below, but the opposite exterior wall in the room shows no signs of this issue, and it was not obstructed. Also, there shouldn’t be any water pooling outside the house, since the slope runs away from the building and there is a terrace above that area, which also directs water away.

What is the best way to determine the source of the mold problem? What should I look for when exposing the area? Do you have any tips?

Thank you very much
Tassimat

Corner view: white wall with baseboard, dark dirt stains along the bottom edge.
A
apokolok
9 Aug 2021 13:58
Was this plastering done recently?
The mold seems to be mainly behind the baseboard. It’s possible that the baseboard was installed on plaster that wasn’t completely dry.
It would be a strange coincidence if moisture from outside or below stopped exactly at the baseboard.
T
Tassimat
9 Aug 2021 14:06
@apokolok New screed (3 months drying time), plaster repaired (1 month drying time). Maybe it was still too damp. That would be a good explanation.
A
apokolok
9 Aug 2021 14:08
What did the basement look like before the renovation?
Concrete screed already retains a lot of residual moisture, and without underfloor heating, it takes a long time to fully dry out.
At this point, I wouldn’t worry too much about water seeping in from outside.
T
Tassimat
9 Aug 2021 14:51
apokolok schrieb:

What did the basement look like before the renovation?
This room had wooden floorboards. The dust, sand, and dirt beneath the boards were completely dry. Overall, I couldn’t detect any moisture issues anywhere. The room used to have two large radiators, and the oil heating was running at full capacity.
H
hampshire
9 Aug 2021 15:15
Did you experience heavy rainfall accompanied by a rise in groundwater levels?
At my sister’s house in Erftstadt, water seeped in with a squelching sound through the basement wall of her home, which has been there for almost 10 years.
The heating system is located far away, with a cupboard in front of the wall, so it’s not uncommon for something like this to happen in older basements with relatively new screed.
A
apokolok
9 Aug 2021 16:55
Tassimat schrieb:

This room had wooden floorboards. The dust, sand, and dirt beneath the floorboards were completely dry. In general, I couldn't detect any moisture problems anywhere. The room used to have two large radiators, and the oil heating was running at maximum.

Well, then it's not that bad.
I would remove the baseboard and let it dry thoroughly again.
Possibly treat it with some kind of anti-mold product.
Ventilate preferably only when it’s colder outside than in the basement. Of course, that’s not always easy in summer.
Have you measured the humidity level?