Why is my basement wall constructed like this?

[Jethro625]

Hello! I live in a split-level house that was built in 1949. When I chipped away some loose plaster on the basement wall, I was horrified to discover that the wall behind had started to deteriorate! I removed all the material that was loose to assess the situation, but it has only led to more questions. I am attaching a couple of pictures of how it looks now. In the first picture, you can see a masonry wall directly under the plaster I chipped away. In the second picture, you see a damaged masonry block and that there is another layer behind it.




From what I can see, the wall is constructed as follows (seen from the inside):

- First, a layer of smooth and painted plaster.
- Then a masonry layer with approximately 6 cm thick masonry blocks of blåbetong (?) or some other type of porous concrete.
- Behind this, another quite rough, seemingly cast, concrete wall. This wall is not made of the same porous concrete and is much harder.

The cracks are in the plaster and in the porous masonry blocks. The cast wall behind it looks intact and fine.

My question is simply why does it look like this? What is the purpose of the masonry wall? It is so thin and made of a much weaker material than the rough concrete wall behind it, so I have a hard time believing it bears any weight. Could it be intended as insulation or just to provide a nicer surface?

Bonus question: Can anyone determine if it is actually blåbetong from these pictures?

 

[surris]

Insulation and for the sake of plaster, lightweight concrete was in vogue at the time, so it was used in all sorts of different constructions.

And yes, it is probably blåbetong, so you should do a radon test in the winter if you haven't already done so.

 

[Jethro625]

Insulation and for the sake of the plaster, lightweight concrete was popular at the time so it was used in all sorts of different constructions.

And yes, it is probably blåbetong so you should do a radon test this winter if you haven't already done so.

Thanks for the answer! A radon test was done many years ago by the previous owner. It showed 210 bq/m3, so indeed above the reference value but nothing I felt was urgently necessary to address. However, it might not be a bad idea to do a new long-term measurement just to be safe.