Problem with base plaster - microcracks?

Hello everyone,

I am facing a puzzle – and unfortunately, our site manager is too. The base plaster was applied during last summer. It was quite hot back then. At first, everything was fine. After a while, these whitish discolorations appeared. We complained to the plasterer and he painted over it again. But that only lasted a few days.

Now the questions are: Does anyone know where this could come from? And what might need to be done about it? Should I get an independent building expert?

Unfortunately, I do not know which plaster and paint were used, but I will ask the plasterer.

I now have the information about the plaster and paint. Knauf Sockel Lup was used as lightweight plaster. The paint was Knauf Autol Premium Siliconharz- Fassadenfarbe mit Selbstreinigungs-Effekt

Do you have a photo of the same spot during the shell construction / without plaster? What kind of masonry do you have? It somehow looks like a liquid is seeping out through gaps (joints) and blooming there.

well actually the floor slab should be there

Looks like the plaster is efflorescing, but the pattern does look strange. Is there no base seal on it at all?

We built with Poroton. There is a red rubber-like substance used as sealing on it.