ᐅ Dark spots on a lightweight concrete slab

Hey everyone

I was at the construction site again today. I noticed some strange dark spots on the concrete ceilings. At first, I thought it might be mold, so I tried to wipe the spots off. However, they won’t come off. Even scrubbing doesn’t help much.

Maybe someone has an idea what this could be. What’s odd is that the spots are mostly above the windows.

Hope you can help me with this

Best regards, Chris

That is moisture, and damp concrete naturally darkens... absolutely nothing to worry about.

First of all, thanks for the response.
But why is there still moisture? The building has been closed up for over 6 weeks (1.5 months).

I think the last picture looks strange.

Best regards, Chris

Many concrete structures have still not fully dried out, and some have been standing for several decades... 6 weeks in winter... return after 6 months

When our drying program was running, it looked quite similar. Actual droplets formed on the ceiling. After wiping them off, it eventually dried out again…

I need to jump in here... our shell construction has been on hold for almost 6 weeks now due to bad weather. At the moment, everything is quite wet because of heavy rain. Does it make sense to use a construction dryer/heater intensively once the windows are installed? I mean before the plaster and screed are applied. The cost for the dryer/heater is not a concern right now. I just want the building to be dry.