Two ceiling lights on one connection

Just looked around the apartment I am currently in. The plaster on the ceiling here is about 15 mm thick...

Exactly, concrete priming - it still wasn't nice though. But the question remains why... why precast slabs then? Of course, I'm not a construction expert, but I already know quite a few buildings. And everywhere only puttying was done - you can often read that too, as it is a completely normal task for the painter.

Aren't 15mm also extremely tight, for example, to properly fit a cable underneath? Otherwise, prisoners have already scratched escape tunnels through hard material, whether it makes sense now for laying cables..

Professionally, you are not allowed to chase into the concrete - if there is plaster, I would simply lay it IN the plaster - in terms of damage, that is acceptable,

With a flat cable, this is not a problem under the plaster (this is how cables were mostly laid at the ceiling in the past), especially if it’s only a small piece.

By the way, with us, the painter did not take care of the ceiling. That was normally the plasterer’s job. It wasn’t even a question and was also very cost-effective. By the way, we don’t have filigree ceilings but classic shuttered ones. However, I also know it – as mentioned – with filigree ceilings. No filling + sanding and possibly compensating for offsets, simply plaster on it and that’s it.

Yes, with in-situ concrete, it depends on the formwork as well. And of course, the painter doesn't do that.

You write it as if it were easier that way - but it isn't. You have to fill and sand a plastered ceiling just the same if you want it smooth. Or do you want to tell me now that the plasterer made it perfectly smooth?

As I said, plastering precast concrete elements seems like a very unnecessary solution to me, and I still don't understand the point.