Laying tiles and substrate preparation

Hello everyone, I would like to introduce myself briefly. I am new here!

My name is boehsepiraten :) , I am 31 years old. I live and build near Gera which is in Thuringia!

So, a bathroom in our place was newly plastered. That means plaster and then white fine plaster on top!

My question is, can you prime directly on this fine plaster and then tile? Or can there be problems because of the white fine plaster!?

Second question, in the shower area there is also this fine plaster. How do I proceed? Prime, waterproof, tile or differently?

I would be happy if someone could help me, I am not so experienced in tiling yet :)

Maybe there are also good tilers here. I still have about 100 sqm to tile, which I probably do not trust myself to do!

Good evening. So the best thing is if you prime the surfaces, then apply a very thin layer of tile adhesive with a trowel, and then you can start laying the tiles. Lots and lots and lots of fun still. Regards MR.N