Level plastered wall (plaster on plaster)

[Lane]

We tore down a wall in the basement, and the different rooms had varying thicknesses of plaster (because there were electrical conduits in one room). There is about a 1 cm difference that we want to build up to make it smooth and able to tile. My question is how do you do it?
How do you plaster on old plaster? The house is from 1968, it's concrete plaster that is attached.

 

[Roundup]

I'm not an expert, but I would probably apply a layer of plaster mix C to the part that needs to be built out. There's a bit of a risk that cracks may appear in the plaster if the addition makes the plaster layer too thick. Normally, one would use a plaster mesh to minimize that risk, but with only 1 cm to work with, it's probably best to take a chance without the plaster mesh. Don't forget to thoroughly wet down the existing surface before plastering, so that the substrate is really saturated. Otherwise, your new plaster addition will be bad.

 

[Lane]

Thank you for the response
Why is 1 cm too little for plaster mesh?
Many on the forum mention "rödgrund" when they talk about plastering surfaces. Is this something that can be used instead of plaster mesh since I have the impression that "rödgrund" is used to get a better grip on the substrate?

 

[Roundup]

Normally, you don't place the mesh flush against the substrate, but you'll probably have to do that if you only have 1 cm, otherwise it might stick out or leave rust stains if it's damp. Rödgrund might not be a good idea, as you'll likely risk having the plaster detach from the old substrate, which probably has lower strength than the rödgrund. It's said that you should never plaster so that the mortar in an outer layer has higher strength than in an inner layer, because then plaster detachment can occur due to the materials moving in the wrong way (or something like that).