Shower niche shelf Ytong

And why?

Think about it.

Your profile suggests manual skills.

Alright, a bit more detailed.

It is a non-load-bearing Ytong wall (11.5 cm stone) with plaster, we have a 14 cm thick wall.

That leaves 2.5 cm stone and 3 cm plaster. That won't work without cracks in the plaster.

Maybe intended to be about 70 cm long, 30 cm high (one tile height) and about 8-9 cm deep.

Not without a lintel.

Would that work?

No.

Especially since the plaster is already on it?

Not possible without damaging the plaster.

And without me knocking through the wall?

That will certainly happen.

The desired depth of the niche simply does not match the depth of the wall. You would have to add something with drywall towards the shower. Of course, this narrows the width of the shower enclosure, etc., and the effort is not insignificant. I would say that is settled.

So if at all, only install a drop over the niche, then break out the opening and close it again from the dressing room with a fiber cement board, repair the plaster in the dressing room and properly seal and tile in the bathroom. Otherwise, it will not work.

Why not limit the depth to 5-6, then it fits with a fall and a 6cm Ytong at the back.

The depth is variable and was just a thought. So far, no counterproposal has been made, thank you. What does it mean to put a 6er Ytong in the back? Where at the back?

A 6 cm deep niche, which will also be lined, is not practical in this way.