Experience with gluing tiles on tiles?

I would also want to get rid of those, otherwise, in 15 years when we have the first bathroom renovation, we'll be talking about layer number 5 and in the meantime the chamber will have lost half of its living space.

Even layer 3 from 20 years ago should be glued and come off more easily. I consider the ambition to always chip down to the bare wall inappropriate on the side with the thin wall (raw 7 cm?). I would have even left layer 3 on there and for future new tilings I would only remove the glued layers again and would not deliberately touch the mortared layer.

Even layer 3 from 20 years ago should be glued and come off more easily. I consider the ambition to always knock down to the bare wall on the side with the thin wall (bare 7 cm?) inappropriate. I would have even left layer 3 on and for future re-tiling would only remove the glued layers again and not deliberately touch the mortared layer.

The tiler was here today. The remaining tiles around the door should still come off (half of them are already down) and then it would be no problem at all. He would do a completely new build-up there and on the other 4 walls would build on the existing tiles.

I would also leave the last two layers on. The wall is so thin that I would be afraid of making a hole in the bricks as soon as I slip with the chipping hammer. And I thought our non-load-bearing walls were thin ^^. We also removed all layers (2) here, then plastered the outer walls and worked with drywall on the inner walls so that the tiler had a proper base. That took two of us two days for a 5m2 bathroom, of course only the removal part. On the floor, we had 3 layers of tiles. We took everything down except for the floorboards. Good luck with the further bathroom construction! For us, the bathrooms were the most time-consuming but also the most exciting projects.

I would definitely chisel everything off there.
It's not a big bathroom, I can't believe that you can't make good progress with a proper hammer and flat chisel.
In my own house, I also chiseled off two layers of tiles from the bathroom, it was done in half a day.
It seems to me they simply don't feel like working for you or they don't know how to do it.
If the thin wall is too fragile, it will just be replaced, it's not rocket science.

Nowadays, bathrooms are no longer tiled all around from floor to ceiling. So everything off, have it properly plastered, have nice tiles put on. This way you gain space and have a beautiful, modern result.

If you save that little extra effort now, you will regret it for years and years, at the latest during the next renovation.

Others install expensive soundproofing under the tiles in the bathroom and you want to get rid of it. That's just how it is.

Because of 4-5cm of space gain. Also, several layers of wallpaper are not problematic as long as none of the layers were done sloppily.

For unevenness, smooth it out beforehand with leveling compound and a long board.

As said: multi-layer wall constructions, multi-layer fibrous wallpapers, etc. are sound insulating, improve room acoustics, act as thermal insulation, and are always mentioned as a showcase feature in high-quality construction, because, for example, an additional fabric layer minimizes cracking. But that's a typically German problem: old wallpaper must come off, no matter what it costs.