Subsequent installation of a shower (laundry room)

My problem: Since my laundry room is relatively large, I have installed a sauna and would also like to install a shower next to it. I have laid tiles on the existing wall parts (located in the earth area/slope) (no grout material yet). Actually, I wanted to build up a wall so that an open I_I space is created, which I can close in front with a shower curtain, but now I am no longer sure because I fear that I missed an opaque undercoat so that water does not penetrate the wall during showering and thus cause damp walls and mold. Or is there something like a seal over the tiles? How steep should the slope from the shower tray to the drain be (concrete blocks for a pedestal construction are available). Or is building up with concrete blocks on a slab floor unfavorable? Could someone please give me tips? Thank you very much in advance mum

Hello mum,

You can already install the shower as desired; you can counteract the forgotten waterproofing by simply tiling the inside of the shower again. But do not forget the sealing system ("liquid membrane"/brush-on waterproofing and flexible grout).

I would execute the two side walls of the shower in drywall construction; metal studs covered with gypsum fiberboards. You can work more precisely, it goes faster, and that is especially more stable for the desired result.
The metal studs and connection profiles are screwed to the floor, ceiling, and wall, so they provide sufficient resistance against horizontal forces.
With masonry walls, this is not so simple. A masonry wall without interlocking or integration into the floor/ceiling/flanking wall is not stable against horizontal forces and could fall over with enough lateral pressure.
You can also manage this with wall anchors, for example. But by the time you have made the drillings and set the anchors at the correct height, the stud wall is long finished.
The tiles would have to be laid in a thick bed (or the side walls plastered); tiles can be glued onto the gypsum fiberboard, which is faster and more precise.

Regarding the slope of the shower drain: it should be 2%. You can construct the base for the shower as planned; there should be no problems.

Thank you very much

I just wanted to briefly thank you for the detailed answer and ask what the material is called that is placed under the bathtub for stabilization. Since I actually only need to build one wall because I wanted to place the shower in the corner - so already two existing (I have already tiled these two) I think I will choose a ready-made round shower and place it on a pedestal. So now I am looking for a round shower, if possible without massage or special features - something simple. Can someone give me information on where I can find something like this? Thank you mum

Hello mum,
You can stabilize the tub with stones or use available tub stands for this purpose (I hope I understood you correctly, it is about stabilizing the tub itself so that it stands level and stable).
There are also ready-made bases for shower trays, smooth surface in common ceramic colors, often offered together with the respective tubs; otherwise, the gap between the floor and shower tray is filled with aerated concrete blocks (which are easy to work with) and then tiled.

There are several suppliers for bathroom fittings on the internet, where you can view various models from different manufacturers and possibly order.