ᐅ Is it possible to make a gypsum surface in the bathroom waterproof?

Hello everyone,
We are currently in the final stages of renovating our bathroom.
We only want to tile the area behind the toilet and the wet zone.

Usually, there is a tile backsplash above the bathtub, but we don’t really like that.

Throughout the entire house, the walls are only plastered and painted. We want to do the same with the bathroom walls so that it visually matches the rest of the house.

Now the question:
Is it possible to seal the plaster surface around the bathtub to be waterproof and water-repellent without affecting the paint finish?

For plaster, we used red band plaster throughout the house, and plan to use the same for the bathroom.

Thanks in advance for your answers.

Gypsum has NO place in the bathroom!!! Usually, lime-cement plaster is used in bathrooms. Gypsum molds when exposed to moisture, and there is NO paint that is completely diffusion-proof. Therefore, in the long term, mold damage will occur in the bathroom.

Good to know. In the guest bathroom, the areas that are not tiled have standard gypsum on the walls. When I asked at the home improvement store, they said it shouldn’t be a problem :/
The guest bathroom also has a shower that has been used for about a year because the master bathroom is not finished yet.

I hope this doesn’t cause any issues now or in the future, even if the shower is used occasionally.

So basically, for the bathroom upstairs, apply a lime-cement plaster on the walls and that should be fine?

And the row of tiles above the bathtub should definitely be installed to protect the wall from possible splash water if you can’t make the wall otherwise waterproof?

With lime cement, it doesn’t matter; it is waterproof and is also used for exterior plaster. You can simply paint over it. However, I would still recommend installing a row of tiles, as it makes cleaning easier when scrubbing around the bathtub edge.

It has happened now.
Apply Stotex adhesive, then paint with Sto Opticryl. This would result in waterproofing and abrasion resistance similar to that of tiles. Karsten

And later, does the lime-cement finish look the same as the surface of the plaster, or is it processed in the same way?
Meaning, applied with a notched trowel and then smoothed out with a fan trowel.
Afterwards, you paint it and then splash water won’t be an issue?

If that’s the case, we definitely wouldn’t install tiles around the bathtub. The bathtub isn’t used that often to require any special cleaning.
You generally don’t clean normal walls in that way either.

The Stotex is the fiberglass wallpaper. That’s not desired, but thanks for the tip anyway.