My brother is going to convert a room from a dull storage area into a room with a sauna and shower cabin. The room is located below ground level, and the house has not been drained in recent years (built in 1962). The interior walls in the room that will house the sauna are plaster on Siporex. In some places, the plaster falls down if you touch it slightly too much.
My brother is thinking of vinyl flooring and tiles on the walls. No waterproof membrane. What should be done about the plaster that's coming off? Should all the plaster be removed, and then tile directly on the Siporex blocks? Should steel studs be attached to the walls, followed by wet room plasterboard and finally tiles on that?
