Tiles, natural stone
Walls which receive a facing of tiles or natural stone need not be filled/smoothed, not even in the area of joints. Only gypsum adhesive swelling out of joints is to be knocked off.
The tiles or blocks can then be applied to the primed wall surfaces using thin-bed adhesive.
Water-repellent gypsum blocks already posses a reduced absorbent behaviour and therefore require no priming. Tile joint mortar with sealant additive increases the water repellent effect of ceramic top surfaces. A further improvement can be achieved through joint filling using joint mortar epoxy resin.