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Phase 1: Structural, which consists of a gradient or slope, an outlet hole, and a foul air trap connecting the floor to the waste pipes.
Phase 2: Waterproofing. Best practice would suggest multiple layers of defense. Grout is used to fill gaps between tiles, but this material is generally porous. Tiles are generally waterproof, so larger surface areas of grout are less waterproof. Thus small mosaic tiles offer less of a defense than large format tiles. This means sub-tile waterproofing is important when tiles are being used.
In building a wet room it is easier to build the slope all in one direction. This allows for larger format tile and fewer grout joints but a channel drain is needed instead of a round or square drain. Grout and tile setting materials are not waterproof for the most part. It is a good idea to have a fail safe drain in the bathroom outside of the wet zone for these curbless showers or wet rooms. In Australia and Europe, but not in North America, this second emergency drain is required by the plumbing codes.