The Short Answer
Shower waterproofing prevents water from penetrating the tile and substrate to reach the framing and subfloor. Modern shower waterproofing systems include sheet membrane systems (Schluter Kerdi, Wedi), liquid-applied membranes (LATICRETE Hydro Ban, RedGard), and foam backer boards with integrated waterproofing. All penetrations — drain, corners, niches, transitions — must be treated. Waterproofing is applied before tile and is invisible in the finished shower.