Contrary to popular belief, tile and grout joints (even sealed grout joints) are not waterproof, and a caulk or sealant joint alone between the tile and the tub will not ensure an overall waterproof assembly. It is essential to provide a waterproofing system beneath the tile to prevent moisture and vapor from penetrating the walls and consequently increasing the potential for mold and damage to the structure.
Today's construction methods, which include the use of lightweight, moisture-sensitive materials, such as plywood, OSB, and gypsum concrete, have made the installation of hard-surface-coverings (example: ceramic tile) particularly challenging. If wood or gypsum concrete substrates are exposed to moisture, the tile layer above can be damaged as a result.
Typical areas that require waterproofing include tub surrounds and showers. However, there are other commonly tiled areas that may, through unexpected circumstances, become exposed to significant amounts of water; for example, an overflowed toilet, or ruptured dishwasher, icemaker, or washing machine lines, which can result in flooding. Waterproofing these floors can save an owner from replacing the tile assembly and substructure in the event of a leak.