Tile underlayment isolation membranes are necessary for preventing water damage from tiled showers. Tiles and grout are not waterproof on their own -- they need a waterproof layer behind them to protect the walls and floors surrounding the shower. The underlayment also bridges any cracks that might form in the substrate (the materials behind and below the shower, such as plywood or concrete).

Tile underlayment isolation membranes are usually made of polypropylene or polyethylene. Polypropylene is easier to install and lays out flatter. Both are tough yet pliable enough to bend around corners.

We recommend Dural Durabase CI as the best underlayment. Durabase features a mesh layer to help tiles bond firmly.

Tile Underlayment