USG Durock Shower System Waterproofing Membrane is perfect for waterproofing custom walk-in showers where ceramic, porcelain, or natural stone will be installed. Tile shower waterproofing underlayment provides a completely waterproof barrier between the substrate and the installed tile when it is applied to code-approved substrates with unmodified thinset mortar. This membrane is a vapor retarder that is thin, pliable, and extremely durable.