Schluter KERDI Waterproofing Membrane by Schluter Systems is the best solution for waterproof and watertight tiled shower or steam room. Schluter Systems KERDI Waterproof Membrane Is A Bonded Membrane & Vapor Retarder Made Of Soft Polyethylene (have Crack Prevention capabilities). Both Sides Of Schluter Systems KERDI Waterproofing Membrane Have Special Webbing Synthetic Fibers That Allows Perfect Bond With Thin-set Mortar. Tiles Can Be Installed Directly On Top of KERDI Membrane. We Recommend To Use Schluter KERDI Trowel In Order To Apply Mortar Evenly On The Surface.