Schluter Systems KERDI Membrane 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 .