Hydraflex™ Waterproofing Crack Isolation Membrane is a ready-to-use, flexible, mold and mildew resistant waterproofing crack isolation membrane for interior and exterior applications. It forms a smooth, monolithic, watertight surface over walls, floors and ceilings. HydraFlex™ stops in-plane cracks up to 1/8″ (3 mm) or up to 1⁄4″ (6 mm)* wide at the subfloor from telegraphing through to ceramic and stone tile. For residential to extra heavy commercial applications.