Fibre Flex Has A Built In Membrane So An Additional Membrane Is Generally Not Required (Except For Areas Susceptible To Significant Movement). Fibre Flex Is An Ideal Compound For Repairing Old Acrylic And Membrane Systems That Have Over Time Begun To Leak. In Areas Of Long-Term Ponding (Ponds And Water Features) Or On Impervious Concrete Fibre Flex Should Be Used In Conjunction With Hypercrete Primer. Not Recommended For Swimming Pool Or Fibre Glass Applications.