Cementitious Waterproofing How fast can Cem-Kote Flex ST be applied to new mortar/block? How long does it need to cure before spray foam can be applied over it? Cem-Kote Flex ST can be applied to new mortar/block after 24 hours; however, 48 hours is preferred. Cem-Kote Flex ST... Can Adi-Con CW Plus be added to Meadow-Crete FNP? Yes. Although not tested, Adi-Con CW Plus will reduce flow. How many days should concrete be cured prior to applying Cem-Kote Flex ST? The concrete should be cured 28 days or has achieved its intended design strength.