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. Was this article helpful? Yes No Related Articles 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? Can Adi-Con CW Plus be added to Meadow-Crete FNP?