EPDM Water Block for Firestone Please note a mastic gun will be required in order to apply this sealant. This water block is to be used with the Firestone RubberCover system. Coverage Approximately 3 linear metres with a 3/8" to 1/2" bead per 10 oz tube. Description Firestone Water Block is designed to provide a watertight seal when applied under compression, i.e. behind termination bars. Firestone Water Block Seal Method of Application Surface on which Firestone Water Block Seal is to be applied should be free from loose concrete, stone, mortar, foreign materials and other contaminates. Apply a 3/8" to 1/2" bead to substrate surface. Bring the mating surface of the EPDM pond liner into contact with the Water Block Seal. Roll or press the EPDM pond liner firmly against the Water Block Seal and substrate avoiding wrinkles.