Synko-Flex Solvent Based Primer penetrates concrete pores and seals concrete surfaces to provide an optimal surface for the adhesion and bonding of Synko-Flex, Hydro-Flex Waterstops and Ram-Nek Concrete Joint Sealant Products. Formulated with a solution of select asphalt base in a petroleum solvent, Synko-Flex Solvent Based Primer is for exterior use only.