How To Apply MasterSeal® P 173 Primer Ensure substrate is structurally sound, fully cured, dry and clean Prime joint before installing backer rod (protect adjacent surfaces from primer) Open MasterSeal P 173 Using a brush apply a thin, uniform coat to the joint surface Allow primer to dry tack-free before applying sealant Sealant must be applied the same day as the primer Refer to the MasterSeal P 173 technical data guide for more information.