PEX Prime Evaploc 20LDescription Prime Evaploc is a water soluble liquid when sprayed on curing concrete creates a plastic film that retards water evaporation in setting concrete. This greatly reduces the chances of plastic shrinking (known as hairlines) while making the concrete more workable for an extended period. Benefits Prime Evaploc reduces the chances of plastic shrinkage by up to 80% if the ground surface has been thoroughly watered prior to concrete placement.