I'm having a plumber complete the installation of a new 1-piece shower in the basement (concrete floor). He 'hammered' out the existing concrete and then moved the p-trap and drain. He then re-cemented up to near the drain - leaving about a 6" diameter area around the drain cement free to allow for more flexibility when he actually moves the shower in place. Now, here's my question - should I ask him to cement this remaining 'open' area up to the drain or is it okay to leave this 'open'. If it were to remain open (without cement), what are the options to cover the dirt area.