My masons are literally working on the pizza oven as I type. They did not do the floor correctly. They used fire mortar underneath the floor, between the floor joints and between the floor and the dome. The directions say to use sand as the base and I read here that you should use no mortar or your flooring will crack. They said they've used the fire mortar on other fire ovens. Do i need them to tear up and redo? HELP!!