The USG Durock™ shower trays can be cut to size using a utility knife. Ideally, the tray should be cut equally on each side to maintain a level perimeter for the first course of tile. In the event this is not possible, minor differences in the elevation of the perimeter can be built up with thin-set mortar. If the area of the shower floor is larger than the USG Durock shower tray, the area beyond the perimeter of the tray can be extended using dry pack mortar.