shower pan

I'm going to try my 1st Kerdi and am having trouble wrapping my head around modifying the Kerdi Substrate (tray). I'll be removing the bottom 6" of a tile shower down to the concrete slab floor in Florida. Shower measures 30 x 46 with a center drain. Should I buy the Kerdi 48x48 or 32x60 tray...

I am currently building my first custom shower and have just completed the final thick bed mortar a day ago. After checking the slope (looking for either 1/3 bubble on a torpedo level or 1/4" rise per linear foot) some areas are not sloping properly due to poor screeding. In some areas the...