So in my bathroom renovation Im retiling the tub surround, this is in a townhouse which has 5/8 drywall. Im having a hard time finding 5/8 cement board for tile backer. The tub surround shares walls with the rest of the bath so I figured get the same thickness backerboard for a seamless transition. I can get the 5/8 in bigger sheets but I was planning on getting the smaller 3x5 which I cant find anywhere. Now the 1/2 I can get just about anywhere.