I am having a corian surround installed in my tub/shower. I had to remove the existing tile, which also meant I removed the drywall about 36" up from the tub. The surround will be 72" high. How high do I need to remove what's left of the existing painted wall, so that I can replace with cement backerboard? Should I go up the whole 72" or should I shorten it to 70" high, so they aren't seaming on a seam? I know I have to leave a 1/2" at the bottom to protect against wicking. Any help would be great!

Thanks,

Susan