The people at Home depot said Wonderboard is too difficult to work with and I should use green drywall and sold that to me. The shower backs up to an outside wall and a hallway over the stairs, so I can't put a door. Its a corner shower. I took more tiles out so I could find a stud and cut the drywall so a tile could cover the seam. The size now of the opening is 2'x3' Do I put joint compund or spackle between the seams between the old and new drywall? I got the mastic for the tiles, but do I need to prime the new dryWall first? Thanks again.