In the process of re-tiling my walk-in shower, I removed the old
drywall about 6 feet up the wall (that's as far up as the old tile
extended) and replaced it with DuRock cement board. I've got the tile
all set, except for the top 2 or 3 rows. I'm wondering how to seal
that 1/8" gap between the top of the new DuRock and the bottom of the
old drywall. There's not only a gap between them, but they are also
slightly different thicknesses. So, if I wanted to use slightly taller
bullnose tiles for the very top row, which would extend them past that
joint, the tiles wouldn't set flush because of the differences in
thicknesses of the drywall & DuRock. Should I put an extra thick layer
of Mastic in and around the joint and feather it out like you do with
drywall joint compound, let it dry and try to sand it to smooth it out?
Or maybe just use drywall compound itself and Mastic over it once it's
dried and sanded?