I'm currently building a tile shower. Using 1/2" Hardibacker for the shower transitioning into 1/2" greenboard outside the shower. I'm going to use mesh and mastic for the corner seam and two seams inside the shower but I was wondering what others use for the transition from cement board to drywall that will eventually be painted. I've read some use a setting type drywall compound while others stick with the mastic. Does this smooth well like mud. Does mastic stick well to oil primed drywall or is it better to go right to the mud/unprimed greenboard. I appreciate any opinions.