I am in the process of redoing my bathroom. I just finished installing cement board around my tub all the way up to the ceiling. We plan to tile up to the ceiling. My question is how do I tie in the cement board with the drywall on the ceiling (as well as on the sides of my tub where it meets drywall? Do I use thinset or joint compound? I thought it would be best to use thinset since it will be a wet area, but can thinset be feathered out like joiny compound so I can paint the ceiling with it showing?