Questions about filling joints in Durock and thinset types.
Hello.. I'm about 2/3rds done a on full gut small bathroom remodel (approx 5' x 10'. I had some trouble with a guy (hack) I hired to install the drywall, so I had to tear it all out and just drywall it myself. The bathroom itself will have porcelain tiles wainscot with a glass stripe up to about 55" on the wall. I will also carry the same pattern into the shower with it being tiled all the way to the ceiling.
Since I plan on a level 5 smooth walls above the tile, I installed the Durock up to 52", allowing for the tile to overlap the greenboard by three inches. Here's where the my questions start. (see photos)
1. Durock asks for Modified thinset w/ latex and fiberglass mesh tape in the seams between the backerboards and backerboard/greenboard. Why can't any brand of tile morter just say "modified thinset with latex" on the package?
2. I purchased Mapei Ultraflex 2 with polymer for fill the seams. Will this work for my application? (Porcelain tile on a non wet wall)
3. For the corners where the durock meets a non tiled greenboard sidewall, do I apply the same thinset and mesh tape? Or, do I finish the green board side of the wall with joint compound and leave the corner to be filled in when the tile is laid?
4. Do I have to prime the 3" of drywall above the durock before I apply the thinset to fill the seam?