I wish more tilesetters would stick to their guns like that.

Jimb54 bring up a very important issue. I also have seen failures on Exterior walls. I was baffled on occasion with fixing a shower and using Wonder board on an exterior wall with a thinset application.Seems the outside wall moved with expansion and contraction with our cold Alberta winters causing my grout to crack. Have you guess ever noticed also how an outside wall will move away from a counter Top? I have Tiled a BackSplash or two and been called back because i've been told my silicone was coming off. Well on inspection the Silicone was fine but the wall had moved 1/4 " or more away from the counter top.. Bizzar!!

Those outside walls move a lot in the summer too. You have the heat of the outside, and the cold of the air conditioned house inside...everything is wood, covered with what ever....next thing you know, someone reminds you that the tile you installed, isn't holding their house together anymore.

Hi all,

Jimb54, you asked what you are doing wrong,......answer, everything. And your 'tile people' aren't helping you any either. :p

Moisture resistant drywall was NEVER intended to be used as a tile backer in wet areas, never was. It can the used in a room that has high humidity, but not where moisture can contact the board. Thru the years many clerks would recommend it for just that, wet areas. Many even went as far as calling it 'water-proof' drywall. Yicks! There is no such thing!

Ok, so....no greenboard around tubs or for shower walls, it's junk! No mastic, use mastic only for dry areas, such as kitchen backsplashes. Don't put a vapor barrier behind wallboard if you suspect the wallboard might ever get moist. If you cheated and tiled over wallboard, the visqueen will make matters even worse. When you have time go to www.USG.com or other maker's site for more info.
Jaz