The name calling, insults, and arguing make you both look like idiots and made me think neither of you were really right.
"Millions of homes have only insulation board for sheathing too, but that doesnt' make it somehow "right"."
Actually, yes, with cross bracing in the framing this would be a correct application to meet code in many areas of the country, and it actually performs quite well when done correctly.
Tile over plain gypsum sheet rock or green/blue board is just a bad idea in area where there is water...with a caveat or two. It can be done in conjunction with products like Schluter's Kerdi and Ditra.
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If you're tiling in a wet area, a CBU should be used. And, despite what's been written here, almost any tile job will eventually fail. It's just a question of time. Even a tile job on Green/Blue board will last for some time, even in a shower. It was common practice to tile over Green/Blue board for many years, but anyone who still does it is probably too arrogant to realize that we learn from out mistakes. Our mistakes? Yeah...despite what the one guy has said, the industry has changed because most green/blue board tile jobs in wet areas have failed.
Recent example? I'm in the middle of a 4 bathroom makeover in a house my friend recently bought. He got a hell of a deal on it. Didn't realize until the first wall fell on his kid that it was because of how the bathrooms were built. All the tubs and showers were built with green board 12 years ago and they're all falling apart now. ALL OF THEM!
I've spent much of my life working in this industry and can say, without reservation, the only acceptable backer in a wet area, as far as I'm concerned is a CBU...Cementitious Backer Unit, i.e. HardiBacker, Wonderboard, Durock. You can go a step better and simply float a wall with lathe and mud, but most folks aren't interested in spending that kind of money. As far as gypsum goes, I can't say as I would ever use it. However, I have heard some guys swear by Denshield for stone walls/floors where there's no real question about whether or not a lot of moisture will get through. Then again, those guys that swear by it, in my experience, are also the ones selling it.
Would I rip out an existing installation over green board to put in a CBU backed installation? Not until it failed or I got tired of looking at it.
And...quit the childish fighting?