Proper way to mud seam between Backer board and Green Board?

I know this has been discussed her before with different responses, but I'm not sure how treat the seam between backer board (cement board) and green board in a shower area. I realize this is a specific and rather picky question.
Rather than make the seam exactly on the tile edge, my first theory is that the tile should slightly overlap onto the greenboard, maybe an inch or less.
I should use fiberglass tape and I should use the seam side of the greenboard. In other words, the side that's indented to allow for the tape.
Questions:
1. Should I try my best to squeeze thinset INTO the seam? I'm not sure if the argument is to have a good seal or if there would be some need for expansion between differnent materials.
2. What do I mud with? On the BB side I'll go with the thinset, but do I also use thinset on the Green board side? Thinset, to my understanding, dries to a hard fine grain hard cement surface. How am I supposed to sand that down and get a nice smooth surface that will accept paint? Is the idea to put drywall joint compond on top of the dried thinset and then sand that flush? Will the indented portion be deep enough to allow this? This is my main question and it's been answered in different ways, so if you're kind enough to offer me some advice, please back it up with as much justification as you can.
3. If the tile overlaps the greenboard seam slightly and if I'm using the indented side of the greenboard, then maybe I could intentionally leave a slightly gap between the tile bottom and the greenboard and fill that gap with caulking? Or is that just making it harder than it needs to be?
Thanks for your help!
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On 11 Feb 2006 08:36:58 -0800, "Mak Wilson"

Here's what I do. I'm not a pro, but it's worked for me.
I plan the seam so that the tile will overlap the green board by about 1/4 inch. This requires some care. It's best if the bottom edge of the greenboard has blocking behind it, but not absolutely required.
I do not tape the seam in any way.
I finish the greenboard before I lay the tile.
I lay the tile, and avoid getting thinset on the area where the tile overlaps the green board. In other words, the tile is attached to the backer board and not the greenboard.
I caulk the joint between the tile and greenboard with silicon caulk.
Here's my reasoning: any time you have dissimilar backing materials, such as greenboard and backer board, they are going to move slightly in relation to one another over time. The silicon handles this with no problem. This method avoids all the issues you asked about with what to finish the seam with.
You do have to make sure the tile (and backer) runs high enough that you won't be getting a lot of water on the greenboard or on this caulked seam, but you should do that in any case..
FWIW, another option is to use thicker backerboard and then use cap tiles (the ones with a curved lip on one edge) to cover the thick edge and then caulk the seam between the cap tile and greenboard as above.
HTH,
Paul
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Can a person use all cement board? then mud the non tile areas? this would be more durable in a warm moist bathroom?
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wrote:

Yes, you could finish it like drywall and give it a skim coat of plaster. But my plastering skills are not good enough to skim coat a large area and have it look decent, so I stick to drywall.
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Apply the wonderboard (cement) anywhere that water or moisture may present a problem including ceilings. Tape the edges with green fiber mesh (waterproof for wonderboard) and tape all seams with durabond setting compound. Feather edges. NEXT STEP:::: USE DURABOND TO ADHERE TILE TO BACKERBOARD!!!! Do not use thinset or acrylic pastes. The setting compound will adhere the tiles far better than anything else. Use siliconized tile grout when finished.

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