Flooring Tile - durarock wallboard?

i am attatching 5/16 durarock over 1/2" green board on a shower wall,to get the needed thickness so the tile on the ends
of the tub will be inside the tub flange,not on top of it.
MY QUESTION
do i need thinset / mastic or anything between the durarock & the green board?
i have read the post about it being necessary on floors,but do not find info about walls.
any info will be apretiated

Skip the greenboard. Shim out the studs to where they need to be, then vapor barrier then use 1/2" durock or other cement board.

I agree, you shouldn't need anything under the cementboard (aside from the VB). I'm having trouble picturing why one layer wouldn't match the existing drywall outside of the tub area. The tile should be able to cover that flange so the cementboard does not need to be over it.

the length of the tub is 60" / old framingg is 60-3/4".
I put 1/2" green board on each end of tub ,to bring surface out to flush w/tub flange.adding1/4 or5/16 duroc will bring tile & wall board inside,&down into tub flange .
I suppose can remove green board, add 1/2-5/8 ply wood shims,
add 15/30 lb felt.then 1/2" duroc.?
is that what you think is better than what I have in mind??
thanks
diy/mike

If all you did was put in the greenboard to pad it out so that the wonderboard is now flush with the existing drywall I don't see any reason to remove it now that it's already there. There probably should have been a vapor barrier under it though. Just make sure you use screws and not nails to attach the cement board. They make special ones that will drill flush and will not rust out. They are usually sold right next to the wonderboard or whatever like "rock on" brand or similar. I wouldn't put any kind of adheasive between them again, just nice long screws into the studs.

Here's vote#3 for removing the greenboard. Since cemtent board is not a waterproofing layer, it time, the greenboard will get moldy and lose it's ability to support the cement board properly. If you put poly behind it or have plastic wrapped batts of insulation behind it, it's even worse. The green facing is you vapor barrier. Using plastic or faced insulation behind the gb will cause it to rot out from back to front. This is what's known as a double vapor barrier.

i decided to remove the g/b add shims & felt / returned the 5/16 duroc/ bought 1/2" hardi backer.

Good move. Thats the right way to go.