In talking to Mr. Barros, the issues are: which walls, including bath tub and shower enclosures he will enclose with Durock (He referred to it as Wonderboard) as opposed to drywall gypsum board. Whether he will coat with plaster i) all Durock, ii) no Durock, or that portion of Durock which will not be covered by tiles. You may or may not have to decide at this time the height of the tiled surfaces i) in the bathtub enclosures, ii) in the shower stalls, and iii) in other walls to be (partially) tiled.  If I remember correctly, in the Addition, I had all the Durock surfaces plastered, and then cemented the tiles onto the lower portions of the Durock plates which had been previously covered with plaster in their entirety. None of the tiles which I cemented onto plaster surfaces in the Addition have come loose.  Because the exact location of the upper edge of the tiling should be a function of the dimensions of the tiles, it would be impossible for Mr Barros to determine exactly what areas of the Durock he should cover with plaster and what areas he should leave unplastered.  Since he does this all the time, he will have his own ideas about how he wants to proceed. Telephone me if you have questions of me.