How to join backerboard and blueboard

Slated

I will be partially tiling the walls surrounding a bathtub.
I plan to up to 6 ft with the tile. If the backer board goes to the ceiling, what do I do with the untiled portion? It looks like hardibacker board has a face that can be painted. But what about taping the joints? Will it look smooth and consistent like regular sheetrock when painted?

Only part of the bathroom will be tiled and I plan to use blueboard on the the untiled portions? Can I just butt together the backer board and the sheetrock, and then tape, prime and paint? That seems impossible with the USG material because it is so rough.

Just Bill

Using 1/2" backerboard and 1/2" drywall, make your joint just below the end of the tile, tape with mesh tape and mud as usual. The tile will cover the junction. Why are you using blueboard, that is for skim coat plaster???

Slated

I mean to say I am using the mildew moisture resistant gypsum board. Specifically I am using a product from Lowe's called Mold Defense made by Lafarge. It is green in color. I understand from Lowes that is equivalent to blueboard.
I;m using this product because of the high moisture level in the bathroom.

Slated

I got a different suggestion from a plumber who had worked with this stuff. He said it is very easy to apply a thin coating of joint compound (plaster) over the surface of the backerboard and then give it a light sanding. It will look identical to the same as the sheetrock once primed and painted.

Jim F

I taped and mudded backer board to drywall. It worked fine. the suggestion of ending the backer board just below the top row of tiles is the usual way to do it and it saves you from having to tape and mud. There is giong to be so little water splashing up there ie will not matter if there is wll board under the tile.