Half bath gut

[valemic]

I am redoing a 4x4 half bath. It is ripped down to the studs and I am about to get started on putting it back together. I will be using carrara marble 3" octagon sheets for the floor and 3x6 subway tiles for the walls about 5' up. So here are my questions:

1. subfloor : Two layers of plywood with ditra, 1 layer of plywood w/ CB board or something else, glue the first layer?.
- dont have the joist info now, but don't think it is a problem.
2. For the walls if I use Kerdi board how do I tie into where it would be painted? How do I handle the seem where the KerdiBoard and sheet rock meet?
3. If I dont use Kerdi board can/should I use ditra on the walls?
4. Recommended thinset/grout for the marble.

TIA,
Mike

[Rd Tile]

1. 2 layers of plywood for either Ditra or cementboard.

2. 4x4 1/2 bath, no tub or shower, correct?

If so, just plain old drywall is fine for the walls.

Ditra is for floors only.

Any white thinset is fine, type depends on whether Ditra or cementboard is used.

[valemic]

Thanks Rd,

No bath, just sink and toilet. Is there any overwhelming advantage to the ditra? Since I dont have any other tile jobs in the near future, should I save the money since the smallest roll I can find is $100?

Thanks,
Mike