On Sun, 16 Mar 2008 08:09:54 -0700 (PDT),
wrote:

Never posted here before . I put new Durock up in the shower , the
rest of the bathroom is new Greenboard . What would you mud the seam
with - Thin set or Drywall Compound wherever the two meet ? Before you
answer , let me explain that the seams I am concerned with are where
the tile will end and transition to the painted walls .

Basically the seam would be under the bullnose tiles , but I am
worried that using the thinset will cause the mortar to be exposed too
far past the seam or bullnose tiles , into the painted area . If I use
joint compound at this seam , it wouldn't be directly affected by
water , but I worry that it is still too close to the wettest area .
From where the bullnose ends , I only have 2 inches to play with from
where the medicine recessed cabinet opening is and the bullnose ends .
Could I use the Joint compound or go with the thinset and make it
work ? The joint on the plumbing side is only 3 -4 inches outside the
tub . What's the best course to take . The old walls were all
greenboard under the tile with compounded joints under the tile .


Thanks - C. Marz

Here's what I do in that situation, but it may not work out for you.
I plan it so the joint is about 1/4" behind the last tile. I don't
mud or thinset the joint at all. The tile is attached only to the
backer board, by holding the thinset back from the edge of the tile
enough that it doesn't end up on the greenboard. When I grout the
tile, I don't allow the grout to enter the edge between the tile and
greenboard. Any that does get in there I clean out before it sets.
Then, I caulk that joint later with urethane caulk (after wall is
painted). The two different materials are going to move relative to
one another. This method allows for it.

For this to work, you've got to have the joint in the right place, and
it's got to be a neat joint without big gaps.

HTH,

Paul F.