Advice on Sealing the Joint Between Drywall and Cement Board?
 

In the process of re-tiling my walk-in shower, I removed the old
drywall about 6 feet up the wall (that's as far up as the old tile
extended) and replaced it with DuRock cement board. I've got the tile
all set, except for the top 2 or 3 rows. I'm wondering how to seal
that 1/8" gap between the top of the new DuRock and the bottom of the
old drywall. There's not only a gap between them, but they are also
slightly different thicknesses. So, if I wanted to use slightly taller
bullnose tiles for the very top row, which would extend them past that
joint, the tiles wouldn't set flush because of the differences in
thicknesses of the drywall & DuRock. Should I put an extra thick layer
of Mastic in and around the joint and feather it out like you do with
drywall joint compound, let it dry and try to sand it to smooth it out?
Or maybe just use drywall compound itself and Mastic over it once it's
dried and sanded?

My shower head also comes out of the wall at about the 6'6" mark. But
the original tiles only go up to about 6', and the original drywall
above it has never had a problem with moisture. It has several coats
of oil-based enamel and that's kept it sealed well.

I don't want to run the tiles all the way up because based on the
shower's FIRST 40 plus years of service it just isn't necessary. I
live in the dry desert Southwest.....maybe that's a factor in moisture
not lingering on the drywall above the tile line.

But back to my original question......what would be the best way to
smooth out the joint between the original drywall and the new
Durock???????

I did a similar project in my house, though the durock and the
sheetrock were the same thickness. A detail you left out: which one is
thicker in your bathroom? If the durock is thicker, I guess I'd just
keep tiling up and use some extra mastic behind the tiles at the top,
and then seal off the top of the mastic with grout-colored caulk. If
the sheetrock is thicker, then I am not so sure.

The sheetrock is thicker, by just over 1/16". That extra thickness my
be the result of several layers of paint over the last 46 years!

if you have a 1/16 gap, i would use a trowel to apply the glue on the
drywall with notches 1/16 less deep than the trowel you used on the cement
board so the glue surface is the same, and put the top layer of tile so it
overlaps the drywall. bead of caulk to seal the top edge when done.

randy

wrote in message
oups.com...
The sheetrock is thicker, by just over 1/16". That extra thickness my
be the result of several layers of paint over the last 46 years!

Should I put an extra thick layer of Mastic in and around the joint and feather it out like you do with drywall joint compound, let it dry and try to sand it to smooth it out?
Or maybe just use drywall compound itself and Mastic over it once it's dried and
sanded?

If the drywall is 1/16" thicker then the durock just sand the drywall
down a bit with a palm sander to even out the transition. Apply some
mastic to the joint and lay some mesh tape over that to make a stronger
joint. Smooth a bit more mastic over the tape and let it dry.

Just decide before hand how far up you want the tile to go over the
existing drywall, a couple of inches maybe is enough. If you go to far
with the sander you will have to cover that up with paint or drywall
compound if it is bad.

This isn't nearly as bad as everyone is making it out to be.

Of all the suggestions, that one (sanding the drywall to smooth the
transition) sounds the most promising.

Damn! Why didn't I think of that?

You're not going to sand a 1/16" off of drywall without removing the
paper. It's a stupid idea.

Hence the mastic and the mesh tape to provide the needed strength on
the joint... and covering that with tile... to hell with the paper.