The
house I grew up in, a featureless boxy ranch from the 1960's, had
a window over the bath tub. The walls were tiled and I recall
there being wood trim around the window. All the houses in the
neighborhood had similar designs, and I distinctly remember that
everyone had plastic curtains over the windows, which did an
adequate job of protecting the wood from direct assault from
water. But plastic curtains are not everybody's idea of tasteful
interior decorating.
I'm not an expert in tiling, but
my approach would be to wrap the window opening with tile and
WonderBoard, right up to the window frame. I would make a slight
slope to the sill so water drains away, and where the sill
cementboard meets the wall cementboard I would be extra careful to
seal up the crack. On floors I have used fiberglass mesh tape with
thin-set mortar to join the adjacent pieces together. But this
creates a thicker layer of underlayment, which might hamper the
tiling job. I suppose you could just apply the tape to the corner
and then be sure to squeeze plenty of thin-set into the gap while
tiling. This should provide a sturdy corner that is able to
tolerate some flexing. You can be sure that the house will flex
over time (especially as moisture comes and goes through the wood
framing), and the corner joints will crack if not taped carefully.
One can look at cement
tile-backer board just like drywall... all the seams and corners
need to be taped and filled or else they will crack over time.
One-half inch Durock has tapered edges, but 1/4" WonderBoard
does not, because there just isn't enough thickness. I'd use the
thickest board possible, if the thickness does not cause problems
where the tile meets the other surfaces.
A few decades ago standard
practice was to glue tiles to drywall. That method has proven to
be inadequate, because the grout lines WILL crack and let some
water behind the tile, causing the drywall to soften. For walls
with drywall around the tub, the recommended procedure is to
remove it and install cement backer-board.
Another tip that might help
prevent water damage (just in case) is to apply a coating of good
quality oil-based primer to all the wood framing and trim that is
around the window opening. If water ever gets in there, the primer
will deter absorption into the wood. Anything you can do to
discourage water from getting to the wood can only help you. Also,
anything that helps stray water to drain away quickly will help
keep the wood from becoming your own personal microbiology
laboratory.
Bruce W. Maki, Editor.
