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Window Over The Tub,

Tile On The Walls 

How Should They Meet ?

I have a question regarding finishing an Andersen Awning window that is on the wall of a tub/shower in an upstairs bathroom. I was planning to put ceramic tile on WonderBoard in that tub/shower (the wall is an exterior wall, newly framed with 2 x 4's). My concern is protecting the window, and also the best way to deal with the connection between the tile on the wall and the window.  Finally, the window sits back from the edge of the WonderBoard by 2" or so. Should the window be finished with 1" pressure treated wood (as jamb extenders and stool), and bullnose tile all around instead of casing? Is there a good way to do this that I am not thinking of?

A. B.

New York

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.



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Copyright 2001

Compiled March 28, 2001