installing cement board tub surround


Old 08-12-08, 04:08 PM
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Cool installing cement board tub surround

I have gutted my bathroom to the studs and replaced the tub and now have to install cement backer board and drywall. The question I have is:
Does the backer board rest on the top of the tub flange or cover it? I assume that is covers the tub flange, and so I must shim it out at a slight angle to accomplish that. If so, 1: how to I get the drywall and the cement board to meet flush at the top of the tub and 2: won't I have to angle the edges of the bottom row of tile to accomodate the angle caused by the shimming?

The tub is the right size but does not fit completely snug against the studs at either end.
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Old 08-12-08, 04:41 PM
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Please, no drywall behind tile!!! Backer board should cover the lip on the tub, but not touch the tub edge. Raise it up about 1/4". If you have to shim to make things flat, that is not unusual. Tubs rarely fit the opening exactly.
Old 08-13-08, 08:01 AM
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You can either end the cement board a little above the tub flange or fir out the studs 1/4" and have the cement board cover the flange and stop approx 1/4" from the top of the tub. Either way, make sure you use a poly vapor barrier and that it overlaps the tub flange. If you stop the cement board above the tub flange, caulk the gap between the flange and the cement board. Your bottom row of tile must be tall enough so that enough of the tile is on the cement board.

If the tub is not fitting well at either end then firring out the walls is probably a better option. Starting with plumb square walls will make the tile job a lot easier and the finished product look lots better as well. This option can sometimes require special trim pieces to transition from the tile to the drywall.

Dont try to shim out just the bottom of the cement board. Tiling out of plum, out of plane walls will cause problems for you, and will be noticeable when its done.
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