Cement Board Detail
The best approach when installing cement board or other tile backer around a tub is to keep the cement board out of the lip area. Apply it to the wall with the bottom edge about 1/4 in. above the lip of the tub. Then apply a generous amount of thin-set to the bottom bathtub tile and position it 1/8 in. above the tub. Fill the gap between the tile and the tub with caulk.
What is Backer Board?
Cement backer board is used as a sub-surface for tiling, usually for showers or bathtubs. Backer boars are generally placed against plywood or OSB board. This treatment is unnecessary if there is already cement backing.
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