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Tile Installation: Backer Board Around a Bathtub

Does tile backer board lap over the bathtub lip, or sit on top of it? It’s a question that’s puzzled first-time bathroom remodelers for years. This article explains the correct method.

By the DIY experts of The Family Handyman Magazine

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 tile and position it 1/8 in. above the tub. Fill the gap between the tile and the tub with caulk.
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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

    • Hammer
    • Cordless drill
    • Caulk gun
    • Notched trowel

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

    • Thinset mortar
    • Caulk
    • Tile backer

Comments from DIY Community Members

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1 - 8 of 8 comments
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October 20, 6:33 AM [GMT -5]

OK, I understand how the bottom meets the tub, what about the top of the cement board ? If I am using 12" tall tiles, does the cement board end just slightly below the top of the tile thereby putting my top grout line on the drywall or do I leave the cement board higher than the tile and necessitate a butt joint/seam of drywall/cement board above/around the tile ? If I go with the seam, how far away from the tile outer grout line should that drywall/cement board joint/seam be ?
Many thanks.


July 01, 8:48 PM [GMT -5]

Some tub installations call for attaching 1/4" furring strips on the studs to just above the flange, and attaching the cement board to them. This makes a level surface for your cement board, so it can overlap the flange without having to bow out. You attach the cement board down to about 1/4" of the top to the tub, then tile over it down to about 1/8" above the tub, and caulk the space. Also, as someone else mentioned, it's generally a good idea to have a vapor barrier, such as poly sheeting behind the cement board, or one of the liquid sealants on top of the cement backer board, but not both (or you could create a sandwich that traps water)..

April 25, 12:56 PM [GMT -5]

This is exactly what I've been looking for. Thank you Handyman


September 20, 9:52 PM [GMT -5]

this picture is awesome. that's exactly what i was looking for. the whole time i am wondering how in the world would the backer board be on top of the lip of the tub?? if you put the backer board all the way to the L lip on the tub, then the bottom of the tile would bulge outboard and look ugly.

thanks so much for the cutaway view. that's awesome.

August 08, 3:32 PM [GMT -5]

The tiles in my shower/tub have come loose and fallen out around the faucet for the tub. I need some advice on how to replace them without having to tear apart the entire wall, if possible. The cement board behind the old tile has disenegrated and will need to be replaced. How do I find the proper materials to repair it?

July 25, 9:44 PM [GMT -5]

Got it, but what if the lip for your tub surround measures over 3 inches? Should the backerboard overhang the fiberglass lip? Related - how should I affix the lip to the studs? On one side, I have a good 1/4 in. gap between lip and stud. Thanks!

April 23, 12:13 PM [GMT -5]

Consider adding a vinyl membrane behind the cement backer board.
when setting the tile leave a little gap between the tub and the tile to allow a space for the silicon caulk.

December 15, 7:53 PM [GMT -5]


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