How far down should CBU go in a shower? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-15-2001, 07:37 PM
Hi Guys,

Just looked at the latest issue of "Fine Homebuilding". This issue has a good article on installing waterproof shower pans but it is unclear in areas. I'm sure this question came up on a previous thread but here goes....

When installing the CBU on the shower walls, should the CBU run down into the mud bed as shown in the article or should it be off the floor 1 to 1.5 inches as the author mentions. I realize the issue here is wicking but the article contradicts itself ( drwg vs text).

If in fact the CBU is to be left 1" or so above the floor, what fills the gap between the CBU and floor when you install the tile? Is the gap left open? Will the tile stand the test of time with the void beneath it?

Pls help clear this up


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08-15-2001, 08:24 PM
Jason, after the the sloped mortar bed floor is finished, install the CBU to within 1/4" and fill the gap with a silicone calk. Your right, it is to prevent "wicking", but you can't tile air, so 1/4" is plenty of gap. It would be a good idea to waterproof the CBU as well before setting tile.

08-15-2001, 08:35 PM
Thanks for the reply,

Any recommendation of waterproofing agents?


Rob Z
08-15-2001, 08:45 PM

Latney is right on the mark. The 1/4" gap, filled with silicone, is the latest recommendation in the business.

The brands I use? Summitville S 9000 or Laticrete 9235. I'm going to try Bonsal's when i run out of my current supply of the 9235.