CBU tape and mud [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : CBU tape and mud

07-30-2010, 02:23 PM
I'm a DIY doing my 2nd tile shower - and have a question about taping and muding the CBU - the last shower I did was more than 5 years ago.

I've done the preslope, laid the liner, and am now installing the Duroc CBU. Should be finished that tonight. Then the next step...

Q: Do I tape and mud the CBU joints before laying the top floor layer or after?

The hospital folds are pushing the bottom 12" of Duroc inwards on two walls. Thought #1 is that the weight of the top floor layer first might push the Duroc back towards vertical if I don't tape and mud first. Thought #2 is that taping and mudding first would give more "integrity" to the joints.

Q: Mud the joints with thinset - right?


P.S. The "professional" who originally did this shower put the liner on the plywood floor, then did the preslope, then did the top layer. (Right steps, wrong order). Nailed through the liner about 4" above the plywood. Weep holes completely cemented shut. Nailed CBU on the inside and top of dam, as well as on the outside. No dam corners. Amazing that it lasted 3 years before the mold started growing.

The good news is that I can't possibly screw up as bad as this guy did!

Sponsored Links

07-30-2010, 02:50 PM
Hey Dave - sounds like fun! You don't want those liner corners pushing the bottom of the boards in, no... You can't scarf out the framing behind to give the liner room to tuck in back there? ISTR a liberry article showing that :scratch:

You want the proper alkali-resistant mesh tape and thinset on the joints and corners, and you want those boards to all sit dead plumb in the end, or the grout joints will say naughty things about you when it's all done... :moon:

Bottom line is you gotta get that liner to play nice nice. Good luck!

07-30-2010, 03:19 PM
You need some room for that liner, either by notching the bottoms of the studs and making sure your blocking (assuming you used blocking) is also recessed (by 3/16-1/4"), or by furring out the studs everywhere ABOVE the top of the liner. Notching is usually a better choice if your durock abuts drywall - otherwise you end up with the edge bullnose or whatever sticking out that 1/4" and it creates an awkward situation IMO. It is too large for a nice caulk joint but too narrow for tile.

08-01-2010, 10:35 AM
I'm pulling off the bottom sections of the Durock and notching the studs - hopefully notching only the two walls where the folds lay will be sufficient. Yes, I did use blocking, but attached it with screws, so removal will be easy.

The problem with being a DIY is that you learn how to do something correctly, but years go by before you do the same kind of job again, and by then, you've forgotten the little details.

Doing a mud shower is a really satisfying experience, even if you've got to take a couple steps backwards now and again.