Hi all. I've got a couple questions regarding the installation of cbu on a shower seat. the framing was done before the preslope and liner so the liner goes up and over the seat. Well it isn't actually a liner but what they call a hot mop. The guy who installed it first did a preslope out of spec mix then a layer of hot ap tar then a layer of 15# felt paper and another layer of tar. My question is what is the best way to do the seat? I have read on other sites that say to nail the cbu through the liner on the face of the seat and on the top deck mud and then the tile (actually it will be a granite slab). the seat is about 20 inches high 4' wide and 12" deep. any suggestions would be greatly appreciated.

Here's how I do mine.

Hi Harry, I like that way with cinder blocks and would of done it that way had I found this site earlier, but the pan is in framing is done floor is alread mudded all I have left to do is mud the curb, put the cbu on the face of the seat, mud the top of the seat and I am ready for tile. problem I have is when i screw on the cbu to the face of the seat I will be penetrating the liner and I don't want it to leak. Here is a quote from askthebuilder.com "Waterproofing is accomplished by using the vinyl membranes that are used beneath ceramic tile floors. Simply purchase and install a continuous sheet from the floor, up the front of the bench over the seat and up the back of the seat wall about six inches. The membrane is only nailed at the top edges. You will have to penetrate the front bench wall surface with nails when you install the vertical piece of cement board. This is not a problem, as I have yet to develop a leak in my shower after 15 years." I don't beleive it won't leak. should I use kerdi membrane over the cbu to seal it? thanks for your help.

You should seal up more than just the seat. If you only do the seat, then water might get past the liner from above and leak behind it. Kerdi is the best way to go, but you could also use a roll on type like Redgard or laticrete 9235. There are others as well, that do a nice job of sealing out moisture.

I would like to use kerdi from top to bottom but unfortunately the money isn't there and I am already working for peanuts. stil I would like to do a decent acceptable job one that doesn't leak. funny thing out here in LA that is how they do it, no redgaurd kerdi or ditra, they hot mop then mud over wire lath They don't use deck mud they use spec mix which is the same as fat mud even on the floors. I have even seen them use concrete wire for the lath over plywood. any way the walls are hardi backer over the vapor barrier I'll use mesh tape and thinset on the seams. i want to be extra sure the seat doesn't leak.