Prep for a tub/shower

I am doing my first bath remodel. I have demo'd the bath to the studs and set the bathtub. We are going to tile above the tub for the shower. Now I am at the point of hanging the cement board. Without actually hanging the board, what I see in my minds eye is a gap between the back of the tile and the tub lip. The tub is attached to the stud, and the 1/2" board is attached to the stud. The lip of the tub is not close to half an inch so there is going to be a gap, I think. Here is what I think is going to occur:



What do I do to fill that gap or am I just wrong in my thinking?

This was discussed on another thread recently.
You could notch the studs so tub lip is flush then run the backer board down over the tub lip but leave a 1/4" gap above the tub so water cant wick up the board.
Or shim the studs out with 3/8" or 1/4" plywood strips, or whatever it takes to make the backer board lay flat when it runs over the tub lip.

I did a search to try to not repeat posts and didn't see it. Thank you for the reply. Since the tub is in I think I will go see what the local HD has in the way of strips.

The general consensus is that if more than 1/2 of the tile is supported by the cbu, you can live with the cantilever. IOW, it's likely only a problem if you plan small tiles. A bit of thinset there, while not necessarily actually bonding, will provide some support. Now, if it were a floor, no way, but you don't walk on the wall.

Note, you either need a vapor barrier behind the cbu, lapped over the tiling flange and sealed to it, or you need to waterproof the top of the cbu and then seal it to the tub.

Here is the thread that discussed this same topic
https://terrylove.com/forums/showth...ile)-install-question&highlight=shower+flange

You would have to rip your own spacer strips, either use a 2x4 and a table saw to cut them to needed thickness, the width will match 1 1/2" wide, or you will have to get a sheet of plywood the correct thickness and cut them but will wind up with a lot left over. Sometimes near the cutting area panel saw at Home Depot they have a rack of scrap wood they sell for 50cents, 1 buck, or 2 bucks each, depending on what the scraps are. I found a bunch of Azek trim scraps one day I bought it all for 5 bucks and was able to make 6 window sills out of it after ripping it and putting a nice edge on it with my router table.

Wow, thanks for all the replies. I am installing additional 2x4's as the existing studs are a bit hap hazard. As for additional blocking, other than the new 2x4's I was not planning on anything additional. Should I?

None of the walls are external. This is a tub/shower install with a shower curtain. I am using cement board as the topical over a drywall just didn't do it for me. It might be perfectly fine, but not for me.

I am planning a shampoo niche. This is a guest bath so I am just going to do a small one in between the existing studs rather than frame it like a window.

LED lighting? Way outside of my comfort zone to do something funky with new lighting around the tub.

Generally, you want all of the edges of the cbu to be supported. Read the installation instructions for the board you choose, the support requirements are not the same for each, but it doesn't hurt to block all edges, regardless. Depends on how you install it whether, or how much you may want to add. Keep in mind, you need to use the reinforcement mesh on all of the seams.

As a minimum, you either put a vapor barrier behind the cbu, or you put a surface membrane on top of it (not both). Niches need some care about waterproofing so they don't become a major problem. They aren't all that hard to frame, but there are some premade versions that are already waterproof. All of the major manufacturers make at least one. Two companies you might look at are Noble and Schluter and there are others. Most of them are designed to fit between studs. But, if the studs aren't where you want the niche, then you need to do some reframing first.