I think the board is in poor shape and I would not have used it in my DIY job. The tub, do you know what kind it is? You can find installation instructions for tubs on the internet. If it is a Kohler you can go to any site that sells them and they also link instructions, as does the Kohler website. Is this a tub with or without a shower? The wall either can be shimmed out with furring strips, or the 2x4s notched in so the tub tile flange can be recessed a bit. But I don't know if it is needed with just a tub installation, as the walls won't be wet like in a shower. As I look on the Kohler web site they set the board down on top of the flange like in your picture, siliconed the tiny gap than tiled over the board with the tile providing the overlap. Then the gap where the tile meets the tub gets caulked with silicone. They don't mention any vapor barrier like Redgard, hydroban, or poly. The installation is probably where there is no shower involved. Again I am not an experienced remodeler, just a DIY on a few things. What you don't want is water to be creeping back behind the wall board to get into your wall/stud space. Now the cast iron shower pan that Kohler has, is installed with furring strips on the studs that rest down onto the the top of the tile flange. Then, the cement board is dropped down over the flange and down onto the deck. The furring strips that are shown in these instructions look to be several feet long. I don't know how this is done in real life. I would have thought that the strips would need to be the entire wall length. EDITED to post link that I had saved. This link has a picture that Mongoct posted, its the 5th post I believe. It is an excellent diagram of how to treat the wall, tub, and tile without using firring strips. This is how I did it on my non-showered tub. Here is a link that might be useful: Is Kerdi-Board Overkill for Tub Surround This post was edited by enduring on Fri, Jul 26, 13 at 7:55

Much depends on exactly WHAT kind of shower you are building. Typically, you will cover the floor with a waterproof membrane, then attach expanded lathe with staples or nails, At this point, you put a "mud bed" over that. NOW, if it is a "traditional" shower floor, a rubber membrane is put in, attached to the drain and over the curb and 10" up the walls. The curb than has the same wire lathe "overbended to the curb and attached ONLY on the outside by fasteners. It is then "mudded" with mason mix with a slight slope inward. At this point, the final mud bed is installed and can be tiled over. The other process is, after the initial mud bed is installed, a "SAM" (surface applied membrane) such as Schluter's "Kerdi" is installed on the walls and the floor. Simpler and the water only goes to that point and then to the drain. You DO need to use their proprietary drain as it has a "bonding flange" as opposed to using the cheap "clamping flange" type drain. For more info on the Kerdi System, go to Schluter.com or just UTube "Kerdi Showers.

You would have to make a small hole next to the tile to see if it is cbu or drywall. Most probably it is drywall because the wall around the tub is more like a backsplash in a kitchen versus a shower in a bathroom. The most important thing is does the tub have a tile flange? If so, then you are in luck. When tubs do not have an integral tile flange, then you install a separate tile flange with silicon caulk, adhesive, screws, etc per manufacturer instructions. The cbu is installed a fraction of an inch above the flange. Nowdays, a surface moisture barrier is installed on the cbu - either a topical paint type (Red Guard, Hydroban) or Kerdi (plastic fabric installed like wallpaper with thinset). The gap between the cbu and the tub is filled with caulk - folks like to use Kerdifix. Then the tile is installed on the wall to where it hangs right over the cbu/caulk gap but doesn't quite touch the tub. Then that gap is filled with colored silicon caulk that matches the tub or tile, and it must be maintained for the life of the tub. Same installation is done for shower pans. You are going to have to tear out the existing tile. The issue is that if the tub does not have a tile flange, can you add one to it . Maybe you can detach the tub from the studs, install the tile flange, and then reinstall the tub. Then install your cbu. If you choose to use Kerdi, you do not have to tear out the sheet rock above the tile because Kerdi can also be installed on drywall. If all else fails and you really need a full shower, it may be better to buy a new tub. A soaker tub is cheaper than a whirlpool. If you don't mind the fab walls, Sterling has some nice tub/shower wall sets. Or you can install a handshower to your existing tub. Many times I wash my hair in my tub with my handshower when I have time to take a bath in the mornings. So do some light digging at the edge of your tub to see if it has a tile flange. Also, look up your tub's specs on the internet and/or call the manufacturer. Acrylic tub walls are usually specifically made to go with their matching brand of tubs because of their lock and fit mechanisms. Search this forum and the John Bridge forum for more specifics and details whether you DIY or hire the work out. This post was edited by Anna_in_TX on Sat, Dec 7, 13 at 15:21

I think the two approaches are completely different Erik. You are bonding tile directly above in your example right? The LynCarr example will see 1.5" - 2" of reinforced mortar. So not really apples to apples. Your head gravel work looks better than what happens on most showers where the fellow grabs a small handful or rocks. I think we should re do this test that took place in California. Can't be too hard. Lets just test a few of our set ups. I would like to see Mapei's 4-1, Mapei's 4-1 mixed with admix vs Laticrete 3701 & maybe an old fashioned home mix of 5-1. Set them into simple boxes with a clamping drain. Give them 1.5" of mortar and see what works best. The NTCA and the TCNA have nothing scheduled to study this to my knowledge. They might talk about it. Share and email about it. But they are not looking deeper into it. I really think we all our heads in the sand if we ignore the warning. Someone has got to step up....