Jadnashua
Retired Defense Industry Engineer xxx
IF you are going to use the tub as a shower, industry standards call for tiling and water/vapor management at least to the height of the shower head, and some prefer to go all the way to the ceiling. If you're going to use a membrane in a shower, go at least that high with it. Most of them are not designed to be painted, so you'd stop it and the tile, with none sticking out.
If the tub does not also have a shower head, then it is only important to ensure you get the tub itself sealed to the wall, and then go up the wall at least a few inches (more certainly doesn't hurt). But, without a shower head, we're only taking about maybe some splashing up the wall, and there shouldn't be enough to soak into the wall behind and create a problem through the tile and grout (although, it certainly doesn't hurt).
There's also the option of using something like KerdiBoard or WediBoard instead of cbu on the walls of the surround which are both structural panels and waterproof that are designed to be tiled to. I've used KerdiBoard, I have not had a good chance to deal with Wedi products yet, although I did consider it on my last shower. CBU is not waterproof, but it is not affected by being wet and is a good, compatible surface to tile to. Getting a tub/wall waterproof seam with it is possible, but you need to be careful. ANohter big thing with water on any tub is to ensure it is level in both directions, otherwise, it can flow where you don't want it, or pool, and then soak the materials, depending on what you have there.
There are liquid and sheet membranes, pick one, and follow the manufacturer's instructions to the T, and it should work fine and you'll get a warranty from them. Most of them are at least 10-years, some longer, but if a problem doesn't show up in 10, it probably isn't going to happen.
If the tub does not also have a shower head, then it is only important to ensure you get the tub itself sealed to the wall, and then go up the wall at least a few inches (more certainly doesn't hurt). But, without a shower head, we're only taking about maybe some splashing up the wall, and there shouldn't be enough to soak into the wall behind and create a problem through the tile and grout (although, it certainly doesn't hurt).
There's also the option of using something like KerdiBoard or WediBoard instead of cbu on the walls of the surround which are both structural panels and waterproof that are designed to be tiled to. I've used KerdiBoard, I have not had a good chance to deal with Wedi products yet, although I did consider it on my last shower. CBU is not waterproof, but it is not affected by being wet and is a good, compatible surface to tile to. Getting a tub/wall waterproof seam with it is possible, but you need to be careful. ANohter big thing with water on any tub is to ensure it is level in both directions, otherwise, it can flow where you don't want it, or pool, and then soak the materials, depending on what you have there.
There are liquid and sheet membranes, pick one, and follow the manufacturer's instructions to the T, and it should work fine and you'll get a warranty from them. Most of them are at least 10-years, some longer, but if a problem doesn't show up in 10, it probably isn't going to happen.