lee, it depends. If it it tile over gysum core board, the gypsum board will likely be wrecked. Which is fine. lol If it's over cement board, it depends on the strength of the bond between the tile and the backer board. If it's over a floated mud wall, you can usually pop the tiles off and then just make repairs to the divots in the mud. Every case is different. Lastly, it depends on the type of waterproofing or drainage plane you have in your shower. If you have 6-mil poly behind the backer board, that will usually remain intact. In that case, you can repair or piece in new backer board as needed, then retile. If you had a topical membrane, then you'd want to try to maintain your existing backer board, and the membrane can be recoated. My preferred way to remove existing tile with minimal damage to the backer board is to chuck a diamond wheel in a grinder. I first cut out the grout around the perimeter of the tiles that I want to remove. I then cut out the grout around a tile in the middle of the wall. Next, it depends on the size of the tile, but I'll usually cut an "X", or on larger tile, a # pattern through the depth of the middle tile. I then use a chisel at a low angle and cleave the tile sections off the backer board. If the tile has a weak bond with the backer board, you might b able to pop the remaining whole tiles right off the backer board without damaging the board. If the tiles take the backer board with them, then you might have to section the remaining tiles with the X or # pattern. The smaller the pieces you section the tile in to, the less damage you'll do to the backer board. It's easier to pop off small pieces than large pieces.

ok,,that's what I thought. then I think you may have a problem. not many people know that these tiles MUST be sealed before install. they are very porous. when the grout goes on, it should not be spread out over the tiles like regular tiles, especially if not sealed. the tile absorbs the grout material and it can stain. Now I don't know if this was done to yours, but you could try some grout release and see if it cleans up. you need to ask,,, were the tops (seal tops only, not the sides) of these tiles sealed before installed? a way to find out is water should bead up on the tiles. if the water absorbs, not sealed. when the tile setter installed them on the wall, did he dunk them in water first? if not, a dry cement tile will quickly suck up all the water from the mortar and possibly lead to poor adhesion. what kind of grout was used? here, read this page for more info. look at the grouting and sealing heading. read carefully: https://www.cementtileshop.com/INSTALL.html If that tile is discolored and won't clean up, hurry up and take it off before it hardens and cures. replace w/a new tile. wash all those tiles well, let dry and seal multiple times (every 24 hrs or so) until no more sealer is absorbed.

If I'm understanding correctly. The original contractor did not shim out the wall studs so the cement board comes down past the tub flange. Instead allowing the flange to cause a bow in the cement board. 1st - The original contractor owes you $$ for material and labor to correct the unacceptable substrate he/she stuck you with. 2nd - Drywall has not been allowed in a wet area since 2006. So you can rule that guy out. 3rd - If you were to cut the existing CBU at the flange so it now is flat against the wall studs above the flange. You could in theory use the existing CBU as the shim and install another CBU over the top. Proper fastening required, taping joint with alkali resistant mesh, proper screws, and possible thinset layers together. Then apply waterproofing. Liquid or Sheet membrane. Personally I would go over with a foam board instead of a CBU. It would minimize weight and the board itself would be waterproof. Yes I would mortar them together thinset method. My preferred foam board would be USG due to high compressive strength (70PSI) Caution - Building wall out could cause a plumbing issue at the mixing valve and finishing edges when meeting existing walls or wood trims.

Thank you for the recommendations and the article. I tried putting bleach on it, it did not come up. I have the same tiles in other areas of the bathroom and there are no rust- looking lines on them. I also looked at spare tiles and they seem evenly glazed. So far it is only on about 8 of the tiles in my shower. The contractor says it is a defect in the tile and won’t fix it, and I haven’t heard back from the tile company yet, but I am sure they will blame the contractor.