Drywall around tub: wrong?

[infinitje]

First of all, this is a great forum and I've yet to discover everything. SOme of the talk is a little beyond my knowledge too lol I'm a tiling newbie, only helping my dad install floor tile on a house.

When it comes to the bathroom project I'm a bit lost and from what I've read I think I may have already went in the wrong direction! I had a slab leak and the plumber had to destroy all the tile walls in the process. After he laid a new tub I installed drywall on the three sides with plans to tile small tiles around as it was before the leak. From what I've read this is the wrong type of underlayment and should've used a cement board? Is tearing out this drywall I just set in the only option? If not, what are my other options?

[bbcamp]

No, Josh, there are other options besides ripping down the drywall you have installed, but that may be the easiest and cheapest solution.

Best solution: Install Kerdi over the drywall and seal it to the tub with Kerdi-fix. Bulletproof installation. Kinda expensive, though.

Second best solution: Remove the drywall compound and tape, tape and mud the joints with thinset and CBU tape, then coat the walls with 2 coats of Redgard or other liquid waterproofing membrane. Caulk the joint between the drywall and tub before setting the tile. Note: this is not a listed method in the Tile Handbook. There are no methods for using a liquid membrane over drywall in a shower. A tub surround/shower is less stressful on the waterproofing, so as long as you are diligent with your caulk maintenance, you should get a lot of service (years) out of the tilework before it needs replacement.

Cheapest solution: Tear down the drywall, install plastic sheeting over the studs and drape it into the tub. Install backerboard. Trim the plastic flush with bottom of backerboard. Tape and mud the joints with thinset and CBU tape. Caulk the joint between backerboard and tub.

[Houston Remodeler]

To underscore what Bob said;

Cement board (cbu) is not waterproof. Aside from cbu, you'll need some sort of waterproofing such as sheet plastic behind it or a surface waterproofing such as kerdi or hydroban.

[jadnashua]

Even more basic...the tile are not to be considered a waterproof layer...what's underneath it must be water resistant and not degrade if it gets wet as no matter what tile you use, some moisture will get behind it. The cbu is not waterproof, but it is water resistant in that it doesn't degrade when it gets wet. Drywall will fall apart and start to support mold growth when it gets wet.

[infinitje]

Thanks for the replies. I can't believe the previous tile installation had no plastic or waterproofing behind the drywall. When the wall was open I could see the drywall in the bathroom that shares a wall and it as well has no waterproofing; it's moldy too. I was just under the impression it was from my slab leak. I'm going to go price out kerbi and see if I can use that, but if not it looks like I'll be tearing it all down