Is there plastic sheeting between the drywall and studs? Are the studs made of wood?

@Sammy I don't believe so, no. Yes, the studs are wood.

I used Schluter waterproofing membrane on my bathroom.

I'd Kerdi over that without a second thought.

Yes you can waterproof what exists. I would like to present my friend Joe with a second thought.

I would install new Foam board directly over the top of the drywall using it as a shim. The board should extend down past the tub flange. Not sit on the top with the tile spanning a movement joint. That is the proper tile detail. Tub manufacturers will say it's ok to set on top. They seem to miss the point of acceptable standards by other trades. A tile or after market profile edge would be needed vertically at the tub ends to cover thickness variation. Question would be. Is the plumbing rough-in out far enough at the mixing valve? The foam board will eliminate the extra step of waterproofing. Laticrete, Wedi, Progress have some of the better ones out there now that USG no longer provides one. You will find many installers who will just go over what you have. I can back up the detail I present in writing. Can others show you anything beyond YouTube videos or "I've been doing it this way for 20 years":)

HINT - Foam boards are available in 1/4" thickness and can be fastened with thinset mortar to your existing wallboard.Consider this method for a proper installation. 1/4" foam board would simply be replacing the additional waterproofing that you require.

Just one tile guy's opinion.

@kindertina: Would you please post some close-up photos of the areas where the drywall meets the tub? Also, do you have your tile picked out yet?

@User Thanks for your comments, particularly with regards to the family friend. Made me smile actually. He said it so arrogantly that, according to code, you just tile directly on the purple drywall... I don't give a crap what code says - according to common sense, it doesn't seem right that you can just tile on a moisture-resistant drywall.

@Sammy I'll be there in the morning and will take pics :) I'm thinking of using a large glossy subway tile, 4 x 12 or 8 x 16, thoughts?

@Creative Tile Eastern CT Thanks for your expert opinion. I understand what you're saying. How can I tell whether the mixing valve is out far enough for your suggestion? Just to clarify, the 1/4" foam board would adhere to the purple drywall and be sufficient waterproofing? What brand would you use?

@Joseph Corlett, LLC Thank you for the advice you continue to share on this project of mine!

Here is some reading material for your family friend. Do notice it is from The Journal of Light Construction in 2005.

https://forums.jlconline.com/forums/forum/jlc-online-expert-forums/building-science/21556-u-s-gypsum-removes-wet-wall-certifcation-of-greenboard

1) Mixing valve. There is only so much room for the face plate to function properly. Usually approx. 1'. You are must likely ok. just be sure. Slip the face plate on and measure distance to wall board.

2) Foam board is your waterproofing. The seams will be sealed with that specific manufacturers method. Membrane, sealant etc.

3) I mentioned a few brands for board above. Which products are available in your area may decide selection.

Ignore your friend, and congrats for checking with your tile pros, and here.

Cement board + Kerdi is the gold standard.

I am thinking of using a large format subway tile (probably 8 x 16”). @Sammy

I would avoid large tiles in a small shower.

That appears to be purple drywall. Wrong application and you realize the drywall manufacturers do not allow this application? How are you waterproofing this?

I'd line that tub with luan plywood. One dropped tile and you're dead.

Even the purple drywall manufacturer recommends cement board in showers and tubs:

" In wet areas like showers and bathtubs, choose PermaBase® Cement Board for the protection you need against every drip, splish and splash."

@User Can you share why? Is it because it would look disproportionate? I was trying to minimize grout lines. What size tile would you recommend? :)

@millworkman The tile will not go directly on the purple drywall - it will be waterproofed. I am waiting to hear back from a couple tile setters, but they mentioned the whole gamut listed here. I will write them down once we connect and post it to see what you think.

@Joseph Corlett, LLC yes, definitely needs to be lined and a cement board will be used. I appreciate your help.

"t will be waterproofed."

The drywall manufacturers prohibit there drywall as a tile backer now for many years. Schluter who says you can use there system over drywall prohibit purple or moisture resistant drywall, only regular drywall. Which is still odd as thee drywall manufacturers say not at all but........................

@User huh? Nothing's been done yet.... so it is not too little too late. And what affirmation are you talking about? I posted close-up photos based on @Sammy's request. Can the cement board be installed over the purple drywall? I thought that was implied below. If you could, please specify what I should ask the tile setters before hiring them. I want advice.

"Can the cement board be installed over the purple drywall?"

No the drywall cannot be in the shower period. It needs to be removed.

Count the pieces of board and the screws...removal and replacement of that purple drywall could be done in less time than it takes to dismiss the recommendations. At this point, I would remove the purple drywall so a tile pro could see what issues might be hidden underneath that drywall. Let the tile installer replace or shim the framing as needed, use his favorite waterproofing system and install the tile. Otherwise you risk having a future problem which could be caused by or blamed on preexisting conditions.

It is cheaper and easier to backtrack now rather than wait until a problem shows up later.

@Lyndee Lee thank you kindly for your advice. Dare I say, that would allow for a shower niche to be easily installed then too, no? It sounds like the removal of the purple drywall is quite easy - just a matter of unscrewing? Here's a picture of what it looks like on the surround.

That should have already been torn out. Rip and tear.

@User it was actually newly installed by the "family friend" I refer to below who knows 'everything' about construction. :P I am so appreciative of all of you on this thread. Thank you all for your patience as I attempt to learn something I know nothing about. I will take the purple drywall out this week.