Novice looking for help with sealing inset cement board

[Monique]

Hello, this is my first time tiling. I was really hoping to do it myself and save some money. Havent even started yet and I'm already stumped.

Contractor hung cement board directly to the studs. Previously there was plywood AND cement board. Consequently the "gap" is set in behind the lip of my old tub (which I'd like to keep). I'm not sure how to handle tiling over that. Will the thin set and tile be thick enough to lay over this 1/2" gap into the other side? Should I hang another layer of cement board on top of current one?
Would love any advise and please forgive my novice lingo...still wet behind the ears over here.

 

[Jadnashua]

Neither tile, nor grout, nor cbu is waterproof...they are water resistant and not damaged by being wetted, but not waterproof.

Industry standards call for either a moisture barrier behind the cbu on the walls with the lower edge draped over the tiling flange of the tub, OR, a surface applied waterproofing over the entire area that can be sealed to the tiling flange.

So, short answer, no, tile alone won't cut it. And, with that horizontal offset, you'll have issues with that last row of tile since there's no way you would put that thick of a layer of thinset over everything.

So, here's what I'd do. I couldn't tell if they've taped the seams on the cbu yet. If not, I'd just unscrew what's there, take the pieces off and note where they came from so you can screw them back on. Install some shims on the walls so that the front face of the cbu will either be flush with the tiling flange, or far enough out so that it can overhang it. It can have a gap to the tiling flange vertically as long as you're using a tile that will be more than 1/2 supported by the cbu. Prior to putting the cbu back up, you'll need to install some plastic on the wall with the lower edge coming down over the tiling flange.

If the wall was not recessed, you could use a surface applied waterproofing such as RedGard or AquaDefense, or others, with their tape to cover that gap. But, it's not.

Industry standards really want either a moisture barrier behind that wall or waterproofing on top of it. There's a difference between the moisture barrier and waterproofing...the cbu, tile, grout WILL get wet unless it is waterproofed on the front. It won't be much, but it will long-term, potentially get into the walls...that's what the moisture barrier behind it does. You do not want both, but one or the other is required.

You could put something like KerdiBoard from www.schluter.com on top of what you have and create a waterproof tub/shower surround. They have some videos on their website that show that technique.

 

[Sponsor]

 

[Monique]

Neither tile, nor grout, nor cbu is waterproof...they are water resistant and not damaged by being wetted, but not waterproof.

Industry standards call for either a moisture barrier behind the cbu on the walls with the lower edge draped over the tiling flange of the tub, OR, a surface applied waterproofing over the entire area that can be sealed to the tiling flange.

So, short answer, no, tile alone won't cut it. And, with that horizontal offset, you'll have issues with that last row of tile since there's no way you would put that thick of a layer of thinset over everything.

So, here's what I'd do. I couldn't tell if they've taped the seams on the cbu yet. If not, I'd just unscrew what's there, take the pieces off and note where they came from so you can screw them back on. Install some shims on the walls so that the front face of the cbu will either be flush with the tiling flange, or far enough out so that it can overhang it. It can have a gap to the tiling flange vertically as long as you're using a tile that will be more than 1/2 supported by the cbu. Prior to putting the cbu back up, you'll need to install some plastic on the wall with the lower edge coming down over the tiling flange.

If the wall was not recessed, you could use a surface applied waterproofing such as RedGard or AquaDefense, or others, with their tape to cover that gap. But, it's not.

Industry standards really want either a moisture barrier behind that wall or waterproofing on top of it. There's a difference between the moisture barrier and waterproofing...the cbu, tile, grout WILL get wet unless it is waterproofed on the front. It won't be much, but it will long-term, potentially get into the walls...that's what the moisture barrier behind it does. You do not want both, but one or the other is required.

You could put something like KerdiBoard from www.schluter.com on top of what you have and create a waterproof tub/shower surround. They have some videos on their website that show that technique.