Master Bath Remodel Saga: Porcelain on Slab, Marble, Alcove Tub, MOLD!

[az1324]

Ok so I've started my master bath remodel.

This is a ~50 sqft bathroom in a second floor condo unit in SoCal. The unit was constructed in 1985 and apart from a ceramic tile floor addition to replace linoleum there hasn't been any work done on the bathroom. The floor is a slab and there is an alcove tub with shower.





[Step 1: Demo]
I'm tearing the bathroom down to the studs, except for where the sheetrock is still ok. I'm taking all cabinets and fixtures out and pulling up the ceramic tile floor.

Upon removing the baseboards, I saw some mold behind the toilet.


I then ripped out the tiles over the tub and found them to be mastic over greenboard.

Under the greenboard on the two unplumbed walls was 5/8" sheetrock. The wall adjacent to the toilet had some mold. The back wall's sheetrock was covered in mold.
Behind that was plywood. The mold had reached the plywood leaving some dark spots.

This wall is adjacent to another condo unit. Removing the sheetrock from the end wall I found some nice green insulation. It's not supposed to be green!
This is also a shared wall and as such is double framed with the back of my insulation meeting the back of the neighbor's insulation. The mold is present on their insulation too.

[Questions/Advice]
And that's where I'm at right now. So I'm wondering where to go from here. Obviously I will remove all the moldy material and dispose, then use some kind of mold killer on the studs, etc. My question is should I remove that plywood or just kill the mold on it? And what about the neighbors insulation? Should I just replace mine and notify them? Finally, is it okay to put sheetrock back up under the cement board to get the wall back even with the others? I think the main purpose of this is noise insulation because all the common walls have double sheetrock.

[Brian in San Diego]

Welcome, Ben!

Originally Posted by Ben

My question is should I remove that plywood or just kill the mold on it? And what about the neighbors insulation? Should I just replace mine and notify them? Finally, is it okay to put sheetrock back up under the cement board to get the wall back even with the others?

I would kill the mold on the plywood. How well do you know your neighbors? The only way they could get to that insulation is by ripping out drywall. I think it'd be much more neighborly to inform them and tell them you'll replace it as best you can if they would cover the cost of the material. Kind of a judgment call. I don't think I would put sheetrock under CBU unless you were going to apply a surface membrane to the CBU. Why not put 5/8" drywall back up and kerdi it? I think it'd end up being less expensive than the drywall, CBU, RedGard treatment. You definitely don't want a vapor barrier, drywall, CBU, tile.

Brian

[Mike2]

I'd spray the plywood with a mild bleach solution and leave it at that. Plywood on interior walls can mean they are structural braced walls, and as such should be left alone. Braced walls are generally placed to provide added lateral resistance to wind and seismic forces.

I don't see a problem placing drywall behind cement board. It's generally not advised but I understand your primary reason for doing this is to bring the tiled surface out flush with the surrounding wall(s). Is that the case?

[Brian in San Diego]

Mike, wouldn't the drywall get wet and begin the whole mold problem again unless a surface membrane was installed? I guess the question neither of us asked is if there is a shower in the tub area. If there is, I don't like the idea of drywall behind the CBU unless there's redgard or hydro-ban on top of the CBU.

Brian

[az1324]

Yes, the leveling is the primary reason, plus the noise barrier. I guess I could shim it out but wouldn't get the noise insulation that I would with drywall. You know... singing in the shower and all. I had planned on doing vapor barrier, cbu, tile before knowing about the drywall but I guess I couldn't do drywall, vapor barrier, cbu since the vapor barrier would be sandwiched between the cbu and drywall?

I don't mind doing Kerdi, just hadn't planned on it. I would actually have to do 2x 5/8 sheets on the two walls then to make them level.

[Brian in San Diego]

Ben,

I'd put up the double thickness 5/8" drywall and kerdi it.

Brian

[Hammy]

Schreech....................... Hold on here a minute...................... You said "double dry wal" Sounds like a fire wall to me. ( between 2 units ) Can you find any marking saying it is "x" rated. Most 5/8" dry is fire rated. Look into it before sealing it up. hope it helps, Hammy

[az1324]

Yes it did say something about type x.

Does that mean I have to replace it with the same and thus kerdi is my only option?

[Hammy]

Regardless of what you cover the drywall with you MUST rebuild the fire wall. Kerdi in my opinion is yout best option, but there are others available. Hammy

[az1324]

[Update]

Added pics. Forum wouldn't accept 640x480 landscape photos so yeah...

Ok so after removing my insulation, I was reminded that the floors of adjacent units are staggered in the building, so the floor of the adjacent unit starts midway up my wall.

So now the mold has potential to reach 2 neighboring units.

I have to check exactly how far it's gotten after I get the tub out.

[Tub Apron Planning]

I am replacing the tub with a 3 sided flange tub with no apron because I want to build a tile apron for the front. I'm debating on whether I should build a flush apron with no deck surface or have a small deck (~2") come out from under the tub. Anyone have photos of either case? Recommendations on the best way to construct this apron and waterproof it would be appreciated. I was thinking 2x4 framed secured to adjacent walls and slab, covered with CBU. But now that I'm doing a kerdi shower I could use that. Is it ok to use drywall there under the kerdi?

[Brian in San Diego]

Ben,

The forum has a limitation on photo size. I think it's 600x480 but the whole skinny is told in this thread. I found it in the Liberry.

You could frame the front of where the tub is going to sit, drywall it and apply kerdi. The critical part IMO is sealing where the tub and framed wall meet. A quality 100% silicone product should do the trick. You would want to put drywall over any dimensional lumber and then kerdi it.

Brian

[az1324]

Thanks Brian. Well the site supposedly accepts 600x800 photos, but in the landscape format that's 800x600 and I guess each dimension is enforced separately not just by # of pixels. Also funny that the example photo is 800x640.

I'm still trying to decide whether it would look strange or less attractive to have the tile apron flush with the tub edge. Since the tub edge profile is hollow I was thinking I could build a dam/flange under it and run the kerdi up it so that the water would never be able to get past there.

[Hammy]

Az, go to Micro Softs website and download PHOTO RESIZER its free and works well. Every photo i post is resized by it. Hammy

[az1324]

I have it but "File Too Large. Limits are 600 x 800. Your file is 640 x 480." It won't let me post a landscape format photo that is clearly smaller than 600x800 in pixel count. Maybe the limit should be changed to 800x800 which would allow for 800x600 and 640x480 photos in either orientation.

Back to topic, anyone have photos of a tiled apron flush with tub edge?

[az1324]

Ok I found a photo of what I want to do with the apron. My question: Is it ok that there is not a horizontal surface for the tub rim to rest on but simply the edge of a tile? I know the tub is not designed to be supported by the rim but seems if someone sits on the tub there should be some support for the rim itself. Expanding foam between top of the kick wall framing and tub?