Repairing old greenboard and drywall shower wall

[MikeinLV]

Hello - I am hoping to get some advice.

I am replacing the Mixet valve I currently have in my shower and have discovered water damage and mold around were the faucet penetrates the wall to the valve. It is currently dry and the area affected is appx. 18" x 18". Currently there is 1 layer of 5/8 drywall attached to the studs with a 7/16" layer of green board attached to the drywall. The green board is in good shape but the drywall has suffered water damage and is moldy. The complete thickness is appx. 1 1/16" to 1 1/8". How should I proceed with repairing the wall to obtain the desired thickness and prevent future damage should water seep behind the faucet trim bezel.

Thanks
Mike

Here are some pics.

 

[Krow]

To start you need to get rid of all mould that is in the shower and surrounding areas (more for health reasons)

Greenboard is not the greatest of materials to be using in a shower. Greenboard is vapour proof, not water proof. You also have compounded dilema of having regular drywall, (if in fact that is the material), in behind the greenboard where mould can flourish and grow quite quickly

 

[Sponsor]

 

[MikeinLV]

Thank you for the information.

It was an apartment, built in 1996, that has been converted into a condominium. I understand that drywall / greenboard is not recommended in the shower area but that is how it was constructed.

I was planning on cutting out that area and replacing it with 2 layers of 1/2" cement board with some thinset in-between to give me the correct thickness. Is this the best solution?

 

[Jadnashua]

What is the covering on the wall in the shower? If a fiberglass wall, you don't actually need to install anything there. Yes, it will flex if you lean on it, but how often do you do that? A shim and the single layer of cbu would probably suffice to get the desired thickness, but how will you attach it to the studs if not removing or rebuilding the shower?

 

[MikeinLV]

The shower is ceramic tile with a fiberglass tub. I was planning to remove the tiles and wall around the faucet (damaged area), repairing the wall and replacing the tiles.

The damaged drywall is limited to what you see in the pics.

 

[Jadnashua]

You're really lucky the area around the tub deck and the sides and back of the shower walls (where the spray hits most often) aren't as bad or worse...greenboard is a lousy backer in anything other than a dry area, and then, regular drywall is okay. So, if you can get to the edges of the studs where you have to replace the stuff, I'd probably use a shim and then a single layer of cbu. Ideally, you'd have a vapor barrier behind the entire wall draped down over the tub's tiling lip to protect the studs. An alternative to that is to use a surface application like RedGard from Custom Building Products (available at HD and most tile stores). You could use two layers of cbu if you wanted. You should be able to compensate for the thickness difference with thinset underneath the tile rather than trying to spread it between the sheets if you go that way, or if you size the shims properly, not need it at all. If you wanted to get it even first, use thinset on the top layer with a screed, let it cure, then install the tile. Thinset sticks to thinset well, and that won't be a problem.

 

[MikeinLV]

krow & jadnashua - Thank you both for the information. Much appreciated.

Mike