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We're about to remodel our bathroom, having tile applied to about 17 linear feet of wall (8' high). 90% of the wall area to be tiled already has green drywall. The remainder is open studs, where a bathtub used to sit. The tile contractor suggests we rip off all the greenboard and they will put up 1/2" kerdiboard instead.

I was thinking to fill in the missing greenboard (about 16 ft2) and the installer would put membrane over the whole thing.

I understand that either way will work.

It seems like it would be cheaper to go greenboard/membrane. I'm doing the drywall work (ripping off or installing).

Which is preferable and which would you do??

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    This answer may be of help to you: diy.stackexchange.com/a/20303/80608f TL;DR: I don't think you should use greenboard for a shower surround. I'm not sure if the membrane exempts from this belief (why this is a comment, and not an answer). It's also highly dependant on your local codes.
    – Sam
    Commented Mar 10, 2021 at 18:20
  • Your question is not enough for us to be dangerous. It is really confusing on whether you want the greenboard or kerdi or whatever on the non-shower section (above the bathtub surround is considered shower) or the showered section. Give us the layout and proposed solution. There is no way anyone can answer your question how it stands now.
    – DMoore
    Commented Mar 10, 2021 at 18:41
  • You only need waterproofing in shower surround area. I am not sure why you are wanting to do the whole room with it. I use Denshield for all shower surrounds, it has a waterproof membrane on it and is easy to install.
    – Alaska Man
    Commented Mar 10, 2021 at 19:25
  • @AlaskaMan Can tile be applied directly to Denshield?
    – Jim Stewart
    Commented Mar 10, 2021 at 21:14
  • Is the old greenboard in good shape? Smooth and flat or does it need cleaned up (more work)? The kerdi or cement board is preferred for tiling over in a bathroom.
    – Phaelax z
    Commented Mar 12, 2021 at 16:51

2 Answers 2

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The answer on what will be easier depends on how square and flat the walls are currently. If the walls are already really flat(no more than 1/16" deviation in 2 ft) and the corners are square then you proceed with the membrane. If there is any work that needs to be done it is easier to shim the studs and/or plane studs before wall install. Take a level to the wall and check it everywhere.

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  • It's a remodel. The bathroom is already green drywall'd (25 years old). It would be less work for me to leave the drywall. But, what about for the installer? Would is save money or cost money to leave the green drywall? If there are slight variances from flat, can the thinset level that out? I assume this problem could exist for either situation?
    – EnoughToBeDangerous
    Commented Mar 10, 2021 at 20:27
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I checked Kerdi's website and the Kerdiboards that are rated for application on drywall studs are 19mm thick and above, using the standard stud spacing of 60mm (EU) or close enough to that (US).

The half inch (12mm) thickness is pretty floppy, it's meant to be glued to an existing wall with mortar, so its back is well supported. This makes your wall flat and waterproof in one step, which is nice, but this stuff is thin foam sandwiched between two layers of fiber reinforced cement.

So... looks like your contractor either didn't read the manual, or wants to sell more stuff.

You only need membrane around the shower and the bathtub if there is one. So I'd say keep your greenboard, finish the rest of the drywall, and put membrane where it is necessary.

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