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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??

isherwood
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EnoughToBeDangerous
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2 Answers2

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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.

bobflux
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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.

redlude97
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