I am in the midst of a full renovation of my home, and now it is up
to me to finish off the smaller stuff. One of the projects is tiling a
shower stall enclosure. It has the pre-made fiberglass base which has
been put in and plumbed. In fact all the plumbing has been roughed in.
The drywallers used the "green board" around the stall area. My
question is...can I use the Schluter Systems "kerdi" water proofing
directly over top of the green board, then tile on top of that or do i
have to put up cement board? I am hoping that just the kerdi will be
enough. Also do I put a caulking seal at the base and the green board
initially, then put on the Kerdi, then tile, then seal again at the
base with caulking?
Any advise would be welcome. Newbie.
Tear out the green board from the wet areas, and put in cement backer
board, with vapor barrier under it (if the brand you buy recommends it).
Green board is water resistant, not water proof. It is fine elsewhere in
the bathroom, but anywhere water will splash, you do not want drywall of
any kind. Grout always leaks eventually, as does any taped or glued edge
of any sealing membrane. I know, I know, they used green board routinely
for thirty years after mud-bed enclosures died out. But now, they are
all failing. You haven't put the tile up yet, which is most of the labor
and expense. Fix it right now, and cuss a little at the rework, or plan
or redoing it all a few years down the road, and cussing a lot.
I agree with aem.
Green board might work under a cultured marble panel (3 of them) but is a
complete waste of time and materials under tile.
You might be able to use the 1/4" hardie-backer but then you would need the
cove or bull-nose tile with the deeper lip and it is sometimes hard to find.
Bite the bullet and rip out the green board.
*According to the handbook drywall is okay behind the Kerdi system however
if it was me I would remove the drywall and install hardibacker.
I would also get rid of the fiberglass base. I've seen several of my
customers get leaks from them after many years of use. Apparently they
crack if they are not well supported or if the floor flexes or maybe as they
age they become brittle.
Yes, Kerdi is designed to go over drywall/greenboard, just make sure to
follow their instructions to the letter. The guys and gals over at
www.johnbridge.com are very knowledgeable about tile, and especially the
It is a proven and reliable system.
Personally, for my recent shower tile job, I went with CBU and redguard, but
that's only because I wasn't familiar with the Kerdi stuff at the time.
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