What is the proper substrate to use on tiled wall?
Gampy1
| Posted in General Discussion on
I intend to use Schluter products in an upcoming bathroom. Schluter videos demonstrate putting their Kerdi membrane over standard Sheetrock walls to gain a completely moisture proof surface. FB video with Meehan shows him using concrete board as substrate only and painting on waterproof material in area that will receive direct water spray. While I would like to avoid the dirt and weight of concrete board, I want to do the job right the first time. Who do I believe???
Replies
Is this an inside-the-shower water contact area, or a behind-the-sink-might-get-splashed-occasionally area? The answer is different depending.
What is the proper substrate to use on tiled wall?
Dan, This is for an inside the shower application on interior walls of the room.
Answer is ...
..."It depends".
Schluter warrants Kerdi being installed of drywall. Regular old gray gypsum drywall. However, the 2006 revision to code specifically limited what materials can be used as a tile backer in wet areas like showers and tub surrounds.
Here's where it gets a little nit-picky and the "it depends" comes in to play. Sure, drywall sucks as a tile backer, and no one in their right mind would ever tile directly on regular gypsum board in a shower. But the gypsum board is protected by Kerdi. So Schluter is confident, and pretty much correct, when they say Kerdi is bulletproof and the gypsum board will never see moisture. That's all fine and dandy for Schluter. But that's where code interpretation comes in to play, as your building inspector may not see things that way. They see Kerdi as the membrane (if they even know what Kerdi is) but they see the regular old gypsum board as the "tile backer" and for them, alarms go off.
I had to educate my inspectors on Kerdi years ago, I was the first guy to use it in my locale. They'll allow me to use Kerdi over drywall, though I don't.
When I use Kerdi, I use it over cement board. Not hardie, but durock or wonderboard. Hardie can be used, but it does give some installers difficulty due to how fast it wicks moisture from thinset. FWIW, I prefer a true "cement board" like Durock (my favorite) or wonderboard over Hardie anyways, so there is a personal bias in there.
As for a roll-on membrane over cement board, sure, they are fine. I prefer Hydroban over RedGard, but again, that's personal. But the marriage of the two products will make for a fine installation.
If you want Kerdi over drywall and you encounter resistance from your compliance officers, print out the Schluter certificates and installation info and go have a sit-down with your building department. Otherwise Kerdi or a topical roll-on membrane over a cement board is fine. Nice thing about Kerdi over cement board is you don't have to mud/tape/fabric seams that you might have to detail when using a roll-on membrane over cement board.
Sheet membrane like Kerdi versus liquid membranes like Hydroban/RedGard? They are all excellent products for waterproofing a shower. Howerver, if I need a bulletproof vapor barrier in the assembly I always use Kerdi.
clarification...
Wanted to add one thing...you wrote "FB video with Meehan shows him...painting on waterproof material in area that will receive direct water spray."
You want all of the walls waterproofed to a heght of 72" off the floor. The 72" height is the code minimum. You can go higher if needed, but that's the minimum.
Thanks for the information Mongo. I appreciate your help.
The cover of the March 2012 issue (No. 225) shows picture of a tiler installing tiles around a tub area, to go with the bold blue cover title for the associated article "Choose the best backerboard for durable tilework" (p. 50). [Um, let me see, this is Breaktime? yup. Sponsored by Fine HomeBuilding magazine? yup. I guess I'm ok on referencing a FHB article here.]
March 2012 issue
You mean the one just to the left, under "Current Issue" ?
Why not KerdiBoard
Never really trusted drywall (even greenboard) as a substrate. What I've come to understand is that Kerdi was developed to replace the use of cement board, so Schluter recommends regular drywall instead of their competition-cement board. Marketing and buyer confidence plays a big part in their claim to use it over regular drywall. They're confident it will waterproof. In a perfect job, it will waterproof. In jobsite conditions and over a long time, who knows. I look at ceramic tile as a lifetime-of the house-product, so I use the best material for the job.I prefer to use cement board as the substrate with the Kerdi on top. Kerdi does admit that you can use cement board.
Been wanting to use KerdiBoard, seems like an ideal product, lightweight, easy to cut and install. Pricey, but the labor savings, wear and tear on your body, dustlessness?,waste disposal and aggravation factor (cutting and drilling cement board is a royal pain) seems to outweigh the cost.