Personally, I feel that Kerdi is better. With Kerdi the shower is waterproofed right under the tile. There is absoluteley no way that it can get to the studs. Water and vapor can get through tile, grout AND durarock. If you don't use a surface waterproofer like Kerdi or Redguard you need to make sure that a vapor barrier is installed behind the backerboard.

Kerdi can be applied directly to drywall. In fact that is what the manufacturer, Schluter, recommends.

As to the mention of the "PreSlope," be advised that, if you're using Kerdi, either over durock or wallboard (entirely acceptable) you WILL be using Kerdi on the floor of the shower as well as the Kerdi drain. With this method, there is NO "preslope" required. It's about the only time you don't need one.

lazarususa,

Just to make sure we're all on the same page, you realize that on the floor, the substrate that the Kerdi is adhered to still has to be sloped, right?

The floor Kerdi can be sloped either by applying it over a sloped Kerdi Tray, which is foam and sloped, or it can be applied over a deck mud preslope.

But the Kerdi on the floor does need to be sloped.

To clarify things for other readers, realize that whatever membrane is used on the floor of a shower, that membrane needs to be sloped. The waterproofing membrane should never be "flat".

Mongo

While this does meet code, it's a recipe for premature failure of the entire shower.

The hell it is. Kerdi does take it up a step. But what it does is take shower building one step closer to being "goof proof". That's not to say that conventional showers will fail prematurely. That's COMPLETELY an inaccurate statement.

Sorry, Bill. I overstepped my knowledge level a bit with that statement. One of these days I'll stop giving advice where I know not of what I speak. Kerdi is great, but that doesn't mean everything else is crap.

My apologies. Joe.

We used both, Durock and Kerdi. Is it like a belt and suspenders? Maybe. But the Durock cost is minimal over regular drywall or green board when you're spending gazillions on the bathroom. So why not be extra cautious?

Ivette

That's kinda my thought, as well.

Mongo~~ Sure, I know that you still need a sloped mud floor....or a Schluter pan to set the Kerdi on. I was just making the point that there is no "Pre-slope" needed for a Kerdi shower.......

Along the same lines....I'm currently doing a steam shower (for some obscene money) where the HO had a regular shower before hurricane Rita. She has it stripped to the studs and wants a "Steam Shower" to replace it. There is currently a good pre-slope, vinyl liner and a finished slope on the floor. Am I going to break it out and start over.....nawwww. Just going to cut away the exposed liner, flash the walls to the floor, Kerdi everything up to and over the existing curb and install their drain. Works for me!