Purple or regular drywall with Kerdi membrane or Ardex 8+9? Looking at the best option

[JohnfrWhipple]

What a loaded question. What's better? Purple or Regular White. The truth is neither should be used in a shower build in my opinion but if you are going to go this crazy route.

 

[Jadnashua]

Schluter's Shower Installation Handbook http://www.schluter.com/media/shower-handbook.pdf?v=201412130601 and the certification they obtained http://www.icc-es-pmg.org/Listing_Directory/pdf/ESR-2467.pdf (and keep re-obtaining as it expires every two-years) lists suitable backings for their membrane which includes drywall (gypsum board). It also includes other suitable solid backer materials, so choose one you are comfortable with. The stuff has been around for about 25-years, hundreds of thousands of showers have been built with it as defined, and if you do it properly, it works, lasts until you decide to remodel, with no problems IF you can read and understand the instructions (they're not really hard). As with anything, if you do not follow instructions, all bets are off. Schluter's Kerdi has been approved for use AS DEFINED IN THEIR INSTALLATION HANDBOOK for use in the entire USA. Some local code enforcement agencies put some restrictions on it, but most do not. John's biases aside, if you build it right, it works. Schluter is not twisting your arm to use drywall, but have found through hundreds of thousands of installations that it is the easiest, biggest panel (fewer seams), and least expensive backer material that works. You can feel free to use any of the backer materials that were tested and approved in that ICC-ES report (which includes CBU) if you chose, but you'll have the same warranty and reliability. Your choice. Don't be badgered into a guilt trip by John. He has a chip on his shoulder when it comes to Kerdi (and ME!). Pick an approved method, and follow the instructions, and it will all work out.