I know from my previous question that in most cases a cement board of some kind needs to be used. However, when the Kerdi membrane system is being used behind the tile, is it still necessary to use a cement backer board?
Schluter says that behind the Kerdi membrane a solid backing needs to be used. They define a solid backing as :
Found this in their Shower System Installation Handbook here. Link : http://www.schluter.com/media/ShowerHandbook.pdf