I'm new so be gentle.
I am currently renovating my main floor bathroom and gutted everything. One of the walls is a concrete exterior wall that I want to insulate with batt unfaced insulation. What I'm planning to do is put a roofing paper first on the concrete wall then frame 2x4s, insert the batt then put the poly. I bought some 1/2" Easyboards and planing to put Kerdi for waterproofing. Is Kerdi over Easyboard over the 6 mil poly okay? Since Kerdi also acts like a water/vapor barrier then it's like sandwiching the Easyboard in between 2 barriers and some say it's not good.
never have two vapor barriers. Having any vapor barrier against the concrete wall is a no-no let alone two. No poly, no tar paper. Leave a 1" space between the concrete and the studs to allow the wall to dry when needed. Use 2" foam panels against the concrete.