Exposed Kerdi / Foamboard Under Shower Bench

[Andrew Kolar]

I find may times that tile is not installed over the Kerdi board at the underside of corner benches in tile showers. Is this directly addressed in the manufacturer's installation instructions? While I am sure it is preferred and intended to be covered, I am trying determine if the manufacturer says is has to be covered.

http://s303.photobucket.com/user/KolarPhotos/media/IMG_6266.jpg.html

[Jerry Peck]

First question: Is Kerdi-Board allowed/intended to be used as such a shelf?

I looked at some installation instruction information and didn't see that use.

I would send that photo to the manufacturer and get their written opinion (email does that) on such use and such installation. If they say "yes", then ask to be directed to the installation instruction part which addresses it ... so you can provide documentation (is the reason you give the manufacturer).

[Jim Robinson]

I did 3 showers with Kerdi. That's probably 3/4" plywood wrapped with the kerdi fabric, although it's hard to tell. That's what I did for my benches. You'd have to get into the instructions to see if they don't allow it. I tiled under mine, but it's not something I would worry a whole lot about. The entire substrate is supposed to be water tight whether there is any tile present or not. It's supposed to be the big advantage of using the kerdi system.