I'm starting my first time Kerdi install and while watching the videos and viewing some of the installations on this site, I wondered why the Kerdi was not applied first to floor then Kerdi band on floor to wall joints, with the walls being done last.

I was thinking that moisture running down the inside of the wall tile would make it all the way to the drain this way but if the walls are done first, there is the chance for it to seep through the mortar at the bottom.

Any thoughts?

the reason for doing the walls first is that walking on freshly set Kerdi usually leads to bumps and bubbles. Most installers want to get all the prep done in one day, hence the walls first.

Schluter considers any 2 inch overlap of Kerdi completely waterproof, but that assumes a perfect install. I agree with you that running the wall Kerdi down over the floor kerdi is better.

I like to make the floor Kerdi about 5 inches over sized in both dimensions and run it 2.5 inches up the wall with the corners cut out. Then install pre-formed corners, then the wall Kerdi.

If you are installing on drywall, moisten it first. then apply a fairly runny thinset (about like ketchup) Work fast so it dos not set up before the fabric in imbedded.

Ok I get it, that makes sense. I guess for me there is no rush so I can do it in any order I want but I like the idea of oversizing the floor Kerdi.

I'll be installing over DensShield not drywall so no need to moisten?

Thanks.

It makes no difference which way the overlaps go. This is not shingles on your roof. The 2" overlap is way overkill too. By actual testing Schluter claims they have never encountered any wicking more than 1/4". Kerdi will hold water.

http://lh3.ggpht.com/_pRjv8Lnmn-0/SuuNifM-K2I/AAAAAAAAH7s/61sJLsD9m3Q/s800/IMG_8511.JPG

Jaz