New shower with Kerdi-board?

kookietNovember 27, 2010


we are in the process of renovating our 100yr old bathroom and that involves adding a new shower area. Having read a lot on these forums around the Kerdi system, I would like to go down that path.

In the most recent issue of 'This Old House' I noticed that Kerdi now has the new Kerdi-board, so I have been wondering if that can be used instead of drywall on the shower side of the wall as i'd think that would make the shower finishing much faster. Would that still need to be sealed with kerdi tape and does it coordinate well with their shower bases and drains?

Finally, does anyone have any ideas on where in or near Seattle I could get more information.



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Try googling schluter Seattle or going to their website.

Here is a link that might be useful: kerdi-board

    Bookmark   November 27, 2010 at 9:18PM
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Kerdi board can go right over the wall studs, so you won't need dryall or any other sort of backer.

Yes, you will need to detail the seams.

Yes, you can use Kerdi board with the Kerdi Trays (sloped foam pans) and Kerdi Drains. It's designed as a complete shower system.


    Bookmark   November 28, 2010 at 2:37AM
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I may be old school, but I still like durock cement board. Humidity will diffuse through and out of it. I use kerdi membrane, but still like durock behind it because bath humidity can saturate the entire space. It seems to me the porosity of the durock allows humidity to dissipate out of the wall more easily.

I do not put vapor barrier behind the durock, and use poured concrete for the shower floors, over metal lath and visqueen. Kerdi over everything except the ceiling, usually.

    Bookmark   November 28, 2010 at 12:11PM
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uniberp, I'm the same. Kerdi over cement board. Either Durock or Wonderboard.

I don't use concrete on the floor though. I use deck mud for the sloped floor, then Kerdi over that. Almost every shower I do is a one-off size or shape. Deck mud is easier, faster, and less expensive than cutting down or filling in around and fiddling with the foam pans.

    Bookmark   November 28, 2010 at 1:59PM
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You can use Kerdi directly over drywall.

I had a tile pro install the Kerdi shower base and drain once as an experiment. Worked out nicely. But way too expensive to use again. However, for a diy, it might be a better bet than mixing and working with a screed base.

    Bookmark   November 28, 2010 at 7:40PM
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Could mongo or uniberp expand on why they like CBU and how humidity factors in? I was planning to layer these:
plywood on the studs/durock/Hydro Ban.

The plywood is for shear strength and the Hydro Ban, I assume, is synonymous with Kerdi for this discussion.

Should I worry about the plywood layer being exposed to moisture? Would using treated plywood help? (Assuming treated is available in structural strength.)



    Bookmark   November 28, 2010 at 9:28PM
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Bill, I have absolutely nothing against folks that Kerdi over drywall. Cement board is simply my personal preference.

Plywood/Durock/Hydroban would be fine, I recommend using exterior grade plywood.

Hydroban is waterproof but not a vapor barrier, so if it's a steam room you still need a vapor barrier due to increased vapor drive.

    Bookmark   November 29, 2010 at 10:27AM
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worthy, I agree regarding the economics of the foam trays.

The one time I found them worthwhile was when working on a building I was converting to apartments. I sized the showers to use the Kerdi Trays and did 11 showers in one day.

Lugging the lightweight foam trays up to the apartments versus transporting the portland cement and sand and having to mix and pack the deck mud, blah blah...the extra $$ was more than offset by time saved, added convenience, and less physical effort.

    Bookmark   November 29, 2010 at 10:35AM
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Thanks, mongo, will do on the exterior grade ply.

Hard to believe that Kerdi has a lower vapor permeance than what appears to be a rubber sheet (I've not actually seen Hydro Ban yet), but it's true:

Kerdi : .75 perms - semi-impermeable (hi end of the range)
Hydro Ban : 1.247 - semi-permeable

    Bookmark   December 1, 2010 at 6:39PM
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Nobel TS out preforms Kerdi in Perm Ratings.

Kerdi Board - wicks water and the "Special Reinforcing Material" looks like carboard or MDF.

Kerdi Board flexes.

Kerdi Board is a waste of money.

    Bookmark   May 19, 2011 at 9:52AM
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What types of installs require less than than a .75 perm rating?

Just about all material will wick water - Wonderboard, Hardiboard, Drywall, GreeneBoard, Durock - the purpose of all these membranes is to keep water from reaching the edges of these "boards" thus allowing capillary action to take over.

Ditto with the flexing - all will flex - some less than others so one needs to choose where certain material are used. Flex is a great thing if you're trying to wrap a tightly curved wall or column - just try that with Wonderboard!

Waste of money???? In many instances there are cheaper alternatives, but this product can useful and reasonably priced in some instances.

    Bookmark   May 24, 2011 at 2:56PM
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