Applying Kerdi in stages [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-05-2007, 10:14 PM
Call me David.

I've lurked around here enough to know y'all need a first name. Before I get to me question, I have to say this is the most civil and courteous trade forum I've found...and I've been to a lot of trade forums. On some, it's "Pros vs. DIYers", or others you need an abestos suit for the flame wars...

Anyway, I am finishing a new shower for your new house, and I've pretty much decided to go with Kerdi...even bought John's ebook. One plan I have is to leave the shower floor exposed, then build a moisture resistant wood slat platform to cover the floor. Does Kerdi need to be tiled over? Can I leave it exposed with no ill effects?


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03-05-2007, 10:31 PM
Two things off the top of my head - the fleece would collect all sorts of soap scum, and other crud. The wood slats might end up abrading the surface and eventually poke a hole. It is pretty tough stuff, but it is designed to be embedded in mortar, not be exposed. There are probably membranes thatcould be used, but I think I'd tile it anyways - it would make cleanup easier. You could use some cheap tile, though.

03-06-2007, 08:30 AM
I'd tile it. Even with nice tile. That way if the wood slat floor gets old, broken, tired of, etc . . . you pick it up and WA LA! a complete finished floor that matches the rest of the shower! :)

Just a thought.

Brian in San Diego
03-06-2007, 08:40 AM
Like Jim said, the membrane has fleece on both sides. Once you install it on a shower floor, you should cover with cardboard if you're going to be walking on it. Don't think it'd make it in the long run. A good looking/quality tile underneath would enhance the look of the wood. It'd look alot better than the orange. Plus if the crud started collecting and growing on the kerdi it'd be near impossible to clean. David, I think I'd tile it.


03-06-2007, 08:42 AM
Welcome, David. Glad you like our site. :)

I think Schluter points out somewhere that the Kerdi is not suitable as a wear surface and must be covered with tile or some sort of trowel-on plaster finish covering. You might call them at 800-472-4588.

I agree with Jim (jadnashua), even if it worked it wouldn't be very cleanable. Tile it with something.

My opinion; worth price charged.

08-17-2007, 03:49 AM
I am working on a new shower with Kerdi and will finish the corners and curb today. While searching through this forum, I came across a post by John Bridge saying the two biggest problem with applying Kerdi is stiff thinset and skinned thinset. Both of which I have.

It was mixed as per instructions, but the thinset was really stiff--to the point where it was not possible to work it all out from under the membrane. I got the walls relatively smooth, but I know there are areas where the membrane is not adhered to my CBU (it stays light orange instead of dark). My bigger concern is the dried thinset in the areas where I have to finish with additional membrane. What do I do at this point? The min 2 inch overlap will go over some areas that has dried thinset. Unfortunately this was not covered in the John's ebook.


Brad Denny
08-17-2007, 04:48 AM
Good morning and welcome, David.
I believe you can cut out the loose part, put in a new patch, and cover the seams with Kerdi Band (thinner than the reg. Kerdi).

08-17-2007, 07:44 AM
Hi David, you can mix the thinset a bit looser for applying the Kerdi. Like Brad said you can cut out the areas that you have and patch them back in, over lapping it 2".

08-17-2007, 07:59 AM
Welcome back, David. :)

This the same shower you were doing back in March where you'd planned to have a wood-slat floor?

The biggest problem I see with what you're doing is your comment that your overlap will go over an area of "dried thinset." The reason Kerdi works the way it does is that you end up with a very minuscule layer of thinset between two layers of the hydrophobic membrane and water can't pass between.

If you have a significant buildup of old thinset between the layers, you could be defeating this principle to some extent. Will it cause you problems? Can't say for sure. But we do know the thinset is not, of itself, waterproof. So I'd advise you exercise a good bit of caution here. :shades:

My opinion; worth price charged.

08-17-2007, 08:52 AM
It was mixed as per instructions, but the thinset was really stiff- you mean the instructions on the bag of thinset? That would be your problem, if so. That would be the proper consistency for setting TILE on Kerdi (or the floor, or whatever), but for bonding Kerdi to substrate it's WAY to stiff. :shake:

08-17-2007, 09:36 AM
Thanks all for the replies. Yeah, there are things like "mixing thinset as per instructions" that always trip me up. Last time I followed instructions for floors, it was way too thin. And this is that shower I originally posted about.

Unfortunately, if I cut out the unbonded Kerdi, I'll have a mosaic patchwork. Disabuse me if I am wrong, but if the integrity of the membrane is still good in the unbonded areas, I'll just go from there. There are no really large areas, well, larger than a single tile, so I think I can live with it.

As for the dried thinset, I am going to remove it as best as I could with a brush and apply the remainder of the Kerdi. Would this be OK? I thought I did the prerequisite research before starting, but I wish I came across those two critical points about the thinset before putting up half the Kerdi.

08-17-2007, 09:49 AM
Unfortunately, if I cut out the unbonded Kerdi, I'll have a mosaic patchwork. not a problem as long as you follow the rules for overlap. The real issue is build that might create a very uneven surface to tile. A little build can easily be compensated, but there are limits. Try to make one big patch instead of several small ones if that helps.

An unbonded area the size of a tile is a bit suspect, me thinks. :crap:

08-17-2007, 10:07 AM
I've merged your threads here so folks can keep up with the history when trying to answer your questions, David. Please bookmark this one and use it for all your project questions. Please also go to the UserCP above, find Edit Signature, and enter a first name there so it will appear in each post and we won't hafta search for it, eh? :)