HELP Quick - Mastic On Kerdi by an Installer [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-06-2008, 01:38 PM
I have been lurking here and learning for some time now. I am now working on a bath remodel using Kerdi for the first time. I have also installed two Nobel show niches. I installed the Kerdi directly over the niches with the plans to cut off around the edge of the opening. I read in another thread here that the Kerdi can be installed directly over the niche edge stopping at the recess. The way I read the other post was that the Kerdi would not need to line the niche because the Noble product is already waterproof.

See the attached pictures for the current state of the project. There is a photo of the wall with the niches. I was planning on simply cutting the Kerdi around the edge of the openings. I am concerned because the Kerdi and thinset under have pulled away from the cross shelf in the large niche. Maybe it is because of the small surface area. I am concerned that the thinset/kerdi is not making a good bond with the niche surface.

Am I doing this all correctly?

Edit- I also have a question on how to do the door opening. The photo shows the top of the door. I don't see a way to install any banding to close the edge where the vertical inside wall meets the curved horizontal door opening on top.

Thanks for any help.


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07-06-2008, 02:04 PM
You're hardly ever correct when mixing products from different manufacturers, John. In your situation I'd cut my Kerdi such that I could fold a couple inches into the niches and thinset the flaps there.

The lip on the Noble niche is only about an inch wide as I recall. While that might be plenty for a good attachment, it's a bit short of my comfort level.

And you're correct, the Noble niche itself is completely waterproof. Nice product, those. :)

My opinion; worth price charged.


Product called KerdiFlex might work there. I've never used it. Don't know what kinda radius it'll turn.

But a fella could cut pieces of KerdiBand and make it work. Ain't gonna be easy, and ain't likely to be pretty, but I think you can get it waterproof. Fortunately, it's an area that won't see a lot of water, eh? :)

07-23-2008, 09:33 AM

I have read many posts here and got a lot of good information. I know you are not supposed to use mastic on Kerdi and I know you are not supposed to use mastic in wet area (at least that seems to be the consensus).

Now here is my problem. I am remodeling a bath. I totally gutted it, framed it, wire it, drywalled it, plumbed it but did not want to install the tile. Just not my bag. I did put in a shower built with WonderBoard and put Kerdi over the top. I found a tile installer with long reputation. They had not used Kerdi before but they looked into it and were comfortable with the long standing reputation of Schluter. I asked the guy who quoted the job what they put the tiles up with and was told they would use thin set. I asked the guy at the show room who is in charge of the job what they would put the tiles up with and he said thin set. I asked the installed what he was going to put the tiles with and he said thin set. When they started putting up the tiles I looked at the product and it was thin set. I came home last night to find a bucket of mastic on the floor of the bath room. After examination of the shower, they set have of the first wall with thinset and then changed to mastic. My guess is that it was going to slow with the thin set so they swiched to mastic. Now have one and a half walls done in mastic. WHAT SHOULD I TELL THEM TO DO! I am afraid if they take down the mastic tiles they will rip the kerdi.

Any advice?


07-23-2008, 09:39 AM
Lucky for you they left the bucket behind. Yeah, you gotta have 'em pull it down and redo it. Probably would be much easier to replace the kerdi than try to clean it off.

Their mistake, their dime.

Is the thinset bag they used laying around? Curious as to what they used.

07-23-2008, 09:40 AM
I would call Shluter (get number off link on the right) and confirm with them what they say about Type 1 mortar (mastic) If they say it is a no no then I would have the company come in and make it right. Hope you have not paid for the complete job or can stop payment until it is right.
Good Luck

Danny Ferguson
07-23-2008, 09:41 AM
I would have them pull it off. I seriously dought the mastic has started to set up yet. You are in charge, if they don't like it, send them packing and call the store owner.

07-23-2008, 10:18 AM
Please don't start a new thread with each new question, John. I've combined you with your initial thread on this shower. Please bookmark this one and use it for all your project questions. We can change the title to something more generic if you like. :)

During my first session at the Schluter school at the CTEF there were some tilers from a Yankee company there who wanted to know how to install the Kerdi and tile with mastic. When all other eyes in the room stopped rolling :rolleyes:, they were told that organic adhesive was not an acceptable product to use anywhere a Kerdi System shower.

Possible they have changed their thinking since then, but I doubt it. You can certainly check by calling 899-472-488.

I would suggest those tiles be removed and the Kerdi replaced on the affected walls. You've got too much work invested in that project to let them ruin it by failing to perform as agreed. Deal's a deal, eh? :shades:

My opinion; worth price charged.

07-23-2008, 10:55 AM
good thing is the Mastic won't even be near setting up on the Kerdi, depending on how big the tlie was it won't dry. best to pull them off and scrape off the mastic best you can.

07-23-2008, 01:05 PM
Thanks for the help. The installer is pulling the tiles off. We will inspect the Kerdi and replace if necessary.


07-23-2008, 01:48 PM
I'd recommend you tell the installer right up front that it's necessary, John. The surface of the Kerdi is gonna be contaminated with the mastic and there's no way Schluter will, nor should be asked to, stand behind the installation with the material in that condition.

Major large PITA? Yep. But you didn't cause it and it should not become your problem.

My opinion; worth price charged.

07-23-2008, 04:51 PM
I think by the time you scrubbed all of the mastic off, you wouldn't have any fleece left, plus, running that down the drain shouldn't be an option, either. Depending on how long the Kerdi was up, you may be able to peel it off. It gets really hard after awhile, but this is likely only a few days old.