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Unread 06-20-2022, 07:59 AM   #1
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Ditra Install Very Bumpy

Hey Everyone, The never ending bathroom reno continues! I posted awhile back about grout haze that wouldn't come off my tile, no matter what the installer tried. We ultimately determined that that it was a problem with the surface of the tile and the tile store I have acontract with agreed to tear out and redo the job. So this is where we're at now - everything was demoed and the job was restarted, however, there was a lot of allset left on the floor after the removal. This was concerning to me. The tile store rep, the schluter rep, and the installer told me that it would be fine as thinset will adhere to thinset. So I said fine go ahead - the pictures I've posted show the new ditra install. Its very wavy and has highs and lows. I believe that the new installer didn't trowel the all set on properly and perhaps the old thinset contributed to this. how big of a problem is this? I'm thinking of asking them to tear out again.
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Last edited by cx; 06-20-2022 at 08:04 AM. Reason: Add Link
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Unread 06-20-2022, 08:07 AM   #2
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Difficult to tell from your photos how big those humps are, Kari. Can you lay a level on top of the hump, make it level, and measure the gap to the floor on each side?

What size tiles are you planning to install?

At a glance, though, I'd call it a re-do. The tile installation is always only as good as the substrate preparation and you seem to have a rather poor job of that.

My opinion; worth price charged.

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Unread 06-20-2022, 10:59 AM   #3
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If the surface isn't flat to start with, it's really difficult to get the tile on top of it to be flat. It's also much more difficult to ensure you get full coverage of the thinset underneath the tile so you get the proper support. Industry wants 100% of the edges, and at least 80% coverage of the rest of the back of the tile. Smaller tile tend to follow the waves of the substrate. BIgger ones tend to end up with lippage as they rock on a high point. Thinset has limitations on how thick it can be applied, and the thicker it is, the more likely you'll get a corner or edge to sink, making the floor uneven with tile lippage.

There are industry standards on floor flatness...it varies with the size of the tile to be installed.

The existing thinset residue should either have been ground down, or the high spots removed prior to installing the Ditra. An alternative would have been to use some SLC to flatten the floor, but that ends up raising it, and if not done well, can lead to other problems, making it worse.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.

Last edited by jadnashua; 06-20-2022 at 04:05 PM. Reason: fixed incorrect minimum coverage percentage
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Unread 06-20-2022, 01:44 PM   #4
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Thank you for your replies guys. I found a great article detailing industry standards for flatness and large former tiles. I only have a 6' level so it's hard to tell.

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