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Unread 03-08-2020, 11:53 PM   #1
amina3871
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Revising a partially failed Ditra installation???

So, I recently renovated my house, and decided to do all the tiling myself (with some help from dear old dad). I have two tiled bathrooms, a tiled shower, a foyer, and a kitchen. All installed over Ditra, and for the most part successfully. I'm pretty pleased with the results having never done this before.

HOWEVER, after about a year, my kitchen floor is failing and I can't figure out why. Specifically, there is obvious flex in the center of the room and the tile crunches when we walk on it - some of the grout has popped up, but the tiles seem to be staying put for now.

There are some weird specifics about the installation - we did 1" square mosaic borders with 1" hexagon fields (!00 year old rowhouse, wanted the right look) with some hand set rose/rossette type patterns thrown into the hexagons.

I realize that the 1" mosaics are not recommended with DITRA - specifically, I got the go ahead from Schluter and the Tile supplier, with the understanding that it would work, but would not be warrantied. Again, only my kitchen floor has failed, the others seem to be rock solid. So not worried about that.

Where I think I might have gone wrong:

1) We tiled the borders in the kitchen AROUND the kitchen cabinets. I know that's a bit weird, but it was so complicated to get the mosaic borders right that it seemed like the only way to do it. Anyway, the square border tiles are fine, only the hexagons/the field/fill is failing.

2) The house is balloon framed, has undersized joists, and generally seems to have been designed by crazy people (Large portions are on piers, the joists run in different directions in every room, etc.) There's not a level floor or square corner anywhere other than the bathrooms. We jacked everything up and stabilized as best and as much as we could, but possible that the kitchen floor needs more support

3) In retrospect, I really wish we'd done heated floors in the kitchen and first floor bath - even though it's insulated and/or partially heated space beneath, the tile was ice cold all winter.

4) Dad helped with the wall tile and backsplashes, but didn't really help all that much with the floors. EXCEPT THE KITCHEN. SPECIFICALLY THE PART THAT IS NOW FAILING. Guess I can't complain, since his labor was free, right?

SOO....

I'd like to rip out JUST the hexagons and try to install ditra heat instead. Is this even possible? What do I do to prevent it from failing AGAIN? How do I know whether or not the subfloor is sound/stable? Again, I don't think it's perfectly level, and don't really care as long as it's workable, the house is 100 years old and well within my tolerance for imperfection - in fact that's part of the charm. But I don't want the tile to come loose/don't want it to move.

Finally, any advice on how I could avoid doing this again? About to do a similar install at a rental property (Also old - we do historic tax credit work, so it's got to be the mosaics, though I'm open to trying a different membrane system).

Thanks in advance and sorry for the long (first) post!
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Unread 03-09-2020, 12:22 AM   #2
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You said it yourself, there is obvious flex in the room and the house has awkward framing. Flex and tile dont go together. Until you get the stiffness of your floor figured out any tile install will be doomed to fail and you'll just be repeating history.
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Unread 03-09-2020, 05:24 AM   #3
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Hi Lee, welcome to the forum.

What John said. Measure the size and unsupported span of the floor joists and run the numbers through the Deflecto tool in the blue tool bar above. You need a minimum rating of L/360 for ceramic.

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Unread 03-09-2020, 05:39 AM   #4
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What do you have for subfloor?

By the way, Ditra Heat mat is 1/4" thick, so you can't use it in conjunction with Ditra on the same area.
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Unread 03-09-2020, 08:02 AM   #5
speed51133
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Quote:
I realize that the 1" mosaics are not recommended with DITRA - specifically, I got the go ahead from Schluter and the Tile supplier, with the understanding that it would work, but would not be warrantied. Again, only my kitchen floor has failed, the others seem to be rock solid. So not worried about that.
Can you elaborate on this part? How did Schluter tell you 1in mosaics would be OK.

Also, as is already stated, there is obvious flex in the room. That is the source of your problem. Case closed. No need to further investigate.

The only thing to do now is either abandon the idea of tile and use a different flooring, or eliminate the flexing. NOTHING you put on top of the floor will eliminate flexing. No about of plywood, ditra, cement board, screws, glue, nails, etc. will address it. You can only fix it by going UNDER the floor and adding joists, beams, poles, walls, etc under the floor. (this is assuming you do, in fact have flexing. calculating the flexing potential using the deflecto calculator mentioned above will confirm this)
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Unread 03-09-2020, 08:16 AM   #6
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Welcome back, Lee.
Quote:
Originally Posted by Kevin, Post #4
What do you have for subfloor?
We need an answer to that before we can go much further.

There are two areas of subfloor deflection that you must address when planning a ceramic tile installation. One is the joist structure deflection. The second, and frequently the more critical, is the subfloor deflection between the joists.

The Joist structure must be addressed from below, but, contrary to Mike's comment above, the subflooring issue must generally be addressed from above.

But first we need to know what the subfloor consists of and what the joist spacing is below the subfloor.

My opinion; worth price charged.
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Unread 03-09-2020, 10:32 AM   #7
speed51133
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true....I was assuming the deflection was from the joists. I guess it could be just the subfloor deflecting....
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Unread 03-09-2020, 04:44 PM   #8
amina3871
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Subfloor material, answers to previous questions

If I remember correctly, the subfloor is 5/8ths OSB - I don't see why it wouldn't be, that's what was used everywhere else. Most of the work was done by a contractor, and I did not install the subfloor myself, so I can't speak to framing or how many layers of OSB. However, The same contractor has done two large jobs for us previously, both of which were satisfactory, and the other floors have held up fine, so I'm reluctant to blame them.

I thought maybe the visible movement was... I don't know... due to the tile being loose but still matted together, since the border tile is fine, but then the border tile is closer to the edge of the room, so presumably less deflection

As for framing, the front and rear (kitchen is at the back) have two piers, topped by a beam which runs parallel to the street. Joists run perpendicular to the street, spanning from the center of the house (which has a proper foundation and basement) to the pier and beam setup at the back. It's a pretty odd setup for a rowhouse, but it makes sense when you see it/seems to have been economical. The problem is that beam COULD be sagging, and then the floor joists resting on it COULD also be sagging. I'll talk to the contractor about what was done, framing wise, in the kitchen.

According to the blueprints, the original joists are still there - 2X8's at 16" on center (but true 2X8's, and 100 years old/better quality lumber, so maybe a little sturdier?). It is possible that the joists are sagging due to being notched/dovetailed - there was a lot of that going on in here, unfortunately, but I'd have to crawl into the crawlspace to confirm.

As for the Ditra heat - it's thicker? Bummer. Like I said, that floor is COLD. Guess I'll have to see if there's anything else I can do. The crawlspace is enclosed, but it's purely a facade wall - only a brick thick. Any suggestions welcome.

As for Schluter/comment about mosaics - If I remember correctly, the company I bought the tile from emailed with them, and I actually spoke to someone at Schluter by phone. Basically it was a "we see no reason it wouldn't/shouldn't work, but can't warranty it because it hasn't been tested" type answer.

It sounds like the deflection is either the joist or the subfloor, so... is there any way to save this, or do I have to rip it out (I mean, I'd love to at least leave the border tile and cabinets in, redoing that would be a bear)

I've attached two photos of the floors as well. Again, the BORDER seems solid, so, is there anyway to stabilize what's there and then re-tile the field/hexagons? I feel like I've seen a video of someone screwing through Ditra to fix this kind of problem, and then putting kerdi band over the screws? But maybe I'm mis-remembering, I can't seem to find it now.

Also, totally expecting this response to generate more questions before we get to any answers, so by all means fire away. Thanks for the help so far!
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Unread 03-09-2020, 05:10 PM   #9
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Lee, you don't wanna be looking at blueprints to determine anything about the structure where there is a potential problem. You want to know what's actually under the floor in question.

If you have a single layer of nominal 5/8ths" OSB you're at the absolute minimum of most tile substrate manufacturers and below the minimum limit of some. And if the OSB does not have T&G edges you've got serious problems. That presumes no greater joist spacing than 16" on center. Those are some of the things you really need to verify to get to the bottom of your problem.
Quote:
Originally Posted by Lee
The same contractor has done two large jobs for us previously, both of which were satisfactory, and the other floors have held up fine, so I'm reluctant to blame them.
Not interested in blaming anyone, but as they say on Wall Street, past performance is not necessarily indicative of future performance. To get to the root of your problem, you really need to determine what's actually under that particular tile installation.

My opinion; worth price charged.
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Unread 03-09-2020, 05:12 PM   #10
PC7060
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Quote:
2X8's at 16" on center (but true 2X8's, and 100 years old/better quality lumber, so maybe a little sturdier?).
Not in my experience. While the old wood is certainly harder and termite resistant; the stiffness is no better and often worse because it was installed green and tended to flex/twist as it dried.

I doubled all of mine in the old house I’ve been renovating, supper bouncy before.

The detail in the tile is very nice but to echo Mike’s previous comment; I think it’s to savage as much of the tile as possible, address the floor stiffness issues and then install concrete backer board. CBU is a approved base for the little octagon tiles you're are using. I believe the minimum size for Ditra is 2” although some people have had good success with it by pre-filling the waffled before setting the tile. Give you a Schneeberger to add heat to the floor too. Just not DITRA Heat.

What is the unsupported length of the joists?

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Edit: pls ignore the ugly pex install.

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Unread 03-10-2020, 04:30 AM   #11
amina3871
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Thumbs up I

So, I believe that the subfloor is at least one layer of 5/8ths tongue and groove OSB and I believe the joists are 2x8s placed 16" on center - I say *believe* because I saw them during renovation (I.e. I saw the framing while the floor was up and I put the Ditra down over the subfloor), but that was over a year ago. Also, the "blueprints" were drawn by an engineer who came in while the house was torn down to the studs and joists and were pretty accurate because they were primarily a drawing of what was already there/visible. But obviously now I'm doubting - I'll try to get into the crawlspace in the next day or two and confirm (I need to drag a big ladder down a tiny stairwell or get creative with some storage tubs, LOL).

If the joist are as I remember and there isn't some other obvious problem, then the deflecto tool is indicating that the deflection is fine. However, if they are actually 1.5" by 7.25" rather than true 2X, the number starts to get close to the limit (something like L / 425 - calculator seems to indicate that it needs to be L / 360 or higher for porcelain tile, right?). Would a row or two of additional blocking between joists be helpful here in terms of stiffening things up? I can also try doubling up or adding new joists between, or a beam in the middle but not sure how we would support them without investigating further.

Are there any other issues that might cause additional deflection that I should be aware of?


Anyway, it sounds like the consensus is that I should address any stability issues and replace the loose ditra with concrete board? Why not more Ditra? I ask for two reasons:

1) I (think) I understand how to waterproof the Ditra if I have to cut out and replace a chunk, but I don't know how I would waterproof the concrete board that I would end up installing in the middle of the floor/how I would tie it to the Ditra. Can it be covered in Kerdi? I would like the floor to be waterproof

2) Ditra is 1/8". I haven't worked much with Concrete board (or Tile in general, before we did this house). Can I get 1/8th concrete board? Is that sturdy enough over the 5/8ths OSB? I assume I would need to much the thickness of the concrete board to the thickness of the Ditra. Also, a casual google search for 1/8 backer board or similar brings up posts on this forum where folks are discussing the difficulty of finding 1/8ths board. Any advice?

Sorry if that's a lot of questions. I really appreciate all the help. I'll check back in once I've climbed into the crawlspace and investigated a bit more.

P.S. - @ CX - I notice you gave me a "welcome back" but I don't believe I've ever posted here before? Maybe you have me mixed up with someone else?
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Unread 03-10-2020, 08:14 AM   #12
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Quote:
Originally Posted by Lee
CX - I notice you gave me a "welcome back" but I don't believe I've ever posted here before? Maybe you have me mixed up with someone else?
Yeah, and I can obviously see that, Lee, but I spend a good deal of my life confused these days, so no tellin' what I had you confused with.

If your drawings are as-built drawings, you should be able to depend upon them to tell you what's under there. I still don't see an unsupported span for those joists, though.
Quote:
Originally Posted by Lee
Would a row or two of additional blocking between joists be helpful here in terms of stiffening things up?
No.

The nominal 5/8ths" subflooring is the most suspect part of the package. Keep in mind that all the testing of those floor installation methods is done with new material in near perfect condition, near perfectly installed over joists with zero deflection, and the test needs pass only once to be accepted. And your particular package with those small mosaic tiles has never been tested at all. What you have is essentially a layer of grout with some small tile fragments embedded therein. The testing was done with 8" tiles.

I think the most likely fix is a second layer of nominal 1/2" exterior glue plywood properly installed over what you currently have. Then the tiling substrate of your choice (preferably one suitable for your tile size) and tile.

My opinion; worth price charged. And however confused.
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Unread 03-10-2020, 08:24 AM   #13
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There's no 1/8" cement board that I'm familiar with.

I would take a moment and find out for sure what your joist deflection is. Anything L/360 or greater will be fine. As for the subfloor, there's not a great lot you can do to strengthen it other than removing everything and starting back with another layer of plywood on top of it.

My guess is that once you start removing some tile you're going to find many more loose tile or other issues.

Hopefully I'm wrong. Good luck.
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Unread 03-10-2020, 04:36 PM   #14
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Unsupported span

Thought I included this. Oops. Unsupported span is Approx 10' , 1.25"

As for adding support, it's an open crawlspace underneath. I see no reason I couldn't add two or three more piers and a new beam in the middle, to cut that span in half. I'd set it in place with screwjacks set on new footings (thinking pumpjacks could be a bit destructive) and support it on new piers. We did this successfully for the front of the house. It's a bit involved, but I was able to do it effectively and inexpensively before.

Ripping out subfloor sounds like I would need to also take out the cabinets and counters, which is a nonstarter for me - or am I mistaken?
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Unread 03-10-2020, 05:50 PM   #15
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Your joists are fine at that span, unleßs they're some unknown wood that is knotty or in poor condition.

It's just the subfloor layer I'd be concerned with.
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