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Old 12-02-2011, 04:29 PM   #1
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Proper floor assembly 18x18 ceramic tile


Hi all, we're demoing our kitchen floor tile this weekend and will be replacing with 18x18 ceramic tile. I'd like to get opinions on the proper floor assembly for the replacement, specifically wondering if ditra or backer board would be more appropriate. I can't notice any deflection right now, but the old tile is still in place and is in 3/4" concrete
We've got 2x8 joists, 16" oc with diagonal 3/4" T&G planks over the top.

Here's what I was planning:
(1) Screw down planks into joists
(2) Layer 1/2" structural plywood
(2) if needed: self leveling concrete for any low areas
(3) Layer either 1/4" backer board or Ditra ( following their recommended setting process)
(4) Lay tiles in medium bed

Any recommended changes?

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Old 12-02-2011, 04:41 PM   #2
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Proper floor assembly 18x18 ceramic tile


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Originally Posted by Dmeyr View Post
Hi all, we're demoing our kitchen floor tile this weekend and will be replacing with 18x18 ceramic tile. I'd like to get opinions on the proper floor assembly for the replacement, specifically wondering if ditra or backer board would be more appropriate. I can't notice any deflection right now, but the old tile is still in place and is in 3/4" concrete
We've got 2x8 joists, 16" oc with diagonal 3/4" T&G planks over the top.

Here's what I was planning:
(1) Screw down planks into joists
(2) Layer 1/2" structural plywood
(2) if needed: self leveling concrete for any low areas
(3) Layer either 1/4" backer board or Ditra ( following their recommended setting process)
(4) Lay tiles in medium bed

Any recommended changes?
Is the diagonal planking pretty rough? Is that why the plywood?

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Old 12-02-2011, 04:45 PM   #3
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Proper floor assembly 18x18 ceramic tile


Actually it was for greater stability and firmness since were going with the large 18x18 tiles.
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Old 12-02-2011, 04:48 PM   #4
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Proper floor assembly 18x18 ceramic tile


Can't tell on the condition of the planks yet - from underneath they look ok, but we've still got to do the demo of the existing tile yet so they may get battered a bit with that. They're from around 1928-
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Old 12-02-2011, 09:32 PM   #5
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Is the diagonal planking pretty rough? Is that why the plywood?
Quote:
Actually it was for greater stability and firmness since were going with the large 18x18 tiles.
The condition of the diagonal boards has nothing to do with why you need the additional 1/2" ply. You can not install concrete backer or Ditra over the planks.

Dmeyr,

Your plan in #1 is essentially good, just note;

1. Yes of course.
2. Make sure you don't buy the cheapo CDX sheathing. You need C/C or better, B/C easy to find. Underlayment grade with exterior glued plies properly space and fastened to the planks.
3. Use the SLC after the concrete backer. If you go premium with Ditra, use it before Ditra.
4. That'll work. You won't find an unmodified medium bed, to keep within Ditra recommendations. But modified will work just fine. It's just against Schluter's wishes.

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Old 12-04-2011, 11:12 AM   #6
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4. That'll work. You won't find an unmodified medium bed, to keep within Ditra recommendations. But modified will work just fine. It's just against Schluter's wishes.

Jaz
Thanks for the info Jaz.

A couple more questions, is the medium bed for the 18x18s to help in making adjustments to avoid lippage? I always hear medium bed for 18s in the forums, but never knew why.

If i go with Ditra, what size trowel should I use with the Ditra and the 18x18s? And if I use modified with ditra and the large tiles, does that increase the setting time?

I like the idea of using Ditra, sounds like a good product & timesaver, but am nervous about straying from the Schuyler instruction, seems very strict-
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Old 12-04-2011, 11:17 AM   #7
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Have you check a deflection chart yet? How long are those 2x8? (unsupported--length)
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Old 12-04-2011, 11:29 AM   #8
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The longest unsupported span is 10'8" through the main kitchen, there is a smaller breakfast area that is 5'. It's the original rough cut 2x8s from the 1920s.

Haven't done the deflectometer yet, since we still need to remove about 1/3 of the tile. Assuming at a minimum, I'll have to go with the 3/4" ply spec'd according to above in Jaz's post. We may need to do more to get the stiffness inline, and that's ok. More work, better result.

The old mud set job started off with about an inch of mud, but that has increased to about 1-5/8", so am assuming that I'll need to do the slc to fix that valley, or there'll be trouble later.
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Old 12-04-2011, 11:39 AM   #9
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I think you are good--deflection wise------

I'm going to leave this for Jaz or Bud ,as you have issues and methods going on that they are more experienced with----Mike---
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Old 12-04-2011, 05:10 PM   #10
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Well, the tile is out and looks like we may have a prob with the orig subfloor. In a 5x7 area there a 7 holes, some patched but with only partial support under each. In the main Kitchen here a five more holes but better supported.

Most of the floor feels pretty decent but around these holes it's not.

So will the orig plan of 3/4" ply still work? Do I have to remove the orig subfloor and start out with two new ply layers? I've got carpet in adjoining spaces with 1-1/4" before the pad even starts - so have the room if adding two layer on top of existing subfloor would work - or would that be bad?
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Old 12-04-2011, 05:26 PM   #11
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Quote:
Thanks for the info Jaz.

A couple more questions, is the medium bed for the 18x18s to help in making adjustments to avoid lippage?
Well....... kinda. Medium bed can be applied thicker, but mainly its formulation is different so that the larger heavier tiles are less likely to sag after setting, which of course will help reduce lippage. Sometimes there is no lippage when set, only to find lippage the next day.

Quote:
If i go with Ditra, what size trowel should I use with the Ditra and the 18x18s?
The trowel to set tiles on Ditra is the same as without Ditra. That is determined by the tiles and conditions. To install Ditra use 1/4x3/16" V, 5/16" V or the special Ditra trowel. Some also use 3/16" square, or a worn out 1/4x1/4". Modified thin set with large tiles will increase set up time, give it an extra day or so if you can. Maybe you can find Ditraset near you?

I thought the original plan was to add 1/2" ply, but ok, go with 3/4". The more the better. How flat is the floor now?

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Last edited by JazMan; 12-04-2011 at 07:59 PM.
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Old 12-04-2011, 05:38 PM   #12
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As far as the flatness - in the main kitchen it is flat in east-west and north -south directions, but not level. Where the main kitchen goes to the break fast nook there the floor slopes down in both directions so I'll definitely need the SLC to maintain flatness.

If we properly support and correct those cutouts on the subfloor, could we still go with just 3/4" ply? Figured that would be better option over the 1/2" for the added inflexibility under these big tiles.
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Old 12-06-2011, 09:45 AM   #13
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Installing the 3/4" ply tonight.

Any thoughts on combining self leveling concrete with another fill layer of concrete below it?

With the amounts that the floor is off, and the price of slc, I'm wondering if there is anything that can be used as a less pricey base layer to fill in the low areas and then slc over the top to get a uniform flat and level surface. I know it just has to be flat for the tile, but really want it to be level like it was before. Ironically, the tile we ripped out was really nice and level, although an eyesore!
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Old 12-06-2011, 11:03 AM   #14
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You can add pea gravel to SLC for additional bulk. This will reduce the over cost of the SLC a little.

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