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Unread 07-28-2021, 11:02 PM   #1
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Join Date: Jul 2021
Location: New Jersey 08234
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Installation of 12x24, 8x8 porcelain body tiles on slab

Installation of 12x24, 12x12 and 8x8 porcelain body tiles on slab.
Recognizing that the tile installation can only be as good as the substrate and it's environment please read further down for expected interior environmental condition for tile flooring;

I intend to install 9mm thick tiles over ditra uncoupling membrane. I've found ready availability of Bostik "Ditra-Set" mortar (Lucky me!). The slab flatness is within 1/16" over 10ft span, and less than 1/8" over 30ft span (stellar skill by an 'old school' mason).

I have a drafted a detail set of (floor) plans and have measured and verified the dimensions (partition walls, utility, structural items) as they may impinge upon the tile placement and installation work access.

I have viewed the NTCA "Trowel and Error" (great demo) and read as much commentary / blogs by CTEF people as I could find (lippage / grout line width / expansion joints). I have carefully read instructions / watched Schluter videos for ditra installation.

I have laid out a plan for the tile pattern including grout width(s) and established how to measure from interior reference points (mostly from saw cuts / intersections) to starting locations for setting tile.

Finally, getting to my questions;
I am a newbie, so I don't expect to finish very much each day!
1) Ditra installation - Total floor area is 700 sq ft.
a) Should I install all the ditra before setting any tile? That might mean repeatly walking over some exposed ditra. Might it be damaged by foot traffic (rough workboots) ?
b) Since "Ditra-Set' mortar has an open time of only 20-30 minutes, would mixing 10 lbs mortar (3-1/2 cups water) per batch to install 30 sq ft (9 linear ft x 1 meter)
be too much ?
c) Is a J-roller any better / easier than a float to embed the ditra on the slab ?
d) Can I fill the top waffle surface of ditra with mortar and delay installing tile ?

2) Tile setting
a) I have a complicated (interesting ?) pattern of intermixed 8x8, 12x24, and 12x12 (split from 12x24) tiles.
I have allowed (mostly) 1/4" grout lines between 12x24s and 1/8" everywhere else.

The 8x8's are usually grouped together in patterns of 2x3 (or 2x4) tiles interspersed with individual or grouped 12x24s.

Some 12x24's are grouped into 3x3 ft (4 tiles surrounding a single 12x12)

Some 12x24's are similarly grouped into 3x5 ft (6 tiles surrounding a 12x12 and 12x24 lined up end to end)

I specifically designed the floor patterns to use whole tiles. Almost none of those tiles will need cutting.

Most cuts will be needed at the perimeters and at a few building obstacles (pipes, structural elements)

Should I layout / set all 8x8's groups first (verifying space allowance for 12x24s) then proceed to set the 12x24's?

b) Tools
I have designed the floor pattern to avoid any lengthwise cutting. Overall I expect to make fewer than 100 cuts.
I'll buy a wet saw that can handle about 14 inch straight cuts max (best cut quality and price) for my single job.
Besides the cost, bigger saws are very big, heavy and take alot of storage space (I would rather rent a saw for a day if needed to make any long cuts).

I'll buy a laser level / straightline to mark parallel lines on ditra. Any suggested marking method or tools for ditra ?

I see many 'tile vibrators' (check amazon) that claim to collapse the mortar ridges. They also provide a suction cup handler for the tiles (seems like a good idea).
Of course it's still imperative to key in mortar to ditra / slab, backbutter tiles and comb straight line mortar! But the hand work of sliding tiles back and forth may be reduced (it also might allow to install tile in cramp working space).

Thanks for listening!

Quick background of supporting substrate;
950 sq ft residential building. Location is New Jersey, 08234. Interior space is entirely open (undivided) except for partition walls surounding bathroom. Construction is a panelized steel S-model 'arch building' (21 ft building height / 19 ft 6in ceiling).

New construction, slab on grade (designed as frost protected shallow foundation, R-10 insulated around entire (exterior) perimeter to a depth of 30 inches below grade. Slab is 5-6 inches thick over 6 mil poly vapor barrier. Steel trowel (smooth) finish.

Overall floor size is 48ft x 21ft. 1 inch deep saw cuts placed so each rectangular area is about 75 sq ft (about 9x8 ft rectangles).

Built 10% better than IRC 2015 energy efficiency standard. Less than 1 air change / hour (ACH).
Windows are Andersen series 200 (low e-glass, argon filled). Also includes (Panasonic spot) ERV, continous (20 cubic ft / minute) mechanical ventilation.

Building heat is provided by 2 direct vent space heaters
(no radiant heat in slab) located on the northern wall. A single 5000 btu/hr window A/C kept the interior air at 75 deg / 50% RH all through June/July/August 2020 (unoccupied).
Attached Images
File Type: pdf Flooring_Tile-Layout-West.pdf (1.26 MB, 36 views)
File Type: pdf Flooring_Tile-Layout-East.pdf (1.35 MB, 38 views)
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Unread 07-29-2021, 08:09 AM   #2
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Welcome, Jonathan.

If you don't put that geographic location into your User Profile the information will be lost before we leave this page and it's frequently helpful in answering some types of questions.

Have you actually laid out some of your tiles in your proposed pattern to determine if your proposed modular patterns will work with your proposed grout joints? If the tiles are actually modular, there is only one grout joint width that will work for the pattern and that will be determined by the tiles.

1. I would install all the Ditra and provide some plywood walkways for the heavy traffic areas. I suppose it's possible to install only part of the Ditra and install more next to it later, but I've never tried that.

b. I wouldn't count on 20 minutes open time for the DitraSet, but you might get that. But when it comes to how much to mix at a time the pot life is the governing factor and I recall DitraSet having a good pot life, like maybe a couple hours. But mixing smaller batches to better match your rate of use is a good idea.

c. Any J-roller with which I'm familiar would be too small to be effective. I use a short piece of 2x4 wrapped in carpet for the task. Lots of options.

d. Schluter accepts that method, but it's not their preferred method.

2. See above.

b. I would eliminate the vibrator.

My opinion; worth price charged.

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Unread 07-29-2021, 12:49 PM   #3
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Location: NW Arkansas, Ozark Mountains
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I use a wood float to smooth out Ditra and embed it into the mortar.

I think you'll find that small batches are going to be used up very quickly with Ditra and the trowel you're likely to use with those size tile. When using a 1/2" notch trowel, I usually figured 35-40 square feet per 50 lb. bag.

Nothing wrong with starting small, though. You can always mix larger batches if you need to.

The top ten reasons to procrastinate:

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Unread 08-01-2021, 09:06 AM   #4
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Originally Posted by Jonathan
...and 12x12 (split from 12x24) tiles
Among the first things I'd want to do is verify the measurements of all those tiles to ensure they are the advertised size. Often they aren't.
If I recall correctly my memory is excellent, but my ability to access it is intermittent.
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