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Unread 04-20-2021, 11:53 PM   #31
otrex
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Well, the tile for my kitchen floor project came in and this weekend will likely be tiling time. I'm nervous...

It looks like a slant-notch trowel is not going to be available to me here in Southern Ontario.

What notch size should I be using with 13" x 13" tile? I note here that the floor is quite flat, though in spots where the Ditra was pressed into the mortar by more weight than other places (my knees, likely) there are some mild bumps/dents. I would assume in cases where the floor is not perfectly flat you'd want higher mortar ridges? In addition of course, I plan to back-butter the tiles.

The tile store suggested 1/2" x 1/2" trowel but I am not sure if that is appropriate. Due to the smaller size of the tile I am leaning away from a lippage control system, but really not certain on that front yet.

Finally, I have been thinking it might be useful to staple some 1/4 sill gasket around the perimeter of the tile field just to ensure that I respect the necessary gap there. I note that Schluter promotes that idea in some of their videos. Is this a worthwhile endeavour for a first-time tiler?
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Unread 04-21-2021, 07:48 AM   #32
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IMO, Kevin, I think the 1/2" trowel will put down too much mortar. If you intend to fill the Ditra and set the tile at the same time I think you're going to have mortar squishing out everywhere if you use the 1/2". Shallow divots won't be an issue if they are truly shallow, but bumps might be if they much higher than, say, 1/16th.

I don't think the sill gasket is necessary. Thinset mortar doesn't spread out on its own so it's pretty easy to control where it goes.
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Unread 04-21-2021, 07:34 PM   #33
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I would say the divots are more than 1/16th, but they quite wide/gradual rather than sharp indents. Basically the indentation left from my knee pads as I put in the last sheets of Ditra in the corners.

I suppose I'd want to start tiling on the highest points?

What trowel notch size would be recommended? Tiles are 0.32" thick and floor with the aforementioned mild divots. I do see there is a 1/4" x 3/8" square notch trowel available locally - maybe that is more suitable? I assume I wanted a somewhat thicker thinset build but since I intend to back-butter these I suppose that probably helps a great deal in that regard anyways.

I also have access, it would seem, to a 1/4 x 3/8" U-Notch trowel if that is more suitable. I suspect that actually spreads a bit less mortar though, so maybe too far back the other way.
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Unread 04-22-2021, 07:17 AM   #34
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I'd be concerned a bit about the divots. If your 13X13's have a bit of a bow to them, and one ends up centered over one of the divots you might end up having very little mortar supporting the tile, and a trowel size that is adequate if everything is dead flat is now too small.

At this point you might consider prefilling the Ditra. If not all of it, at least where the depressions are.
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Unread 04-22-2021, 06:55 PM   #35
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Okay, today I grabbed a 1/4" x 3/8" trowel and, as a backup plan, a 3/8" x 3/8" trowel in case coverage isn't good enough.

When you say "pre-fill the Ditra" do you mean as per manufacturer's suggestion? For example, using the flat side of the trowel from two different directions to ensure the Ditra is completely filled before adding more on top for the notched side of the trowel to create the ridges? Or do you mean something else?
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Unread 04-22-2021, 07:47 PM   #36
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Kevin, I believe Dan meant for you to pre-fill all the Ditra waffles and let that mortar cure before setting your tiles.

Many users of Ditra do that all the time and it also makes marking layout lines easier. Schluter recognizes and accepts the method, but it's not their primary recommendation.

My opinion; worth price charged.
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Unread 04-22-2021, 10:38 PM   #37
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Thank you - I assume the intention here would be to just fill the waffles themselves on the flat and high spots and NOT to "screed" across the divots/impressions so as to "overfill" in an attempt have it be flat for next day tiling?

If that's correct then I assume when I return the next day I would key-in more thinset with the flat side of the trowel and then add more and use the notch side as per normal tiling routine? Not quite sure I understand how that would improve the divots situation, but am certainly willing to try this method - and I see lots of other folks on this forum also swear by it too.


EDIT: I realize I might be a bit picky about the "high spots" and "divots" here - having no experience with laying Ditra it's hard to estimate the impact of those areas of concern. I think most of the divots are fairly mild - probably no worse than 1/16" (maybe ever so slightly more in one or two cases).

But after putting a 4' level across the floor I do detect a high spot that runs parallel with the joist and to be fair, it probably is a joist that is a bit higher than the rest. Sitting that level on the highest point of that ridge and extending it 3.5" on either side of this high spot I am getting about an 1/8" of drop measured from the underside of the level to the top of the Ditra. Other spots seem quite a bit flatter than that, so I think this is really the biggest challenge in the room. Using 13"x13" tile, is it wise to lay the first tile right onto the highest ridge and press it down very tight to the Ditra and work down from there or do you try to have that highest ridge fall under a grout line?
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Unread 04-23-2021, 08:17 AM   #38
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Quote:
Originally Posted by Kevin
Using 13"x13" tile, is it wise to lay the first tile right onto the highest ridge and press it down very tight to the Ditra and work down from there or do you try to have that highest ridge fall under a grout line?
What's truly wise is to eliminate the high ridge, but that ship appears to have sailed. I think what Dan was trying to do with filling the waffles beforehand was to keep you from trying to flatten/level your tile installation while setting the tiles. While experienced tile setters do some of that on a regular basis, it's not an industry recommended practice. What you really want to do is ensure your substrate is sufficiently flat before starting to set your tiles.

At this point you'll just need to evaluate what you've got and do the best you can with it. Schluter clearly specifies that you must flatten the substrate before installing the Ditra and they prefer no flattening be done on top of the Ditra by adding or subtracting bonding mortar thickness and Dan was noting that such flattening while setting is even more difficult when you must also fill the waffles in the Ditra at the same time.

Mostly you just do the best you can with what you've got at this juncture.

My opinion; worth price charged.
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Unread 04-23-2021, 05:48 PM   #39
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Perfect, that explanation makes good sense to me, thank you. I am just having one of the outside doors in this room raised by 1.25" and then I will be ready for tile. I am thinking I will try the pre-fill option as recommended.
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