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Old 01-10-2018, 03:13 PM   #1
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porcelain adhesion

What can go wrong with setting 2"x2" porcelain with unmodified mortar over Ditra?

The last 4 SF of tile I set in the bathroom did not adhere and I have been able to pick it off with my fingers. I found this as I was cleaning the joints in prep for grouting.

- I used 1/8" DITRA, DitraSet, DALTILE 2x2 Keystone porcelain tile.
- I washed the tile sheets for good measure and let them dry prior to setting.
- I can see the towel ridges flattened off on the top of the mortar under the tile.
- There is the slightest bit of thin set on the bottom of the tiles and washed off under water while rubbing with my thumb.
- The DitraSet dried hard and adhered to the DITRA.
- There were some tiles that were 100% embedded. No mortar ridges just flat. These were accent tiles and had been back buttered.
- Most curious is that this installation overlapped some the same tile along one edge and the DitraSet is firmly adhered to the top of those porcelain tiles. Admittedly I scored the tops of those tile.

Best guesses:
- old mortar (bag was maybe 6 months old and had been open for 3 months ... there are no hardened granules in the powder)
- thin set skinned over before pressing in tile
- thin set was too wet ... it was mixed so that it would just start to sag on a trowel held sideways
- mortar drying too fast ... this section of tile was done after a change over to heating for winter

Ditra and DitraSet can not imagine anything other than the "best guesses" above that could go wrong.

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Old 01-10-2018, 04:21 PM   #2
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Sounds like thinset moat likely skinned over. Did these tiles have a glued on mesh backing? If you wash the back it could have smeared glue all over the backs and then inhibited the bond.
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Old 01-10-2018, 07:02 PM   #3
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porcelain adhesion - no glue on backing to smear

Not a mesh as I understand it. Only 2 rubbery dabs at the sides.
I did not wash the failed tile differently than the other 15 SF that have not failed.
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Old 01-10-2018, 09:47 PM   #4
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Got it, then definitely would lean toward either old mortar or skinned over thinset.
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Old 01-11-2018, 07:06 AM   #5
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That's usually a sign that your thinset had started to dry before it was covered.

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Old 01-16-2018, 07:54 AM   #6
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I don't know the root cause of your failure but it cuts to the heart of why the tile industry recommends polymer modified mortars for porcelain. The tiles you are describing typically have a flat back and close to 0% porosity, there is nothing for a mortar to mechanically 'grab' onto. When there isn't a mechanical bond with the cement, there needs to be an adhesive bond with the polymer. Since you don't have any polymer, you don't have any adhesive bond.

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Old 01-23-2018, 06:09 PM   #7
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porcelain adhesion - solution

It was one of two things.
1) I back buttered the tile, which was a pain on 2x2 tiles, by pressing a thin coat of DitraSet on the back using a small putty knife.
... and
2) I covered the area with plastic, for two days, with the intent of slowing down the curing. The plastic was still holding moisture on the surface of the tile when it was removed.
---I think I read or heard that Ditra is now allowing modified thin-set (?) after years of saying it would cause a tile failure. That would be worth back checking.

I know 1 & 2 worked because one of the black accent tiles twisted sometime after being set. It not only could not be popped out I had to use a roto-hammer to break it out in pieces.

3) The two above solutions could point to not sliding/twisting the tile enough into final position so the the thin-set did not smear the back side. I would still cover the installation for a slow cure - on small tile at least.
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Old 01-23-2018, 06:26 PM   #8
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Poreclain imperfections?

I have installed Daltile, 2x2, Cinnamon, Keystone porcelain tile on the floor and am now grouting it.

The Polyblend white sanded grout is revealing a lot of scratched and water type spots on the tile.

The scratches are substantial in places. From working on cutting and shaping the tile with a diamond file these scratches did not happen by rubbing sanded grout over the tile during grouting. I can only imagine they were done before curing. In that vain there are what look like thin lines that show up when I wipe the tile and some deep enough to look like scratches. I would guess they were from the kiln rack but they are on the top of the tile.

The water type spots appear like flakes in the surface of the tile where the white grout has gotten under the edges, and like raised bumps that are holding white grout around the base.

Clean water and rubbing with a moist cloth do very little to nothing to remove these eyesores.

- Does the haze remover, Polyblend recommends, work for cleaning out these types of defects that are holding grout?
- Do I just go to spot application of muriatic acid?
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Old 01-23-2018, 07:23 PM   #9
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Safety first:
First, and foremost: Do not bring muriatic acid indoors to work with it under any circumstances. It can cause permanent scarring of your lungs if you breathe it in. Besides that, it has the capacity to rust every single piece of metal the fumes run into. A haze remover is far safer.

Onto the rest of your problem...Do you have a picture you could share with us to see what you've got there?

And what application is the tile in?

What was used for its setting material and how long has it been installed?

And are we talking 10 square feet? 50? 100? More?

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Old 01-23-2018, 09:52 PM   #10
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A porcelain tile is very nearly impervious, and so is the Ditra, so covering the area won't make much of a difference in the overall bond strength in this situation.

I've found that just spreading a coat of thinset on the back of porcelain may not actually do much unless it is done just so. You need to use a fair amount of pressure to get it embedded into the pores, and, if done right, the only way to get it off is to scrub it off (assuming it's not cured!), otherwise, it sort of tends to actually ball up a little if you get what I mean, and not really stick well.

There are a couple of types of modified that will work on both Kerdi and Ditra, but, the USA ANSI spec does not differentiate that characteristic, so Schluter was unwilling to let modifieds used, since, if they contained latex, they had problems, or at least could. But, there are 3 other classes of modifiers that can be used in thinset that could work...it's just that you can't tell by the ANSI spec (the European spec does differentiate). An unmodified, installed properly over Ditra or Kerdi does work, as will certain modifieds. One reason why Schluter came out with their own is to ensure people had an easy choice of one they know will work. That makes it a bit easier when you're dealing with a tile, such as glass, where the manufacturer insists you use a modified. FWIW, they've set glass tile for centuries before modified thinsets became available...done right, it works.
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Old 01-24-2018, 04:17 PM   #11
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porcelain defects? - pics - added info

Thank you for the caution on muriatic acid.

Pics - left to right. top to bottom:
1) abrasion
2) abrasion
3) water spot
4) water spot
5) kiln lines?

Bathroom floor - not in use

DitraSet cured for over 7 days

39 SF

How do these answers help?
Attached Images
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Old 01-24-2018, 06:12 PM   #12
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nothing will help 1&2....try some "bar keepers friend" cleanser on the other areas.
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Old 01-24-2018, 10:39 PM   #13
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Tile manufacturers usually have no problem replacing damaged tiles before they are set. Looks like pic 1 and 2 would have been noticeable before you set them. I would look thru my left over tile sheets and see if there any damaged tiles in them and just how noticeable they are. Once they are set, they are usually yours.

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Old 01-25-2018, 12:06 AM   #14
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You might be able to find a sharpie or paint to make 1 and 2 less noticable. 3 and 4 i would think you could just scub the snot out of with a scotch brite pad.

That might help with 5 too but wtf is up with the grout on that one?
I probably have no idea what I am talking about.
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Old 01-29-2018, 01:43 PM   #15
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porcelain tile blemishes - hard solution but works

The tile is 100% porcelain making it a sold color all the way through.

sand paper, grits:

I was able to sand out the scratches and spots with the above sand paper in my hand.
Start with 100 on deep scratches, 150 on raised bumps and 220 on spots
working down to 600 to polish the surface.

Time consuming but effective.
About 1 1/2 hours so far. Expecting another 2 hours. Have not tried a pad sander since the blemishes are so isolated ... but still thinking about giving it a try.

Might be less time consuming than inspecting each of 1728, 2x2 tiles on 12x24 sheets and cutting out bad ones and then patching in good ones ... and of course not seeing all of them until white grout is applied.

I can not imagine this is how it is "supposed to be" done.
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