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Unread 10-19-2019, 11:40 AM   #1
red3
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HELP! thinset cracking behind tiles

Here's the deal.. I made some large format tile(2'x2'), for my shower,out of fiber glass reinforced concrete. They are being installed on the walls over kerdi using Customblend unmodidied thinset. I pre-moistened the back of the tiles with a spray bottle of water the keep the tiles from sucking the water out of he thinset. the tiles are back buttered and thinset on the wall is combed with a 1/2" notched trowel. I am getting close to, if not , 100% coverage with the thin set. I then cover the perimeter of the tile with plastic wrap, held in place with tape, to control moisture loss of the thinset during curing. After about two days I have found that the thinset has cracked behind some the tiles and that the thinset is no longer attached to the tile where the cracks are. What am I doing wrong?
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Unread 10-19-2019, 11:59 AM   #2
Lazarus
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First thing is the "customblend" morter. The cheapest and, quite possibly the lowest quality stuff ever produced unless it is mixed with an additive. Good for "yard bunnies" and precious little else.

Versabond would be a far better choice.....
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Unread 10-19-2019, 12:17 PM   #3
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For bonding those concrete slabs to the wall, about the only thing you could use that would be worse is chewing gum.

And even then it'd be a close contest.
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Unread 10-19-2019, 12:44 PM   #4
Davy
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Hi Don, after making the concrete tiles, how long did you let the tiles dry and cure before installing them?

And you are spreading thinset on the backs of the tiles and letting it dry, That's when you noticed the cracks in the thinset?
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Unread 10-19-2019, 08:54 PM   #5
red3
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Thanks for the quick response guys...now the quest for decent thinset. If anyone can recommend a specific thinset that would be great....I'm limited in choices because of where I live. the nearest town is 15 miles away and it only has one stop light. Thenearest city is 65 miles and it isn't much better..

Davy...The tiles are 4-5 days out of the mold....I did back butter the tiles but I immediately installed them. I did not let the thinset dry in the back of the tile before installing. Everything looked fine for a day or so then the crack appeared in the thinset. Specifically, the crack is where the thinset is bonded to the back surface of the tile. The thinset seems to have bonded to the kerdi just fine. Its the junction of the thinset to tile where the problem is.....

Thanks for everyone's help
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Unread 10-19-2019, 11:24 PM   #6
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Where did you get the Custom Blend? If at HD, you should be able to get Custom's Versabond LFT mortar.

If you're building the mortar up thicker than what the maximum buildup is, you'll get cracks like that.
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Unread 10-20-2019, 07:49 AM   #7
Davy
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Hi Don, thanks for explaining. You haven't said that the tiles have come loose but I'm trying to figure out how you know the thinset cracked without the tiles coming loose from the wall. Concrete tiles will want to shrink and I have no idea how long they need to cure. It's possible some of your problem is bonding the tiles before they have cured enough. I've seen concrete tiles being made in molds and a heat room was used to help dry out the tiles. I think the thinset is also a problem, like the others have said.
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Unread 10-20-2019, 02:16 PM   #8
red3
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Thanks for the response guys. The thinset most likely came from HD. I am going to try to locate some Laticrete 272 (it seems very popular) unless somebody recommends something better. I didn't know that there was such a difference. I just thought the important thing was that it be un-modified...I'm an Idiot....


Davey.. I am only about halfway done with the install so I can see the thinset along the edge of the tiles where the cracks are (no grout yet). None of them have come loose but one tile did flex a little along one edge when I pushed on it so I pried the tile off the wall. I was surprised when I pulled the tile off that it had about 99% coverage. All of the thinset, except for about 4 square inches, stayed on the kerdi

That's about where I am at this point. I am still in the process of making tiles to finish the shower. Kind of installing as i go....Gonna stop installing until I get some good thinset. Also going to contact concrete admix company tomorrow and confirm the cure time for the tile.
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Unread 10-20-2019, 03:43 PM   #9
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If all you have is Home Depot to shop at, Versabond LFT is good along with Pro-lite. I'd use modified.
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Unread 10-20-2019, 06:45 PM   #10
smifwal
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I like ardex products myself. No idea where you are located but if you can find them I would recommend Ardex X77 or Ardex X5
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Unread 10-20-2019, 10:27 PM   #11
Davy
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I believe "The Tile Store" has Ardex products. I just learned this yesterday.
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Unread 10-21-2019, 08:17 AM   #12
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Don, I’m going to echo the comments of the fine gentlemen above by saying: get a decent LFT mortar to hang those big boys up with. LFT mortar is typically nonsag and nonshrink so you should have a better experience.
Definitely do as you said and check with the concrete company on cure time. You don’t want those tiles shrinking after they’re already installed. That would make for a bad time...

Also, can we see some pictures of these tiles? I (and others I’m sure) am curious to see your custom creations.
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Unread 10-21-2019, 07:53 PM   #13
red3
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Thanks for all the help guys. I contacted the concrete admix company and they said that the admix can leave a polymer film on the surface that needs to be sanded/ground off so the thinset can bond to the tile. The cure time didn't seem to be an issue with them.

On the thinset side, I found a masonry store 70 miles away that has Ardex x77 in stock, so I will be making the trek tomorrow to get real thinset....I'll post the results when I get some more tile put up.


Again, to everyone that replied.... thanks for all the help
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