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Unread 08-24-2021, 07:24 AM   #1
yusrag
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Cracked Marble in new bathroom reno

Hi,

I am almost finished with a master bathroom remodel. 3 weeks ago, I noticed a few pieces of cracked marble. My contractor replaced them but it was messy (he had to replace lots of surrounding ones). We noticed a couple more afterwards and he figured out a way to remove the individual marble pieces without cracking others. He did this with a few pieces.

I am now noticing for 4 more cracked marble on one side of the bathroom and I'm pretty sure they are new and I would've noticed it if they weren't. I'm so concerned. I marked these recent ones in blue and I'll circle the tile that was replaced most recently .

Floor marble used: Floor & Decor Bianco Orion Marble Tile 4x12.


This was previously a master bathroom which we just renovated.

Install: he used cement board and the contractor says he used "mortar called type 2 mastic from menards made for setting tile but does need 24 hrs minimum before walking." I will post a photo of the mortar that was in the bathroom.

I'll also post photos from when he first removed cracked marble/surrounding marble..after that he was able to Take out individually cracked marbled without all this damage.

When I asked him why the cement board looked so clean , he said he used mortar but when he took the cracked tile off he scraped the old mortar off exposing the cement board. He said he sealed off the seams.

About that extra piece of wood in the subfloor, he said " the wood is there secured to the joists because the hole was there because of the jacuzzi tub which was carved out of the subfloor."

Thank you guys in advance
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Unread 08-24-2021, 08:27 AM   #2
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Welcome, Yusra.

We need more information about your subfloor and substrate to be of much help here.

Did your contractor evaluate your floor joist structure to determine if it qualified for a natural stone installation? Wood framed floors rarely do unless natural stone was included in the original design.

Did your contractor install a second layer of plywood subflooring to whatever subfloor you originally had in place? The stone tile industry requires a double layer of structural subflooring regardless the joist spacing.

What CBU was installed over your subfloor? Be specific.

Did your contractor apply a layer of thinset mortar under the CBU as required by the product manufacturer?

Let's start with that.
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Unread 08-24-2021, 08:34 AM   #3
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The mastic alone is grounds for a redo. I don't know of any of them that are compatible with natural stone, and they stay soft for a good while when not exposed to air, which may contribute to the cracking you're seeing.
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Unread 08-24-2021, 08:40 AM   #4
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TEC does indicate their organic adhesive for floor tiles, including natural stone, Kevin. And they mark the bucket as "Mortar," the same deceptive practice used by some other installation materials manufacturers, unfortunately.

My opinion; worth price charged.
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Unread 08-24-2021, 08:53 AM   #5
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I see that now in their specs.

Still, no way I'd use that in that application when there's so many other options.
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Unread 08-24-2021, 09:02 AM   #6
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Can't argue at all with that.

But I don't think that's the primary problem with this floor. I think it goes much deeper.
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Unread 08-27-2021, 08:52 PM   #7
yusrag
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Answers

Hi,

Thanks for your feedback! I have the answers to your questions @cx:

Contractor: there is thinset applied to the cement board a 5/8” thickness. no there was no extra sheets of ply wood. the CBU installed over the subfloor is called Durock.

Hoping this isn't so bad. Thanks in advance,
Yusra
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Unread 08-27-2021, 09:34 PM   #8
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Industry standards for a natural stone tile is TWO layers of subflooring, with the second one required to be plywood...then, whatever you want for a compatibility layer to set the tile, which CBU would qualify. Unless you want thicker to match levels, a thicker layer (1/2" versus 1/4") does not buy you any strength...it is a compatibility layer when used on a floor, it does not make your floor stiffer. Joists are not likely stiff enough for natural stone, either, unless the house was designed for it. Subflooring makes the flor stiff between the joists, but the joists supply the strength along them.

A mastic that thick could take a long time to harden up...think about it in the bucket...stays spreadable for probably at least a year until you open it up. A day, when applied that thick, probably could be an issue all by itself. Normally, you'd never have it that thick and that one (probably) isn't specified to be applied that thick.

Thinset is a method, but many people think of it as being a cement based product (which it is, but so also is a mastic, one-part material).
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Unread 08-27-2021, 09:46 PM   #9
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Quote:
Originally Posted by Yusra
...there is thinset applied to the cement board a 5/8” thickness.
That doesn't compute, Yusra. As Jim points out above, thinset is a method, not a material. Thinset mortar is a bonding material in the tile industry. My question is whether your contractor applied thinset mortar, or his organic adhesive, to the floor per the manufacturer's instructions before he installed the CBU . Very, very important step.

My opinion; worth price charged.
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Unread 08-28-2021, 08:44 AM   #10
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I'll repeat what the others said. If the marble wasn't cracked right out of the box, which I doubt it was, then movement has caused it to crack. Usually it's the lack of having the floor stiff enough to begin with (2nd layer of plywood or adequate framing) or it could be the lack of thinset mortar under the CBU. When there's no thinset mortar under the CBU, I've seen floors flex just enough to crack the grout and not the tiles, usually in the traffic areas. It also could be your mastic is still soft enough to cause flex, again more so in the traffic areas.

Did they tape the joints in the Durock? I looked at a job the other day that had marble over CBU. The floor has cracks every 3 ft apart, telling me the cracks are over the CBU joints.
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Unread 08-28-2021, 06:12 PM   #11
yusrag
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Thinset mortar was applied

Hi,

I confirmed that he did apply Thinset mortar before the cement board was secured. Does this mean the likely issue is no double layer of structural subflooring? Is this going to lead to a lot of problems and definitely more cracked marble ?
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Unread 08-28-2021, 06:53 PM   #12
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Like Jim points out, the premixed mastic "mortar" could take quite a while to dry out and actually support the tile. I'd bet that the installer probably grouted way to soon, walking, crawling all over the tile that had uncured mastic underneath and caused the cracking.
Another good bet is that if the seams are taped at all they are taped with mastic. Useless. If he used thinset....... "thinset mortar" under the cement board, why would he not use it to set the tile?

There's a good chance that you might be starting over on this one, in my opinion.

Look at the backs of the tile that were pulled up. Looks to me like the mastic was still wet at the time the tile was removed
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Unread 08-28-2021, 07:02 PM   #13
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Quote:
Originally Posted by Yusra
I confirmed that he did apply Thinset mortar before the cement board was secured
I'd wanna verify that, Yusra. I agree with Jerry in questioning why he would use thinset mortar to set the Durock panels and they use the organic adhesive (mastic) to set the natural stone tiles.

I also agree with Jerry that this is almost certainly a do-over. And the expense should be borne by whomever decided not to use the double layer of subflooring as required by stone tile industry standards.

[Edit] Jerry, USG actually does indicate the use of Type 1 organic adhesive to fill and tape the joints. I agree with your assessment of that, too.

My opinion; worth price charged.
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Unread 08-28-2021, 07:05 PM   #14
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Does anyone know of a cbu panel that allows installation with mastic underneath it? I've not seen one, but haven't perused the instructions carefully for awhile.

Your subflooring and cbu might absorb enough out of the mastic for it to harden, but then again, it will still likely take awhile, especially on a larger tile.
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Unread 08-28-2021, 07:23 PM   #15
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Unfortunately, yes, Jim. At least Durock and Hardiebacker permit that application.

[Edit] I just reviewed James Hardie's site and where it previously allowed organic adhesive or thinset mortar under the panels, it now says "Apply a supporting bed of mortar or modified thinset to the subfloor using a 1/4" square notched trowel." While under Materials Required they do not mention organic adhesive at all, but only modified thinset mortar or, for under panels only, un-modified thinset mortar. The Hardiebacker installation instructions have always been a bit "mushy" in my view and that's another example.

The manufacturer of that natural stone tile is not likely to look kindly at it's being set with an organic adhesive, though.

My opinion; worth price charged.
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