Cracked concrete subfloor under ceramic tiling

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Old 11-17-15, 07:19 AM
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Cracked concrete subfloor under ceramic tiling

Hi,

We moved into a 15 year old house in Florida a few months ago. I noticed the grout popping & cracking around about 8 tiles in the kitchen. The tiles are 20" x 20".
I tapped on a few of them and they sounded hollow, so I thought it was just a bad Thinset application. I just took a few of them off and they were Thinsetted to some sort of mesh fabric sheet. It's very tough stuff, I had to cut it with a utility knife. The fabric was not adhered to the concrete. There was a very long crack in the concrete though, so I'm guessing the fabric allowed the tiles to "float" thus preventing the tiles themselves from cracking. However, the grout cracks instead.

Any suggestions? I have to re-lay the tiles now and gout them. I'm not sure what that fabric is or should I even use it. Is there something like "Redgard" that might work?
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Last edited by onthegulf; 11-17-15 at 10:15 AM.
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Old 11-17-15, 02:15 PM
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Is the concrete cracked under the thinset? If so, you'll need a membrane like Ditra.
 
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Old 11-17-15, 04:00 PM
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This one is going to be tough to jump in and simply repair. You need an uncoupling membrane which will change the height relative to the other tiles. How thick is the mortar bed that the tiles sit in? A painted on membrane probably will not suffice in this instance.
 
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Old 11-18-15, 08:06 AM
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Sorry, failed to notice you did say the concrete was cracked.
 
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Old 11-18-15, 08:41 AM
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Red face Cracked concrete

Czizzi,

I was afraid you guys might say what you did. The crack is under 8 tiles that are 20 x 20. The problem is that I can't (or won't) rip up the whole floor which is massive and carries on into 3 more rooms and hallways. (Cost & effort)
To answer your question, the tough fabric on top of the concrete is roughly 3/32. With the Thinset it comes to about 1/4 total. The fabric allowed the tiles to move preventing them from cracking, but the grout was cracking all of the time.
A person on another site recommended several coats of RedGard with a nylon mesh tape over the crack.

Maybe I should move
 
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Old 11-18-15, 11:09 AM
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RedGard is not the answer here, take a look at Ditra.
 
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Old 11-18-15, 02:48 PM
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Trying to be creative here for you. Kerdi, while a waterproofing membrane, does provide limited crack isolation properties. It is thin enough to work in your situation. Additionally, instead of putting grout back on these specific tile, I would use a color matching sanded CAULK to simulate a portland based grout to eliminate your cracking. Keep in mind that uncoupling membranes take an unmodified thinset so use the proper mortar for whatever membrane you choose.
 

Last edited by czizzi; 11-19-15 at 09:34 AM. Reason: Change Grout to "Caulk" as highlighted
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Old 11-19-15, 08:17 AM
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Thanks Czizzi,

That sounds like a solution for my particular problem.
A thin membrane was needed in order to match the existing tile height. I'll give it a try

Thank you all for your insights.

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Old 04-08-16, 08:13 AM
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Just a quick update,

Because of the thickness issues of matching the existing height of the adjacent tiles, I decided to use RedGard. I applied 2 coats to the crack, let dry, then taped over the crack and applied another 2 coats. Its been 5 months now and the job is still perfect. Not one crack in any of the grouted joints.

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Old 04-08-16, 08:18 AM
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Great, glad to hear it
Thanks for the update.
 
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