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Old 09-23-2008, 11:44 PM   #1
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Saving a porcelain floor (not replacing)


We did a bathroom renovation on the second floor and did not install a think enough layer of thinset (my stubborn husband won the discussion with the contractor) and now we have issues. One tile is cracked, another is wobbly and the grout is cracked in several places.
Last note - the floor has radiant heat, so I am not sure how much is flex in the floor and how much may be from expansion/contraction.
Is there any solution other than replacing the floor?
Please help! Thanks!

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Last edited by deannas; 09-23-2008 at 11:54 PM. Reason: Added a note
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Old 09-24-2008, 12:23 AM   #2
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Saving a porcelain floor (not replacing)


Sounds to me like the floor's structure is not substantial enough to support a tile floor without allowing deflection or movement...Hence the cracking.

I can't imagine that thermal issues would cause a tile to crack. Poor bedding certainly would.

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Old 09-26-2008, 07:33 PM   #3
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What type of radiant heat did you utilize, electric or hydronic? If electric, what brand?

As far as thickness of the "thinset" is concerned, the first rule in laying tile is to be sure and have a minimum of 1-1/4" of subfloor below it. That can be 3/4" plywood with 1/2" of backer board or thinset or any ridgid combination.

Your floor is probably not THICK enough and that's why it's flexing and allowing the grout and tiles to crack.

The only time the radiant would have anything to do with a problem is if it was used to speed up the drying process of the thinset or mortar under the tile.
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Old 09-26-2008, 08:49 PM   #4
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Saving a porcelain floor (not replacing)


Deannas, You're implying your husband insisted the contractor not use the proper trowel notch size, hence not enough thinset and poor bond. Tell me, who was the expert (if any) on the job? If I was installing the tiles I'd ask him to go read the newpaper, because I charge an extra $20 per hour when customers want to help.

Tell us what was used as adhesive and the type of trowel. Also need to know how the floor is built from framing up. By the sounds of this, I also think you'll need to start over.....probably.

Warmsmeallup, You're on the right track, but your specs are not true. Where did you get them from? Maybe something you've heard and done for a while?

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Old 09-26-2008, 10:40 PM   #5
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Saving a porcelain floor (not replacing)


When things start cracking and popping loose, usually that means removing it all and starting over, doing things right this time. But It's hard to say for a certainty without inspecting the site personally.

I have a sub contractor who believes in that 1 1/4" thing too. Drives him crazy when I use 1/4" backer board over 3/4" plywood, cause in his mind I'm still a quarter inch short of his spec. TCA handbook says otherwise though :-)

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Old 09-27-2008, 12:45 PM   #6
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Yes, it was what I've been told by tile installers whom I've witnessed to be excellent at their trade. We install the radiant, not the tile.

But just curious...what's the difference (other than 1/4") if you have more, rather than less? Wouldn't a 1-1/4" subfloor be more supportive than a 1" sub? And, how can 1/4" of board or mortar support 8-10" of joist that flexes? Serious question, not sarcasm.
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Old 09-27-2008, 04:35 PM   #7
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1/4" backerboard is made for floors, and 1/2" isn't necessary. Backerboard is of no value structurally and doesn't add to the stiffness of the subfloor. If additional stiffness in the subfloor is needed, plywood must be added first.
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Old 09-27-2008, 09:49 PM   #8
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Saving a porcelain floor (not replacing)


That's right. so lets summarize.

Although I and many here wouldn't recommend it, a single 5/8" t&g plywood subfloor on joists at 16" o.c. meets the requirements of most CBU manufacturers. Personally I think that is garbage. The specs do mention though that everything has to meet L360 max deflection for both the joists and subfloor. Problem is while we do have span charts for the joists, there isn't a way to easily measure deflection of the subfloor. From experience most of us know that 5/8" at 16" is very risky. Believe it or not, a CBU manufacturer tells us that we can use 5/8" on a 24" o.c. system too. WOW, that is ridiculos. Of course the next line mentions the L360 for ceramic and L720 for stone requirements. I wonder how many people have a clue what that means? OK, I'm getting a little off here.

So, most of us will probably agree that a single 3/4" t&g exposure 1 subfloor at 16" o.c. will give you a good base for any CBU or sheet membrane such as Ditra or Noble CIS.

There is not doubt that the more plywood you have the better, but the is no such rule as 1 1/8" or 1 1/4" when a CBU or membrane is being used. All this info is assuming we are installing ceramic or porcelain tiles. Natural stone tiles are another matter.

The other scenario is if you were installing ceramic direct over plywood. (I don't recommend that). In that case of course you would also need the 2 layers totalling at least 1 1/8".

Jaz

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