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Discussion Starter · #1 ·
I posted this on the sister site, but I hoping to get a quick answer.


Floor Joists = 19 inches center to center
Subfloor = 3/4 OSB

what would be the proper substrate for the tile....
 

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I'm not a tile 'expert', - - but I'd sure as hell add 3/4" plywood, - - to me, cement board doesn't do 'jack' for rigidity, - - and with 19" centers, and OSB, - - you need some 'beef', - - combined with some longevity. Then some 'Flex-Bond' and your set.

I would think most tile guys will take the 'Thin-set followed by cement board' route.

Risky.
 

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Cement board screwed or nailed to the sub-floor (not the joists) is not used to add rigidity, it is used as a de-coupler, to separate the tile and it's mortar from the different expansion rate of the subfloor. Your floor must be rigid enough to support the tile regardless of the cbu.
As to your question Flor, you need the span of the joists from support to support. And the depth of them. Also, what tile? Granite eg needs twice the rigidity than ceramic floor tile.
All that having been said I sure would add 3/4 ply to it. :cheesygri Rich.
 

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Discussion Starter · #4 ·
thru body porcelain
 

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reveivl said:
Cement board screwed or nailed to the sub-floor (not the joists) is not used to add rigidity
I'm not really saying they're necessarily using it to 'add' rigidity, - - I'm just saying that it doesn't, - - and in this case more rigidity is called for.

The other part of 'risky', - - is applying a LATEX-based 'Thin-Set' to OSB.

Swell. :cheesygri
 

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WDF? 19" centers? Never heard of it but it's better than 24's.
I'd pull up everything, install crossmembers and put in parallel scabs on 12's or 16's. Here, everything has to come to current code.
 

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19"+ centers save you one stud or joist every 8' (5 studs or joists instead of 6). Look on your tape measure near multiples of 19", - - this is usually represented by a black diamond. :Thumbs:
 

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But without joist height (depth) and span you have no idea whether this floor can support tile, 19" o/c, 24" or 12".
 

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This is true, - - just trying to work with the information at hand, - - he made no mention of a 'weakness' issue, - - and where minimum of 1 1/4" mimimum wood subfloor is recomended, - - I'm (we're) going with 1 1/2".
 

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Discussion Starter · #10 ·
I do not think it's a deflection issue after further inspection.
Tile is loose and so is grout.
I pulled up a full tile and there was barely any thinset on the back of the tile.
So I believe because it is a Porcelain, it was set too dry...
Porcelain does not absorb much at all, so it needs wetness when set.
 

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reveivl said:
Cement board screwed or nailed to the sub-floor (not the joists) is not used to add rigidity, it is used as a de-coupler, to separate the tile and it's mortar from the different expansion rate of the subfloor. Your floor must be rigid enough to support the tile regardless of the cbu.
As to your question Flor, you need the span of the joists from support to support. And the depth of them. Also, what tile? Granite eg needs twice the rigidity than ceramic floor tile.
All that having been said I sure would add 3/4 ply to it. :cheesygri Rich.

Really granite can be comparible in weight to many of the ceramics out there now if you count some of these heavy porcelain tiles that sell so well. Porcelain is a heavier material than the ceramics of red clay bisque. You need plywood subfloor absolutely with your 1/2" concrete underlayment on top. Fully latex modified thinset underneath and screwed ever 12" squared. Fully modified thinset on top as well. NEVER over just plywood or it will fail.
 

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HuckabayHolding said:
NEVER over just plywood or it will fail.
Been putting tile (ceramic) directly on 'layered' plywood (1 1/4" minimum) with Flex-Bond for 26 years now, - - no failures.

But if that 'line' sells to your customers, - - MUM's the word!!
 

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I believe micheal bryne(famed master tilesetter,author or many books on tiling.)is a big proponent of tile over plywood underlayment,done correctly it can work.
 

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Never put a quality tile or stone job on wood. Expansion of plywood will start to pop the grout sooner or later. Tile and stone have been set on concrete for a hundred years for a reason.
 

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K custom home said:
Never put a quality tile or stone job on wood. Expansion of plywood will start to pop the grout sooner or later. Tile and stone have been set on concrete for a hundred years for a reason.

That's why they make 'FLEX'-bond!!

I've got a regular customer whose kitchen floor I put in about 16-17 years ago on plywood (12 X 12 ceramic tile), - - I'm over there doing other work once or twice a year, - - no problems to this day.

Plenty of other jobs too, - - (including 'my' bathroom 12 years ago), - - it's just that the 17-year-old one is the oldest I can think of that I still see all the time.

Sure wouldn't do my 'own' floors this way if I thought there was even a remote chance of failure.
 
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