Subfloor question

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Old 02-01-09, 07:14 AM
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Subfloor question

I'm planning a kitchen tile project. Kitchen is 15 x 15 using 12x12 tiles. I plan to rip up the subfloor down to the joists, lay 3/4 in TG plywood on the joists, then 1/4 in hardibacker, then tile. Is this sufficient surface under the tile, or should I add another plywood layer before the hardibacker?
 
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Old 02-01-09, 07:59 AM
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Is this the same kitchen as your other thread? If so, its best to keep all questions in 1 thread so that folks answering your questions know all the facts.

As long as the tile is ceramic tile and not natural stone, then yes. If you have unsupported edges of plywood around the perimeter of the room where you did your cutout, you'll want to put blocking between the joist to support the edges of the plywood. This assumes 16" oc joist spacing. What do you have for a subfloor currently?
 
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Old 02-01-09, 08:10 AM
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Yes, this is the same kitchen, sorry for the confusion. The existing subfloor in 1/2 the kitchen is TG boards approx 3inches wide, like you'd see under a hardwood floor. The other half is plywood, not sure how thick, but judging from the bathroom I did, which is on the same part of the house, it's probably 1/2-5/8 in plywood (jury-rigged, I'm sure). In that bathroom, I used 3/4 TG ply w/ 1/4 hardibacker, but that floor is only about 25 sf. the kitchen is alot bigger.
 
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Old 02-01-09, 08:16 AM
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As long as you are using ceramic tile and the joist spacing is 16" on center then your plan is a good one. A second layer of plywood is insurance and always a good idea if you can afford the height. If you cannot afford the height you will be fine with your plan as well.
 
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Old 02-01-09, 08:32 AM
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Thanks for the help. One last thing: I keep reading about isolation membranes. Is there any need for one in this application, or are they only needed when installing tile over concrete slab or SLC?
 
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Old 02-01-09, 12:23 PM
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Typically, its either isolation membrane or cement board, not both. Is it absoluted needed here, no.
 
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Old 02-03-09, 08:26 PM
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We are building a new house. We would like to match our hardwood floor which is 3/4in with granite tiles that are 7/16in. If we want to match the hieght of the tile with the hardwood floor, what is better: wiremesh or cemement board? In general, are there what are the disadvantages of cement board versus wire mesh? I have heard that sometimes when you install granite tiles over wiremesh/thinset, then the tiles absorb water from the thinset and settle and as a result become un-leveled...is this true?
 
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Old 02-04-09, 06:20 AM
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Natalie

The install over wire mesh is a no no. This is an unacceptable method with a very high rate of failure, and you should stay away from any installer that suggests it.

You should be aware that any natural stone tile like granite needs a minimum of 2 layers of plywood totalling 1 1/8" in thickness. Additionally, the floor joist system must be twice as stiff as that needed for ceramic tile. Most floors are stiff enough for ceramic tile, however most are not stiff enough for natural stone without beefing up the joist structure and adding additional plywood. On top of the 2 layers of plywood you either need cement board or an isolation membrane.

It will be difficult to match the height of the hardwood floor unless you add more plywood under the hardwood as well.
 
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Old 02-04-09, 08:00 AM
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I'd like to add to what Johnny said, since this is new construction. You need to specifically ask your architect,"Does the joist system where we intend to install ceramic meet or exceed L/720 and will you verify it in writing?" If they won't verify it in writing, don't proceed with granite or any other stone install. DOn't accept an answer like "DOn't worry it will be fine," because when the warranty on the new home is gone, at that point fatigue will begin to set in to your building materials and that is when you will start having problems. Furthermore, if the installers are talking about mesh/thinset as an option then I'd bet they wouldn't install the cement board properly either. Your closest to even and best installation would be 1/2" bc underlayment plywood over the areas to receive stone with DItra as your underlayment for the stone and 3/8" plywood underlayment where your areas will receive hardwood. That will give you hardwood that is 1/16" proud of the stone. Another underlayment option would be Noble CIS whcih is only 1/16" thick installed and would be just about dead even between the hardwood and stone, but the CIS is about $1 sf more than Ditra.
 
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