Subfloor - Install Plywood or Not?

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Old 11-29-09, 04:58 PM
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Subfloor - Install Plywood or Not?

I'm about to start my kitchen remodel. The subfloor is tongue and groove plank layed diagonally. My plan was to install 1/2" c grade or better plywood over existing subfloor, then ditra then tile. Will this be sufficient or overkill? Is installing 1/2" cementboard directly to the t&g plank subfloor an option or is it not recommended? Any help is most appreciated.
 
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Old 11-29-09, 05:12 PM
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Don't guess there's a way to increase the top layer to 3/4" T&G Advantech, is there? If not, then the 1/2" would suffice. You don't want to install the cement board on the planks. Too much individual movement.
 
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Old 11-29-09, 05:21 PM
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Originally Posted by chandler View Post
Don't guess there's a way to increase the top layer to 3/4" T&G Advantech, is there? If not, then the 1/2" would suffice. You don't want to install the cement board on the planks. Too much individual movement.
Sure, if it's the right thing to do. We haven't even gutted the kitchen yet... just trying to get all my ducks in a row. It will obviously add 1/4" to the overall height, which would require me to install a transition between rooms. Is the Advantech that much better that it's worth the added height? I'm assuming whether it's plywood or Advantech it will be installed the same? That is to say, both would be layed perpendicular to the joists and screwed to the subfloor but not the joists. Any glue?

Thanks again.
 
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Old 11-29-09, 06:22 PM
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The more plywood the better...but, there is no need for 3/4" ply when you already have a subfloor. You can stick to 1/2" or even 5/8". C/C or better is required, but B/C might be easier to find. And you don't need "subfloor" type, which means it's t&g.

Do NOT glue ply underlayment to any subfloor, fasten only to the sub and not the joists as you said.

At that point you'll be ready for Ditra, (my choice too).

NO CBU's over plank floors, and 1/2" CBU is made for walls, not floors.

Jaz
 
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Old 11-29-09, 07:27 PM
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Originally Posted by JazMan View Post
The more plywood the better...but, there is no need for 3/4" ply when you already have a subfloor. You can stick to 1/2" or even 5/8". C/C or better is required, but B/C might be easier to find. And you don't need "subfloor" type, which means it's t&g.

Do NOT glue ply underlayment to any subfloor, fasten only to the sub and not the joists as you said.

At that point you'll be ready for Ditra, (my choice too).

NO CBU's over plank floors, and 1/2" CBU is made for walls, not floors.

Jaz
Exactly the info I needed. One other question. I read on another forum that I should leave 1/8" between the boards in the field and 1/4" from the wall on the perimeter. Does this sound accurate or do I just install them flush against each other?

This will be my first tile job using Ditra. Looks super easy to use... guess we'll see. Thanks again guys.
 
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Old 11-29-09, 09:36 PM
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Plywood is always installed with a gap between sheets and about 1/4" space short of all vertical objects. Be sure to use the proper fasteners that are just a bit longer than the total thickness of the 2 sheets. Do not use drywall screws.

If you've done tile work using cement boards, you'll be smiling when you install Ditra. Are you straight with how that is done?

Jaz
 
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Old 11-30-09, 09:19 AM
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Watched a few You Tube clips and saw it on the DIY channel. Looks extremely easy. Spread the thinset, roll out the ditra, embed it with a grout float, wait a day, install the tile. The only caveat seemed to be what you embed it in. From what I've read, for a plywood substrate I should use a modified thinset. Whatever the big box stores have will be most likely what I use. Sound about right?

Also, it seems Home Depot doesn't carry 1/2" BC plywood, but they have 15/32. I assume that will be fine.
 
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Old 11-30-09, 11:20 AM
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All plywood measures 1/32 less than the stated thickness.

If the You Tube clip is the one by Schluter OK, if it's Joe blow's video, better ask here and/or go the Schluter's website for accurate info. Many tiling videos on You tube are wrong.

The modified thin set at HD is fine. Their Versabond will work fine and it's cheap. But, they do not have a good unmodified to install the tiles. Try Megabond from Lowes, or isn't there a real tile shop near you?

Jaz
 
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