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Old 12-04-2013, 04:04 PM   #1
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Preparing subfloor for tile


Hi guys,

I am planning on tackling a tile project in my entrance, roughly 150 square feet.

The adjoining rooms have 3/4" hardwood installed. I would like to make the tiles flush with the hardwood, there will be a 3/4" marble threshold separating the hardwood from the tile.

The original subfloor is currently 5/8" plywood sitting on 2x8s, 16" OC.

I plan on laying down a 12"x12" porcelain tile, using Ditra for the underlayment.

After I screw down the existing 5/8" plywood to the joists, I am assuming I need to install an additional layer of plywood on top of it.

I have read that 3/8" is the minimum, while 1/2" is better.

I believe the thickness of regular Ditra is 1/8", please correct me if I'm wrong.

What is the standard thickness of porcelain tile? I am trying to figure out what thickness of plywood I need to make everything flush.

Thanks.

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Old 12-04-2013, 08:55 PM   #2
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Preparing subfloor for tile


There is not a standard thickness. I've seen it vary between 3/16 and 3/8 or more.

But don't worry, because you won't be able to have your floor flush anyway.

Your wood floor will probably be 11/8 above the joist, which is the 5/8 plus 3/4.

Your tile floor will be 5/8 plus 4/8 plus 1/8 plus a bit of mortar and the tile. You are already at 10/8 without the mortar and tile. Going with 3/8 plywood will only give you another 1/8, and I think your tile will end up being at least 5/16.

There is nothing wrong with a bit of an elevation change.

On another note, how are you planning on making the 3/4" marble work?

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Old 12-05-2013, 09:45 AM   #3
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Preparing subfloor for tile


My initial plan was to use Ditra XL, which would allow my tiles to be flush with the 3/4" marble threshold.

I was told where I purchased the threshold that usually between the tile and threshold no transition piece is used, the gap is filled in with grout after the tiles have been installed.
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Old 12-05-2013, 10:54 AM   #4
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Preparing subfloor for tile


How do you plan to get your 3/4 marble flush with your 3/8 or so tile?
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Old 12-05-2013, 02:07 PM   #5
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Preparing subfloor for tile


I wanted to use either Ditra XL and tile over that or another layer of plywood, with regular Ditra, then tile on that.

Is that the proper way to do it?
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Old 12-05-2013, 02:13 PM   #6
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Preparing subfloor for tile


You're going to want to lay your tile and marble on the same floor. So you will start at x and your tile will put you at x + 3/8 and your marble will put you at x + 3/4.

I think you may want to forget about the marble and just go with another contrasting tile which has the same thickness. So maybe do your floor with 12x12 tile and then do some 2x2 accent instead of the marble.
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Old 12-05-2013, 03:12 PM   #7
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Preparing subfloor for tile


I already ordered the marble threshold, so it's a bit too late. I have no choice at this point. My better half also really likes the marble so you know how that goes.

Is my best option to use the Ditra XL?
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Old 12-05-2013, 07:47 PM   #8
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Preparing subfloor for tile


It doesn't make much sense to use Ditra XL instead of plywood if your floor is only 5/8" on top of 8" joists. First priority is stiffening the floor. Ditra XL doesn't do anything for you except add height.

Even 3/8" would be helpful, however you'll still be a bit over your wood floor. Not a big problem, however the height difference is normally handled with a tapered wood transition, or a fancy Schluter trim.

You will be at 3/8" plus 1/8" Ditra plus at least 1/4" tile plus at least 1/8" thinset. That puts you 1/8" over, and that's a minimum (don't forget there is thinset under the Ditra, and tile might be 5/16", etc.) So plan on being up to a quarter inch high. By the way, to get 1/8" thinset under your tile, you need a 1/4" x 1/4" trowel. If you think about that it will make sense. However, while I'd be OK with that in my own house, that's really the lowest I'd go with 12" tile. Many sources would recommend more thinset.

I personally would not like to 12" tile on 8" joists over only 5/8" subfloor. The Ditra XL would actually help a bit with crack avoidance over that subfloor (even though that's not its intended purpose in this context.)

Last edited by jeffnc; 12-05-2013 at 07:49 PM.
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Old 12-05-2013, 08:34 PM   #9
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Preparing subfloor for tile


Quote:
Originally Posted by jeffnc View Post
It doesn't make much sense to use Ditra XL instead of plywood if your floor is only 5/8" on top of 8" joists. First priority is stiffening the floor. Ditra XL doesn't do anything for you except add height.

Even 3/8" would be helpful, however you'll still be a bit over your wood floor. Not a big problem, however the height difference is normally handled with a tapered wood transition, or a fancy Schluter trim.

You will be at 3/8" plus 1/8" Ditra plus at least 1/4" tile plus at least 1/8" thinset. That puts you 1/8" over, and that's a minimum (don't forget there is thinset under the Ditra, and tile might be 5/16", etc.) So plan on being up to a quarter inch high. By the way, to get 1/8" thinset under your tile, you need a 1/4" x 1/4" trowel. If you think about that it will make sense. However, while I'd be OK with that in my own house, that's really the lowest I'd go with 12" tile. Many sources would recommend more thinset.

I personally would not like to 12" tile on 8" joists over only 5/8" subfloor. The Ditra XL would actually help a bit with crack avoidance over that subfloor (even though that's not its intended purpose in this context.)
That's really helpful information.

I don't mind if my tiled floor is higher than the wood floor, as long as I can make the transition look nice I'm fine with it.

I have seen the Shluter transition pieces, they look really good.

OK so in this case is 3/8" plywood on top of my existing 5/8" plywood enough or am I better off adding 1/2" instead?
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Old 12-05-2013, 08:45 PM   #10
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Preparing subfloor for tile


Well, 1 1/4" is really ideal (although keep in mind that no amount of plywood can really save a droopy joist structure - I'm assuming that's fine.) So to answer your question, more is always better so in that sense you're better off. But if it causes you a transition problem in height, it might not be worth it. 1/8" isn't much, but if it happens to raise that tile 1/8" too much to where it bugs you, it might seem like a lot.
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Old 12-23-2013, 04:15 PM   #11
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Preparing subfloor for tile


I figured I would add on to my existing post instead of starting a new one.

After I reinforce the existing 5/8" plywood subfloor by screwing it to the joists with flooring screws (or deck screws, not sure if it matters) do I add my additional layer of plywood, then level the floor with some type of self-leveling compound before applying the Ditra?

So would this be the correct sequence:

1-Reinforce existing 5/8" subfloor by screwing it to the joits
2-Install another 3/8" or 1/2" plywood screwing it to the 5/8" plywood
3-Level any dips in the floor with a self-leveling compound
4-Install Ditra, then tiles

Thanks!

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