Another subfloor question

Hi all, another newbie subfloor question again ! I am in the middle of doing a renovation on my1976 home and I'm getting ready to do some flooring, it is now a wide open space that will be hardwood and porcelein tile. I want the floor to be level at the meeting point of both surfaces and the hardwood is 3/4" thick, how thick if any do I need to go with the subfloor? The tile is a 20x20 3/8" thick tile and I am using the Schluter-Ditra membrane . The flooring right now is 5/8 plywood , 2x10 joists 16" o/c . Will the thin set, Schluter, then thin set with tile be 3/4" overall ?
I checked the deflection and the calculator told me it was L/618

[kwfloors]

No I don't think so, I have used 1/4" wonderboard and tile to get even to 3/4"wood flooring.

[TFP Admin]

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[Kman]

Your tile will most likely be a little lower than the hardwood given your description. Ditra is about 1/8" with thinset underneath, you can figure another 1/8" for thinset under the tile, plus the thickness of the tile. Ceramic tile is unlikely to make up the other 1/2".

You could step up to Ditra XL for a few cents a square foot and probably come out pretty close to the same height. Ditra XL was designed just for this.

Here's the biggest risk with your project as I see it: Your subfloor is at the absolute bare minimum for a tile installation. If you use Ditra XL and porcelain tile, you're using the best materials you can, but no amount of quality materials can make up for a substandard subfloor. I would hate to see you invest all that money in tile, Ditra XL, thinset, etc., not to mention the time involved, and have your installation fail.

I would rather install a 1/2" layer of ply (3/8" at the minimum), then Ditra and tile, and deal with the transitions however they turn out. Having both floors at the same height will mean nothing if the tile and/or grout cracks.

You could also add some height to the hardwood section if the transitions are that important to you.

[outlaw17]

Kman, thanks for the input, if the thinset and Ditra is about an 1/8 with thinset , then another 1/8 under the tile , and a 3/8 tile , that puts me at 5/8 overall , only 1/8 below my hardwood, can that be made up with just a wee bit more thinset on the first row or 2 at the transition point? I have been considering putting down another layer of plywood over the whole are, not sure what size though, just to be sure the floor is sound.

[Jaz]

Outlaw,

Don't be encouraged to go ahead with your present subfloor by the L618 joists deflection you got at JB's place. Most failures happen because of too much deflection between the joists, not along the length of the joists. Your 5/8" plywood subfloor is real scary at Kevin told you above.

You should consider adding plywood on all areas if a smooth transition is that important to you. Generally though, a variation of about 1/2" or so is very easy to deal with, even an inch isn't that bad.

Jaz

[outlaw17]

Jaz,

I was considering was putting down a layer of 3/4 where the tile is going to be and a layer of 5/8 under the hardwood area , that would theoreticallly get me pretty level, right? I've got 2 other areas 1 is a foyer that will be tile and the other is going to be an office , both of these areas only have 2x8 joists on 16" centers so I was planning on adding the 3/4 for sure just to give them some strength.

[Jaz]

Some would say 3/4 & 5/8 in the other area is over kill. Maybe? But go ahead if the extra height won't hurt you, the more plywood the better.

Once again, the joists had nothing to do with the in-between-joists deflection. Run the numbers for the 2x8's in the Deflecto to see what you get, or if you know the species and grade, I can give you a more accurate answer.

Jaz

[outlaw17]

Well I looked i nto the Ditra XL and it will for fine for what I am trying to achieve with the even floors and it works out cheaper because of the roll size or something like that , not sure just was told by supplier it works out cheaper. I guess I would like to get away without having to put another layer of subfloor down but it sounds as if its going to be necessary right ? I guess what I would like to know is if 3/8 would be fine or do I really need to jump up to 1/2"?
The subfloor on about 65% was just carpet so it is pretty clean , the other 45% had a glued down carpet, they both seemed original from 76 , the glued down side is a bit rough from the glue , do I need to get that smoothed right out both with or without another layer of subfloor?

[Kman]

If I had to choose, I'd go with more plywood and standard Ditra as opposed to less plywood and Ditra XL. Don't know exactly how the height will work out for you on that, but 3/8" ply, while pretty flimsy, is better than nothing. I'd rather have 1/2" ply and Ditra.

As for the leftover glue/padding that's on the floor, you need to get as much of that up as you can, particularly if you're planning on bonding Ditra directly to it. Padding and/or glue will interfere with a good bond.

If you're going over it with another layer of ply, just make sure you don't have anything sticking up on the floor that might make a slight hump. Traces of glue/padding won't hurt you in that case.

[kwfloors]

Why not go with 1/2" wonderboard instead of plywood?

[outlaw17]

What is wonderboard, and is it available in Canada?

[Jaz]

Kevin & I have been suggesting more plywood because Outlaw's subfloor is only a wimpy 5/8" plywood. Although 5/8" does meet minimum housing standards and some companies says it's OK to set their product over it, it is still the bare minimum. Furthermore they always include the "*" saying the floor structure has to meet L360 deflection. Well, of course it does. But, how will you measure that?

Adding Wonderboard or any other CBU or membrane will not strengthen the floor, it'll just make it higher. I'm sure you knew that since by your name I guess you're into floors.

Jaz

[kwfloors]

outlaw17 said What is wonderboard, and is it available in Canada?

It is a concrete panel 3x5 that you thinset and nail to your floor for a tile backer.

[outlaw17]

I just finished running about 2000 screws in the existing original floor that was nailed down and I'm going with 1/2 subfloor tommorrow , whats the best pattern to be screwing the new stuff down?