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# Thickness of floor+tile+membrane

#1
11-13-19, 06:51 PM
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Thickness of floor+tile+membrane

I want to use this membrane in kitchen and bathrooms for under floor heating:
https://www.homedepot.ca/product/schluter-ditra-heat-3-ft-3-inch-x-2-ft-7-inch-membrane-sheet/1000859103?rec=true

It's 1/4" thick and then time goes on top.
However it joins rooms that have 3/4" flooring.
How can I make the 2 rooms level?

#2
11-13-19, 07:58 PM
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You can't make them even because no tile floor will be 3/4 thick. That's what transitions are for.

#3
11-13-19, 08:54 PM
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I was thinking 1/4 cement backer, 1/4 membrane, then thinset and tile would be close to 3/4. Not possible?
or some sort of wood underlay..

#4
11-13-19, 09:16 PM
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1/8" thinset and 1/8" tile, huh? That would be a trick. Must be some new math I'm not familiar with.

It all starts with the existing subfloor. You need 1 1/8" of subfloor for starters. So if your 3/4" wood floor is on top of a 3/4" subfloor, well right off you need to add more subfloor. This assumes your joists and their span are ok.

#5
11-14-19, 04:59 AM
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So, with all the techniques in building, there's no way to get tile and wood level?! That's crazy.
it's 3/4 subfloor on 24" joists oc

#6
11-14-19, 05:16 AM
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I was just using your math. I looked it up and according to Kerdi, you don't need to use 1/4" cement board. They say you can lay on 3/4 subfloor and the total of 2 coats of thinset provides the other 3/8". You notch trowel thinset, then set the kerdiheat. Then notch trowel thinset and set your tile on that. Again, assuming your joists and subfloor are appropriate size and span to resist any deflection. But that's a big if. You don't want to have the same problems as the guy who posted the thread about "cracked tile the length of the kitchen" by putting all that \$\$\$ on joists and subfloor that are going to deflect.

Look up and follow their directions. I'm sure they have a YouTube video on kerdiheat.

I think most guys would still prefer to add more subfloor first.

#7
11-14-19, 05:30 AM
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Yeah I'm finding the 3/4 subfloor does deflect a bit. Some of the joists must be slightly more than 24.
so if I do 1/4 cement, 1/4 membrane, 1/8 thinset, it would be best to choose a 1/4 tile?
is there 1/8 underlay for wood floor?
I've also seen some push down the last few rows of tiles to give the illusion of level...

#8
11-14-19, 08:27 AM
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Before you go ahead here, The Ditra-Heat Handbook says you need two layers of plywood if you are installing over joists that are 24" oc. First layer (subfloor) must be at least 3/4". Second layer (underlayment) must be a minimum of 3/8". That's the bare minimum for 24" oc.

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#9
11-14-19, 08:51 AM
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Yeah I'm finding the 3/4 subfloor does deflect a bit.
3/4" sub floor w/16" OC joists, if correctly sized, is the absolute min for tile.

CBU is not considered a structural material so you probably need 1/2" ply!

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#10
11-14-19, 09:55 AM
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And a cement board 1/4 won't be stable enough as an underlay for tile on 3/4 subfloor? Surely that's stronger than 1/2" ply?

#11
11-14-19, 10:14 AM
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Actually, the plywood is the way you have to go. Cement board isn't structural. It's purpose is to be a good bond for the thinset and tile.

#12
11-14-19, 10:16 AM
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Cement board is not structural, it is only a surface to which thinset bonds well. Stick with the 1/2" plywood.

EDIT: Sorry, slow - Johnny beat me.

#13
11-14-19, 11:28 AM
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1/2 ply + 1/4 membrane + 1/8 thinset + at least 1/4 tile
min 1 1/8"
Now how do I bring the wood floor up to that, put 1/4" ply on top of the subfloor. Still not quite close enough

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Last edited by qwertyjjj; 11-14-19 at 11:47 AM.
#14
11-14-19, 03:19 PM
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All you need to do is make a bevelled wood transition that is 1 1/8 on one side and 3/4 on the other. Then stain and finish it to match the wood floor. This is quite common... it's what I mentioned in my first reply.

#15
11-14-19, 04:40 PM
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It's an open plan lounge/kitchen. Just concerned it will look crap doing a transition like that. If it was room to closed room I wouldn't have an issue.

#16
11-15-19, 05:52 AM
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If you're going to install tile, you need to quit thinking about height differences in the different floors. Period.

#17
11-15-19, 05:56 AM
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If the tile had been installed first, you also wouldn't have an issue because you could add more subfloor to raise the wood floor to the same height.

#18
11-15-19, 06:26 AM
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There's nothing installed yet, I'm planning how to level it.
i could add a 1/4 plywood on top of the subfloor for the wood. Would be close enough to level out the tile and squash down the last few rows.

#19
11-15-19, 06:52 AM
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Found this on Schluter:
DITRA-XL

• Allows for ceramic tile application over single layer plywood/OSB subfloors on joists spaced at 24" (610 mm) o.c.

• 5/16" (7 mm)-thick – creates an even transition between typical 5/16" (7 mm)-thick tile and 3/4" (19 mm)-thick hardwood flooring

#20
11-15-19, 09:51 AM
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Ditra is a different underlayment. Did you give up on the floor heating system?

#21
11-15-19, 10:35 AM
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Not only that but in new construction when joists are 24" on center they are usually large floor trusses or I joists... Something that will not have the sort of deflection that will ruin a tile job. They aren't making a blanket statement that you can use those products on any size joist with a ridiculous span. They also aren't Ditra heat instructions.

You can only lay it on a single layer 3/4 when the joists are 16" on center. (As Stickshift said) If 24" on center it is double layer 3/4 and min 3/8" (like HeresJohnny already said.)

https://resources.schluter.com/media...ationGuide.pdf

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