Sub-floor Thickness for tile...

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Old 03-25-13, 07:28 PM
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Sub-floor Thickness for tile...

I am looking to install porcelain tile in my kitchen.

I currently have lino installed over top of play wood and particle board. I plan to remove the lino and particle board which will leave 5/8" plywood.

From reading this forum I understand that my sub-floor should be 1 1/4". So my question is what is the best way to achieve this:

1) Install another layer of 5/8" plywood and don't use any cement board at all.

2) Install 1/2" cement board to take me to 1 1/8" and don't worry about being 1/8" short.

3) Some combo of plywood and cement board to take me at or past 1 1/4"

Thoughts?
 
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Old 03-26-13, 04:47 AM
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Welcome to the forums! CBU offers no support at all, so that's out of the equation. Subflooring should be a minimum of 1"and more if possible. If you are removing particle board then using the same size plywood will bring you back to the right height that you had before. If it was 3/4", you could install 1/2" plywood over your existing 5/8", then 1/4" cbu, then your tile.

With all that out of the way, you need to know more. What is the height of your floor joists? What is the distance between joists? What is the longest unsupported span of the joists under this room? THIS will determine if you have a good substrate for tile floor or not. Let us know the answers to that, and we'll forge forward.
 
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Old 03-26-13, 12:48 PM
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Thanks for the help. I have been a long time reader

What is the height of your floor joists? 10"

What is the distance between joists? 16"

What is the longest unsupported span of the joists under this room? 12'

Local flooring guy told me to screw and glue an additional 1/2" plywood. He didn't think I would need the CBU at all.

Talked to another flooring company and they said the same as above - also thought CBU was overkill for kitchen if I had two layers of plywood to take me to 1 1/4".

I would also interested in comments as to whether it would be silly not to do any CBU in the kitchen.

Some additional info:

- I have to transition down to hardwood in the next room so I would like to keep the height of the tile as low as possible without compromising the installation.

- I plan to put in a in floor heating system: Premier Floor Warming System
 
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Old 03-26-13, 03:10 PM
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Hi guys,

Originally Posted by oginvest
From reading this forum I understand that my sub-floor should be 1 1/4".
There is no place that I know of that specifies any such thing for ceramic tile.

You should decide what brand of concrete backer and method of installation and read their installation data sheet.

In general, most manufacturers say 5/8" t&g ply subfloor properly installed, 16" o.c. and in good condition is enough to meet minimum deflection standards of L360 for ceramic. 5/8" scares me and is bare minimum under the best of conditions. I recommend 3/4" min.

In this case I recommend adding min. 3/8" underlayment grade ply or thicker if it doesn't cause other problems. Then install your favorite CBU or membrane such as Ditra.

Let us know you plan. Your answers to Larry's question about the framing signifies you should be fine there.

Originally Posted by oginvest
Talked to another flooring company and they said the same as above - also thought CBU was overkill
Yea, some think doing a job the right way is overkill.

Jaz
 
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Old 03-26-13, 04:45 PM
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He didn't think I would need the CBU at all
He's not suggesting you install the tile directly on plywood, is he??? You'll need either cbu or a product like Ditra.
 
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Old 03-26-13, 05:10 PM
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Yes, they suggested no CBU.

I calculated the deflection to be L/915 so it appears I should be good for the porcelain tile.

Based on the response it sounds like the recommended sub-floor would be:

- add 3/8" plywood to take it to 1"
- add 1/4" CBU

The local big box store carries WonderBoard, HardieBacker, and Durock - is there are preferred product for kitchen tile?
 
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Old 03-26-13, 05:30 PM
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Preferences are like children, difficult to narrow it down. I prefer Hardibacker mainly because it is a more solid product, cuts easily with a grinder with diamond blade, and has screw schedule imprinted on the face.
 
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Old 03-26-13, 05:44 PM
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Thanks for the feedback guys.

I am also looking for some info on the proper way to attach the 2nd layer of ply wood. Here is what I got so far.

Original 5/8 subfloor:

- Make sure the original subfloor is screwed down tightly using deck screws.

Additional 3/8 layer:

- Don't glue
- Attach to first layer in opposite direction and avoid fastening to joists (ie. only fasten to first layer of plywood).

Some additional questions I have for attaching the second layer:

Deck screws or ring nails?
length of screw/nail?
Screw/Nail pattern?
1/8" expansion gap between all seams?
 
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Old 03-26-13, 06:05 PM
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Be sure to use the proper type of plywood, fasteners and install according to specs. Decide which thinset you'll use under your favorite concrete backer in case they want something special, like fill or do not fill the gaps between sheets. I'd be using Ditra, but it does cost more.

I see you've up-dated your thread with more info, so let's see.....

Don't glue, is correct.

Attach the underlayment in opposite direction, is NOT correct.

Additional q's

Deck screws or ring nails?, either
length of screw/nail? 1 1/4" is good and easy to find
Screw/Nail pattern? 4" perimeter 5-6" in field
1/8" expansion gap between all seams? Yes 1/8", and 1/4" around perimeter and any vertical items

Jaz
 
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Old 03-26-13, 06:14 PM
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Thanks Jaz, I think I have a good grasp of everything up to the CBU now.

I have not picked out my tile yet so I have yet to review their installation instructions - but whatever I get will be porcelain tile with a mixture of 12x12 and 6x6 tiles.

I do plan to go with an in-floor heating system and they indicate that the tile can be installed over their product in a number of ways.

Any suggestions on the best method?


http://www.premierunderfloor.com/lit..._Manual-EN.pdf (page 13)


Thin-setting Techniques:

1) One-step application: Directly
apply the thin-set onto the mat with a
1/4" × 3/8" notched trowel, and then
lay the tile directly onto the thin-set.

2) Two-step application. Apply the
thin-set onto the mat with the flat side
of the trowel to fill in the voids of the
mat. Then trowel more thin-set with
the notched side and set the tile.

3) Back-butter. Apply the thin-set
with the flat side of the trowel to fill
the void areas of the mat. Then “backbutter”
thin-set onto the underside
of each tile with the flat side of the
trowel, and set the tile.

4) Double-layer thin-set. Flat trowel
thin-set over the entire mat. Let dry.
Then trowel fresh thin-set on top
of the dry layer, and set the tile. This
technique is especially recommended
when laying mosaic and other small
tile (smaller than 6" × 6").

5) Self-leveling mortar. Pour a layer
of self-leveling mortar over the mat.
Let dry. Then thin-set the tile, stone, or
other floor covering over the mortar.
 
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Old 03-26-13, 06:16 PM
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Underlayment in same direction, just with offset seams.
 
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Old 03-26-13, 08:44 PM
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I would go with #5. The mat will not cover the entire floor areas. You're not gonna get a flat floor if you just thinset over the mats. The SLC will make the floor flat, and also stiffen it.

Negatives; it needs help to "self level". Total thickness may end up thicker than anticipated.

Jaz
 
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Old 04-05-13, 02:08 AM
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If I go the SLC route to cover the in floor heating wires then does that eliminate the need for a CBU?

ie. sub floor thickness

5/8" plywood
3/8" plywood
3/8" SLC over top of the heating wires
 
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Old 04-07-13, 03:47 PM
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If the SLC is thick enough according to the manufacturer's directions, then yes you do not also have to use the concrete backer. Most of the time it's best to do both if the thickness is unknown. If you're using Ditra, you'll be doing both and gain more benefits.

Jaz
 
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Old 11-10-13, 10:06 AM
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Just a quick update.

In the entrance:

Installed 1/2" plywood over the existing sub-floor. Installed 1/4" CBU. Installed tiles with Ardex X5. X5 was a fantastic product to work with.


In the kitchen:

I ended up putting 1/2" plywood over the existing sub-floor. Installed radiant heating wire on top of that and yesterday I poured Ardex Liqiud Backer board over the wires.

I will be using Ardex X5 to install my tiles directly on the SLC.

Thanks you for the help and advice.
 
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