Floating membrane under Tile - Contractor Talk - Professional Construction and Remodeling Forum

mjay · 02-08-2006, 07:43 PM

Installing tile over 3/4' cdx. Always used 15lb felt - wire mesh - mud - tile. Floor is solid {2*10' 16o.c 8" span}. Don't expect movement, but always willing to try new stuff if it gives me less chance of call-back, and this new membrane looks good stuff.
Any input/experience/advice is welcome.

Tile store is recommending cement board for floor.
Any input/experience/advice is welcome.

Also installing electric radient heat pads - Any input/experience/advice is welcome.
There's some top class people on this forum,........and then there's me

R&D Tile · 02-08-2006, 07:55 PM

CDX isn't an acceptable grade of plywood for under tile, if you have to leave it, the only wat I would do this, is a full mud job with roofing felt and wire lath, mud 1 1/4" thick.

Nothing out there can beat a mud job.

You can probably also get away with another layer of 3/4" ext.grade AC or BC over it, then a CBU or membrane of choice.

3/4" is bare minimum for a subfloor for tile, wood between the joists addresses the flex there, the joists themselves determine the overall flex in the whole floor, your fine there.

**Floorwizard** · 02-08-2006, 08:08 PM

Actually the bare minimum is 1 1/18. That is IF your using the correct plywood.

R&D Tile · 02-08-2006, 08:14 PM

That has been an on going debate for a awhile now now, as to what makes up that height, all CBU manufacturers warrantee there CBUs over 3/4" ply as does Ditra, but they say to use 1/2" cementboard, even though it adds no strength to a subfloor, 1/4" is for floors and can be used instead, I personally won't tile over a single layer wood floor and give a guarantee.

That is for 16" joist spacing, anything wider has to have 2 layers of wood, the top layer being sheet plywood or OSB, same as single layer floors, yuo can only go over plank flooring with a mud job, CBUs must be installed over Plywood or OSB, same with membranes.

Hope this helps.

mjay · 02-08-2006, 08:35 PM

Thanks for the prompt replies. Yes, there are a lot of opinions on materials and methods.
It's good to hear healthy debate.
Still looking for opinions on the membrane applications, and electric radient heat pads.

**Floorwizard** · 02-08-2006, 09:00 PM

I love debates. I always learn a thing or 2.

I was using the T.C.A. as my guide. But I would break from their rules in my own home in some cases.

R&D Tile · 02-08-2006, 09:17 PM

Quote:

Originally Posted by Florcraft

I love debates. I always learn a thing or 2.

I was using the T.C.A. as my guide. But I would break from their rules in my own home in some cases.

Just Curious where it states that, I have the 03 to 04 book, it shows single layer plywood as minimum under CBU and membranes for 16" on center.

Still wouldn't do it though, more is better.

**Floorwizard** · 02-08-2006, 10:22 PM

I will have to check at work.
What page?

Tom R · 02-08-2006, 11:22 PM

Don't know where it's written (besides in my head), - - but it was always 'minimum' of 1 1/4" built-up wood for under tile, - - as of about 10 years ago it conveniently (for contractors?) got changed to 1 1/8", - - I still stick to the 1 1/4".

I would think that anything stating 3/4" is either a mis-print or a mis-understanding. Think about it.

I guess it's 'possible' someone is stating you could use 3/4" plywood as long as (and only as long as) you ALSO were adding 1/2" CBU.

Mike Finley · 02-08-2006, 11:36 PM

Quote:

Originally Posted by mjay

Installing tile over 3/4' cdx. Always used 15lb felt - wire mesh - mud - tile. Floor is solid {2*10' 16o.c 8" span}. Don't expect movement, but always willing to try new stuff if it gives me less chance of call-back, and this new membrane looks good stuff.
Any input/experience/advice is welcome.

Unless I am missing something I don't see any big deal here.

1/4 hardi, electric heat then tile, as always I would be using FlexBond thinset.

or

Ditra, electric heat, then tile.

You said the floor has no flex right?

R&D Tile · 02-09-2006, 06:47 AM

Quote:

I guess it's 'possible' someone is stating you could use 3/4" plywood as long as (and only as long as) you ALSO were adding 1/2" CBU

I agree, all CBU manufacturers and even Ditra can be used over single layer 3/4" plywood, therefore the 3/4" minimum, yes, adding 1/2" brings it up to the 1 1/4".

Ditra can be used over 3/4" OSB or plywood & CBUs DON'T add any strength to a subfloor, more plywood does, Hardie says it's 1/4" CBU can be used over 5/8" minimum sheet plywood, in other words that 1 1/4" means nothing, it's what's under the CBU or a membrane that counts first.

Remember, you first have to meet the strength in the joist system, L/360 for ceramic & L/720 for stone, the joist system dictates the overall flex in the floor, plank flooring and sheet products only help strengthen the flex in a floor between the joists.

All of that said, as long as the joists system is fine, I always add a layer of 1/2" plywood over all single layer subfloors, before adding a CBU or Menbrane, unless, doing a full mud job.

R&D Tile · 02-09-2006, 06:58 AM

Quote:

Originally Posted by Florcraft

I will have to check at work.
What page?

Check the specs on pages 21 on, read prep by other trades, single layer of plywood or OSB is used, yes with the CBU it brings it up thicker, I'm just stating the minimum needed subfloor before adding a tile backerboard, membrane or mud job.

As said above, someone who reads the 1 1/4" minimum thinks their floor might be stronger, but it's not, unless that is all wood and not CBUs in the mix, hope this makes sense.

firemike · 02-09-2006, 11:09 AM

Quote:

Originally Posted by Tom R

Don't know where it's written (besides in my head), - - but it was always 'minimum' of 1 1/4" built-up wood for under tile, - - as of about 10 years ago it conveniently (for contractors?) got changed to 1 1/8", - - I still stick to the 1 1/4".

I would think that anything stating 3/4" is either a mis-print or a mis-understanding. Think about it.

I guess it's 'possible' someone is stating you could use 3/4" plywood as long as (and only as long as) you ALSO were adding 1/2" CBU.

I have the same minimum floating here in my head for an all-wood base, plus I was always taught that the minimum final layer of wood should be no thinner than 1/2" (3/4" + 1/2" = 1 1/4").

**Floorwizard** · 02-09-2006, 01:09 PM

R&D,

I hear what you are saying. Sounds like you know what your talking about. There is a paver question I would like to hear your thoughts on. It has just been posted.

R&D Tile · 02-09-2006, 01:47 PM

Quote:

Originally Posted by Florcraft

R&D,

I hear what you are saying. Sounds like you know what your talking about. There is a paver question I would like to hear your thoughts on. It has just been posted.

Can't find it.

mjay · 02-09-2006, 04:05 PM

O.K. It will take me a moment to digest all that. But, Does everybody agree to 'No, to CDX'.
I have installed an 'Uber' OSB in other homes, (used as a finished floor) and was very impressed with the quality of the material.Before people shout Noooooo to an OSB sheathing the specs are impressive -

Panel deflection 0,106 inch at 330psf. at 24" o.c.

Thickness Swelling 3.5% after submersion for 24hrs.

MOE 250psi [load required between two joists for deflection]

MOR 7psi
Comes with 50 year warranty.
I'm looking for further info from company for suitabilty for this application, and researching the reasons to add another layer of sheathing to the floor. This is the ground floor with 2*10" - 16" o.c. 8' spans sitting on masonary walls, I haven't done the math but I'm confident it surpasses the L-720 (and yes i will do the math to be sure).

Someone, mentioned Ditra and any tips or advice would be helpful. I understand the radient pads go under the Ditra.

Tile is not my speciality, and I appreciate all your opinions.

Bill_Vincent · 02-09-2006, 04:12 PM

Over 3/4" subfloors, just about ALL manufacturers will warranty even 1/4" CBU. Over 5/8" subfloors, then it has to be 1/2".

Tom R · 02-09-2006, 04:17 PM

Quote:

Originally Posted by firemike

I have the same minimum floating here in my head for an all-wood base, plus I was always taught that the minimum final layer of wood should be no thinner than 1/2" (3/4" + 1/2" = 1 1/4").

Yep, - - that's how I've always done it.

R&D Tile · 02-09-2006, 05:00 PM

Quote:

Originally Posted by mjay

O.K. It will take me a moment to digest all that. But, Does everybody agree to 'No, to CDX'.
I have installed an 'Uber' OSB in other homes, (used as a finished floor) and was very impressed with the quality of the material.Before people shout Noooooo to an OSB sheathing the specs are impressive -

Panel deflection 0,106 inch at 330psf. at 24" o.c.

Thickness Swelling 3.5% after submersion for 24hrs.

MOE 250psi [load required between two joists for deflection]

MOR 7psi
Comes with 50 year warranty.
I'm looking for further info from company for suitabilty for this application, and researching the reasons to add another layer of sheathing to the floor. This is the ground floor with 2*10" - 16" o.c. 8' spans sitting on masonary walls, I haven't done the math but I'm confident it surpasses the L-720 (and yes i will do the math to be sure).

Someone, mentioned Ditra and any tips or advice would be helpful. I understand the radient pads go under the Ditra.

Tile is not my speciality, and I appreciate all your opinions.

CDX is the lowest grade of ext. grade plywood there is, if you even want to call it ext. grade, too many voids and rough, use AC or BC grade for subfloors getting tiled.

**Floorwizard** · 02-09-2006, 08:29 PM

Never CDX is my 2 cents.