Ceramic Tile Advice Forums - John Bridge Ceramic Tile

Welcome to John Bridge / Tile Your World, the friendliest DIY Forum on the Internet


Advertiser Directory
JohnBridge.com Home
Buy John Bridge's Books

Go Back   Ceramic Tile Advice Forums - John Bridge Ceramic Tile > Tile & Stone Forums > Tile Forum/Advice Board

Sponsors


Reply
Thread Tools Search this Thread
Unread 01-28-2015, 11:35 AM   #1
s10apl
Registered User
 
Join Date: Jan 2015
Posts: 2
Thinset between OSB and plywood?

Hey folks, first-time poster here. I've spent several days researching this question to avoid posting a question that's already been answered, but have come up with nothing... so here goes.

Want to tile the master bath in my new house (new construction). Engineered 2x4 trusses, 19" OC, deflection way good for ceramic. 3/4" T&G OSB subfloor with correct axial orientation (perpendicular to truss).

Plan to use Ditra membrane under ceramic tile. Would like to use warm tile heating wire, too. Want to keep all additions (subfloor, mat, wires, thinset, and tile) to an inch.

My plan (OSB up) is: 1/2" plywood, thinset, Ditra, thinset/heating wires, tile. I want plywood instead of CBU because I want added stiffness from the plywood to combat the inherrent springiness of the OSB.

My question pertains to installing the plywood. I understand why adhesive doesn't work and may actually make things worse. And I undertsnad that thinset under CBU is not for adhesion, but for stability. Then why wouldn't we use thinset under the plywood too?? Plywood is less uniformly flat than CBU. Why does everyone just screw it to the OSB?

And intuitively, it seems I could help the thinset stay uncoupled from the OSB by starting with roofing felt, then putting the thinset and plywood down over that?

Am I on the wrong track entirely, and should I just plop the plywood down (with correct orientation and staggered joints of course) and quit my fretting?

Thanks for any help!

Scott
__________________
Scott
s10apl is offline   Reply With Quote
Sponsored Links
Unread 01-28-2015, 11:51 AM   #2
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 95,342
Welcome, Scott.

Here is a good article from our Liberry on what I consider the very best way to install that second layer of subflooring.

Layering the structural subflooring you want to take advantage of the friction between the two sheets as well as the inherent stiffness of each layer. You don't want anything between the layers to compromise that.

There is no more "inherent springiness" in OSB than in plywood subflooring, but with your 19.2" joist spacing I'm very much in favor of a second layer of subflooring.

The CBUs have no real structural strength of their own and any gaps between them and the subfloor would be a very flexible area even with the required mechanical fastener schedule. That's why they require a bed of thinset mortar under them.

If you use an electric radiant heating system and Ditra, you want the Ditra on top. But I would suggest you look at the Ditra Heat system and incorporate both in one layer, thus reducing your overall floor height and making the heating installation easier.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is offline   Reply With Quote
Unread 01-28-2015, 07:04 PM   #3
cpad007
hack of some trades
 
cpad007's Avatar
 
Join Date: Feb 2013
Location: San Jose, CA
Posts: 1,245
I used the Ditra-Heat in my tile install, Scott. It is likely the most expensive way to go in terms of floor-warming but it really is a breeze to install. It is further a breeze to take up and reinstall and take up and reinstall again on accounta you keep messing up where things are supposed to end or not with the wire. Finallly, it works beautifully! Warm tiles...can beat 'em.

Check out the link below my sig for my thread.
__________________
Chris

DIYer-us Extrem-us Non-Pro-us

Chris' Orange Tile Project
cpad007 is offline   Reply With Quote
Unread 01-28-2015, 07:12 PM   #4
jadnashua
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

 
Join Date: Jul 2004
Location: Nashua, NH
Posts: 14,923
FWIW, not all OSBs are created equal. FOr example, Advantec's typically tests out at 10% stiffer than the same thickness plywood.
__________________
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
jadnashua is offline   Reply With Quote
Unread 01-29-2015, 08:42 AM   #5
s10apl
Registered User
 
Join Date: Jan 2015
Posts: 2
Thanks, everyone- much appreciated! I love it when things make sense... due to the iffy performance of adhesives I had given up on adhesion in building up the subfloor, and ignored friction. I get now why floating another layer of plywood on thinset wouldn't add as much stiffness as screwing a layer directly over the OSB.

And good to know more about the OSB itself.

I'll check out the integrated Ditra / wire, too. We live in central Minnesota and as far as I'm concerned, warm floors are the only way to keep these bones thawed. First floor is slab on grade with hydronic loops... looking forward to that, too!!
__________________
Scott
s10apl is offline   Reply With Quote
Reply

Stonetooling.com   Tile-Assn.com   National Gypsum Permabase


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
osb vs plywood mae t Tile Forum/Advice Board 1 02-07-2012 07:37 PM
OSB + Plywood? UberDave Tile Forum/Advice Board 5 07-10-2010 11:21 AM
3/4 Ext plywood vs. 3/4 OSB WalleyesAndTNT-MN Tile Forum/Advice Board 10 07-04-2009 11:23 AM
OSB, Advantech, or plywood busher Tile Forum/Advice Board 2 11-30-2007 03:51 PM
plywood or osb?? floydturbor Tile Forum/Advice Board 1 06-07-2004 10:22 AM


All times are GMT -6. The time now is 02:22 AM.


Sponsors

Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
Copyright 2018 John Bridge & Associates, LLC