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 02-20-2020, 08:03 PM   #1
soloracer
Registered User
 
Join Date: Feb 2020
Posts: 9
Subfloor - Uneven OSB

Hello,

This is my first post. I couldn't be more green about this stuff so I'm researching every step of the way. I also have a friend helping with a good deal of remodel experience but neither of us have a tile background.

So here's the scoop Small bathroom remodel (5x7) - I checked the Deflecto tool and we are good there. I just need to figure out our next step with the floor. The plan is to use Ditra heat but we need to flatten the floor first and I suspect we need another layer of subfloor.

A contractor put down 3/4" OSB, glued and nailed to the joists - no gap between the 2 sheets but plenty around the edges. This was done as a "favor" during another project and they didn't ask what I wanted. I would have spec'd plywood.

-First issue is that from the center of the room to the left corner (see pic), the floor drops 1/2" Most of that drop will be under the cast iron shower pan and that pan can be shimmed so strictly speaking we wouldn't have to tackle that but I would prefer to level the whole floor.

Questions:

-Do we use SLC to level over the OSB? Is 1/2" too much for this?

-Do we need a layer of plywood over the OSB and if so would it be best to level after laying that down? It was posited that we could use SLC between layers but something about that seems weird to me.

-Do we then need cement board over the plywood before putting down the Ditra heat or could we choose between cement board and plywood?

Sorry for the lengthy post. I've been searching and reading but this seems kind of unique.

Thanks!

Sorry for the sideways pic. The OG isn't rotated and I couldn't figure out how to fix it!
Attached Images
 
__________________
DJ
soloracer is offline   Reply With Quote
Sponsored Links
Unread 02-20-2020, 08:29 PM   #2
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 89,584
Welcome, DJ.

I'd ask your contractor to stop doing you favors. The optimum time to flatten or/and level that floor would have been before installing the subfloor.

You don't indicate your joist spacing nor whether the OSB was tongue & groove edge style. You may not need a second layer of subflooring, but it may still be a good idea.

If you elect to use a SLC to level and flatten the floor, you must read and follow the manufacturer's instructions. Most require a primer of some sort and most require reinforcing lath and have a minimum required thickness. Some may not want you to install over OSB. If your floor is flat, I would recommend you simply shim your CI shower receptor as necessary and leave the subfloor alone.

You absolutely do not want to put the SLC between layers of subflooring.

Please go to the Schouter website and download the installation instructions for the DitraHeat product you intend to use. There is no need to add a CBU to your subfloor if you use that product.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is offline   Reply With Quote
Unread 02-21-2020, 09:31 AM   #3
soloracer
Registered User
 
Join Date: Feb 2020
Posts: 9
I kicked that contractor out of my house. To say everything they did was half-baked would be to give them 25% more credit than they deserved. I could write a book!

House is 104 years old. Joists are 2x8, 16" centers, 11' span. 2 of the joists under the bathroom are sistered to old joists over about 40% of their length and one is doubled-up for the whole 11ft span.

OSB is not T&G, just 2 sheets, butted together. I'm totally fine with a layer of plywood but the tile is kind of thick (7/16")s o I'd prefer to keep it on the thin side if possible. I just want to do it right/once.

The floor outside the shower pan, where the tile will go is about 5x5 and not flat but not too far off. The problem area is in the corner under the shower pan.

Thanks for your help. I actually should have realized I wouldn't need CBU. I understand what Ditra is, I just have too many things in my head at once right now!
__________________
DJ
soloracer is offline   Reply With Quote
Unread 02-21-2020, 11:37 AM   #4
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 89,584
Depending upon the species and grade of your joists, you may or may not qualify for a ceramic tile installation. Are the joists full dimension 2x8 inches?

If you have access to the under side of that floor such that you can install blocking for those non-T&G joints, you should do that. Otherwise you have a serious problem for a ceramic tile installation.

If not, I would consider the second layer of subflooring mandatory and would want nothing less than nominal half-inch exterior glue plywood and I would want to pre-drill and screw it on both sides of that non-T&G joint such that the edges of the bottom layer are pulled tightly against the bottom of the new layer. Still not optimal, but it might work OK.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is offline   Reply With Quote
Unread 02-21-2020, 11:48 AM   #5
jadnashua
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

 
Join Date: Jul 2004
Location: Nashua, NH
Posts: 13,347
Should you add a layer of plywood, you'd want to ensure you've offset it from what's below so no joints line up. Ideally, the end would be about 3" or so beyond a joist. And, you don't want your screws to hit the joists. There's an article in the 'Liberry' (sic) that describes how to attach it properly.

Ideally, the first layer would have also had construction adhesive applied so the bond to the joist was reinforced. WHen that happens, the fasteners are more of a glue clamp than final strength.
__________________
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 02-21-2020, 12:58 PM   #6
soloracer
Registered User
 
Join Date: Feb 2020
Posts: 9
OK so I just went and took another, closer look at everything (I do have access to the underside).

I was wrong about a couiple of things:

-The OSB is T&G. I couldn't tell from above but it was obvious from below.

-There are 4 joists under the bathroom. The sistered joists - the old joists cover 70% of the span (90/132"). The middle 2 joists are like this and there is one nearest the foundation that is solo. The joist at the other side of the room (under the wall that separates the bath from kitchen) consists of a sandwich of 2 full-length joists with a layer of OSB in between.

The joists are not full-dimension, which makes them 1.5" x 7.25" Southern pine. #2 grade. Max span recommended for a floor joist is 11' 10" so I'm close but think I should be OK.
__________________
DJ
soloracer is offline   Reply With Quote
Unread 02-21-2020, 01:08 PM   #7
soloracer
Registered User
 
Join Date: Feb 2020
Posts: 9
@jadnashua

Thanks for the advice. The contractor told me they used glue. Not sure I would be able to verify. I understand on the plywood direction - makes sense.
__________________
DJ
soloracer is offline   Reply With Quote
Unread 02-21-2020, 01:10 PM   #8
soloracer
Registered User
 
Join Date: Feb 2020
Posts: 9
If adding !/2" plywood over the OSB makes everything better, I think I have room for that. I would only be hesitant to do so if it will require a significant step up to the bathroom from the level of the floor outside. I've yet to really figure all that out.
__________________
DJ
soloracer is offline   Reply With Quote
Unread 02-21-2020, 01:53 PM   #9
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 89,584
Your current subflooring currently meets the minimum requirements for all manufacturers of ceramic tile substrates of which I'm aware. More that is not technically required, but certainly makes for a better subfloor. And plywood makes a better bonding surface if you elect to use a membrane rather than a CBU.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is offline   Reply With Quote
Unread 02-21-2020, 02:33 PM   #10
soloracer
Registered User
 
Join Date: Feb 2020
Posts: 9
Great! So you wouldn't bother flattening the corner then, correct? Just level out where the tile is going and be done?
__________________
DJ
soloracer is offline   Reply With Quote
Unread 02-22-2020, 07:02 AM   #11
ss3964spd
Moderator
 
ss3964spd's Avatar
 
Join Date: Jul 2005
Location: Fairfax, Va
Posts: 2,792
Send a message via Yahoo to ss3964spd
If you can effectively shim your CI shower pan in such a way that it is well supported that's what I would do, DJ, then just deal with the 5'X5' section. How best to shim it is hard to say without seeing the bottom of it.

If you can squeeze in the extra 1/2" ply definitely do so. As for the OSB being glued down; if you look closely at the joists from the bottom you should see some glue squeeze out somewhere along their lengths If there is no evidence of glue anywhere the contractors claim is dubious.
__________________
Dan
---------------------------------------------------------------------------------
If I recall correctly my memory is excellent, but my ability to access it is intermittent.
ss3964spd is offline   Reply With Quote
Unread 02-22-2020, 09:57 AM   #12
soloracer
Registered User
 
Join Date: Feb 2020
Posts: 9
Thanks. Good advice on the glue. If it's just nailed, perhaps we can fix it properly.
The shower pan is designed to be shimmed and has pylons on the underside for this purpose. That said, I think I'll put down ply anyhow.

Just purely for my understanding, is there a technical reason to not use SLC between layers to get the ply level?
__________________
DJ
soloracer is offline   Reply With Quote
Unread 02-22-2020, 10:43 AM   #13
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 89,584
You mean other than the fact that it will likely shatter when you drive fasteners through the top layer of plywood, DJ?

If you want to use a SLC, use it per the manufacturer's instructions on top of your subflooring or on top of your CBU if used.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is offline   Reply With Quote
Unread 02-22-2020, 10:59 AM   #14
soloracer
Registered User
 
Join Date: Feb 2020
Posts: 9
I have no prior experience with self leveling concrete so didn't know that would be the result. Makes sense though. I just wanted to understand the 'why' behind the admonition.
__________________
DJ
soloracer is offline   Reply With Quote
Unread 02-22-2020, 11:00 AM   #15
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 89,584
Knowing the whys is always helpful, DJ.

Some SLCs are harder than others when cured and you may be able to get by sandwiching some of them between screwed down plywood layers, but I'd bet against it every time.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx 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
Uneven subfloor twack26 Tile Forum/Advice Board 4 11-26-2012 10:52 PM
Uneven subfloor fix? jdeveny Tile Forum/Advice Board 2 05-12-2010 04:29 PM
Uneven subfloor PA_DIY Tile Forum/Advice Board 6 04-13-2006 10:15 PM
A little uneven subfloor chrishallowell Tile Forum/Advice Board 2 04-24-2002 05:39 PM
subfloor uneven, what do i do? mitcheal Tile Forum/Advice Board 10 11-02-2001 06:55 AM


All times are GMT -6. The time now is 11:56 PM.


Sponsors

Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright 2018 John Bridge & Associates, LLC