# OSB subfloors



## angus242 (Oct 20, 2007)

This has been confusing me for awhile. It's not so much of an issue for me with CBU over OSB as I don't use the stuff but definitely a concern with Ditra over OSB. Schluter specifically states Ditra can be used over OSB. However, what thinset do you use?

I have not taken the time to investigate every option from every manufacturer. But the ones that I have looked into never say it's OK to use them over OSB. Mapei goes as far to state it's not OK to use some of their thinsets over OSB. All of the others that I've checked out never specifically say OSB is OK but they will unequivocally say EGP plywood is fine.

So, what do you guys use over OSB. What if the TDS spells out materials specifically but omits OSB as an approved substrate? My fear is one day I'll have an OSB install lose bond and end up eating the repair as Schluter would blame the thinset and the thinset manufacturer can say, OSB is not on the list of approved materials to install over. Currently, I've been adding a layer of 1/2" EGP to any proposal with an OSB subfloor but with the added cost, I don't ever land those jobs. Too many bilingual guys will do the job minus the EGP with $4/bag Keraset (which specifically says NOT to use over OSB) for a lot cheaper.

:blink:

So, anyone know of a thinset brand/manufacturer that specifically has OSB listed as an approved substrate?


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## neolitic (Apr 20, 2006)

Can't answer you directly
(and I had to Google EGP)
but what about 1/4" baltic birch
underlayment, like FlorPly,
instead of 1/2" BCX?


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## angus242 (Oct 20, 2007)

Sorry :blush:
EGP = exterior glue plywood

Neo, I really don't believe any 1/4 wood underlayment is acceptable for tile. I suppose I could always 1/4 CBU but that stuff's a bigger pain than installing the ply.


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## neolitic (Apr 20, 2006)

angus242 said:


> Sorry :blush:
> EGP = exterior glue plywood
> With plywood, X is exterior to me.
> 
> ...


It is supposed to be.
I have used it for linoleum
and vinyl, and with thinset
under Durock and Hardi.
Can't find their site right now,
but this stuff is pretty much the same.
http://www.halexcorp.com/halex_underlayment_4.shtml
I'd trust the baltic birch before I'd
trust YP BCX.


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## jarvis design (May 6, 2008)

I have done a few floors in the last couple of years on OSB. I don't trust the stuff so I screwed down 3/8" EGP, then ditra.


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## neolitic (Apr 20, 2006)

Here's another,
http://www.floor-ply.com/floor-ply/specs.htm

I wonder where you guys buy ply?
Is it stamped AC-EGP, or ACX?


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## Kent Whitten (Mar 24, 2006)

Neo is right guys. "x" as in ACX or BCX. 

We use 1/4" sureply for underlayment which I believe is like what Neo says, Baltic Birch. 

Never ever use SYP, not even OSB with SYP chips.


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## angus242 (Oct 20, 2007)

neolitic said:


> Here's another,
> http://www.floor-ply.com/floor-ply/specs.htm
> 
> I wonder where you guys buy ply?
> Is it stamped AC-EGP, or ACX?


It's tile speak. Throughout the TCNA Handbook, it's referred to as EGP.

Yes it's marked/stamped A/C where I buy it. Can't be positive they use the X. But wouldn't doubt it's on there.


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## neolitic (Apr 20, 2006)

Tile speak!








Seriously, look at that last link.
Yellow pine absolutely sucks for stability.
Baltic birch is stable, they
use more plys, no voids,
and absolutely the best grades
of exterior glues.
Fir ply wood is the only thing
even close, and it ain't that close.
You have Menards, right?
They carry the FlorPly brand in 
4X8s.


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## WarnerConstInc. (Jan 30, 2008)

Everything is OSB around here.

There are pictures of them installing Ditra over OSB right on their site and in their installation guide.


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## angus242 (Oct 20, 2007)

I'll check it out when I get home. I'm on my phone waiting for the slake.


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## neolitic (Apr 20, 2006)

WarnerConstInc. said:


> Everything is OSB around here.
> 
> There are pictures of them installing Ditra over OSB right on their site and in their installation guide.


All my floor guys are over
the flippin' moon when I put
BB down for them.
Never used it for direct to tile,
but I'd but that before OSB or SYP.
Don't even want to know about 
this Radiata stuff that's popping up everywhere...


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## WarnerConstInc. (Jan 30, 2008)

neolitic said:


> All my floor guys are over
> the flippin' moon when I put
> BB down for them.
> Never used it for direct to tile,
> ...


I have put down the 4x4' BB underlayment before.

Not sure what kind it was but, it was not cheap.


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## neolitic (Apr 20, 2006)

It's good, and it's fast....
Two out of three is the best
I can ask for.











ETA:
4X5 $17
4X8 $20
Not bad by my lights.


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## angus242 (Oct 20, 2007)

WarnerConstInc. said:


> Everything is OSB around here.
> 
> There are pictures of them installing Ditra over OSB right on their site and in their installation guide.


Right but now tell me what thinset is approved & warranteed over the OSB :whistling


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## rbsremodeling (Nov 12, 2007)

angus242 said:


> Right but now tell me what thinset is approved & warranteed over the OSB :whistling


Which one isn't?


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## neolitic (Apr 20, 2006)

angus242 said:


> .......... But the ones that I have looked into never say it's OK to use them over OSB. *Mapei goes as far to state it's not OK to use some of their thinsets over OSB. *All of the others that I've checked out never specifically say OSB is OK but they will unequivocally say EGP plywood is fine.
> ...........
> So, anyone know of a thinset brand/manufacturer that specifically has OSB listed as an approved substrate?


That one?


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## PrecisionFloors (Jan 24, 2006)

Neo is on target here. Halex lists tile specifically in their literature. If you've ever installed it, you would feel comfortable tiling over it (with a suitable tile underlayment of course). Very, very, void free. I use my TS-55 to slice it up and install with narrow crown 1" staples 3" on perimeter and 4-6" on field.

All that bein said, I've installed tons of Ditra over OSB with VersaBond with 0 issues or callbacks.


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## ROVACON (Apr 19, 2010)

Angus-

Fortunately for me, I have access to Ditra Set. However, i never apply the DITRA with any other thinset to OSB. I always add plywood and it is a minimum of 1/2 T/G but typically 5/8 if i have the room. Glued and screwed every 6'' f course. :thumbsup: I also always tell this to the potential homeowner and give them the literature as well. In the end, they get what they pay for...right?!?!


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## angus242 (Oct 20, 2007)

OK folks, Halex 1/4" is not acceptable for tile underlayment. 

The 3/8" version is. After digging around some TCA stuff, looks like you need a minimum of 7 plys before TCNA will endorse it.

Rory, like I said, most of the Mapei thinsets I use specifically say NOT to be used over OSB. After digging around, I also noticed while most manufacturers don't say OSB is not allowed, I have yet to see ONE that says it is an acceptable substrate. They will go out of their way to mention other materials (EGP, vinyl, concrete, etc). 

Even Ditraset makes no mention of OSB or describes anything like OSB....just EGP.

I guess more investigating is necessary. :detective:


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## PrecisionFloors (Jan 24, 2006)

Sometimes I just use experience and personal knowledge to trump a manufacturer :whistling....but I'm a professional - don't try this at home kids :laughing: We _all_ know that 99% of the time their warranties ain't worth the recycled paper their printed on. Sometimes I think you guys get a little _too_ carried away with having to see it written down somewhere to make you feel all squishy inside. Common sense is still free :thumbsup:


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## angus242 (Oct 20, 2007)

I know what you mean Paul


but


How come no manufacturer of thinset specifically says OSB is an OK substrate? How come OSB is not mentioned in the TCNA as an approved substrate?

Yeah, I read all the "_I've done it that way 100's of times without an issue_" comments but if it's _really _an OK substrate, how come any of the companies that put tons of $$$ into testing this kind of stuff never say "It's been tested and is acceptable"?

Warranty be damned....


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## PrecisionFloors (Jan 24, 2006)

I wish I had an answer for ya man, I really do. The first time I had to do it I called Schluter. Not only was it OSB but it was on 19.2" centers :blink: Big Orange gave me the go ahead using modified thinset....I did it, had no issues, and collected the check. I made damned sure I had proper coverage and the fleece was embedded well. What else could I do? Since then I have been back on two different ones and had to pull some tile. One was a cracked tile due to the husband dropping a 4lb baby sledge and the other was a full bath tear out for a re-model (decided to re-model the whole bath after I did just the floor a year or so earlier). Both were stuck like Chuck who just didn't give a **** :laughing: No cracking, no grout cracking, no bond issues whatsoever.


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## angus242 (Oct 20, 2007)

I mean am I really crazy when the TDS of the thinset singles out OSB?

ok, don't answer that


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## PrecisionFloors (Jan 24, 2006)

Yeah, but playin devil's advocate here....they also say vinyl is a perfectly good substrate for tile :whistling

When are they full of **** and when are they not :laughing:

Not disagreeing with ya - just sayin.


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## angus242 (Oct 20, 2007)

I hear ya. I guess I thought when I asked the question, the answer would be out there. Apparently, it's not. 

I don't see OSB very often but I know it will most likely be a long time before I contract one of those jobs. Adding _something _on top of the OSB will over price myself almost every time. :sad:


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## PrecisionFloors (Jan 24, 2006)

angus242 said:


> I hear ya. I guess I thought when I asked the question, the answer would be out there. Apparently, it's not.
> 
> I don't see OSB very often but I know it will most likely be a long time before I contract one of those jobs. *Adding something on top of the OSB will over price myself almost every time.* :sad:


Of that, I can guarantee you :sad:

Ask me how I know


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## Anderson (Sep 7, 2009)

Wouldn't the reason no one is endorsing an OSB install be because there is such a large possible variance in exact structural properties of a piece of OSB from one to another.


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## PrecisionFloors (Jan 24, 2006)

Would make sense Anderson.


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## Zack78 (Dec 1, 2009)

latex p.c.mortar on osb unmodified thin-set mortar on ditra


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## Zack78 (Dec 1, 2009)

You can always call your schluter rep


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## Zack78 (Dec 1, 2009)

what is your joist spacing? if is 16 o.c. than minimum subflor thickness-19/32", 5/8" nom. T&G with 1/8"gap between sheets. If you add another pl or osb there is a specific way to do it but no glue between them


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## angus242 (Oct 20, 2007)

Zack78 said:


> latex p.c.mortar on osb unmodified thin-set mortar on ditra


Did you read the question. WHAT thinset?????????????????


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## angus242 (Oct 20, 2007)

Zack78 said:


> You can always call your schluter rep



Schluter does not make thinset. :no:


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## JazMan (Feb 16, 2007)

All the thin set manufacturers tell us not to bond tiles to OSB. When you install Ditra over OSB you are not bonding tiles to OSB, you're bonding Ditra to OSB. Makes a big difference. 

Latex modified thin sets stick very well to OSB, possibly even better than to ply, it's just not as stable. Ditra takes care of that. I don't see what the problem is.

Jaz


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## Bud Cline (Feb 12, 2006)

JAZ is spot-on.

The limitations that are being referred to are for installing ceramic and stone "tile" directly to those materials. You should not try to install tile basically because of its smaller dimensions. The limitations are not referring to the larger dimension sheet goods such as DITRA or cement boards. 

I think too often installers want to have some kind of warranty to lean on or point to or maybe collect on if something happens down the road. The sorry facts are my friends: "It's your baby". Rarely are you going to come out on any kind of warranty the makers are offering. Most of those warranties are simply "feel-good" offerings used in a marketing effort to trump a competitor. Every mainstream product on the market today is a good product if installed properly and common sense is used. Very few products from mainstream companies experience failures due to a flaw in the manufacturing process. It just doesn't happen. Installer shortcomings are responsible for 95% (or more) of the failures that exist these days.


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## angus242 (Oct 20, 2007)

Still, no one has answered the question.

I would assume _most _installers use CBU over the subfloor. A few might use a membrane over the subfloor. An even fewer might bond directly to the subfloor. Regardless of what's used, I'm fairly certain the manufacturers are aware of the current trends.

So based off those assumptions (argue with them if you will) why is there not one supplier of thinset that I can find that says you can use their product over OSB S-P-E-C-I-F-I-C-A-L-L-Y; regardless if there's an underlayment above it or the tile is laid direct on top of it?

:sad:


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## Bud Cline (Feb 12, 2006)

I wonder if in the case of OSB, the manufacturers want to maintain some distance from any failure exposure and leave themselves with a window of deniability. Therefore if it isn't written on the bag (to be OK by them) the user assumes all responsibility.


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## rbsremodeling (Nov 12, 2007)

angus242 said:


> OK folks, Halex 1/4" is not acceptable for tile underlayment.
> 
> The 3/8" version is. After digging around some TCA stuff, looks like you need a minimum of 7 plys before TCNA will endorse it.
> 
> ...



I mis-read the question.. I was wrong.. your on the right track and correct on your observations.. I personally distrust osb and never use it for anything..


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## Zack78 (Dec 1, 2009)

Schluter does not make thinset. :no: durabond d-25 ditraset, durabond d-25 ditraset (mixed with d-l 16 over pla or osb


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## Anderson (Sep 7, 2009)

Ditraset is not made by Schluter. They just let them use the name ditra on the bag.


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