Tiling over OSB Sturd-I-Floor?

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  #1  
Old 01-14-07, 03:02 PM
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Angry Tiling over OSB Sturd-I-Floor?

Need help, please! I am desperate!
I have done a lot of research on this subject, but I am still in a quandary about how to proceed. I would like to put tile in 2 rooms of a home that was built with subfloors consisting of 2 layers of 19/32" OSB Sturd-I-Floor over 16" centers. I have purchased Schluter Ditra as a tile-backer in order to keep the transition at a minimum to adjoining laminate floors. I hit a road block when trying to select a compatible thinset for the OSB. Nobody to my knowledge makes one. Someone suggested using Redgard on the OSB to seal it prior to using thinset. If that is the way to go, then I need to know which thinset to use (latex-modified, or un-modified). Schluter recommends using the un-modified between the tile and the Ditra. If the thinset is also trapped between these 2 moisture-impervious layers (Redgard and Ditra), then I am thinking that I should use un-modified for the lower layer as well.

Is this correct, or does anyone know of a better solution altogether???

Thanks!
 
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Old 01-14-07, 03:22 PM
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I am sorry to say, you cannot lay Ditra over osb it will void your warranty, plywood only.Get your money back and go with 1/4 hardibacker.
This will elimate a lot of your questions.

Use a unmodified thinset when laying Hardi over osb, be sure to sand your osb joints level first. Dont skimp on the thinset, and let dry over night before installing tile, just to be safe. Nail it off with a roofing nailer on 4-6 inch pattern.

I dont like using 1/4 over osb but they say you can do it and I have done it the past when required to do so.


Not that it matters now; but when laying Ditra you use modified over plywood, this is the reason thet osb will not work, the moisture in the modified thinset will permeate the osb before it drys and could cause swelling.

Redgard is really moot in this application unless you want it as a moisture barrier, or you can run your joints in the osb with a fiberglass tape and redgard.
But you can save yourself the money on a gallon of regard and just run the joints with mesh tape and thin set.
 
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Old 01-15-07, 12:57 PM
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Money Pit

Go to the Schluter website and read about ditra. I have their 2005 handbook which I refer to on a regular basis. According to the handbook, you can indeed use ditra over osb. I have not personally done this, but Schluter says you can. So heres my suggestion. Call Schluter, they have some good technical people that will answer your questions.

Schluter-Systems Technical Support, United States
Tel: 1-800-472-4588, Fax: 1-800-477-9783
 
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Old 01-15-07, 02:15 PM
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Money Pit

If you get an answer from Schluter, please post back and let us know what they say.

Bostik makes Ditra Set which is a thinset designed for use with Ditra. My understanding is that they are somehow tied in with Schluter on this project. I havent used Ditra Set but was reading up on it a little. I would appear to be a dry set mortar than can be mixed with water or can be mixed with one of Bostik's additives. Theres no mention of osb though.

http://www.bostik-us.com/TDS/TDSFiles/D25DitraSet.pdf
 
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Old 01-15-07, 02:27 PM
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OK an update

I did some reading and research on some other forums. Apparantly you can use most modified thinsets to bond ditra to osb. What thinset manufacturers dont want is for you to use their thinsets to bond tile directly to the osb. That doesnt work as osb is not stable like other substrates and moves to much for tile. Apparantly its not an issue with osb and ditra because ditra moves with the osb. My thinking would be to use a premium modified thinset, but your best bet will be to check with Schluter as noted above.
 
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Old 01-15-07, 09:56 PM
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Smile Thanks for the advice!

Many thanks to those who replied...especially you , HeresJohnny! I called Schluter today. The person who helped me seemed surprised at the question. They said that Ditra is used directly over OSB all the time. So...I guess I will go for it. This Sturd-I-Floor is pretty dense and very smooth on top. It is probably safer than most forms of OSB in this case.

I just don't understand why the thinset mfg'ers say you can't do this, but many users say you can (I posted on other forums as well). Guess it is all about minimizing product liability.

Thanks again for helping a stranger!
 
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Old 01-16-07, 06:59 AM
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Your welcome and good luck with your project.
 
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Old 01-16-07, 07:22 AM
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Live and learn eh.
I was told personally by the local Schulter rep that Ditra could not be used over OSB.For the very reason I explained

I also am looking at the TCA handbook and can find no acceptable conclusion that dictates the use of OSB under any uncoupling membrane.It cleary shows only plywood.As matter fact the very next page show the only use of OSB in the handook and it is to be covered with plywood and or a cbu
I hope it works well for you.

Thank you for your enlightening post Johnny.
I will email the rep and ask him why he told me this then I will pull out my Schulter book and confirm it.

EDIT: I research the Ditra info and it is very clear that osb is an acceptable substrate if properly installed and is tongue and groove:
That means glued to the joist and screwed in accordance with ANSI specs

Good luck
 

Last edited by ifllc; 01-16-07 at 07:36 AM.
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Old 01-17-07, 09:42 AM
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Here, read up.

http://www.schluter.com/english/products/2002/pdf/DitraHandbook(32)_052005.pdf
 
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Old 01-17-07, 03:31 PM
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Talked to my Schluter rep. He does not advise installing over osb. He stated that 80 % of the osb installs are installed improperly. If the confirmation is made the osb is installed properly then go for it.

If a Ditra floor fails while laid on top of osb the chances are very good the osb was installed improperly and your warranty is void.

I will not install it over osb. I will use only plywood.
I also offer personal warranties and I have yet to see an osb floor without moisture damage and glued and screwed on the joist.

I will stand by my statement,I do not advise it unless these steps have been taken to inhibit movement and swelling in the osb.
 
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Old 01-17-07, 03:35 PM
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I won't use it over OSB either, just showing what they say about it.

CBU on the other hand is fine over it.
 
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Old 01-17-07, 04:09 PM
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Certainly we agree.I figured so. I think I have seen your tile shower before but I cannot remember what sight. Your work is exceptional.

Like Dave Gobis says we have to be "Swiss" on these issues.
 
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Old 01-17-07, 04:30 PM
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Thank you.
 
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Old 01-22-07, 03:47 PM
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Sturd-I-Floor is not your daddy's osb, it is a much more stable product like advantech with a plywood veneer. Ditra will be fine.
 
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