# How well does Mapei mortar work on installing Ditra system over OSB?



## Ned's Floors (Jan 5, 2011)

How well does Mapei mortar work on installing Ditra system over OSB?


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## angus242 (Oct 20, 2007)

It doesn't. At least of the varieties I use, Kerabond + Keralastic, Ultraflex II or LFT all don't allow use over OSB.


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## Ned's Floors (Jan 5, 2011)

*Schluter Ditra Installation*

Which mortar is good for the installation of Schluter Ditra over OSB. I am looking for a specific mortar brand that can be found in local store. I have been using Mapei, but I am not sure if the quality is good enough. Anyone with suggestions/feedback would be appreciated. Thanks


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## Tech Dawg (Dec 13, 2010)

Does it have to be on osb?


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## Ned's Floors (Jan 5, 2011)

Yes, it has to be on OSB.


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## angus242 (Oct 20, 2007)

I merged your 2 threads because they are about the same subject.

I don't know of any thinset made that is actually recommended for use with OSB.

Here's my discussion on the subject:
http://www.contractortalk.com/f73/osb-subfloors-81336/


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## Tech Dawg (Dec 13, 2010)

Y...? Juzz wonderin


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## angus242 (Oct 20, 2007)

Most likely he's worried about overbidding the project by adding an additional layer of ply. I'm sure there's a line of Holiday Inn Express guys that will sell the job without carrying about doing it correctly. 

Sometimes the added floor height isn't feasible either.


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## Tech Dawg (Dec 13, 2010)

Set..., Spike, SCORE!


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## JazMan (Feb 16, 2007)

Hey guys, did you miss that he's not installing tiles over the OSB, he's installing Ditra to the OSB, then tiles. 

Any modified thin set will work for the purpose of installing Ditra to an OSB subfloor.

Jaz


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## angus242 (Oct 20, 2007)

Why does no manufacturer specify OSB as an approved surface to use thinset to?

Let's face it, a majority of installs over OSB are most likely done with CBU. Why wouldn't a manufacturer recommend their thinset in that scenario? Hell, after the CBU is fully supported and mechanically fixed, who cares if the bond breaks? Yet, Mapei says no to using thinset over OSB.


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## opiethetileman (Apr 7, 2005)

here is a picture of why you should follow directions with ditra over wood


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## JazMan (Feb 16, 2007)

Angus,

You're misapplying the manufacturers' recommendations. Tiles, therefore thin set, can not be applied to OSB along with several other substrates as we know. That is different from applying thin set to install a CBU or Ditra. OSB can be a bit unstable, that is why it's not an approved underlayment. Ditra's characteristics more than makes up for this instability. Modified thin set bonds very well to OSB. 

Oppie's deal is a completely different situation. As I recall the Ditra was installed with unmodified mortar to either plywood or OSB. Never had a chance. Someone didn't read the directions.

Jaz


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## HS345 (Jan 20, 2008)

JazMan said:


> Someone didn't read the directions.
> Jaz


How's this for not reading the directions? Yes, that's mastic, and yes it looks like they used a tiny v-notch trowel, and yes, there's mastic under the Ditra as well.


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## opiethetileman (Apr 7, 2005)

wow greg i think the ditra bandit is getting around. Well jaz i was just posting why its important to follow the dirctions. and oh yeah to top it off theese homes are less than 3 years old. can ya say WARRANTY wow....thats gonna eat someones wallet


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## JazMan (Feb 16, 2007)

Hi Dan,

I know you were not implying that your rip out was done by someone following any directions. I posted because some seem to think that OSB means it has to be covered with plywood underlayment. We know it doesn't. I believe you've know that for many years. 

Jaz


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