# Ditra and unmodified



## primetimeon (Mar 16, 2009)

Hey guys, I am really enjoying using the material from schluter.

My question is about the modified vs. unmodified. I have a client that has heard really bad things about the bond of unmodified and wants to use modified on the ditra floor. Can this be done or not. Why exactly do they want you to use unmodified.

The job is in california in an area with alot of ground movement so the H.O wants to take all the precautions he can.


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## angus242 (Oct 20, 2007)

Schluter requires the use of unmodified thinset over Ditra when installing tile. There are two exceptions. 1) Using a rapid set modified thinset. 2) Using a self-curing modified thinset. In either case, you can use them without affecting the warranty but I would call Schluter first an get their OK in writing.

There are some guys that use a low count latex modified often. That is not a method that is warrantied by Schluter.

Why unmodified? Because modified mortars must air dry to cure properly. When sandwiched between two impervious layers such as Ditra and porcelain tile, drying takes place very slowly through the open grout joints. According to the TCNA, this drying period can fluctuate from 14 days to over 60 days, depending on the conditions. Therefore, extended cure times would be required before grouting if using modified thinset mortars between Ditra and porcelain tile. If extended cure times were not observed, the results could be unpredictable.

However, why the big worry over unmodified? A test performed by the TCA showed that using non-modified thinset to mount porcelain tile to Ditra achieved an average shear bond strength of 190 psi _OVER_ the minimum spec of ANSI 118.4.

I make sure porcelain tile is back buttered before setting over Ditra. Also, the use of a quality non-modified with a high portland ratio is recommended. I personally use nothing but Kerabond. If you look at the shear ratings after 28 days of curing, Kerabond is equal to or superior than Versabond.

If you can get your hands on it, Ditraset is even better but is a ***** to find and when you do, it's been ridiculously expensive.


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## Bud Cline (Feb 12, 2006)

> According to the TCNA, this drying period can fluctuate from 14 days to over 60 days, depending on the conditions.


...and I take issue with that alleged finding. This is then to say the minimum drying time would be fourteen days and frankly I have never ever found that to be the case in my experience. I have used modified thinset with porcelain tile and over DITRA and even tho I will allow some extra time for curing It has never never never taken fourteen days.

A lot of this has to do with interior conditions and atmospherics as far as I'm concerned. Schluter's move in allowing only unmodified is a CYA technique on their part I think. I won't argue with the master but at the same time my field experience is greatly to the contrary.


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## angus242 (Oct 20, 2007)

Bud Cline said:


> A lot of this has to do with interior conditions and atmospherics as far as I'm concerned. Schluter's move in allowing only unmodified is a CYA technique on their part I think. I won't argue with the master but at the same time my field experience is greatly to the contrary.


And therein lies part of why I do not feel comfortable saying modified is OK to use over Ditra. Look at a lot of the posts here asking questions about this. I feel it's safe to say, your field experience _vastly _outweighs that of those guys. 

If an experienced tile guy says it's OK to use modified, how is the inexperienced guy supposed to know when and where to do so?


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## Bud Cline (Feb 12, 2006)

*Always follow the recommendations of the manufacturer.*​








I don't know if you remember when DITRA first became a part of the installation landscape, but, Schluter's recommendations then ARE NOT what they are saying today. I think that is noteworthy!


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## angus242 (Oct 20, 2007)

:laughing:


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## PrecisionFloors (Jan 24, 2006)

Bud Cline said:


> ...and I take issue with that alleged finding. This is then to say the minimum drying time would be fourteen days and frankly I have never ever found that to be the case in my experience. I have used modified thinset with porcelain tile and over DITRA and even tho I will allow some extra time for curing It has never never never taken fourteen days.
> 
> A lot of this has to do with interior conditions and atmospherics as far as I'm concerned. Schluter's move in allowing only unmodified is a CYA technique on their part I think. I won't argue with the master but at the same time my field experience is greatly to the contrary.


Same here Bud. I've been usin modified with Ditra for a long time...pretty much from day one. I trust my field experience and know what I can get away with and allow for extended cure times prior to grouting, when necessary...I don't know that about most other setters so its a "do as I say, not as I do" thing. 

Imho, if your askin the question, odds are u ain't got enuff sperience to go outside the Herr's recommendations.


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## kevjob (Aug 14, 2006)

I use versabond and somtimes with monsters I use marble and granite, will I get schluters warranty nope but I know that it works for ME.


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## Bud Cline (Feb 12, 2006)

I have never had to call on anyone's warranty and I never will. If something goes to hell it's nobodies fault but my own. I'll correct it, digest it, and move on. In thirty-four years I have never eatin' a job and I don't plan to start now.:no:


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