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Should I use Ditra?

Posted by lindalana (My Page) on
Wed, Mar 5, 08 at 9:54

Did my research from previous posts. Settings- house 60 years old, second floor bathroom, all of 30 s.f. Floor will be repaired back from plumbing job to the wooden planks over joists, wood strips on top to accommodate electrical piping,then will put back plywood/ what thickness?/ as foor.
1. What kind of primer do I need for plywood floor?
2. Ditra vs cementboard? height is the issue but not life threatening. What is easier for DIY in terms of making it level and better surface prep for ceramic 12x12 tile?
3. If Ditra, then cable goes under with modified thinset. Am planning on one step at a time approach- putting cable and thinset over it, letting it dry, applying unmodified thinset and Ditra, letting it dry, applying unmodified thinset and tile. It sounds as it is best way for inexperinced person to make this work./ I am familiar with putting tile over cement board but not Ditra or heat cables./
4. Is SLC better in terms of leveling cable application to plywood instead of using thinset?
4. Easiness of application of Ditra vs. cementboard aside
thermal stress prevention of Ditra is enough reason to choose over cement board?

Follow-Up Postings:

RE: Should I use Ditra?

If you've got plank subfloor down now, all you should need is 3/8" plywood, being that the planks will give your subfloor the strength.
1) no primer. The difference is in the thinset used, depending on whether you use Ditra or cement board. For cement board, you want an unmodified thinset. For Ditra, you want it to be as modified as you can find. When I use Ditra, I'll usually use an unmodified thinset, and then for bonding it to the plywood, I'll mix it with a liquid latex additive, and then for setting the tile, I'll mix it with water.

2) Ditra is probably better all the way around. Cement board, like Ditra, provides no structural support. But in the case of cement board, all it DOES provide is a more stable bonding surface. With Ditra, not only do you have a good "bonding" surface, but you also have what's called an uncoupling memrbane. Short explanation is it does as good a job as any membrane can, to protect your floor from movement.

3) Sounds good.

4) depends on who you ask. From my point of view, I like thinset better. Others prefer SLC. If you use SLC, make sure you use their primer with it.

RE: Should I use Ditra?

As a DIY-er I second (resoundingly) a vote for Ditra over cement board. Bill gave you all the technical reasons for it, but my big thumbs-up goes for the ease of installation. We did our master bath with Hardibacker (filling the room with cement dust when cutting it, putting in all those #$%@ screws every 6") + radiant heat wire + tile, and our kitchen with wire + Ditra (cut with utility knife)+ tile. I will never go back.

FWIW, we didn't do a scratch coat over the wire. I just carefully trowelled the thinset over/around it, which was the biggest PITA part, closely rivalling screwing in cement board.

RE: Should I use Ditra?

Thank you very much, I just got myself a roll of Ditra. I will look into troweling thinset and laying Ditra in one step just not sure how easy is to make it level.

RE: Should I use Ditra?

When I put the Ditra over the wire it wasn't completely 100% level. It was a tad bumpy/wavy. But once I got the top layer of thinset on, it wasn't any problem to get the tiles level.

Bill, feel free to pipe up if I did this wrong or if you'd recommend differently. You won't offend me.

RE: Should I use Ditra?

One thing I've taught my stepson since day one, and it's pretty much the "secret of my success": No matter what you do in this trade, there's always going to be several steps from prep to finish. The better and more complete you perform each step, the easier the subsequent steps will be, and the better they'll turn out.

IOW, you want to get that float coat over the wires as flat as you can, so that once the Ditra goes over it, the less you're going to have to mess with it. In addition, because the floor wasn't flat when the Ditra went down, there's a good chance that there are voids under the Ditra.

RE: Should I use Ditra?

Update with more questions-
Secured heating cables to subfloor with hot glue, checked for continuity. Mixed fairly fluid modified thinset Versabond/ slightly thinner as I would have normally use for floors and walls, able to pour from bucket but still firm enough to create a shape and stick to the trowel/. Spread thick layer of thinset over cable layout, evening it out at the top of the cable or slightly over.
Placed Ditra into thinset with long board, checked for level. Lifted part of Ditra- coverage appeared to be full and even. Some uneven parts created where Ditra pieces came together.
1. When is better to lay tile? Surface under Ditra was squishy so I was afraid to walk on it. Is there estimated number of hours?
2. Is it ok to use unsanded grout if I put tiles very close to each other?

RE: Should I use Ditra?

1) I'll normally wait till the enxt day, although I know of several good installers who will tile over Ditra the same days as the Ditra is installed.

2) Yes, but if you're going to set the tiles that tight, they better be either natural stone, or rectified porcelain, or you'll run into problems.

RE: Should I use Ditra?

Let me get this straight. Are you saying that you can:

1) Set your heating mats (because I am too chicken to use wires) with a 'fairly fluid modified thinset Versabond', and spread a THICKER layer of thinset over the mats because you are intending to place the Ditra over the mats right away?

2) Or for the more inexperienced, is it better to do it in two steps? Put the mats down with a skim coat of thinset, level this as best as possible, and come back and apply Ditra the next day. Schluter's video for applying Ditra only, (no mats) shows the installer putting down thinset, then Ditra, and then using some type of 'wide trowel' looking device to bond the Ditra to the thinset and the floor. The thought of crawling around the floor firmly imbedding the Ditra in thinset, with delicate wire mats underneath that could be nicked at any moment, makes me very uncomfortable. It's obviously done all the time, I just find it a little scary. Any suggestions for the best procedure to accomplish this?

Of course securing mats to the floor with thinset, and using that same coat of thinset to adhere the Ditra, is certainly less time consuming.

Schluter's rep also said that you could lay the thinset and Ditra, and IMMEDIATELY lay more thinset and tile over the just-laid Ditra. At this point I fainted. Someone in my house eventually hung up the phone. LOL. It would seem that 'just-laid' Ditra would be "squishy" as lindalana described above and I, too, would be afraid to walk on it, let alone lay tile over it. I know, "Big Chicken."


3) I am confused over the type of thinset to use when applying the Ditra. I thought is was Unmodified. Please clarify your statement above:

"For cement board, you want an unmodified thinset. For Ditra, you want it to be as modified as you can find. When I use Ditra, I'll usually use an unmodified thinset, and then for bonding it to the plywood,..."

Thanks, Bill


RE: Should I use Ditra?

Anne-- You're even mixing ME up!!

Okay-- Instead of going down the line answering your questions, I'm just going to outline what needs to be done. Set your mats and then pour your leveling layer, whether that be loose thinset or self leveing compound. LET THAT DRY. Once dry, go back with MODIFIED thinset to install the Ditra. You want modified thisnet to make sure the Ditra adheres to what's beneath it. Unmodeified won't always do that for you. As for the times I've talked about using unmodified thinset under the Ditra, it's mixed with a liquid latex additive instead of water, which makes it MORE modified than most modified thinsets. Once the Ditra is down, I'll then use that same unmodified thinset mixed with water this time, and set the tile.

As for this statement:

For cement board, you want an unmodified thinset.

That's true. In this case, the thinset isn't being used to bond the cement board. it's being used to cushion it and stop vibrations between the layers that would otherwise exist. The screws (or nails) are what holds the cement board to the subfloor-- not the thinset.

NEXT!! :-)

RE: Should I use Ditra?

Aw shucks, Bill

NOBODY can mix YOU up, but if you say so, I guess I could make a pretty good stab at it. That was a good explanation ...but

My statements above were based on what I 'thought' lindalana was saying that she did. I was unclear whether she allowed the first coat of thinset and mats to DRY before applying the Ditra. You have explained that you 'LET THAT DRY', but for how long?

I think my questions refer to the waiting times between the different steps in the process.

AFTER the mats and thinset dry, then you apply the Ditra and a second coat of thinset, right? How LONG do you wait for this to dry before you apply the tile? I thought I understood you to say the next day.

So the whole process could take how many days? For a rookie?

Did I confuse you, AGAIN? Sorry. :)

RE: Should I use Ditra?

you can do either or. You can either let your first application dry and then apply Ditra or apply it right away. I did applied it right away, it was not a problem. All I had to do is precut Ditra, cover small amount of floor with thinset/ like about 2 feet/ and press Ditra in with wide board. Then I placed dry tiles on top of it to keep weight down and make sure it stays flat/ my own thinking, no data on that one/
Since I had level subfloor making level floor with Ditra was not a problem. Had little bit of issue on the edges as there were no cable there and apparently thinset layer I applied was not thick enough but as it goes under baseboard I corrected it while doing tile install.
I had to wait for drying longer than I normally would, I guess it is normal for Ditra.
Overall I find laying tile on CBU much easier.

RE: Should I use Ditra? yeah

talking about major PITA was not being able to find white unmodified thinset for my white tile anywhere in my area- every tile store or big box store carry only grey one! I had my daughter working with me with jeweler precision cleaning up every edge and surface to protect from showing.

RE: Should I use Ditra?

AFTER the mats and thinset dry, then you apply the Ditra and a second coat of thinset, right? How LONG do you wait for this to dry before you apply the tile? I thought I understood you to say the next day.

That's correct.

Since I had level subfloor making level floor with Ditra was not a problem.

Not to be argumentative, but I'd be curious how you had a level subfloor if you had wire elements on it? I can't recommend against what you did strongly enough. It would be way too easy to create divots or humps in the floor using your method.

RE: Should I use Ditra?

I'm going to put my mats down with a coat of Unmodified thinset or self leveling concrete ... and let that dry for a whole day. Is that O.K. with everybody? :))

Then in about a week, I'll have enough courage to go on with the rest of the project.

Big Chicken

RE: Should I use Ditra?

NO!!!! Either MODIFIED or self leveling compound!! If you use unmodified for the mats, your floor will come up within a matter of weeks, if not days.

RE: Should I use Ditra?

OK, Bill

You're right. I have been running like crazy the last couple of days and haven't been able to check in on this post. When I did, I could hear you yelling all the way to Texas!!

The reason I said "Unmodified" thinset with the first step is that I had spoken with the Schluter rep earlier that day, and he had been absolutely emphatic that unless the consumer uses UNMODIFIED thinset, Schluter will not warranty the Ditra.

When I asked for clarification on yesterday, he said that Schluter does not want the consumer to use anything but UNMODIFIED on TOP of Ditra, that is, between the Ditra and the Tile. The company does not care what type of thinset goes UNDER the Ditra, and Modified is fine to secure the mats.

So for the last time, my steps. On my slab:

Modified thinset or SLC over the heating mats; let dry.

More modified thinset and apply Ditra. I'm going to let this dry cuz we're rookies.

Unmodified thinset on top of Ditra layer and lay tile.

Phew!! If this isn't right, just shoot me.


RE: Should I use Ditra?

Nope-- I'll save my bullets for another day. :-) By jove, I think you've got it!!

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