Ditra/porcelain/unmodified vs modified thinset

[Jeff_kitchen]

Hi there (from Jeff),
(my first post). I hope I don't get run off the board on a rail for this one.
Maybe I should have entitled it "here we go again".
Here's my situation:
* about to tile a kitchen and adjoining laundry room: total about 400 sq ft.
* Have 3/4" ply on 16" raised floor.
* I've removed old vinyl and glue.
* Was recommended Ditra over ply then Crossville empire series 14" unpolished porcelain.
* After having purchased both Ditra and porcelain tile, then of course I find out the nitty gritty issues regarding the thinset.
* Crossville email'd me and said use latex modified thinset; and Schluter as you know, recommends unmodified. Crossville rep is talking with another rep about this and will get back to me.
* In addition; and I don't know how much an issue this is, but the floor is not completely level. There's a beam that is up maybe a half inch from either side of the kitchen. I thought about a SLC, then Ditra, but from what I'm reading on your site, it appears my subfloor would not be adequate although that's yet another argument (e.g. LevelQuik claims).
Could I use a larger trowel depth to achieve some cheating to get those tiles somewhat level over the hump? I was reading many of your threads regarding trowel size and Ditra; particularly where others could not find those odd-size v-notched trowels. I was considering using a 1/4x1/4 with the Ditra and trying to put a little less morter under the matt where it contacts the beam. Then also, do some "tile smooshing" if necessary across the beam area.
I would love for somebody's input on this leveling problem.
* Ok; while writing this post, Crossville has called back and said to go with Schluter's recommendations.
So, my questions are:
* Ok for unmodified thinset? Would anyone recommend a specific latex modified thinset and any particular drying time if I decided I wanted to go that route or you wanted to convince me?
* Do you all recommend the latex modified grout like Laticrete? Or, should I just use standard sanded grout? The durability aspect of this modified grout appeals to me, but I wanted to know if you all like this new stuff. btw; I'll be using 1/8" grout joint. I was originally considering a 1/4x3/8 sqaure-notched trowel for this job, however Crossville recommends 1/2x1/2x1/2. Given my leveling scenario, what do you all think?

[michael_brown]

You use latex modified between the Ditra and the plywood, and UNmodified between the tile and Ditra. From what I've read here, there are issues with modified thinset never fully drying if used between Ditra and porcelain tile. For the trowel (I presume you were asking about which one to use to lay the tile with), I personally used a 1/4"x1/4" and it worked fine. John mentions in his book that going with too large a notch can give you lots of thinset squirting up in the joints, which you then have to scrape out.

I'm still working on my first bathroom, though, so please wait for a real pro to give you a final answer. I'm just echoing my experience and what I've learned from this great group of guys!

[Jeff_kitchen]

Thanks for your input Michael.
I'm with you on all the info you stated. For clarity though;
my trowel/notch size question is really this: Can I use a larger notch
size to achieve some leveling, even though I may end up removing
more cement from between tiles? Seems that in other posts the pros are saying you can use a pretty small notch trowel as long as the floor is flat. I took that to mean you can use a larger notch size to achieve some leveling
or maybe what they really mean is just coverage.
I'm hoping someone will help explain whether I should lay this tile down
when the floor is not completely flat; and if so; what's the best way to make it look good.

[jadnashua]

You need to check out the specs on the thinset. Most do not allow a large thickness. The largest I've seen (and I haven't looked too far!) is 3/4" for a granite and marble thinset. Something you probably don't want to use unless you have to because of its cost (and many of them are modified). I read some of the discussion on the modified vs unmodifed thinset, and the Schluter seems to be recommending unmodified (because it sets via hydration rather than the combo of hydration and drying that is required by the modified thinsets). For a tile 14" sq over Ditra, it would take a very long time to set up fully, if ever prior to grouting (maybe a week or more?). Prior to full setup and grouting, your floor is at risk from traffic.

"Normal" thinset thickness (again, check the manufacturer) max is around 1/8-1/4". It is much easier for the novice to level the floor prior to the Ditra than to try it after.

When I asked the question about flattening a surface, the suggestion was to put down 1/8" layers, let dry, then repeat as necessary. The pros (some of them anyways) use a bigger notched trowel when setting their tile to help compensate for the unevenness of the floor.

Maybe some slc first? Then the Ditra.

[Jeff_kitchen]

Thanks jadnashua,
I guess I'll use unmodified thinset as Schlueter recommends. The remaining issue is the flatness of the floor. I still don't know what exactly to do about that. I can't proceed with my tiling til I know how to handle this issue. Thanks for your help !

[Jeff_kitchen]

Hi,
my tile job is on hold til I can figure out what to do about
the flatness issue. I had a tile contractor come over today to look at
the floor (3/4 ply on 16oc). He said to make it perfectly flat he could lay lath and a mudbed for $6/sq foot (not including tiling) . I asked him if he felt the floor was level enough to tile as is. He said an experienced tiler could do it and he's done it before with floors like mine, but he didn't recommend the job for a first-time tiler like me. He said he would lay the tile on my somewhat un-flat floor diagonally for $7/sq foot or $6/sq foot straight. I would have to purchase all materials including grout and thinset.
These prices sound high to me. What do you all think?
I spoke with another outfit that talked about leveling the floor with patching compound. What is that and is it viable?
I sure would appreciate some help from someone that knows.
Thanks.

[jadnashua]

From what I read, if he is a real pro (depending on where you live of course) his price isn't too bad. Not sure what they intend to use as a patching compound. Some of them designed to be used under a piece of plywood or prior to putting down vinal probably should not be used under tile. How far off is the floor? slc, while expensive, is fast and not too bad to use. A mud bed is purported to be the best thing. This is something that you could also do yourself.

If the problem isn't too bad, you can use thin layers of thinset, let one dry, then add more if needed. Screed it off with a long straightedge. You can't exceed probably 1/8" at a time (maybe a little more - read the spec on the one you choose, if you go this route).

[lazybumranch]

Originally Posted by michael_brown

You use latex modified between the Ditra and the plywood, and UNmodified between the tile and Ditra. From what I've read here, there are issues with modified thinset never fully drying if used between Ditra and porcelain tile. For the trowel (I presume you were asking about which one to use to lay the tile with), I personally used a 1/4"x1/4" and it worked fine. John mentions in his book that going with too large a notch can give you lots of thinset squirting up in the joints, which you then have to scrape out.

Happy New year to all!

A 14" tile should be set with a large notch trowel. When in doubt, set one and pick it up. You should have full coverage, if not, get a bigger trowel .

The purpose of a notched trowel is to meter the amount of mortar. The larger the plane of the tile is, the more deviation in the substrate it must overcome. The more drastic challange the deviations present, the more mortar is required.

The hump in the floor re-enforces the need for the larger trowel. You can "float" the low spots and hold the notch down towads the middle. Make sure you get full coverage over the hump. Can you lay out the floor to have a joint break on the hump? That will save you from some proud edges.

As a tilesetter in New England, with lots of old Swamp Yankee builders of yesteryear building Dr Suess Houses to tile, I learned that a slightly larger joint than 1/4 may help hiding the multitude of sins we must fight with.

Good Luck!

[stullis]

Hi Jeff,

What is causing this hump in the floor? A floor joist that has bowed up? The house settling and the bearing wall not settling? Do you have access to the area underneath the hump? If so there are ways to possibly take care of the problem.

[David Taylor]

Hi Bumranch (Jim),

We've had this discussion before about trowel sizes relating to tile size....

What you're suggesting is a tad backward, and although I agree with you about the quality of work by previous trades that we have to deal with, using a larger trowel to make up for an unlevel floor is incorrect.

Let's say that you were painting a car and one of the panels was not flat: you wouldn't use more paint to make it look good, would you? The same goes for tile - if the floor's not flat, you make it flat before you lay your first tile. Don't depend on the trowel because you've just ignored the 1st law of tilesetting: consistency.

Consistent level and/or flatness
Consistent mortar thickness and coverage
Consistent grout line width and depth

Remember that the mortar (thin-set in this case) should be 3/32" - 1/8" after the tile has been pressed into it. If you're pressing it in this much, why the need for the bigger trowel? The rest is going to ooze out and you're essentially following the contour of the unlevel floor. If you're not pressing it in this much, you've just exceeded the limitations of the thinset.

If the tile itself is not flat, employ backbuttering. The middle of the tile might be domed, but rarely the edges. Again, don't rely on the trowel.

If you made the floor flat initially, I don't think you'd have to use a wide joint such as 1/4". Hey, show off the tile more, not the joint.

[John K]

Jeff,

Let me see if I have this correctly. There is a support beam in the middle of the kitchen that is a 1/2 in higher than the surrounding areas? If the floor was floated level. How would it make the transitions to the other rooms?

If it is as I imagine. Put the joint,as previously stated, over the beam and tile on..

[Jeff_kitchen]

Wow; you all are on the ball ! Thanks jadnashua, lazybumranch, stullis, David Taylor and John K for all of your responses.
The tile setter I spoke of is supposedly a real pro, so maybe his rates are ok. Problem is that I don't want to spend that kind of money right now, so I'd like to do this tile job myself if I can. I'd also like to do it for the sake of having done it; if you know what I mean.
One thing seems clear; that is, the floor must be flat. One thing I didn't know but found out after re-running a 6 foot level all over the floor was that I have issues in both directions and irregular low and high points in a number of locations in the kitchen and adjoining laundry. I had heard of doing some patching with layers of thinset, but I'm not sure where these layers should be exactly. It's hard to tell if I build up one low spot, will the same spot measured in the perpendicular direction be also fixed or worse in that direction.
Regarding John K's question about the hump in the middle; if the floor were
flattened using SLC, the join to the foyer would be probably at least 1/4" higher than it would otherwise be. I realize I have to install a sloping threshold. I don't think this would be as bad as if I were using concrete backer board and extra plywood vs Ditra and SLC. I had originally chosen ditra over my 3/4 ply before I removed the vinyl and realized these leveling issues. Ditra would supposedly save me some height over concrete board.
I really like the idea of patching some areas with layers of thinset if I could determine exactly where to put them.
But, let me ask another hotly debated question; If I used something like Custom's LevelQuik with Lath and leveled/covered the entire floor, would I then be able to skip the ditra and tile directly on the SLC? Remember I've got 3/4 ply on 16 oc. All ply is screwed down with non-corrosive screws. Or, would anyone suggest that if I did level the entire two adjoining rooms with SLC, should I go ahead and use the Ditra anyway (e.g. height vs add'l de-coupling)?
Last question; does anyone know if I "have to" use SLC to cover the entire adjoining floors, or could I just start pouring in the areas that I am reasonably sure are the worse and only do parts of the floor? In other words; fill in the bad valleys to reach some of the humps. In that case must I use Lath if I intend to Ditra over the SLC "patches"?
Sorry so long-winded...

[Jeff_kitchen]

Hi,
I called Custom today to ask about installation of Tile directly over LevelQuik over 3/4 ply which is supposed to be a supported method when using metal lath. I spoke with two different tech support people who said Custom only supports installs where there's minimum 1" plywood. I pointed out that their technical PDF file has the paragraph below:

"The installation system consists of a LevelQuik® Self-Leveling
Underlayment installed at 1/2" (13 mm) thick over the
23/32" (18.2 mm) plywood subfloor with metal lath installed.
The metal lath must be a minimum of 2.5 lbs./sq. yd.
(1.13 kg/.83m2). This system provides a more stable
substrate on which to set tile than the double layer of
plywood method and is less expensive and labor intensive
than the uncoupling system."

The Custom Building Products support rep said they have to get with the dept that writes those tech support bulletins for their web site and get that changed. I thought some of you might find that interesting. So, it looks like I'll be installing some lath in the low points and using SLC in only the very low areas. Then I'll Ditra over that.

[Hamilton]

Interesting situation for a doit yourself job. have you checked the seems
where the subfloor sheets meet. sometimes these areas will buckle up-
wards a bit causing even more trouble to the prep job. you can counter-
sink nail heads and sand or plane these edges down if they are severely
crowned. i never use level quick but in your situation it seems like it might be appropriate. make sure you can get the proper installation instructions from the manufacturer and follow them closely, this way the warranty if any will stand behind your investment in your floor should anything fail.

Hi Hamilton,
thanks for your thoughts. There are a couple of joins that were tight,
although not in the location where the worse of my flatness problems are.
I ran my circular saw along those two seems at a 3/4" depth to provide some relief.
I have received input from Custom reps whom had read my previous thread. They say the specs on their web site are correct and that there's some misunderstanding. I'll be speaking with one of them later on today if I can get a chance. I would say however that the misunderstanding is not on my part. I read both the title and paragraph of interest from the technical bulletin directly off their web site to the second tech support person I spoke with. She said flat out; "that's incorrect and our web site needs to be changed".
I'm hoping that I do have the option to use LevelQuik if that's the way I decide to go.