I don't believe that any unmodified thinset is approved for porcelain tile. You might want to refer to the TCNA (Tile Council of North America) for their guidelines and recommendations.

For me, I can't see any savings in using unmodified thinset to be worth the high potential for adhesion failure down the road.

 

Most people should be using modified thinset for their tiles, but......... If you're installing over Ditra or Kerdi, Schluter wants you to use unmodified. Modified will work, but it'll take longer to cure and will void any possible claim against Schluter if you don't follow directions. There's an exception when the tile is glass.

When neither Ditra or Kerdi are involved, you'll want to use modified mortar. If the tiles are regular soft bisque ceramic over a concrete base, you can also use unmodified, although modified is better. If the tiles are porcelain, or even a semi-vitrious tile, you definitely need to use a modified thinset. Same goes for glass tiles. Always read the directions that come with the tiles when there's a question, or ask here.

So in general, modified thinset is better, more versatile and generally preferred. As to which over liquid membranes.......as far as I know, they all want modified.

SML, your explanation in the first paragraph is rather convoluted and makes no sense to me.

Please follow with any questions you now have.

Jaz

 

Thanks for the responses!

Jaz-Sorry for the confusion. I will be using modified to set my tiles. However, I would like to understand the rationale a little better and figure out "why?"

You said in your response that you definitely want to use modified with porcelain. However, you also said that you want to use unmodified over Ditra or Kerdi. The way I have always done things is that the latter statement rules. So, if I am setting porcelain over Ditra, I use unmodified.

If is my primitive understand that which one you use depends upon the ability of the surface you are putting is on to absorb water and thus allow the thinset to dry out and fully cure. So, when you are laying Ditra, if you are doing so over plywood, you use modified, since that is stronger and the thinset can fully cure by drying out into the plywood. However, if you are laying Ditra over sealed concrete, you use unmodified. I use unmodified to set tiles over top of Ditra regardless of the type of tile I am setting. My understanding of why Schluter wants you to use unmodified over top Ditra is that the Ditra will not allow water to penetrate and thus the thinset can only dry out through the grout lines or by seeping through the tile. Thus, unmodified is preferred.

What I don't understand is why if you use unmodified over top of Ditra and Kerdi, can you use modified over top of hydroban. All of those substances will not allow water to penetrate. So, from the standpoint of the thinset drying out, they are all the same since they can only dry through the tiles or grout line, but not through the surface you are placing them on.

Correct me if I am wrong, but it seems like to me that modified bonds better. However, for whatever reason, Schluter recommends unmodified over Ditra and Kerdi. Based on my research, it seems like the only reason we use unmodified is that Schluter says to and we are worried about not doing what they say. Ditra or Kerdi knock-offs or other impervious substances (such as Hydroban or Redguard) theoretically should be treated like Ditra but we set tiles with modified over top of those substances.

I guess I am trying to figure out "why?" we use unmodified over Kerdi or Ditra but a knock-off product it is ok to use modified. I think the answer is "Because Schluter says so." but if there is a better explanation, I would love to hear it.

 

Are you just covering the taped seams, screws and window openings with the sealer or all of your backer boards?

I'm not understanding what you're worried about.

 

You said in your response that you definitely want to use modified with porcelain. However, you also said that you want to use unmodified over Ditra or Kerdi.

Yes, that's right. Ditra & Kerdi relieves much of the stress that always happens between the tilework and the substrate, that's the difference. Here's some info I stole from Schluter;

QUESTION
Can ceramic tile, including porcelain tile, be set on DITRA
with unmodified thin-set mortar?

ANSWER
YES. In fact, we recommend it. Here’s why:
Portland cement-based unmodified thin-set mortars are dependent on the presence of moisture for hydration in order to gain strength. Since DITRA is impervious, it does not deprive the mortar of its moisture. This allows the cement to properly hydrate, resulting in a strong, dense bond coat. In fact, after the mortar has reached final set (usually within 24 hours), unmodified thin-set mortars achieve higher strengths when cured in continually moist conditions.

QUESTION

Can ceramic tile, including porcelain tile, be set on DITRA with latex-modified thin-set mortar?
ANSWER

We DON’T recommend it. Here’s why: Latex-modified mortars must air dry for the polymers to coalesce and form a hard film in order to gain strength. When sandwiched between two impervious materials such as DITRA and ceramic tile, including porcelain tile, drying takes place very slowly through the open joints in the tile covering. [According to the TCNA Handbook for Ceramic, Glass, and Stone Tile Installation, this drying period can fluctuate from 14 days to over 60 days, depending on the geographic location, the climatic conditions, and whether
the installation is interior or exterior]. Therefore, extended cure times would be required before grouting if using modified thin-set mortars between DITRA and ceramic tile, including porcelain tile. If extended cure times were not observed, the results could be unpredictable. This is even more important to consider in exterior applications that are exposed to rain as there is the additional concern of latex leaching.

Jaz

 

Clarence-I am not really "worried" about anything. I am just trying to understand "why" instead of just doing something. Yes, the Hydroban is covering absolutely everything--the screws, seams, walls, etc. It is one complete waterproof coating!

Jaz-Thanks for those explanations. They do make sense. I guess my only outstanding question would be, how is hydroban different than Ditra? If would seem to me that on my shower wall I have a completely impervious layer (hydroban) and a tile such as ceramic in their example which is pretty impervious. So, the thinset is "sandwiched between 2 impervious layers" which means it only has the grout lines to dry out. Although Hydroban is not Ditra or Kerdi, it is just as impervious as either of them so why is the thinset used to set tiles over top of it different?

 

how is hydroban different than Ditra?

Completely different. But maybe you meant to ask about Kerdi instead?

But let's talk about Ditra. Maybe you've noticed, that the Ditra squares have dove-tail walls which is how the thinset "locks" into Ditra to increase its bond. That's one of the "secrets". Ditra also moves horizontally with the stress from the subfloor system's normal shrinkage and expansion that is always going on.

Also, each manufacturer has its own theories and testing and you should follow their desires if you expect things to work out as intended and keep any warranty in force.

I used premium modified thinsets over Ditra for years before I was advised I could/should go with unmodified and at the same time save $10-15 per bag. Then when Schulter & Bostik came out with Ditraset in '06, I used it almost exclusively.

Regular ceramic tiles are NOT impervious, but porcelain ceramic is. I think we were talking about why not use modified for porcelain over Ditra & Kerdi.

To those who think you gotta use modified to bond porcelain tiles...... Thinset mortar was invented in the '50's, and latex additives to "modify" dry set mortar was developed in the early-mid '70's with the growing popularity of large Italian glazed quarry tiles. (Let me note that porcelain tiles had been installed for many years before the '50's.) This allowed these tiles to also be installed over plywood for the "retail" market. Until then tiles were installed by real tile setter over a real "mud" base, the ole fashioned way.

Jaz

 

Hi SMLWinds,
Good question. Easiest answer is to simply follow manufacturer instructions. Hydroban calls for modified thinset.

Ditra and Kerdi both call for unmodified when setting tile. If you would like a decoupling product where you can use modified thinset, try STRATA_MAT. It has holes in it to allow the thinset to dry. Of course this means the installation can't be waterproof, as Ditra can.

In general, always choose modified, except where unmodified is specifically required, or where you'll be mixing in the additive yourself of course. If you only want to keep one type of thinset on hand, then you can choose a product such as Mapei Kerabond, and also keep on hand Keraply to make it modified whenever you want.

Good luck,
The New Hope Handyman

 

Thanks for the responses! NewHopeHandyman--welcome and thanks!

Jaz-you are correct....I should have said Hydroban vs. Kerdi. So, I understand the dovetail waffles in Ditra which I suppose one could say "substitutes" for the lack of modified thinset. However, the "drying out" explanation Schluter gives still does not make sense when applied to other products with similar function.

So if you compare Hydroban to Kerdi.....Hydroban recommends modified thinset while Kerdi recommends unmodified. The reason Schluter gives for using unmodified is the impervious nature of Kerdi. The comment that unmodified cures best in continually moist conditions is true, but would apply as a principle to Kerdi and Hydroban! While Kerdi and Hydroban are different, they are both completely impervious so if the only reason for using modified or unmodified is the ability of the thinset to cure with the substrate being impervious then you should theoretically use the same thinset with both.

In the end, I think the answer is "do what the manufacturer says" and that is what I plan to do. I was just hoping to understand things better. I understand how Ditra has hold power in the dovetail waffles so I can rationalize why you use unmodified. However, the scientific answer and explanation about how thinset dries means that either Hydroban or Kerdi's recommendations are inconsistent. I don't see where they are any different from a drying standpoint and thus there is not reason why you should use different thinsets. I was hoping to understand the science here but I think the answer is that there isn't as much consistency as we would like that thus "just do what the manufacturer says!"

Thanks for the help!

 

However, the scientific answer and explanation about how thinset dries means that either Hydroban or Kerdi's recommendations are inconsistent.

I agree with you and I don't know the answer. I suppose neither are perfect solutions, but at the same time both work pretty well in practice. So I suppose it comes down to marketing and how the manufacturer prioritizes things.

Cement actually cures harder if water is present the whole time, which is more likely when waterproof substrates are used. Modified thinsets didn't even exist 100 years ago and yet we have tile installations lasting much longer than that. On the other hand, I really doubt Ditra or Kerdi installations done with modified thinset would fall apart. I mean really, is there much force acting on wall tiles or even floor tiles? Even if not 100% cured, thinset still has plenty of compressive strength in a typical floor tile situation, and there normally is very little sideways pressure. I suppose that's why so many crappy floor tile jobs do not fail, unless there is something wrong with the substrate.

Did you ever wonder where the name Laticrete came from? Sounds suspiciously like Latex + Concrete.... hmmmm.

 

SML.... I'm with you entirely.... and thank you for pursueing/chaseing an answer.

Your question/argument is well reasoned.... something I've tried to find an answer to also.

(From my very limited GC knowledge, and from what has been presented in this thread, perhaps the answer to the inconsistancy lies in the manufacture's subjective assesment of failure risk....

At least in the Ditra example, adhesion is somewhat improved mechanically and modified's adhesive properties are somewhat less important than it's curing problems/properties and consequently Shulter recommends unmodified for it's prefered curing properties under the circumstances. that does not explain Kerdi.

And perhaps Redguard and hydroban, make the subjective judgement that modified's adhezive properties are more beneficial/important than any slowness in ultimate curing.

Basically... there seems to be a tradeoff here that perhaps different products and manufactures judge differently for their product as to it's ultimate performance.)

Just a layman's guess.... but thanks again for seeking an answer.... that and where Jimmy Hoffa is buried I don't believe I am destined to know.:wink2:

Best

 

By the way, I have also wondered why Schluter recommends modified thinset for Ditra over plywood, but unmodified thinset for Kerdi over drywall.

 

So if you compare Hydroban to Kerdi.....Hydroban recommends modified thinset while Kerdi recommends unmodified.

You forgot about the fleece. Liquid applied membranes are more difficult to stick to cuz they're smooth. The fleece is the secret weapon. Unmod cures by chemical reaction called hydration. No air necessary. Modifieds need air to cure, which takes about 28 days.

Think about this; How does cement cure when poured in the construction of bridges and tunnels? Huge columns that are mostly underwater, lots of moisture no air.

You keep comparing Ditra and Kerdi to other waterproofing systems, why? The one thing they do have in common might be that all can waterproof, create a vapor barrier and isolate the tilework from substrate. That doesn't make them the same.

Did you ever wonder where the name Laticrete came from? Sounds suspiciously like Latex + Concrete.... hmmmm.

Very good guess. Laticrete was founded by Dr. Henry Rothberg (who passed recently, RIP), a chemical engineer in 1956. He studied the tiling process and invented thinset to use as the bond coat replacing ancient methods. Although some latex was involved in the original formula, it can't be considered the latex modified we know today. The early chemical formulas were called 'water-retentive' to allow a cure. True latex modifieds came in the 1970's.

By the way, I have also wondered why Schluter recommends modified thinset for Ditra over plywood, but unmodified thinset for Kerdi over drywall.

That's an easy one, figure it out yet?:wink2:

Jaz

 

That's an easy one, figure it out yet?

I assume you are going to say the "open air" channels on the bottom of Ditra.

But in the installation manual for Kerdi, it says "Dampen particularly dry and porous substrates in order to help prevent premature drying or skinning of the thin-set mortar." The picture associated with this shows the installer dampening drywall with a sponge. So they acknowledge that drywall is a porous substrate that absorbs moisture.

The same is true when installing the Kerdi shower pan over plywood.

I think in either case, the thinset is going to "dry into" the substrate, and over time the substrate will dry out via natural means in the "other direction". Maybe they're concerned about the amount of time this might take.

 

I assume you are going to say the "open air" channels on the bottom of Ditra.

No, there's nothing to do with the channels, the channels have another purpose. It's just common sense. You must use a thinset that is appropriate to the substrate you're installing Ditra. Simple. Over ply or OSB you have to use modified or it won't stick so good. Over concrete you should use unmod.

Moistening a very dry substrate is something you're supposed to do whether or not there's Ditra or Kerdi being installed. One example is when you're going over Hardie, which is notorious for being thirsty. Yes, Hardie sucks!

So they (Schluter) acknowledge that drywall is a porous substrate that absorbs moisture.

There's nothing to acknowledge. We all know wallboard is porous, but the main reason they wipe it is probably to remove dust and show good technique. Thinset will not bond as well if the substrate will not absorb some moisture. That's one of the tests recommended by Custom you perform before you bond to concrete as an example. I see no need to damped regular drywall using the thinsets I'm used to, mixing them the way I do/did and doing the work in my region of the country. That's why they make hot weather formulas for the south to be used in the summer. Your application technique is also a factor. We have to figure it out as we go and that's why you make the Big Buck$. :wink2:

Kerdi Shower Tray over ply, they want you to use UNMOD. Yikes, some people think it's a typo.

Schluter could have saved themselves lots of doubting if they'd just say to use modified and be done with it. But they've done extensive testing and I can tell you Mr. Werner Schlüter is a tiling method genius.

Jaz

 

No, there's nothing to do with the channels, the channels have another purpose. It's just common sense. You must use a thinset that is appropriate to the substrate you're installing Ditra. Simple. Over ply or OSB you have to use modified or it won't stick so good.

Of course you could make the same argument for the tile installation too - for porcelain tile the "appropriate" thinset is modified - "everyone" will tell you that!

If modified thinset needs to dry to reach full strength, and it doesn't dry "through" the plywood, then it's pretty convenient that the channels are there for drying (the stated design purpose of the channels is for water vapor to escape).

Or else, how could Schluter say in one breath that they don't recommend modified thinset for installing porcelain tile because the thinset can't dry and fully harden fast enough, and in the next breath say that you should use modified thinset on the bottom of Ditra? The only way they can get away with that is if the thinset underneath can dry quickly one way or another.

It's also convenient that they don't recommend Kerdi over plywood - and that way they have no explaining to do about how the modified thinset might dry. So they just say "don't use Kerdi over plywood". Not a big deal, but it would come in handy if Kerdi could be used as a crack isolation membrane on floors. NobleSeal seems to have no problem with this, for example. NobleSeal TS with modified thinset above and below. As far as I know, no one has ever complained about NobleSeal - "hey, modified thinset can't cure right with your product, that's a bad product."

 

This is one very informative thread

 

Of course you could make the same argument for the tile installation too - for porcelain tile the "appropriate" thinset is modified - "everyone" will tell you that!

For Heaven's sakes....Yes of course,:smile: *except when you're installing over Ditra & Kerdi. Again Why? Cuz with those two substrates, unmod thinset develops more than enough strength and Ditra & Kerdi are able to relieve the stresses than can cause failures over normal "solid" substrates that do not "give" with the stresses ALL substrates encounter. Plus....what type of thinset was used for porcelain before modified mortars were invented?

Ever see pavement buckle in summer, ever see those "finger' looking steel thingies on bridge pavement? They are there to relieve the stress of expansion and contraction. Do you know a 20 story building can shrink & expand about 6" in height? Ever read about the difficulties is building high flying airplanes such as the U2 & the SR71 spy planes? Space shuttles?

Let me look for an old video illustrating how Ditra does all these magical things. I'll post it when I have a chance.

If modified thinset needs to dry to reach full strength, and it doesn't dry "through" the plywood,

Who said that? You're introducing too many subjects at the same time that only cause confusion by rationalizing the reason for point "A" to the results of point "B". Example; Your reference to the channels in Ditra. Ditra wasn't designed that was for the purpose of allowing thinset to cure, although yes it can/will help do that when using modified thinset. But channels are immaterial to the reason Schluter wants us to use a specific type of thinset.

Or else, how could Schluter say in one breath that they don't recommend modified thinset for installing porcelain tile because the thinset can't dry and fully harden fast enough, and in the next breath say that you should use modified thinset on the bottom of Ditra?

HUH...If you don't see the difference in what you just wrote......I can't help you. :smile:

It's also convenient that they don't recommend Kerdi over plywood - and that way they have no explaining to do about how the modified thinset might dry. So they just say "don't use Kerdi over plywood". Not a big deal, but it would come in handy if Kerdi could be used as a crack isolation membrane on floors.

LOL Kerdi is for waterproofing and used mainly for wet installations. Why would you wanna use Kerdi as an isolation membrane for a floor? That's what Ditra is for. Kerdi isn't gonna isolate anywhere as good as Ditra.

If you plan to do much Tilework for $$$ in the future, get in touch with Schluter asking for the date of their next workshop in your area. It's either 2 or 3 days and free to attend.

Noble is a great company and located right here in MI too. Although their stuff can be used anywhere, they mostly concentrate on commercial projects. Their CIS is real kool to bridge control joints while maintaining the tile layout. If you know and like Noble, I suggest you stick with it so you won't have to learn the Schluter stuff. :wink2:

Jaz

 

There's too many videos to list, here's one to start.

To learn about the types of mortar to use and when, you'll need to visit their site and read, or just ask here.

Jaz

 

I think you're looking for reasons to disagree rather than consider other perspectives. Therefore you're missing the points I'm trying to make. (I have been to the Schluter seminar at the TCNA in Clemson, by the way.)

Here is a simple question. If Ditra channels are taken out of the equation, then what is the explanation for using modified thinset for installing Ditra over plywood, but using UNmodified thinset for installing Kerdi shower pans and curbs over plywood? Remember, you said it has nothing to do with channels, and that it's common sense that the thinset be appropriate for the substrate, and it's too hard to stick to plywood without modified thinset.


No need to get defensive, I'm not here to argue with anyone, just discuss the science and technique.

 

I have been to the Schluter seminar at the TCNA in Clemson, by the way.

Oh, your workshop was at TCNA in Clemson? I was part of JB's Tile Your World group, we held the program at The Ceramic Tile Education Foundation down the road at their main teaching/workshop. Glad you were able to go too.

I think you're looking for reasons to disagree rather than consider other perspectives.

Actually you've obviously got it backwards. You are the one who is arguing with Schluter's specs for installing their products. Their directions trump your opinion, heck, Schluter's direction trump all opinions including the general opinion of the TCNA, TDNA, CTDA and TTMAC of Canada and all others.

To your question in this post, again........ Anything......Anything....Ditra, Kerdi, Ceramic, Porcelain etc, over ply or OSB is installed with modified thinset. Installing any of these with unmod mortar will still bond, but not as well as we'd want, but why do it and risk a sure failure down the road. (Also please do not try to say that I am suggesting people install tile direct to ply or OSB.)

I think you're surprised about Schluter's recommendation about using unmod for under their foam shower tray. Didn't they cover that in Clemson? Who did the workshop? Yes, I was kinda surprised too, but once we get it in our thick skulls that unmod will bond good enough to ply for the purpose of setting the tray, you'll get over it.

You/me are not the first to ever come across this subject and I assure you Schluter knows 10x more than both of us together. So, don't try to reinvent their system, they are the experts.

I was gonna try to find their literature xplaining their theory about thinset, but since you attended, you should already know/have the info. If you missed it, let someone know.

Jaz

 

You are the one who is arguing with Schluter's specs for installing their products.

I am not arguing with any of their installation instructions. If you think that then you simply misinterpret what I'm writing. I am agreeing with the OP that ideas among different manufacturers are inconsistent, and they don't all see things the same way.

(I do have a small disagreement with them technically about how thinset dries into drywall that I alluded to earlier, but this does not mean I don't use their method or think it doesn't work well. We can discuss this in a different post.)

The bottom line is the subject of this thread - different manufacturers give different instructions that are contradictory - more to the point - different manufacturers disagree with each other.

To your question in this post, again........ Anything......Anything....Ditra, Kerdi, Ceramic, Porcelain etc, over ply or OSB is installed with modified thinset.

We all know that Ditra should be - it's right there in the instructions. It's the science behind that the rest of us are interested in.

There is a family of Kerdi products. Kerdi Shower ST goes over plywood/OSB with unmodified thinset. Kerdi Shower SC goes over plywood/OSB with unmodified thinset. Kerdi Flex is designed as a isolation membrane over large joints like movement joints, although it's for use over Ditra. There is no reason to use standard Kerdi membrane over plywood as a decoupler nor as an isolation membrane because there are other products designed and recommended for this.

Speaking of Kerdi Flex, this is a good example of another industry inconsistency - back to the point of this thread. This is basically the same stuff as NobleSeal TS - although the latter is a little thicker. Noble specifies that this product can be use as a crack isolation membrane, and also that modified thinset can be used above and below, but Schluter does not. Why is that? This is the sort of thing the OP is asking. Schluter's philosophy is simply different. They don't think a membrane this small can handle the shear forces involved when a substrate moves. Noble does, and they warrant it that way (claimed more than 1/8").

I think you're surprised about Schluter's recommendation about using unmod for under their foam shower tray.

I'm not surprised at all because I understand their reasoning and their philosophy. The problem - to the OP's question which is the context of this entire thread - is that it's not consistent with the rest of the industry always. So there are some things you're either not understanding or not acknowledging about the context of this thread.

 

Here is an interesting question related to the OP's question.

Strata Mat is basically the same thing as Ditra. However there is one significant difference. Because of this difference
a) Strata Mat can NOT be used as a waterproofing solution like Ditra can
b) You CAN use modified thinset to install tile on top of Strata Mat

The difference is: Strata Mat has little holes in it. This has certain implications related to this thread.

 

Your post #23 above is full of errors and misconceptions, (previous threads too), I can't help you by chatting in this manner. You're gonna haveta edumacate yourself. I suggest you follow directions supplied and just do what the expert who make the stuff tell us to do.

Jaz

Merry Christmas Everyone!

 

Your post #23 above is full of errors and misconceptions, (previous threads too)

I seriously doubt that. There is nothing controversial there. But go ahead and point them out for the forum public record. More people will be referencing this thread later. We are all here to share knowledge. I'd also be interested in hearing about the other threads I've posted in that are "full of" errors and misconceptions. I find that impossible to believe. Sometimes I'm sarcastic or play Devil's Advocate with a question and maybe you misunderstood.

Getting back to the Ditra vs. Strata Mat topic - the channels on the bottom end up being the key to how these 2 products work differently.

Schluter's basic philosophy on thinset use in a nutshell is, if the thinset is "trapped" between 2 surfaces where they feel the thinset can't dry adequately, they want you to use unmodified thinset. (I can't think of any exceptions to this off the top of my head, but I haven't used every single Schluter product so there might be one). So trick question: is it true that you can never put modified thinset on top of Ditra? Well, let's say you're installing Ditra over plywood using modified thinset, and when finished you have a bunch left over. You are not going to be tiling for another day or two. Can you use the leftover modified thinset to pre fill in the waffle holes? Yes. Why? Because now it's not going to be trapped between 2 surfaces where it can't dry. It can cure to full strength.

So, why does Laticrete approve the use of modified thinset over Strata Mat when Schluter does not for Ditra? Ultimately it relates to the channels on the bottom. Laticrete looked at the design of Ditra and said how can we copy that and improve on it?

Probably the biggest image problem Schluter has with this otherwise outstanding product is the fact that they don't recommend modified thinset on it, and this drove many installers crazy. Responses to this ranged from
- sounds good, you know what you're talking about, to
- that sounds fishy, but if that's how I gotta get it warrented, ooookaaaay, to
- no way man, I'll use Ditra but I'm definitely using modified thinset for my porcelain tile, because that's what that manufacturer calls for, to
- no way man, I'm not using that stupid product

(I'm in the first camp by the way.)

How did Laticrete avoid this? They poked little holes in the plastic. This allows the thinset to dry out down through the plastic and out through the bottom channels.

Another answer to the trick question about using modified thinset over Ditra. Technically, it's actually OK by Schluter if you use modified thinset, as long as you let it dry before grouting. So, wait a few months to a year for larger format tiles, so it can dry out through the grout joints. The smaller the tile, the less the waiting. If you get down to 1" or less mosaic, Schluter would probably be OK with you waiting only 24-48 hours, but they won't say that because it's a moot point because they don't approve of tile smaller than 2" anyway (but that's due to a different design problem.)

If anyone doubts this, simply call Laticrete technical support and ask. Or call Schluter and ask if modified thinset can be used to prefill Ditra if it can dry first. (Both products have the same design issue with tile smaller than 2".)

Really, Schluter should have thought of this from the beginning, and understood the American resistance to anything knew that wasn't understood. They should have made Ditra in 2 versions. Version 1 as designed, for waterproofing solutions. Version 2 for use with modified thinset. They would have avoided tons of confusion and controversy and made more sales.

 

I'm curious now, has anyone here had long term experience with liquid crack isolation membranes vs solid ones like Proflex, Protectowrap, Schluter, etc over flat (non lipping or offset) cracks and expansion joins in concrete slabs? I'm a tile newbie and none of my installations are older then 5 years. I can't see the paint or roll on membranes working, if there is future movement at the crack zone. I've used Proflex and Protectowrap and both have worked fine so far, but I don't know if there has been any slab movement since laying the tile.

 

Hi Clarence,
I have no experience with the liquid ones, but if you want to visualize how they would work, just envision them as a solid, because they are going to dry. Now they are basically like the solid ones. So at that point, the things to consider are:
- how thick is the membrane? (all else being equal, a thicker membrane will offer more movement)
- what material is it? (some with move more for a given thickness than others)
- how well is it adhered to the substrate and tile?

So the liquid applied membranes can work, but to get them as thick or thicker than some solid membranes, you might be able to apply multiple coats depending on manufacturer instructions.

It seems intuitive that a liquid membrane could potentially adhere to the substrate better than thinset, but not necessarily. It also seems intuitive that tile would adhere better to NobleSeal TS, for example, than to the liquid applied membrane, because of the fleece fabric on the TS.

Ditra is also technically a solid isolation membrane, and intuitively you can envision that allowing more movement than the membranes we're talking about above. I would use Ditra except where I can't. For example, if you have to do a tile repair of just a few tiles over a slab movement joint what wasn't protected to begin with, then Ditra would raise the level of the new tiles too high. Or if you're installing tile smaller than 2", you would also have to choose a different system. Those are two situations where I've used NobleSeal instead of Ditra.

 

Doesn't a membrane work as an uncoupler? The bottom layer is adhered to the slab and the top layer is adhered to the bottom of the thinset layer. The center layer is a type of rubber that can flex slightly. If the slab moves just a tiny bit, the flexible rubber center stretches and keeps the movement from going to the non flexible thinset and tile. How can a paper thin layer of anything work like that?

 

I'll answer your question literally, just for some perspective on this. Let's say the thickness of paper is .05mm, which is 2 mils. Now take NobleSeal TS (there are others, I'm just familiar with this), which is 30 mils. So you're right - a paper thin layer can't hope to do nearly as well as the thicker layer of the same material.

But to answer your question literally again, a paper thin layer can still "work like that". It just has very, very little movement that it can handle. Too little to be of much practical use.

Now if you can get that liquid membrane applied at 30 mils thick somehow, it would have much more movement in it - the same as the NobleSeal when solid.

Frankly, it surprises me that NobleSeal can move more than 1/8" that way! But that's what they claim, and I'm not a materials scientist.

 

Handyman,

I think it's not a good idea to refer to Laticrete's directions when we were supposed to be discussing Schluter's Ditra. They are two different products and if you want a warranty you should follow directions. You should follow directions even if you never expect a warranty issue to arise. Heck, I never used the warranty cry to do things the right way.

Yes, I know it's just a way to confuse the issue, when you really just disagree with Schluter's directions. If you know more than Schluter, I suggest you contact them and tell them so. In any case I'm positive Schluter will be very happy if you decide to use a different system.

Having said all that........... as I stated earlier, I too was slightly confused (actually didn't know I should/could use unmod), many years ago when I finally decided to use Ditra instead of CBU for the first time on floors. I naturally used the same high quality modified thinset as always. Tec's Full Flex. While other contractors were buying Versabond for $11 retailI at the orange place, I was paying $23 wholesale. I thought I had to use modified for porcelain, plus I needed a modified to install Ditra over ply anyway, so..........

Then finally in '06 while at The Surfaces Trade Show in Las Vegas, Schluter announced they had licensed Hydroment/Bostik to develop an unmodified mortar that they could put their name on. There were other high quality unmods around, but some people weren't sure what to use.

You probably know that to this day some contractors still can not bring themselves to install porcelain over Ditra unless they use a modified, and heck with the warranty. They therefore justify this by using an entry level (cheap), modified such as Versabond or an even cheaper one. Fine, no problem.

You are absolutely correct that Schluter woulda been better off to just not say anything about using unmod over Ditra and avoid all the arguing and doubting since we've been accustomed to believing that unmod thinset will not bond to porcelain. Of course that thought is wrong, but some people still don't grasp why it works well over a product like Ditra.

Jaz

Merry christmas Everyone! :smile:

 

JazMan, I'm not sure why you're coming to some of these conclusions about what I'm saying. I'm sure you're good at what you do (anyone who has researched these things to his extent probably is). You sound like a real pro. You probably pay attention to detail and think logically. I wish you would do so in this thread. I also don't appreciate the accusation that I'm making posts in other threads that are "full of errors", without providing any references to them. I would like to think you would not try to create doubts about someone's competence just to win an argument, because that is beneath us.

I'll address a couple of your specific points, but first let me be perfectly clear. I always follow manufacturer directions, including Schluter's. I am a big fan of Schluter products and use them for 90% of my tile work. I am not recommending anyone not follow manufacturer directions, including Schluter's. If you think I've implied anything contrary, you've misunderstood me. If i say something that seems confusing, just ask.

I think it's not a good idea to refer to Laticrete's directions when we were supposed to be discussing Schluter's Ditra.

This thread started with 2 questions, a specific and a general regarding modified vs. unmodified thinset (I even just repeated the thread title). The difference in recommendation between 2 manufacturers of 2 competing products is extremely topical and relevant.

Yes, I know it's just a way to confuse the issue, when you really just disagree with Schluter's directions.

I do not disagree with Schluter's directions. I follow them always. There is a concept or reason that I disagree with that I will explain in a separate post, but that's not saying I disagree with their directions. Hopefully you can appreciate the difference. I do not claim to know more than Schluter, but I do have master's degree in the sciences, I have a brain, and sometimes I like to exercise it a little. Questioning things and not always taking everything for granted can be a good way to do that.

I too was slightly confused (actually didn't know I should/could use unmod), many years ago when I finally decided to use Ditra instead of CBU for the first time on floors.

That is perfectly understandable, and I applaud you and any other contractor for trying new technology. One of my pet peeves is when tradesmen do the same thing they've always done, for the reason that "they've always done it that way". So my hat's off to you.

However, by saying "I too", you imply that I was confused or thought I should use modified thinset over Ditra. I have never been confused about it nor have I ever done it. I read the instructions, I made a quick call to Schluter's tech line to ask a question, and satisfied with their anwser, I was on my way.

You probably know that to this day some contractors still can not bring themselves to install porcelain over Ditra unless they use a modified, and heck with the warranty. They therefore justify this by using an entry level (cheap), modified such as Versabond or an even cheaper one.

Agreed, and in addition you raise a good point I hadn't thought of. There probably are installers using lower quality thinset than they otherwise would have had they used modified thinset!

You are absolutely correct that Schluter woulda been better off to just not say anything about using unmod over Ditra and avoid all the arguing and doubting since we've been accustomed to believing that unmod thinset will not bond to porcelain.

Nope, not what I'm saying. What I'm saying is that back from the beginning, Schluter should have developed 2 products - Ditra A for standard use with modified thinset, and Ditra B for when waterproofing is desired. Ditra A would have holes in it (i.e. like Strata Mat), and Ditra B would be their current product, requiring unmodified thinset. This design of Ditra A would not be in contradiction of their philosophy on thinset use. They could have virtually cornered the market, with no confusion about thinset for everyday contractors, and at the same time offered a solution for waterproofers who, like you, were man enough to step up to the plate and learn something new. It would have been gold.