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ProvaFlex vs Ditra

by Roger

Ditra vs ProvaFlex

Ditra vs ProvaFlex

That’s right, I said typed it! Bring it on :guedo:

In the last month or so there has been a lot of hype about Loxscreen’s new polypropylene tile underlayment membrane. That’s just a big phrase for plastic tile underlayment. It is being marketed as a replacement product for Schluter Ditra.

Since I use Schluter Ditra almost exclusively as my preferred underlayment for floor tile I felt it would be a good idea to give this stuff a try. I did not do this in order to find a replacement for Ditra, I’m extremely happy with Ditra. I do feel, however, that due to the way this product is being ‘marketed’ to consumers and since it claims to be a replacement for a product I regularly use, people may want a professional opinion about the way it performs. AND! if there is something better out there – I want it.

There is also another very good reason I decided to do this: there happens to be one person all over the internet claiming this product to be better than a silk jockstrap. I’ll save that rant for the end of this post but suffice it to say that, at the very least, I vehemently disagree with his marketing tactics. If you would prefer to start with that rant please feel free to scroll to the end.

I will attempt to be as unbiased as I can as a firm believer in Ditra and the mechanical way in which it works. So to understand the key points of this comparison we should first begin with a basic understanding of that. I will just give an overview of a couple of key parts but you can read the official line from Schluter Here.

Tile being installed over Ditra

Tile being installed over Ditra

Schluter Ditra is a polyethylene membrane with square dovetailed cavities and an anchoring fleece laminated to the underside. The Ditra is attached to your flooring substrate by embedding the anchoring fleece in thinset (modified or unmodified depending on the substrate to which you are installing it). The dovetailed cavities on top are then filled with unmodified thinset and thinset is combed over the top and your tile is installed to it. The photo to the right shows the tile being installed.

The key component  is the dovetailed cavity of the Ditra. See, the thinset does not actually adhere to the polyethylene (which, for purposes of not confusing anyone, and you know, not sounding like an uppity bastard, I will hereafter refer to as the ‘orange plastic’) This is completely normal and in no way compromises the installation – it is normal and on purpose.

Ditra utilizes a mechanical fastening rather than a chemical one. Thinset ‘sticking’ to the orange plastic would be a chemical bond to the plastic. Filling the dovetailed ‘waffles’ forms a mechanical bond by locking the thinset into the cavity.

Cross-section view of Ditra's dovetailed cavities

Cross-section view of Ditra's dovetailed cavities

The photo to the right is a cross-section view of Ditra. You can see how the cavities are angled back from the top opening of the cavity. The cavity gets wider as it gets deeper – that is the ‘dovetail’. After this is filled with thinset and the thinset cures it is nearly impossible to pull the thinset out of this cavity – it will not move, it’s locked in there. That is what I mean when I refer to a ‘mechanical’ bond.

A mechanical bond is the main reason I use Ditra. This will allow the ‘micro-movements’ in the substructure without transferring them through to the tile installation. The entire tile installation becomes one large monolithic structure which is able to move independently of the substrate. This means that the joists below your floor, or the concrete, can expand, contract and shift with the small movements inherent to structures without compromising the tile installation.

Or, more specifically and simply, when winter hits and your joists expand a little bit your tile and grout will not crack.  Get it? Now I’m not talking typing about a major movement like a bulldozer crashing into the side of your house because  I someone was doing roadwork while intoxicated. I mean the normal movements of any structure under seasonal changes.

That is basically how and why Ditra works. ProvaFlex, according to all the marketing and hype, is supposed to do the same thing. In fact if you read through all their (online) literature (yes, I have) it is nearly identical to everything Schluter has published about Ditra. So let’s start with the similarities.

Both products are marketed as an uncoupling membrane (this is what I’ve described above – the independent movements).

Both are marketed as having waterproofing ability when coupled with the respective band or tape for the seams. However, ProvaFlex is not recommended for use outside of a covered structure – you’re not supposed to use it on your porch.

Bottom of ProvaFlex next to bottom of Ditra

Bottom of ProvaFlex next to bottom of Ditra

Both are marketed as having vapor management properties. This is a method of equalizing or dissipating vapor through the open channels beneath the membrane to prevent moisture build-up below your substrate. Confused? Nevermind, then, for the sake of argument let’s just assume that they both do that.

Both have an anchoring fleece laminated to the underside. The anchoring fleece is what is set into the mortar on the substrate to attach the membrane. They appear identical to me, and are identically difficult to pull off of the plastic membrane itself. I didn’t put a scale on it to gauge the difficulty, but it seems nearly identical to me – so let’s go with that. They’re the same.

Both are a form of plastic. Ditra is polyethylene and ProvaFlex is, well, I’m not really sure what ProvaFlex is. The online literature states it is polyethylene as well but the written literature included with the product states “Polypropylene material – Impermeable against other building chemicals. Easier to install and lays out flatter than polyethylene.” I do know that it did indeed seem to lay out a bit flatter than Ditra but that may be due to the smaller cavities in the top or the type of material – I can’t say which for certain. Someone apparently has their wires crossed somewhere and it is my opinion that it is the available information online because, well, why in the hell would you send erroneous information with the actual product? But, I really don’t know. There will be more about this in my rant. :D

So it would seem that both products are marketed with identical benefits. But we all know that without actual hands-on use I could market a baseball bat as an environmentally friendly hammer – doesn’t make it true. So let’s move on to the differences.

Top of ProvaFlex

Top of ProvaFlex

The ProvaFlex has an overlaying mesh or webbing attached to the top of it. I like this. It just seems like it would add more of a mechanical fastening to the membrane and stiffen up the installation itself. Whether that is actually true or not – I have no idea, but I still like the fact that it is there.

ProvaFlex with overlaying mesh removed

ProvaFlex with overlaying mesh removed

When I peeled this webbing off, however, I was a bit disappointed in how easily it was peeled back. I expected it to be nearly as difficult to remove as the fleece on the underside – it was not. It is attached fairly well but not nearly as well as I would have liked or been comfortable with. Maybe I’m just an anal bastard a demanding consumer – I don’t know. I still like it, though.

Ditra’s surface is comprised of 3/4″ square ‘waffles’. ProvaFlex’s surface is comprised of alternating 3/4″ circles and 7/8″ ‘flared’ squares – or whatever the hell you wanna call that shape, with raised circles in the center. Shape-wise (is that even a word?) I don’t think it makes much of a difference but I can’t say for sure one has the advantage over the other so I’m callin’ that a wash. I will say type that the ‘pillars’ created by the Ditra will have a bigger, more consistent footprint in contact with the substrate.

The thickness of both products seem identical but if you slam a micrometer on them I would guess the Ditra is just a platypus hair thicker. (A platypus hair is really thin, by the way. Don’t ask me how I know that, let’s just say it involved a midget and a case of scotch…or so I’ve heard :whistle: )

So this far I would call it fairly even as far as a practical application indoors. If you don’t agree, well, start your own damn blog. I’m callin’ it even – up to this point. There is one major difference that is almost certainly a deal-breaker for me – the ProvaFlex cavities are not dovetailed.

The online literature and marketing hype – all of which compares it as an alternative for Ditra at a lower price – states, and my computer quotes “…with a grid structure of square, cut-back cavities…” Just a bit (ridiculously) misleading if you ask me. The shape of the cavities is most certainly not square and if by ‘cut-back’ they mean dovetailed – they most certainly are not that either.

This may or may not be a marketing ploy – it is not for me to say (yet) but the description can ‘technically’ be described as accurate if by ‘cut-back’ they mean the shape of the funny looking squares and by ‘square’ they mean the shape of the cavities in the z-axis, as it gets deeper.

Physical literature included with ProvaFlex

Physical literature included with ProvaFlex

This, however, only seems to be on the online marketing sites. The physical literature included with the product itself specifically states “Square Cut Adhesive Cavity” pointing to a square (not dovetailed) cavity on the surface of the membrane. It does not seem to me that the Loxscreen company, the manufacturer of ProvaFlex, is attempting to pull the wool over anyone’s eyes as far as comparing it as an identical product in form and function. Not as far as the mechanical bonding process, anyway. It appears to only be the online marketing.

Cross-section views of ProvaFlex and Ditra

Cross-section views of ProvaFlex and Ditra

The photo to the right shows the cross-view of both products right next to one another. If you click on it and ignore my shitty photography skills you can plainly see the dovetails in the Ditra (top) and the square (or slightly rounded) cavities in the ProvaFlex (bottom).

If you can envision filling the cavities of each product with thinset and allowing it to cure then pulling straight up on each, what’s gonna happen? Without the mesh or webbing on the ProvaFlex that little fill of thinset will pull straight up and out – the Ditra will not, it is locked in due to the dovetail.

I’m no expert or anything (yes I am) but it appears to me that the ProvaFlex’s mechanical bond relies on the mesh or webbing attached to the top of the membrane. The method of the mechanical bond is different.

The bond for the Ditra relies entirely on a mechanical process, the aforementioned dovetails. The bond for the ProvaFlex relies also on a mechanical process, the webbing or mesh attached to the top of the membrane. This webbing, in turn, is attached by means of a chemical process.

I’m unsure what this chemical process actually is. I’m certain it is a trade secret and they would send black helicopters after me if I were to divulge it. I don’t know – I don’t care. It does not change the fact that the bond with ProvaFlex is not truly and entirely mechanical. The entire bond of your tile installation relies on the process and durability of the mesh webbing attached to the face of the ProvaFlex membrane.

So when you decide which product you want to use under your tile installation you should take into account the method of attachment. ProvaFlex seems like a decent product for a small application such as a small bathroom without excessive traffic or maybe a small countertop. It is entirely up to you whether to use it or not.

It will work to an extent and with certain applications. I just did two bathroom floors with it which I now own. That means if this stuff fails I’m paying to replace them, so it better not fail. But with any new product someone has to take that risk. If it does fail I will absolutely let everyone know – believe that.

This product will not be a replacement for Ditra for me. Anywhere I can use ProvaFlex I can use Ditra instead. I don’t believe the reverse to be true. If you install hundreds or thousands of dollars worth of tile do not nickel and dime the price of your underlayment. Saving one or two hundred dollars now may lead to replacing the thousands of dollars worth of everything later on down the road.

I am not saying it will fail – I’m saying I don’t know. With Ditra I know.

RANT-RANT-RANT-RANT!

This is not a rant against ProvaFlex, it is a rant against particular individuals marketing ProvaFlex on the internet. If you want to know who it is – google it, this jackass is all over the place.

I have no problem with marketing a product. I do have a problem with the method it is gone about. If someone needs to bash another company in order to sell their own (or one they are shilling) it is not only disingenuous, it is absolute bullshit.

The marketing descriptions and literature available online from this particular individual seems to be at complete odds with the product’s own marketing information. That is a big red flag.

This person apparently has had a disagreement or falling out with the Schluter company (as well as a couple of other very large, major companies in the industry) and has taken it upon himself to attempt to discredit everything about them.

Under the guise of ‘Schluter is crap and they screwed me so here’s a better product…’ he attempts to peddle ‘Prova’ products claiming they are better engineered and cheaper than Schluter products. They are cheaper, no question. Better engineered? You be the judge, that’s why I did this.

This guy bashes everything about Schluter, attempts to make false arguments such as ‘thinset doesn’t even adhere to Ditra’ (no shit) then turns right around and copies their marketing literature and substitutes his product in place of Ditra and Kerdi. THIS is where the inconsistency in things such as the polyethylene and polystyrene differences come from. Oops, forgot to change that part – jackass. The “…with a grid structure of square, cut-back cavities…” quote earlier happens to be exactly how Schluter describes Ditra – which is accurate.

The descriptions, methods, and even chemical makeup of the product, is at complete odds with the product’s own literature. Why would that be? I have absolutely nothing against Loxscreen or Prova-flex, hell, I tried it myself. I do take issue with assholes attempting to discredit one product in order to sell another. I believe if Loxscreen wishes to own a decent market share of this industry in the United States they should prevent this asshole from selling their products.

ProvaFlex may indeed be a product inspired by Ditra but it works differently, people need to know that. Attempting to force-feed the idea that it is an identical but cheaper product is bullshit. You are taking advantage of people inexperienced and uneducated about what the product should do for the purpose of profit. Please kindly go throw your own dishonest ass off a large cliff.

Please, please research anything you plan on using for a tile installation. Get more than one opinion – always. Even if that one opinion is mine (which is right, by the way) go get it from someone else. The better educated you are about it the better off you will be.

Now that you know how ProvaFlex works you can make a more informed decision about whether the amount you save is worth it for your particular application. If you want to use it and it sounds like the right product – use it. Just don’t buy it from the asshole.

If you have any questions please feel free to leave a comment. I’ll help if I can. Please understand I’ve only used this product for one installation so all my information is based on that. I have used Ditra (literally) hundreds of times. If you are the particular asshole I’m ranting about – and you know who you are – stop taking advantage of people’s inexperience and feel free to go find the aforementioned cliff.

Rant over. :censored:

Tell your friends what a jackass I am!
greg February 6, 2012 at 11:39 pm

I had a question about tile in my bathroom. I planned on putting tile directly over the existing tile. The old stuff is solid and in a mud bed. The problem I came across is I changed the tub and found some rot in the 3/4 planks. had to change some under tub and I had to change the first one going from tub under the old tile. I cut out the 7″ of tile and mud neatly with a diamond blade and changed the board. I’m about to fill in this hole now thats 5×1 and 2.5″ deep. what can I fill it with and how do I prevent it from cracking where the old floor meets the new cement or whatever is used. can I put a liquid crack membrane over the spot or over the whole floor? I don’t want to get into the whole ditra thing. Thanks greg

Reply

Roger February 7, 2012 at 7:08 pm

Hey Greg,

You can mix up some deck mud and fill it with that. A liquid membrane would work well at least over that area, the entire floor would be better.

Reply

greg February 7, 2012 at 8:39 pm

Okay thanks ! So I can use a liquid membrane over the existing tile as well? What brand membrane would you recomend?  would it be helpfull or okay to put a mesh type tape over the joint of old to new before I apply the liquid membrane?

Reply

Roger February 7, 2012 at 10:26 pm

Yes you can. My choice would be Laticrete hydroban, but redgard will work also. I always helps to tie old to new with mesh tape.

Reply

Tony February 3, 2012 at 7:55 am

Are these materials effective when used to repair a stress line crack in tiles that were initailly layed without them? Thanks. Tony

Reply

Roger February 3, 2012 at 8:18 am

Not in the tile itself but they can be used over stress fractures (spider-webbing) in the concrete to prevent future cracks. The problem with using these materials as a crack-suppression membrane is that they both have considerable thickness (relatively) and cannot be used to repair a small area, it adds height to your tile. If you just need a crack-suppression membrane to repair a small area you can use a liquid membrane such as redgard or any of the crack-suppression specific products available such as NobleSeal CIS. These products do not add noticeable height to your installation beneath the repaired area.

Reply

Buddy January 30, 2012 at 6:49 am

Roger,

I have just finished installing porcelin tile over ditra and am having problems with grout color. I am installing porcelin 12″ tile indoors over some cement and the rest plywood. I am using Mapei Keraset mortar above and below the ditra on the cement and Mapei Ultraflex mortar below the ditra and Keraset above the ditra on the plywood. I am doing 1/4″ grout lines and started with Keracolor S Mocha sanded grout. My problem is that the mocha color turned chalky white upon drying.

I did a little research on the Mapei site and they suggested that I might be using too much water in the mixing or cleaning stage. I made sure I did not use too much water in the mixing stage and I also tried bottled water (I am using Well water and was worried about minerals being too high). I retried using much more care in the cleaning step with regard to how much water I used. I did this several times and while the results did improve some, the color still has chalkiness to it and is not consistent (everywhere is somewhat chalky but some areas are more than others). I still think this has to do with water but I have tried everything I can to minimize or be more careful with water. I have several small areas that I am restricting myself to until I resolve this issue but am getting tired of digging up grout. I have done it twice now.

By the way, what is your suggestion on how best to remove grout? I used a Spider grout blade on my reciprocating saw with pretty good results. But the blade wears quickly if you are not careful.

So, any answers/suggestions on what I should do? How about using an epoxy based grout? Suggested manufacturer?

Reply

Buddy January 30, 2012 at 6:51 am

Oops – Porcelin = Porcelain

Reply

Roger January 30, 2012 at 5:19 pm

Hey Buddy,

Certain Mapei colors are touchy, the mocha seems to be the worst. (Not that it helps) Try taking a drywall sanding sponge and going very lightly over the surface of one of the parts where it is white or lighter than normal. If you have the correct color under the very top layer then you can likely just overfill a bit, let the grout cure (and the efflorescence show up) then go over it with the sponge. You can also try some enhancing sealer and see if that works – sometimes it will.

When I do remove grout (very rarely) I just use a small hand grout saw. Never used one of those blades but a bunch of guys who do that stuff regularly like them very much, so if you’re taking out a lot what you currently have is likely your best option.

You can also go with a different grout – tec’s accucolor is very, very accurate, as are laticrete’s grouts. If you want epoxy laticrete’s spectralock is ALWAYS a dead match for the color samples.

Reply

Buddy January 31, 2012 at 5:52 am

Thanks for the input.  I have not tried the drywall sanding sponge but I had tried a wire brush in one area and the efflorescence seems to be not just a surface issue.  I have tried scrubbing, haze remover, sealer, regrouting with bottled water and being extrememly careful in cleaning multiple times and the color looks better at first but in the end the color seems to go back to chalky white.  As one might expect, it looks right when wet but after drying it is back to white.  It is not even an issue of it not matching exactly the color samples, it is not even close.  Such that something in the process must be wrong.  I have even tried a different bag of grout to see if there were something wrong in the first one.  I may move on to epoxy.  It is not that I want epoxy, I just want approximately the dark chocolate brown color or at least close to it.  While epoxy has advantages (I assume from reading), I am not set on using it.

Reply

Buddy February 8, 2012 at 5:15 am

Roger,

Just as an update, I tried TEC Invision Premixed and Laticrete SpecraLock and both worked well.  As you said, the SpectraLock was spot on and other than the fun of smelling Vinegar, it worked well and I liked it.  It is just quite expensive for a large area.  The TEC invision was a little annoying.  It seemed to want to stay wet for a long time and their directions did not seem to indicate times between putting down and cleaning so I was not sure if that meant immediately or not.  Other than the cost, I would choose SpectraLock but the Invision is 1/3 of the cost and the color seems to be good.  Do you have any suggestions on when to clean the Invision?  Immediately or X amount of time?

Reply

Jackie January 27, 2012 at 11:18 pm

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Hi Roger, I came across your site, thank you. I am getting overwhelmed with conflicting information from the big box stores. I have lots of questions, I will start with one.  I want to tile the walls in a small toilet room, 43” x 46”, I only want to tile 3 ft up the wall actually.  Do I have to use backerboard?  The walls are drywalled, finished and painted.  Can I apply the ceramic tiles, 6 x 8, directly to the walls with the premixed adhesive?  It is a very small area, water and moisture will not be an issue.  I have tiled several small floor areas, but never vertical walls. Thank you for your advice. Jackie

Reply

Roger January 27, 2012 at 11:25 pm

Hi Jackie,

You do not need backerboard, you can tile directly to the drywall. You should use thinset, but you can use a type II mastic (premixed) if you want. Make sure the particular adhesive is approved for tile that large – it will give you the maximum sizes on the bucket.

Reply

Andrew January 27, 2012 at 2:44 am

Hey Roger,
Your site is great, thanks for the advice.  I know you have covered part of this before, but I would like to further clarify your opinion on using modified thin set between Ditra and tile.  I have used Ditra many times with Laticrete 253 Gold on smaller jobs like bathroom floors and had no problems.  I am soon to do a much larger job, in a kitchen, and would like to use 253 again.  I would prefer to set it all at once instead of filling the Ditra one day and then setting tile the next.  253 is listed as being suitable for use over plastic laminate and over vinyl, so I wonder if it has different qualities that would allow it to set properly with limited drying?  Have you ever used 253 with Ditra in this way?  I’m not worried about warranties, just practical application.  I read elsewhere on your site that Schluter no longer restricts use of modified thin set in Europe.  Why not?  If you were to use the method I suggest with 12×12 porcelain tiles, how long would you wait to grout? Finally, I want to use 253 because I am hesitant to trust an unmodified mortar and have had good success so far with the 253.  It sounds from your many posts that you also prefer modified mortar, am I correct, or would you think I’m better off using 317?
Thanks

Reply

Chris January 27, 2012 at 3:14 pm

Andrew, you use the 253 gold to mortar the ditra down with. Then you use the 317 to put your tile on top of the ditra. You don’t have to fill the Ditra and let it dry, you can fill it and set tile as you go. If you use the 253 to set your tile it will not fully cure between the Tile and Ditra. Modified Mortar (253 Gold) needs air to cure, the latex in it gives it a longer cure time. Unmodified Mortar (317) does not need air because it’s just sand and portland cement (no latex). And the mortar will not stick to the ditra that is why they call it mechanical fastening and that is why the ditra is dovetailed to lock the mortar and tile into place. Hope this helps and good luck which ever way you choose to go on it!

Reply

Roger January 27, 2012 at 6:12 pm

253 does not have any particular properties regarding the lack of air required to cure the polymers, it simply have the ability to adhere to those product. It will not adhere to the ditra. If you use the 253 you NEED to pre-fill and let it cure overnight before setting the tile, especially with porcelain. The polymers require air to cure, if you slam a porcelain tile over the 253 in the dovetails it will not cure in any reasonable amount of time. I would not suggest doing it with the method you mentioned, but since you asked I would wait 45 days before grouting. :D

I prefer modified mortar for porcelain tiles because the tca standards require modified for porcelain. That said, manufacturers recommendations always trump those standards, but it’s simply my choice. If you use modified you need to pre-fill. I have used the 253 over ditra plenty of times, most recently on 1200 square feet of marble, but I pre-filled it all. They don’t restrict it in Europe partly because their modified is different and partly probably because everybody bitches about it – that last part is just a guess, though. :D

EDIT: My comment section in my website (on the backend) lists comments in the order they were written, I just noticed Chris’ reply below. He is correct – that is exactly how Schluter wants you to do it. He is absolutely correct about everything he’s written.

Reply

Andrew January 27, 2012 at 11:18 pm

Hi Roger,
Thank you for the reply.  I am well aware of both Laticrete and Schluter technical documents on the correct use of their respective products.  Laticrete specifically states that you should not use 317 over Ditra with porcelain tile and they recommend 253R or 254R (rapid set) both of which are modified mortars (Laticrete TDS 147).  I am hoping to avoid the rapid set because of the large area I need to cover.
I get the general concepts of why modified might not set right, but I was hoping for a bit more technical discussion with someone who obviously has had a lot of experience with the products.  Here are the two things that I find, shall we say, “hard to figure out.” 
First, if the 253R is OK and it is a modified mortar why would there be any difference between that and 253 other than time.  Since 253R has a set time of 4 hours and 253 has a set time of 24 hours what significant difference is there in evaporation rate due to the substrate.  It seems you are still trying to evaporate the same amount of water or move the same amount of air through the same surfaces.
Secondly, as to your method of filling the Ditra then setting tile the next day, you still have an impervious substrate under the tile.  You have added some dry mortar between the plastic and the tile but you still have a sandwich which is impervious (or mostly so) on both sides.  How much impact can an extra 1/8 inch or less of mortar under 1/2 the tile (i.e. the space of the dovetail recess) make to the overall drying time? 
Final question, based on your previous comment.  It sounds (reads) like you would not see any difference in a job of 10 tiles vs. a job of 100 tiles from the perspective of air circulation for curing.  If that is true, would it be reasonable to test the various installation techniques, using a small sample of say 5 or 6 tiles set on a test board, and torn up 24 or 48 hours later, to determine the bond strength?
Thanks again for your answer and your site.  This is the first place I have come across where anyone has provided even a basic discussion of the practical implications of modified thinset over Ditra rather than just “cuz the manufacturer says so” explanations.  I’m one of those crazy people that never learned to stop asking why.  BTW, I really enjoyed reading the discussion you had with “Michael” last June under the “effects of improper Ditra application” thread.  I don’t really think he ever really “got it”, though.

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Roger January 28, 2012 at 12:32 am

To answer your questions it would be easier to separate the two main ingredients in the thinset – portland and powdered polymers. The portland, as you know, cures strictly through hydration which does not require air exposure. The polymers in the regular 253 require air to cure. The rapid set, however, contain a different polymer – rapid set does not require air to cure. So even though it is modified the rapid set thinsets do not require air exposure to fully cure.

You don’t necessarily have an impervious substrate beneath your tile by pre-filling your waffles. Half of it is – the top of the plastic. The other half, the waffles, contain cured thinset. However, when thinset cures the portland does not always utilize a complete hydration process. By that I mean that by adding more water you can restart the crystallization process in the cured thinset. The crystals in the waffles will only grow until they are out of water to hydrate with – once it’s gone they stop growing. Introducing more water reactivates the crystals and they begin growing again. The substrate (filled ditra) will suck moisture from the fresh thinset and utilize it. The cured polymers in the waffles, however, will not rehydrate or re-emulsify with this moisture – once it’s cured it’s cured forever. This is why the hardest concrete was cured underwater and you can make your installation stronger by keeping it covered – it’s why they cover driveways after they pour them – makes ‘em stronger.

So once you fill the waffles and let it cure it would be no different than installing tile directly to concrete with a modified thinset, which is the recommended procedure. It will add a bit of (full) cure time to the installation, but not exorbitantly so. If, however, you fill the waffles and set at the same time with modified the polymers (in regular 253) in the bottom and sides of the dovetails will not fully cure in any reasonable amount of time. When filling it will cure because you have the entire top of the waffle open to air, it can get into the thinset (or more literally the water can evaporate from the dovetails creating a type of ‘air-flow’), if you cover it with porcelain it will take much, much longer. It is less than 1/8″ but it really does make a big difference in curing times.

I encourage you to make sample boards! There is no real difference in 1, 10 or 100 square feet with curing time – it’s the same. Make one board with filled and cured waffles then install both the same day and take them apart the same day. One with pre-filled and one filled as you set the tile. You’ll notice that the one that was pre-filled will be cured much more quickly than the one you filled as you set. You actually only need one full tile – cure is the same. The one you fill as you set will have darker (less cured) thinset in the bottom, and around the inside, of the dovetails. Mostly toward the center of the tile. The thinset against the back of the tiles (between the ditra face and tile) will both be cured, or nearly so. The cure in the dovetails is where the issue lies.

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Andrew January 28, 2012 at 5:17 pm

OK.  Thanks, Roger.  I’m still a little confused about why 253R would not need air, but your explanation makes sense.  I think at this point I would probably need a better knowledge of the chemical make up of the polymers which is beyond the scope of this site, and probably my brain in general!
 
Anyway, thanks for the input.  I will probably run a test board for my own curiosity and if so, I’ll let you know the results.
 
Last question.  When you pre-fill your Ditra do you fill it flush so the orange grid still shows or do you completely cover it with a skim coat above the surface?
 
Thanks!

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Roger January 28, 2012 at 7:36 pm

It is a bit beyond the scope of this site, but not beyond the scope of the jackass who runs it. :D The easiest place to begin understanding it would be by understanding what is called ‘controlled-cure technology’. Developed by Custom building products it essentially controls the rate of hydration in the cement. You can read about that here: Conrolled-cure technology. If you care to delve deeper into it a basic (HAH!) understanding of cements, silicates, curing processes and methods is a good place to start – you can find that here: Specialty cement facets. Good start, if you’re interested.

Just fill the ditra flush. If you go over the high plane it will just flake off as you’re working on it – it’s a mess. If you use your grout float to fill the waffles it’s much easier and cleaner.

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Vance Moore January 7, 2012 at 3:45 pm

Hi, Roger *
We’re in South Florida and we want to put 6×24 porcelain wood look tiles on our concrete slab ground floor.  Our local contractor is recommending Pro-Flex 90 (ProFlex Industries, Inc.) and we  though Ditra would be a better product.  ProFlex does not appear to be the same as ProvaFlex.  We’re confused!  Would you insist on the Ditra??  Thanks !!
 
 
*(a/k/a The Floor Elf)

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Roger January 7, 2012 at 4:21 pm

Hi Vance,

Pro-flex 90 is a different product and has nothing to do with provaflex. Pro-flex is a sheet crack-isolation membrane, which would be suitable for tile installation over concrete. I have never used it so I cannot speak to it’s durability or effectiveness, but I have used several different similar products and they are all essentially the same (OVERALL – Don’t want to deal with the hate mail :D ) and work just fine.

That said, a crack isolation membrane will do just that – and only that. You do not get the uncoupling properties nor the vapor management abilities of ditra. In my opinion, given the choice in an area where either was suitable, I would take the ditra every time. If you want ditra, tell him you want ditra. If he doesn’t want to use ditra – tell him you’ll find someone who will. YOU are paying the bill, no? It is YOUR house, no?

I understand some contractors do not want to, or refuse to, use certain products – I’m one of them. However, if I have a customer who insists that a product I will not utilize be used I have absolutely no problem letting them know that I am not the contractor they were looking for. If you want ditra, tell him to use ditra or hit the road. :D But the pro-flex 90 will work just fine for your installation, he isn’t trying to rip you off or anything, it’s likely just a product he prefers.

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Ulf December 9, 2011 at 8:32 am

Hi Roger:

I want to use Ditra for my bathroom floor. But I also want to use a electric heating membrane where we’ll be standing by the sinks. Do you have any experience with electric heating and ditra?

Thanks.

Ulf.

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Roger December 9, 2011 at 10:39 pm

Hi Ulf,

Yes, I do it all the time. Read through this: http://floorelf.com/how-to-install-suntouch-warmwire-in-floor-heating-part-1

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sue November 19, 2011 at 7:02 am

I used the prova flex, And I did everything it said but I feel the tile going up and down like it’s still sofe why?

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Roger November 21, 2011 at 5:56 pm

Hi Sue,

How long has your thinset been curing? What is beneath your prova flex? Does your floor have the proper deflection ratio? Was your thinset mixed too dry? Did it skim over before you placed the tile on it? Does the tile sound hollow when you knock on it? It could be (literally) a couple of dozen different reasons, but I would need to know a lot more about your installation to be able to help.

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Gordon November 9, 2011 at 6:37 pm

My project is an outdoor patio 13′ x 17′. The existing base is a 4″ slab, intact but rough surfaced. I have about 1 1/4 to 3/4″ elevation remaining to fill. Half of the finished floor (6″x 12″ porcelain tile) will be flat; the other half will drop 3/4″ to a scupper drain in the brick perimeter wall.

1) What would be the best material to float the final bed, allow for the slope, and support the DITRA?

2) Will DITRA conform to the 3/4″ over 8.5′-13′ slope on the drained end?

Thanks for your thoughts.

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Roger November 9, 2011 at 9:49 pm

Hi Gordon,

I would use regular deck mud to float that out where you need it to be. Ditra over a mudbed is fairly bulletproof. And yes, ditra will conform to whatever you need it to.

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Carolyn September 24, 2011 at 12:47 pm

Two questions…..1. Can you use Ditra with porcelain tile…i keep hearing conflicting answers related to the type of thinset? 2. The holes that are cut for the water supply for the shower…..how is that waterproofed?

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Roger September 24, 2011 at 6:04 pm

Hi Carolyn,

Yes, you can use porcelain with ditra. You can use modified or un-modified with porcelain – modified is better. You can use modified with ditra – you’ll lose your warranty. Waterproof all extrusions with regular silicone or with kerdi-fix.

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Carolyn September 26, 2011 at 10:54 pm

The silicone goes on before the tile…after the tile but before the fixtures are installed or after the fixtures are installed?

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Roger September 27, 2011 at 6:50 am

After the tile but before the fixtures are installed.

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judd September 19, 2011 at 5:15 am

My first time using Ditra. I want to install electric floor heating mats. Do I install the “orange mat” with the heat mat on top then tile or heat mat under the detra Schluter underlayment.
Thanks
Judd

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Roger September 19, 2011 at 4:38 pm

Hi Judd,

The electric cables or mat is installed beneath the ditra membrane.

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Sheryl August 25, 2011 at 7:48 pm

I have a shower that has its interior walls covered in a fiberglass type panel. The shower is waterproof so I am very hesitant to go tearing down the panels…but I hate the panels and would love to tile over them. They have a small raised bump over the surface for texture…yes, think old stalls in MacDonald’s or other commercial bathrooms. Can I install Ditra over the panels and tile over that?

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Roger August 25, 2011 at 8:09 pm

Hi Cheryl,

There isn’t really anything that will adhere tile to those panels long-term. Epoxy may stick the tile to the panels but the biggest issue you’ll run into would be the flexing of the wall. Any movement behind tile will eventually cause the grout to crack followed by tiles coming loose. There are several ways to waterproof showers and some are as easy as painting on waterproofing liquid and installing tile directly to it. You just need to remove those panels and replace them with cement backerboard and paint on two to three coats of redgard or a like material. That will give you a totally waterproof substrate for tile installation. You can read about redgard here: Installing redgard in a shower.

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Sean August 25, 2011 at 10:35 am

I was doing more reading and realized that dryset mortar is the same as unmodified mortar. That is correct, right? If that is the case I will just return the modified stuff and buy dryset. I was just having trouble finding anything that said “unmodified”.

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Roger August 25, 2011 at 5:41 pm

Dry set mortar is unmodified, as long as it doesn’t state that it contains latex or polymers. Dry set mortar is the same as thinset – it can be modified as well. It will not necessarily state unmodified but it WILL specifically state if it is modified. KnowWhatIMean?

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Sean August 24, 2011 at 3:54 pm

I know you’ved dealt with this subject plenty so maybe your tired of it by now. I’ve already bought the Ditra and Mapei Ultralight Mortar (Light weight tile mortar with Polymer). From what I’ve read above this is fine to use with the Ditra (Let me know if I’m wrong) but how long will it take to cure before I can walk on it. Are we talking a couple days, a week or more. It is on a concrete basement floor in a bathroom I’m finishing. It will just be an extra bathroom so I don’t need to use it so waiting a couple of days is not a big deal but is that plenty of time. Thanks for your input.

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Roger August 24, 2011 at 6:20 pm

Hey Sean,

If you can allow about 48 – 72 hours it should be ok. Should be. I don’t know what type or size of tile you have there so it’s difficult to tell. However, the easiest way would be to install your ditra and fill all the dovetails – then let that cure for a day. The problem with using modified is that the polymers in the dovetailed portions have difficulty curing because that requires air. If you fill the dovetails it will cure just fine without tile over it. Then you can go in the next day and set tile and walk on it the next day.

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Sean August 25, 2011 at 6:00 am

Hey Roger,
I am using 12×12 tiles. Forgive my ignorance but if I let the mortar cure for a day before I install the tile what do I do if it is dry? Do I put more mortar on? And if it is still wet do I tile from the door to the back wall instead of the other way. If I do that when I get on the newly installled tile will my weight affect how the tile sits? Sorry about all the questions. Thanks again.

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Roger August 25, 2011 at 5:35 pm

Hey Sean,

You fill the dovetails with the flat side of the trowel so that after it cures the next day you have a flat floor. Then install the tile as normal with more thinset. You’re simply doing it in two stages to allow the thinset to cure first in the dovetails before installing the tile. Set your tile from the back of the room towards the door so you don’t need to walk on it until it is fully set.

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