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Unread 06-15-2020, 03:06 PM   #1
wwhitney
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Different Modifiers Types in Thinset?

Hello,

My recollection from past reading here is that there are different types of modifiers used in thinsets, and that some modifiers will work fine between two impermeable surfaces. Whereas other modifiers depend on sufficient drying (loss of water) and may take far too long to cure between two impermeable surfaces.

So my general question is whether this is correct, and if so how to tell from a product data sheet which type of modifiers are used? More specifically, will Versabond work adequately to bond Durock Shower System Band to Goboard?


Thanks,
Wayne
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Unread 06-15-2020, 04:10 PM   #2
Lazarus
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Yes, it should. Modified (lightly) thinsets like Versabond may take a little longer to set up, but should be just fine.
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Unread 06-15-2020, 05:16 PM   #3
jadnashua
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Cement cures regardless of whether it is kept wet of not! There are things that can be mixed with cement to slow that chemical reaction down. Take something like hydraulic cement...made of the same stuff, but has no inhibitors in it...gets hard in minutes. A typical thinset may have a usable pot life close to 2-hours, depending on temperature and type.

Cement literally grows crystalline structures as it cures. Those are relatively fragile. IF the modifiers that are coating them needs to dry to be able to perform their job, they could either be washed away if used too soon, or not provide the support for those crystalline spikes. Once those spikes are broken, they don't grow back as they become inert as they chemically change.

So, yes, there are different modifiers. They also get used in different quantities in the recipe selected by the manufacturer along with how consistent the particles of cement are, and the type and volume of aggregates (nominally sand) selected and other things that may help in storage or spreadability, etc.. That's why there are so many different brands and types within a company's selection.

Many of the modifiers sold in products today get stable while still wet as the cement cures. The hassle is, the ANSI standards used to classify them don't necessarily give the uninformed user any clue as to which ones will work in this situation or not. Historical experience is usually good, but beware of following old recommendations especially if the product says new, improved...something obviously changed, and it may no longer work well.

If the manufacturer says they'll work, you've got some assurance that it's a viable product for that application.
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Unread 06-15-2020, 08:38 PM   #4
wwhitney
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Thanks for confirming my background understanding. It sounds like the answers to my questions are:

1) Yes, some modifiers will cure very slowly due to captive water of placement between two impermeable surfaces.

2) Datasheets won't explicitly identify these modifiers, but you can make an inference based on the recommended applications.

3) Versabond should be fine for the example application.

Yes?

Yours,
Wayne
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Unread 06-15-2020, 08:53 PM   #5
cx
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Wayne, beware also of statements such as Versabond being "lightly modified" and that being the reason it will work in certain environments. Not sure where that got started (Versabond is lightly modified) nor do I really know what that means. I don't know what polymer(s) is used to modify Versabond, nor how much of it is used and I doubt anyone on these forums does with the exception of our good friend Steve Taylor who usta be the head chemist for Custom Building Products. Aside from Steve, I wouldn't depend upon any statements about the content of that particular thinset mortar. The manufacturer states that it meets the standards of ANSI A118.4 and .11 and that's the full extent of my personal knowledge of it's makeup.

That said, I can personally testify that a baseball sized ball of Versabond will cure quite well while encased in double Ziplock freezer bags on accounta I've tried it more than once. Does that mean it will cure properly and exhibit its advertised properties when used in your proposed application? I can't prove that, but if I were in a position to want to do what you're proposing I would not hesitate for a minute to use Versabond. See my warranty information below.

My opinion; worth price charged.
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Unread 06-15-2020, 09:48 PM   #6
makethatkerdistick
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What CX said about Versabond is true for Flexbond as well. My samples cured without air in a ziplock bag as well. Just in case you were wondering.
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Unread 06-15-2020, 11:16 PM   #7
jadnashua
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Cement based thinsets will grow their crystals and cure, regardless of the moisture as long as it has enough to fully activate their growth. You can think of them as fine glass fibers. They'll shatter when they're bent more than their limits. The modifier coats them, can act like a glue, and helps limit how far they can move before they break. So, ultimately, the bond can be stronger with a modifier since it's using both the interlocking spires of the crystals and the glue with its protective cover. That full functionality doesn't happen until the modifier has cured. On some, that just takes time. On others, it needs to dry. The ratio of the modifier versus the cement will vary, and that can be critical. A modified thinset may have less actual cement in it than a premium one without it to compensate. It's the magic mix that does its thing, tailored to the specific needs of the application. That's the difference. That happens over time, not necessarily the moisture content. Thinset is mixed with more water than it needs so that it can be spread and will provide good coverage. Those crystals literally grow, crosslink, and get into microscopic pockets in the mating surfaces. Industry rates the ultimate strength at 28-days, but in reality, it continues to get stronger for decades and probably longer, but the majority happens fairly quickly as you might notice since you can usually walk on a tiled surface overnight, if not hours (some of the fast setting types are good to go very quickly). You wouldn't want to roll a safe across it then, but a smaller load would work.

If you bend a steel coat hanger back and forth enough, it will break...exceed the limits on the cement crystals, and they too will break. The modifier helps cushion them, and to do its work, it needs to fully cure. With the random structure of those crystals, it may not fail for a long time but will get weaker as some of them break. So, some of it is how stressed is the application and how long can you wait? Schluter did a demo with a large plate of glass over a modified thinset. It took something like 82-days before the middle was visibly dried out when installed over Ditra. If it was one that needed to dry to reach full strength, that could be an issue.

If you follow the manufacturer's recommendations for the materials you use, you should get a good result. That's still possible when you substitute, but you need to know what you're using. You can get an idea from the materials data sheet, but for product protection purposes, as allowed by the regulations, they don't have to tell you everything, otherwise, anyone could copy their hard earned research results.

So, yes, some modified thinsets will work quite fine between a tile and a waterproof membrane...some won't. It's not about the cement curing, it will...it's what those modifiers provide in the overall mix for that product, and how fast and under what conditions.

If a manufacturer has a waterproofing system (most do) and you see what thinsets they recommend, they will likely work with other similar membranes.

Schluter, until recently, did not make its own versions of thinset, so relied on what they knew would work under the ANSI specs. They now have some modified thinsets that they know will work with their products, and other manufacturers with similar products do, too. There are differences, but...
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