Differences in USA Thinset Mortars

Discussion in 'Tutorials' started by jadnashua, Sep 6, 2014.

  1. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Thinset is a lot more complex that many people think! While a basic thinset is always made up of cement and an aggregate (often, a fine sand), there are many different chemical compounds that are called cement, lots of different aggregates, and their preparation and capabilities can vary not only by the type of cement, but by the aggregates and the proportions of each.

    To help make some sense out of these, we have ANSI standards, but they are meaningless unless you have at least a cursory understanding of what they mean.

    Right now, there are four different major groupings of thinsets for the USA customer: ANSI A118.1, A118.4, A118.11, and a new one A118.15. Then, those can have an extra character on them such as E or F where 'E' stands for extended working time (takes a little longer to start to set up) and 'F' stands for faster setting (often referred to as rapid set).

    Keep in mind that as the .X part of the specification increases, it also has the properties of the lower numbered specification as well. So, an A118.11 will have at least all of the specifications of an A118.4 mortar. Also note, that the specifications are a MINIMUM, and often, within a particular specification, there can be an economy version and a premium version, and, it is possible that a lower numbered specification may exceed at least some of the properties of a higher numbered specifications, but not all of them, so according to the specification, you cannot call it that higher numbered material. There are some thinset manufacturers out there that are saying that they meet the A118.15 specification, but when you read the fine print, it may only be in one or several key characteristics. This is against the 'rules' of the ANSI organization, so beware...if you actually need a mortar that meets a particular spec in ALL capabilities (often, that is the goal, especially if you are a professional where the job specification calls for a particular thing), make sure to read the fine print or follow the asterisk or whatever and read the fine print.

    So, now let's look at the basic characteristics of the different specifications. When it comes to A118.4, .11, and .15; they are all referred to as modified mortars. This means that they have some additional admixture in them to make them more flexible and other characteristics, which can include freeze/thaw, hot/cold, impact, shear strength, and a bunch more 'features'. For a rough indication, you could call these good, better, best in the modified thinset mortar groups. Keep in mind that any particular job may never stress the products involved, and good may be much more than is required. Then, there may be a job where best is the only one that might survive under the conditions. It is somewhat foolish to always go for best when it won't make any difference...sort of like using premium gasoline in your car when it is designed to run on regular.

    What I haven't touched on is A118.1 mortars. These are not a modified mortar (meaning it does not have an admix in it), and are sometimes called an unmodified or dryset mortar. Depending on the products used, and the manufacturer's recommendations, this may be much more than adequate, and often is chosen for some very important reasons.

    A quick word on admixes. Often, these are mixed into the cement and aggregate mixture in the factory as dry particles. They can be made from laytex, acrylic, and other materials. They each have their unique characteristics. Every manufacturer of a dryset mortar (A118.1) also sells a liquid admix that can be used to create a modified mortar. Depending on how much of the stuff and whose (do not mix manufacturer's products or you'll get unreliable results!) you may be able to turn that A118.1 mortar into one meeting one of the A118.4 or A118.11 types (have not seen one that can make a A118.15 with admix, but it may be out there).

    A final word, each of the manufacturer's includes some fairly specific instructions on how to mix their products such as the amount of liquid to add, how long to mix it, at what speed to mix it, and how long to let it slake before using it. If you do not follow those instructions, you will NOT meet the whole specification for what you bought.
     
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  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    What happens when you add more water to a mix?

    The amount of liquids in a cement product, be it thinset, concrete, grout, etc. is designed to have certain specifications IF it is mixed and used as originally designed. Over watering a thinset or any concrete mixture can mean that it ends up weaker, sometimes MUCH weaker than it was designed to be. The types and mix of ingredients are designed to be a fairly contiguous substance, and if you add too much water, the heavier components can sink (cement often is one of the lighter materials), so instead of a nice consistent mix of materials, you can get much of your sand on the bottom, and too much water and the cement on the top.

    How does cement bond to things?

    Once activated by simple water, the cement will start to grow crystalline spikes. Those spikes are relatively fragile. The spikes will have different shapes depending on the actual composition of the cement (remember, cement is more than one item, and it is the purity and mix of the different types that help determine it's characteristics). Those spikes end up being sort of like the hooks of a hook and loop fastener (Velcro is one brand of hook and loop fastener). If you've ever dealt with that stuff, you know there are different designs with different holding strengths - just like with cement. The difference is, the spikes of cement are only marginally flexible. The aggregate helps provide some of that overall strength of the mixture, and if all of it sinks to the bottom with too much water, that's one reason why it ends up weaker. The second is, the cement grains end up further apart from something it can literally grow into, creating a cross-hatch of spikes. Once the crystals form, that's pretty much all she wrote! They can only grow so far. On a microscopic level, even glass has some irregularities in it, and the spikes of the cement crystals criss-cross into them and sort of hold together like the branches in a beaver dam...individually, not all that strong, but woven together properly, very strong. A modified mortar, when mixed properly, adds a layer of that admixture around the cement crystals and helps cushion them. That is what gives it more flexibility. THe crystals are slightly flexible without that, but the admixture or modifier helps to reinforce them, but only if your mix is right!
     
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  4. DonL

    DonL Jack of all trades Master of one

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    Nice Jim.

    <Deleted this part>

    Yes I said that... DonL


    Sorry to Hose your thread Jim. I am not done Yet.
     
    Last edited: Sep 22, 2014
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  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    What you can infer from the previous discussions, is that there are lots of variations on what is called cement. There's a lot of research that goes on, and still things to learn about it after centuries of use. How fast it makes a bond, how strong it is, how flexible it is, how well it handles freeze/thaw cycles, the compressive strength are just a few of the many variables that a cement, and therefore a mortar manufacturer needs to balance to get just the right desired properties. Then, trying to make that consistent from batch to batch, and from factory to factory where the raw materials may slightly differ, make it a tough job to have batch-to-batch, and factory-to-factory consistency. Because of the sheer weight and bulk of the raw materials, few companies ship their cements and mortars huge distances...they have factories located where the raw materials are and ship the shortest distance possible for both the manufacturing and retailing of the materials. Throw in how the size of the particles, the proportions of the various types of cement and aggregates will change the properties not counting any of the admixes that may be involved in a modified mortar (or cement). This is one reason why different thinset mortars have different properties both within the same company, and across the many of them out there. Many of these variables are at direct opposition to each other. For example, to make a mortar that has a stronger compression strength, may mean that it isn't as flexible, or one that has better flexibility may not have as good freeze/thaw characteristics. So, just like making a chocolate cake...there's lots of different recipes out there. Balancing the components and tailoring them to get the desired properties is best left to the people with the engineers and laboratories to test the possibilities. And, if you want to replicate those properties, you need to prepare the thinset as designed - that means the right amount of water, the right mixer, the right time, the right rpm. Failing that, you are going to end up with a product that can differ, sometimes radically, from what you paid for.

    There's lots of info out there, but this article is not too hard to understand and discusses the differences in the various components in what we call cement http://elearning.vtu.ac.in/16/ENotes/ConcreteTechnology/Unit1-RVR/Unit1-L2-RVR.pdf . There are some micro-photographs in this article that show some of the crystalline structure of cement with the 'spikes' I discussed earlier...it is the interlocking of those spikes into irregularities and pores of the various materials that create the bond. How much cement there is in the mix, the size of the particles, how much, and what type of aggregate is in it, and then, maybe as important as any of those, is the amount of water you add so that they all perform as designed is the main component that you, the user, can control.
     
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  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The following micro-photographs are from Mapei. They show different kinds of cement as can be used in a mortar. What is called Portland cement contains a mix of different chemicals that combined are called as cement. Because they have different properties and strength, and growth rates, making up a magic mix of them leads to lots of permutations - IOW, you as a manufacturer can tailor the product to meet your specific desired capabilities. Then, throw in what and how much you use as an aggregate, or other component to slow down the hydration process (the act of growing the crystals). It is those spikes that grow during the hydrating/curing process that create the bond. Those spikes interlock, and poke into any small irregularity of the tile and substrate. They are slightly flexible. The last photo (assuming they upload properly!) is of a latex modifier. When mixed properly with the mortar, it covers the spikes as they grow, and cushions them. But, that only goes so far. Also, keep in mind that the modifiers that may be added to a mortar are not all created equal...some set, many need to dry (pretty much all of the latex versions), and some will soften again, and even wash away if they experience a lot of water. They are not a panacea...they cannot overcome a poor, entry level mix of materials and perform as well as a premium one, and some modifieds may exhibit less bond strength than a premium dryset/unmodified that may contain a lot more cement. Also keep in mind that a modified keeps the spikes of the cement crystals apart to a degree, and if you then wash away the modifier, you'll end up with mush - essentially cement grains that are not actually bonding to anything. Cement1.png Cement2.jpg Cement3.jpg Cement 4.gif Cement1.png Cement2.jpg
     
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  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    There are four classes of modifiers generally available for use in mortars out there:
    Polyvinyl Acetate (PVA), Ethylene Vinyl Acetate (EVA), Styrene Butadiene Rubber (SBR), and Acrylic.

    They each have slightly different characteristics, but all are used in modified thinset mortars (and concrete). Throw in what concentration is used, the ratio of cement to sand, and the sizes of the cement grains and the aggregate used with its structure (porous, sharp edges, rounded edges, etc.) all will affect how it reacts and the ultimate end result in flexibility, porosity, compressive strength, and shear strength. The combination of all these different components is one reason why there are so many different mortars out there – modifying any one or more of the items will change the characteristics and performance of the mortar, sometimes VERY significantly. IOW, they are not all created equal!

    Some general characteristics of the modifiers are:
    PVA is not recommended since it offers very little water resistance. SBR has a tendency toward yellowing and should not be used in grouts, especially out-of-doors where degradation from sunlight is prevalent. SBR, they don't talk about much. Acrylic affords the user maximum water resistance and freedom from yellowing due to aging and weathering.

    One thing that is often overlooked is one of the limitations of these polymer systems is that they may re-emulsify in humid alkaline conditions. Re-emulsification means, essentially, that the modifier can soften and wash away, leaving you with a weak, or failed installation. A typical mortar is in the range of a pH of 10 or so (give or take a little) on a scale where below 7 is increasingly acidic, and above is increasingly alkaline with 14 being defined as a maximum value and 7 being neutral.

    Some interesting reading is linked below (they were too big to attach, sorry), if you’re so inclined. One thing you’ll notice is that in the listed articles, the reference mortar which contained no modifiers, sometimes out-performed those with a modifier. An advantage of a modifier is that it traps some moisture around the cement paste, allowing it to fully hydrate, which creates the maximum strength. When a mortar is used between a waterproof membrane and an impervious tile, you get the same effect, and do not need the drying required to allow a modified mortar to work at its optimum. There are numerous tradeoffs to be made based on what characteristics any mortar ends up having - IOW, you can optimize one thing, and it may hurt another...depends on what's important to your job. Another interesting finding in one of those articles was that things continued to change up to 80-days after initial mix of some modified mortars, and this was under ideal, laboratory conditions of temperature and humidity. The 'normal' timeframe for specifying characteristics of a mortar are at 1, 3, 7, and 28-days. Throw in non-standard conditions, and the timeframe can become quite extended and uncertain with a modifier in the mix.

    As opposed to what some here say: testing is bogus and useless...we would not have any of these products if people and companies didn't test them to determine what works not only short-term, but long term, and their overall characteristics. Most of that testing can only occur in a laboratory to get consistent and reliable results. Don't know of anyone that has an electron microscope in their backyard, and some of the info can only be obtained by such analysis, and following the scientific method which ensures repeatability, which is critical to determining any results.
    http://www.scielo.br/scielo.php?pid=S1516-14392005000300004&script=sci_arttext
    http://www.iasj.net/iasj?func=fulltext&aId=68276
    http://www.qualicer.org/recopilatorio/ponencias/pdf/0823092e.pdf
    http://www.aimetatorino2013.it/cdrom/cdrom_pdf_fullpaper/001180013101.pdf
     
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  8. mikel101

    mikel101 New Member

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    Great article sir, "PVA is not recommended since it offers very little water resistance." I had have some experience with PVA but not really notice the water resistance problems. What you suggest as alternative?
     
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    That comment on PVA was the result of research with no personal experience. It also indicated that not that many manufacturers use it, so it probably isn't a major issue but something to consider if, for example, you were doing a shower verses a floor that would be dry 99.9% of the time. The key here is to read and understand what the specific product you are looking at was designed for...IOW, by no means are they all created equal! Price, to a degree, buys you a more capable product, but the characteristics and features gained may be a total waste for your application. Often, since there are so many choices, even from the same manufacturer, it's safest to call them, describe your anticipated application, and let them help you decide which would be best for you. It's sometimes a cost/benefit decision, where the benefit and potential risk isn't worth the additional cost (this may be more important on larger commercial jobs verses a small job by a homeowner maybe only needing a few bags of material - the cost difference between good and best isn't much in the total scheme of things and may compensate for less than professional skills, but even then, may not be worth the costs).

    Hopefully, another thing that became clear was that actually mixing and applying the materials as designed can make a big difference in how they perform along with the sometimes forgotten notion that cement based products DO go bad with age before use, and especially fast if they are not treated or handled and stored properly. The chemical reaction that makes cement cure is referred to as exothermic...it gives off energy becoming a more stable item as it cures. This means that it REALLY wants to combine with the required moisture to reach that lower equilibrium state (sort of like the rock wanting to fall down, not up!). None of the packaging is perfect, and some moisture will get in, especially if it is in a hot/humid environment or over time, so again, age is critical. IT can affect the modifiers in the mix, but often, the more critical one is the cement itself.
     
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