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Unread 12-16-2019, 08:04 AM   #1
fhueston
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how setting mortars bond

How Setting Materials Bond and Why Resin-Backed Tiles Fail
By Frederick M. Hueston
Educational information that adequately explains how a bond forms between tile and thinset or other setting materials can be hard to come by, despite the abundance of information available online. Manufacturers do provide some information, but it is mostly marketing jibber jabber that cites bonding agents and secret formulas, without providing details into exactly how the bonding process happens. This article examines the basic chemistry of thinset and other setting materials and explains why some setting materials do not bond properly or at all. Armed with this information, installers may be able to avoid bonding failures.
Setting Material Ingredients
Thinset and other setting materials are made of Portland cement. Although setting materials contain other ingredients, including bonding agents, the main ingredient is Portland cement. So, all one needs is a basic understanding of how Portland cement cures to understand how these setting materials bond to tile.
What Is Portland Cement?
A common misunderstanding is that concrete is the same material as cement. They are actually two different materials. A typical bag of concrete, or Portland cement, is a combination of aggregate and a cement mixture. The cement mixture is made from either a combination of limestone, shells, and chalk or a combination of marble, shale, clay, slate, blast furnace slag, silica sand, and iron ore. Limestone, etc., is heated at high temperatures to form a solid material, which is ground to form a fine powder that we call cement.
How Concrete Cures
Adding water to a mixture of cement and aggregates will cause a reaction called hydration. The cement paste reacts with the water, forming microscopic crystals and branches (see photo #1). Plainly stated, the concrete cures. Without water, the hydration process cannot happen, and the concrete will not cure.
How Setting Materials Form a Bond
Tile setting materials are basically concrete. In order for these materials to form a bond with the back of the tile, there has to be some moisture exchange. In other words, the back of the tile must be absorbent. As the concrete cures, the little crystals and branches enter the pores of the tile, creating a bond.
Causes For Lack of Bond
Setting materials, in and of themselves, will not bond to non-absorbent tile, because non-absorbent tile lacks pores. Remember, bonding takes place when the crystals and branches enter the pores of the tile. Resin-backed tiles (whether absorbent or not) will not bond properly, because the resin forms a non-absorbent coating on the back of the tile.
Bonding Agents
Bonding agents, such as acrylics, latex, etc., are added to many setting materials to help create a strong bond, however, in most cases the back of the tile will still need to have some absorbency. Manufacturers often recommend using an epoxy setting material on resin-backed tile. Epoxy setting material creates a chemical bond that does not require tile absorbency.
Most thinsets and setting materials have limitations listed on the bag or information data sheet. Review these limitations carefully and take the necessary precautions to avoid bonding failures.


Figure 1 crystals and branches forming during hydration
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Unread 12-16-2019, 10:00 AM   #2
Just In Tile LLC
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Which is why I'm still amazed when bonding glass tiles they are stuck so well.
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Unread 12-19-2019, 09:46 PM   #3
Lou_MA
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Quote:
Originally Posted by Justin
Which is why I'm still amazed when bonding glass tiles they are stuck so well.
I’ve had the opposite experience, especially with large format glass tile with painted backs.

They appear to be well bonded, and checking while setting with a high quality glass thinset reveals good thinset coverage and transfer.

Yet in the cases where I’ve had to remove them, a couple gentle taps with a hammer and cold chisel and they pop right off with the tile backs clean.
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Unread 12-19-2019, 09:50 PM   #4
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Fred - in light of your post, how can thinsets bond to porcelain tiles where the absorption rate can be half of one percent or less?
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Unread 12-20-2019, 05:32 PM   #5
jadnashua
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The crystals grow into imperfections as part of the hydration process, sort of like how a hook and loop fastener works. Painting the back of the glass fills in most of those imperfections, and is not particularly rigid, plus, any imperfections are not deep into a relatively soft (in comparison) medium, so can be fractured, releasing the tile. Porcelain is nearly impervious, so it traps whatever excess moisture is in the mortar, allowing the crystals to hydrate to their maximum extent unless it is wicked away by whatever is beneath it. This is one reason why tiling over a moisture barrier like Ditra works so well...all of the moisture can be used to hydrate the cement fully.

How finely the cement particles are ground, their actual chemical structure, and their consistency will affect the size and shape of the cement crystals, and how strong the bond is. Modifiers can aid the process by holding moisture and coating the crystals. That coating can help protect the fragile crystals from fracturing, causing a failure in the bond.

It makes a big difference in the actual composition of the Portland cement...that isn't an exact formulation, but a recipe with common components sort of like the fact that there are numerous chocolate cake recipes...IOW, they're not all the same and can be tailored to have different characteristics, but are all generally, similar. I've got a couple other microphotographs somewhere, and will add them if I can find them. One of them has crystals that look more like columns than the spikes shown in these pictures of cured cement.
Attached Images
  
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Last edited by jadnashua; 12-20-2019 at 09:03 PM.
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Unread 12-23-2019, 08:01 AM   #6
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Lou

The answer is additive used in the thin set create a chemical bond as well as what Jim said
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Unread 12-23-2019, 08:45 AM   #7
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Quote:
Originally Posted by Fred
A typical bag of concrete, or portland cement, is a combination of aggregate and a cement mixture.
I think this should read, "A typical bag of concrete is a combination of aggregate and portland cement mixture." A bag of concrete is not a bag of portland cement. I think it's more clear in other parts of your post but this one sentence is misleading.
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Unread 12-23-2019, 08:49 AM   #8
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I'm with Lou. I have used some of the best and well known names in the industry and all but one fail in the adhesion test, particularly underwater. Grani Rapid sticks tenaciously but even after a few years submerged even it becomes not so stuck.
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Unread 12-25-2019, 11:11 PM   #9
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Some modifiers can re-emulsify if you let it sit in water, some do not ONCE THEY CURE. Prior to their curing, excess moisture can be an issue. Latex based stuff can tend to re-emulsify if it sits in water, and definitely needs to dry to attain full capacity in any application.
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Unread 12-26-2019, 06:14 AM   #10
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While that's true on paper Jim, in the real world even those that do not re-emulsify lose their adhesion to glass substantially. Every thinset that I've used in a pool has shown that. 3 years later after tiling a pool using Grani Rapid I was called out to repair the top edge of the spa where someone broke a couple pieces. I pulled the broken pieces with little effort. Before submersion the brown coat mortar came with it. The same goes with Laticrete 254 and Custom Mega Lite. I had the pleasure of removing some tile with these two thinsets years later and they came up easily. They both had well over the cure time. While they were not falling off, they surely weren't bonded like they were originally.
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Unread 12-26-2019, 09:48 AM   #11
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My experiences are similar to Jerry's but I am not aware of any long term studies. Know a pool guy in FL who got hammered on several occasions for that type of claim. He spent a boat load of time and money proving the point but as there are no recognized parameters he was only marginally successful in his defense.
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Unread 12-26-2019, 12:01 PM   #12
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If it's the same guy I'm thinking of, he used Kerabond with Keralastic for a while and that proved to be a big mistake. He also has crews out there doing the setting. I will have others help me float but all the glass mosaics pass through my hands so's I can sleep at night. Attorneys make way more than I do and I prefer to take the slow but safer method. That's just me though. As far as long term studies, I don't think it will officially happen.
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Unread 12-26-2019, 05:05 PM   #13
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FWIW, geologists sometimes refer to water as the universal solvent. Their time scales are much longer than humans, but who really knows how it affects things in real life.

What about using epoxy thinsets for glass? Expensive, but how does it hold up in the real world? I would think painted back glass would be problematic, regardless...another layer you don't really know the properties of that could fail.
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Unread 12-26-2019, 11:07 PM   #14
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Very interesting discussion on mortars subjected to submersion.

Yikes!
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Unread 12-27-2019, 01:54 AM   #15
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I haven't tiled a swimming pool in years, (best tan I have ever had)with all this talk about letting go, I am glad that it was when I was working for another guy. If I had one to do today I would go 100% Ardex. I have been using their products almost exclusively and only ardex for the ,I need it to stick jobs. They got some gnarly products out there. I am all about research and I have a close relationship with my Ardex rep so if I don't what I should be using then I shoot him a text and he lines me out on what he recommends
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