Aquatic Technology Pool & Spa, "Creating Water as Art."™

Aquatic Technology Pool & Spa, "Creating Water as Art."™
Pools as an art form - the way it should be!

Tuesday, June 15, 2010

Glass tile mosaics - tessellated stress cracks fissures microstresses

Recycled glass: Bad for glass tile, but good for the environment (and manufacturer's profits)!

Tessellated stresses and microstresses (cracking & stress fissures) within glass tile mosaics that contain recycled glass as a portion of it's formulation, are problems that many tile mosaic manufacturers simply do not understand. Most are not even willing to subject their tiles to any thermal shock performance testing. They bury their heads into the sand.. hoping that the problem will go away. It won't... (and I won't!).

If the manufacturer's never test their tiles for thermal expansion stress cracking, then they can continue to "play dumb." This allows them to "blame" the installation, because they know that it will be difficult & costly for an installer or property owner prove that there are materials or manufacturing issues. However, the underlying problem actual lies in their manufacturing process & the improper mixing of dissimilar materials.

With so many companies jumping on the environmentally "green" bandwagon, many are manufacturing products that are not durable. They simply do not understand material science and physics.

It will only take an Act of Congress, Consumer Product Safety Commission, a State Attorney General or a Class-Action Lawsuit to enforce minimum quality & performance standards upon these manufacturers.

Lack of Quality Control & Education

Almost all of the manufacturers fail to understand the importance of a homogeneous mix of virgin materials with the recycled materials. The recycled materials must be mixed thoroughly with themselves and with any additives or raw materials that are added.

If there are portions of the batch that are not homogeneous, there will exist a differential blend of material throughout the finished product. The laws of Physics dictate that different materials have different rates of thermal expansion.

Because these different materials expand at ever-so-slightly different rates, and because glass is not elastic, this stress will cause stress cracking or fissures.

Inconsistent Temperatures

Adding to the problem, is another law of physics. Thermal expansion occurs within matter at a rate in proportion to the temperature. In an installed application there exist temperature gradients throughout glass tile. The surface is heated or cooled at a rate that is faster than the back of the material.

Remember: the back of the material is usually mounted against a cool concrete structure. When the surface of the glass is exposed to the sunlight or swimming pool, it heats up at a faster rate than the back of the tile.

This "temperature gradient" can cause cracking within the tiles. Coupled with the use of recycled materials, and you have the formulation for failure.

Material Size and Thickness

We've established that there can be a temperature gradient within a singular tile. Physics also dictates that thicker tiles will have greater degrees of temperature gradient than thinner tiles, from top to bottom.

Stresses will be less likely to occur in smaller format tiles (1x1's) than in larger format tiles (3x3's, 4x4's, 6x6's +). Irregular sizes (rectangles, triangles, circles, etc.) can also create unusual stresses within the glass tile. This is not to say that they will not occur in small tiles - they do. Given that a small tile may crack, it is almost guaranteed that larger formats of the same tile will crack.

This occurs because the edges remain cooler than the center, creating gradient temperatures across a larger surface area. On a smaller tile, the gradient is less as the core is closer to the edges.

Thicker tiles also contribute to the gradient temperature issue, as thicker tiles cause "shading" of neighboring tiles, allowing the sides & edges to remain cooler than the core or surfaces.

Add coatings to the glass, and you have further altered the possible temperature gradients, by absorbing or reflecting heat in an irregular fashion.

Unknown Raw Materials

Just because a manufacturer receives all of their "raw recycled glass" from one source, does not automatically mean that it is all the same. If a manufacturer uses only recycled soda bottles from one brand of soda - there is no way on God's Green Earth that they can be 1000% certain that all of the bottles are EXACTLY the same.

The soda bottle manufacturer may change formulations ever so slightly from batch to batch, manufacturing temperatures may vary slightly, or even their raw minerals or suppliers may vary slightly.

Since most manufacturer's rely on the "say so" of their supplier to verify that all of the bottles are the same, there is another source of doubt as to the "quality" of the recycled glass. Because the recycled glass is already ground up (aka: "cullet"), there is no means to test the glass to verify the veracity of their claims. It could have soda bottles, old windows, automobile glass (argh!!!), beer bottles, food jars, or contain labeling contaminates such as cobalt (like is found on Corona bottles).

If there is the slightest piece of heat-resistant glass like Pyrex or borosilicate glass present in the cullet, it will alter the viscosity of the fluid in the furnace when it is remelted.

Add to the variance equation, the fact that there may be multiple suppliers of soda bottles to the bottler - each with their own formulation & raw material suppliers, and you have sufficient material variances to wreak havoc with the performance of glass mosaic tiles.

The recycled glass association's standards allow variances in the cullet mix, proof again that there are contaminates and variables in the "raw recycled glass." Here are their acceptable standards:


Composition: Soda-lime-silica container glass.
Container Glass Cullet Colors Segregation: Flint Cullet
Flint 95-100%
Amber 0-5%
Green 0-1%
Other Colors 0-.5%
Total NON-Flint Cullet = <5%>Size: Various sizes from whole glass containers to -100 Mesh.
However, the ideal material size is 3/8" to 3/4" with a 10% minimum
of fine particles. Material size is based upon buyer and
seller's agreement.
Contaminant Listings:
Outthrow Materials: Organic Matter, allowable percentage
based upon buyer and seller's agreement.
Prohibitive Materials:
Ferrous Metals
Nonferrous Metals
Ceramics (such as cups, saucers, dinnerware, pottery, etc.)
Other Glass (for example, plate window glass, heat-resistant
glass—such as Pyrex—and lead-based glass—such as
crystal ware, television tubes, vision ware, etc.)
Other Materials (such as bricks, rocks, etc.)"

Unpredictable Results

Most of the models for predicting the performance characteristics of glass formulation rely on multiple regression analysis or by additivity equations. But the primary principle for utilizing these mathematical predictions, is that you know the formulation of ALL of the raw materials - totally impossible when using recycled glass!

As with any quality control procedure, these equations are the same: garbage in, garbage out. Since they cannot possibly ascertain the chemical composition of 100% of the recycled glass cullet, they are forced to either "guesstimate" or use a random sample of the cullet (and assume that it is all the same!). This is where the variability begins... right on the loading dock!

Why so Random?

Because the materials are not thoroughly mixed, it reasons that there are areas of the sheet of glass, wherein there exists higher concentrations of heterogeneous material. Because the mixing may be more thorough in one batch than the next, concentrations throughout the glass may vary, and tiles may be mixed with other batches of the same color, the resultant cracking in tiles will appear to be totally random.

It may not occur in every color or size of the same tiles. It may appear in adjacent tiles or they may appear in isolated tiles. But there is often a major commonality... the cracking is not linear. Tesselated stresses may transfer into an adjacent tile.

However, if the cracks are directly in line with each other and through a minimum of 3 tiles, then thermal stresses are probably not the cause. Linear cracking through multiple (3+) tiles is probably the result of substrate flexing or movement. This is not to say that tesselated stresses can not coincidentally align across 3 tiles. But there is a statistical probability of this occurring in 2 adjacent tiles, so 3+ has become the rule of thumb.

If the cracks are not through the entire tile, then there is a high probability that it is not installation related. This is "clearly visible" on clear tiles - if they look like fissures within an ice cube, then they are probably thermal stress cracks.

Remember, the larger the format of tile, the lower the tolerance for substrate movement & the greater the chance of thermal stress cracking. The problem is compounding itself!! Example: A lot of grout joints in 1x1 mosaic tiles across an area are a lot more forgiving than rigid 12x12 tiles!

Getting it Mixed Right

There are a few approved methods to ensure that recycled glass is utilized correctly. However, it requires that the glass formulation is mixed thoroughly.

One method is to actually mix the molten glass with a mixer, something that is difficulty, costly & dangerous. Most manufacturers utilize linear kilns - a conveyor belt within a long furnace. This makes mixing molten glass in this method impossible.

The second method, involves multiple stages & involves grinding the glass multiple times. First the recycled glass is ground as small as possible (cullet). The finer it is ground, the more thoroughly the blend can be mixed. Virgin materials are mixed into the mixer along with the ground recycled glass. This mix is then fired into glass utilizing a linear kiln.

Unfortunately, this is where most manufacturer's end their processing. They form their tiles and ship them out the door.

To ensure that the various glass formulations are thoroughly blended, there are two more stages of processing required.

To ensure a thorough homogeneous blend, the glass that is made during the first stage above, is process again. It is broken up & ground up as fine as possible. This fine pulverized glass is again thoroughly mixed. Now it can be fired and made into consumer ready glass mosaic tiles.

Ensuring that there is a homogeneous mix entails additional processing and a double firing of the glass, which is costly. The production time, energy and labor costs more than double! Therefore, most manufacturers who utilize recycled glass merely skip this step.

Some manufacturer's add chemical that they claim solve the issue of homogeneous blending. However, it is statically impossible to prove that the end result will be a homogeneous and isotropic blend. And since there is a very high probability that the cullet is contaminated, there is no means to chemically treat for all possible variations - Who's fooling who???

Principals Founded in Physics & Material Sciences

These are not my hypothesis or mere suppositions... something that I made up.

These are facts based upon over 100 hundreds of years of the investigation of physics & material sciences. In fact, the phenomenon of glass stress cracking from non-homogeneous blending was discussed in scientific papers as far back as the 1890's! Many organizations have investigated this phenomenon:

National Institute of Standards and Technology
Corning Glass Works
The American Ceramic Society
International Symposium on Glass Problems
and countless foreign entities.

The Lack of Standards & Differential Expansion

The development of tessellated stresses in glass tiles that utilize recycled material will continue to occur, until manufacturers are held to some standard for thermal shock performance.

If they subject their tiles to the CTIOA (Ceramic Tile Institute of America) thermal shock testing (who's tests are designed for ceramic tiles - which do not apply to the performance testing of glass tiles), they only have to submit a mere 5 tiles for testing.
This is not a representative sample of the tile's performance. Again - simple statistical analysis...

Nor is allowing the testing of ONE size of each product line, representative of the entire products line's performance. Glass of different colors contain different chemicals and formulations, and glass tiles of different sizes perform differently. Given their choice, the manufacturer's will submit clear glass 1X1 tiles, who tests will then be proffered as representative of an entire product line.

Manufacturer's are not required to re-certify or submit subsequent production lots for verification of continued compliance and quality control. As the recycled glass (raw materials) change from day to day, so will the final product's performance - yet they will still be relying upon those initial test results.

The CTIOA testing also tests the tiles in their "loose" unmounted state. Now who buys tiles to throw them loose into a pool? They should be tested in their mounted condition, with approved setting materials. Yes, multiple variables & various manufacturers. At least they'd have testing data for compatible setting materials.

Currently there are no performance standards for glass tiles.

It truly is the...

"Wild Wild West!"

"Buyer Beware!!!"

Paolo Benedetti - Aquatic Artist"Creating water as art."™Aquatic Technology Pool & Spa©

Pitfalls of Owner Supplied Materials

Many owners believe that they are saving money by supplying materials to a design or construction firm, and then only paying for the installation labor and materials. However, this is a very myopic and narrow view of the entire "what can go wrong" scenario.

Material Warranty
First of all let's get something straight right now... there ISN'T ONE! Nada, bumpkiss, zero, ziltch, squat...

Since the installer was was not the specifier, they are not responsible for any of the myriad of failures that occur with materials. When there are material failures, the homeowner is not going to say, "golly gee, the deal on that cheap material wasn't such a great deal afterall." I have consulted in many of these situations, and the homeowner response is very predictable. IT ALWAYS IS "they must have done something wrong during the installation to cause this..."

Because the homeowner is not an expert in construction materials or the particular application where they are to be used, they do not know the particular questions to ask when sourcing materials. Just because the vendor says "it's fine for that use," does not mean that it is! Just because you saw the same (or a similar looking material) used for a particular purpose, does not mean that it is! Just because you saw a material that looks just like it (used this way), does not mean that it is (the same material)!

Sourcing materials is a science in and of itself. Below is a short list of things to consider (and not even close to being inclusive of all of my selection criteria):
Freeze/Thaw Climate
Material composition (chemical make-up)
Reactivity of the material with the environment (snow, rain, swimming pool chemicals, wind, sun, heat)
Material Offcast (will the material bleed minerals or decay when subject to the environmental influences - above)
Hardness (is the material hard enough & durable enough for the purpose)
Porosity & Stain Resistance (will it resist staining from common materials)
Heat Retention (important in the dessert/tropical areas)
Slip Resistance (polished materials are not always the slipperiest!)
Available Finishes
Component Sizes & Thicknesses
Workability (how hard is it to fabricate & install)
Installation Specifications (does the supplier provide them?)
Who's going to create the mock-ups?

So, do you really still want to source your own materials to save some money on the specifier/installer mark-up?

Installation Warranty
The only warranty provided for the installation of any owner's supplied materials, is that they won't come loose or fall off (unless the material falls apart). PERIOD.

So, do you really still want to source your own materials to save some money on the specifier/installer mark-up?

Repairing Material Failures
Guess what - any cost associated with any of these repairs is the homeowners responsibility also! Most homeowners are so embarrassed that they were "penny wise & pound foolish," they will argue to the death about reimbursing the installer for these related repairs. Most installers will require payment in advance for these type of repairs (to the maximum allowable legal limits).

No one wants to perform any repairs to someone else's substandard materials, to get shafted for the payment after making corrections - and it happens all the time. It's one of the oldest homeowners scams in the book...

This is the largest cause of litigation in the area of construction warranties and workmanship. So put it all in writing- any repair or modifications to ANY owner supplied materials will be performed on a predefined "time and materials" basis - and don't forget the contractor is entitled to include profit in these rates too [because they're there - they're not working somewhere else making a profit (it's called "opportunity cost")]. Pay the contractor at the end of EVERY day, for the repair work that they performed.... it limits everyone's exposure!

So, do you really still want to source your own materials to save some money on the specifier/installer mark-up?

Installation Specifications
Does the vendor of the materials provide DETAILED installation instructions and specifications for any setting/finish materials? If they do not provide such details, then who is going to research & specify the methods and materials to be used? If those methods fail, then who is going to be responsible? Will the manufacturer or vendor approve the use of the material for the intended purpose (e.g. submerged underwater, subject to the high temperature steam in a steam bath, exposed to temperature variables or direct sunlight, etc.)?

There are standards for establishing the proper substrate (backing surface) and rigidity for the installation of almost every type of stone or tile imaginable. There are specifications that cover masonry walls, wooden floors, concrete floors, building facades, sheetrock walls, counter tops, and so on.

What about crack control, uncoupling, and waterproofing membranes? What about movement joints & their placement?

So, do you really still want to source your own materials to save some money on the specifier/installer mark-up?

Installation & Setting Materials
Not all setting materials and methods are the same. In the days of old, masons & tile setters used to "site mix" various home brews of setting materials. A little of this, a little of that, etc....

With the high cost of labor & finish materials, there is just too much liability involved to install things that way. If the concrete cracks or the walls settles, what will prevent those cracks from migrating through the finish veneer?

Yet the available "homeowners grade" setting materials at most warehouse home improvement stores are not the best available. They might be from the same vendor or manufacturer the pros use, but almost every manufacturers reserves a few higher end product lines exclusively for the professional's use. This is usually due to the idiosyncrasies of these products and the additional skills required to install them: reading instructions, working quickly & effectively, installing them properly, and using them for the correct application.

The density of a material is very important when selecting an attachment method on a vertical or overhead area. A slab of granite or veneered wall of stone falling onto someone will ruin their day.

Are expensive specialized stone epoxies or mechanical clip systems to be utilized? Who shall perform the sheer testing or provide the standards?

Does the manufacturer of the setting materials offer a warranty on their products? Some offer a warranty if you stay with a "single source" vendor throughout the project. This is a great idea, as it also ensures product compatibility - that the setting material from one vendor does not degrade a component from another. Add to the confusion multiple vendors pointing their "blame fingers" at each other if there are any issues.

So, do you really still want to source your own materials to save some money on the specifier/installer mark-up?

If the designer or contractor specifies and provides ALL of the finish materials, setting materials, and labor - then guess what?

They assume the responsibility for any failures with the material and or the installation (unless there are manufacturing defects - like those that occur in the manufacturing of glass mosaic tiles that contain recycled materials).

So, do you really still want to source your own materials to save some money on the specifier/installer mark-up?

Paolo Benedetti - Aquatic Artist"Creating water as art."™Aquatic Technology Pool & Spa©