Aquatic Technology Pool & Spa

Failure of Glass Mosaic Tile

Failure of Glass Mosaic Tile - Cracks, Fractures, Fissures & Spalling

By Paolo Benedetti, TUESDAY, JUNE 9, 2009

Failure of Glass Mosaic Tile - Cracks, Fractures, Fissures & SpallingPaolo Benedetti - Designer & internationally renown expert consultant for hillside pools, vanishing edge pools, infinity edge pools, negative edge pools, disappearing edge pools, slot overflow pools, perimeter overflow pools, knife edge pools, wet edge pools and spas, and founder of Aquatic Technology Pool & Spa, discusses recent glass tile mosaic failures, namely fracturing & fissures, and all contained some recycled glass!

Though glass mosaic tiles have been around for centuries, their use in swimming pools & construction projects has exploded exponentially in the last decade. Many new players have joined the ranks of glass tile manufacturers. However, as the use of the material has grown, so have the problems.

Do not get me wrong, glass mosaic tile swimming pools, spas, and fountains are the top of the line! They are the pinnacle of pool finishes, and installed correctly should last for decades. I have glass mosaic tiles in my own backyard! And they are performing wonderfully, I might add!

The primary issue is the lack of a minimum industry performance standard for glass tile. The most important factor missing is a standard for their performance against thermal shock. Adding to the problem, is the current trend to be "green." This has led a number of manufacturers, both domestic & foreign, to utilize recycled glass for a portion of their production. Many Asian factories have no concern for the quality of the raw materials - glass is glass! The images shown here are from various projects from around the country - and all involve manufacturers who use some recycled glass in their tiles.

The use of recycled glass in the making of mosaic tiles, especially those that may be subject to any temperature differentials, will result in internal fractures/fissures within the tiles. While this will not lead to the glass tiles crumbling or decaying, it will cause unsightly fissures within the tiles - like those found within an ice cube. If these "cracked" tiles are subject to any subsequent impact or external stresses, they may crack or come loose - resulting in sharp pieces of glass tile on the floor. In a swimming pool, spa, steam bath, or shower application, this will definitely result in lacerations.

Over the past 5-10 years, a number of manufacturers that utilize recycled components have been experiencing performance issues with their materials. In most instances, they have been able to keep these cases isolated. In every instance that I am aware of, the property owner & installer have been led to believe that they are alone in their troubles. Failure of Glass Mosaic Tile - Cracks, Fractures, Fissures & Spalling (click on the image for an enlarged image and a closer look) The "factory experts" have always blamed the installer for a faulty installation, leaving the installer to defend themselves against the homeowner. They will cite the use of "unapproved setting materials," failure to exactly follow their installation instructions, or the failure to follow proper curing procedures as the leading causes.

However, when the T's are crossed & the I's dotted, and a project is installed to the EXACT letter of the directions & standards, and there is still a material failure - where do the manufacturer's lay their blame? Again, they blame the installer & the installation.

They will grasp at straws, throwing out every excuse they have ever used - even going so far as to blame the concrete structure. This may have worked on a pool that was sliding down a hillside, but for a project that was supervised by the manufacturer of the setting materials, a site visit from the tile manufacturer, inspections by the structural engineer, inspections & observations by the geotechnical engineering firm, independent laboratory testing of the materials, deputy inspectors inspecting the reinforcing steel & monitoring the shotcrete placement, psi testing of the in-place shotcrete, complete documentation & tracking of all materials & batch numbers, and documented compliance with all TCNA & ANSI standards - they simply look like the fools that they are. And they begin to paint this segment of their industry with a big brush of cow dung.

However, with the advent of the internet, the "victims" of these manufacturers are bound to come together to compare notes. It is starting to happen. Here are some of the findings...

In every instance the cracks are totally random - they go opposite directions and are not in adjacent tiles. As can be seen in the image to the right, the cracking is totally random. Failure of Glass Mosaic Tile - Cracks, Fractures, Fissures & Spalling (click on the image for an enlarged image and a closer look) The grout is intact and the cracking does not extend through to the setting material, so apparently the thinset is not the cause. These were the tile where we were able to duplicate similar cracks in loose unset tiles, so the setting materials & grout cannot be the cause.

When the manufacturers blame the installation, they will almost always try to hang their hat on something, even the smallest detail. Maybe in the end they will "be a nice guy and provide replacement tile." Whoopdie doo! It is the installation where the money is!

They may blame "unapproved" thinsets & grouts. Almost every commercially available thinset that is approved for submerged applications, meets the appropriate ANSI standards. Some manufacturers claim that some thinsets grab to tightly, preventing the glass from expanding & contracting. However, they are playing on the installer's naivety regarding material science. A 1" square mosaic tile expands to infinitesimally, it is almost unmeasurable. To blame a thinset for this internal cracking is ludicrous. For this to actually occur as they claim, there has to already be an inherent stress present in the tile.

These same manufacturers also blame epoxy grouts, as being too rigid and inflexible, thereby preventing the glass mosaic tiles from expanding. Again this argument is laughable... Here's an experiment your child can do: take a pair of pliers & attempt to crush a equivalent size of tile & epoxy grout. The child will not be able to crush the glass tile, while the grout will explode as it is pulverized. It will be apparent to even a 5 year old, that the glass is much stronger than the epoxy grout. Additionally the expansion of the tile, being sooo microscopically small could not develop such pressures - but if there was a pre-existing stress within the tile...

Some have blamed the use of additional admixes (latex fortifiers), when the thinset manufacturer does not advise to. While this will effect the performance of the thinset & grouts, it will not cause them to become so hard or inflexible, as to crack the tile. Again, they are pretending to be "experts" in the field of material science, and because they are from "the factory" - the property owner believes them. Most "factory experts" are merely businessmen or trades persons who, like myself learned through the "school of hard knocks." I've yet to meet one that possessed a formal degree in material or molecular science [I have a chemical engineer/MBA/JD, a polymer research chemist (this is material sciences up the wazoo), and 2 orthopedic surgeons (biological science) in my immediate family].

To reinforce this point - these same manufacturer's tiles can be made to crack by merely exposing them to the thermal changes in a typical backyard spa. Left loose in a plastic tray (and therefore not subject to any external forces from thinset or grouts) and subject to the normal temperature changes from 60-104ยบ F - these tiles will begin to display the same internal stress cracks that are found in an installed application. So guys, how can it be the thinset, when the tiles crack while loose?

Another case I looked at involved tumbled glass tiles that were installed in a steam shower. The edges of the tiles were spalling. And this was only occurring on the side of the shower opposite the shower & steam heads. As you can see from the image to the right, the edges of the tiles are "chipped." Failure of Glass Mosaic Tile - Cracks, Fractures, Fissures & Spalling (click on the image for an enlarged image and a closer look) First, the chipping was blamed on rough handling during installation - but I dismissed that notion. Look at the edges of the tiles... if they were "mishandled" the chips would have been filled in (even slightly) during grouting. These are recent, fresh & shiny chips that show no sign of grout in them - proof that they occurred after installation. And it could not be from any impacts - they are from the floor to 6' high! To further reinforce this failure, we were able to recover shards of glass from the floor of the shower using duct tape... guess what we found? ...small chips of glass, exactly the size of what was coming off of the installed tile on the wall. Coincidence? Hardly!! One of the unique characteristics of glass is that it radiates heat quickly. So, glass tile installed on a wall in a room heated to 80?F, may be 65-70?F. When an "instant hot" 120-130?F shower (such as those with recirculating hot water) or a 160?F steam shower blasts the surface of the tiles with a severe temperature shock - something has to give! And that something is the glass tile - lots of little sharp pieces of it. Then Mr. or Mrs. Zillionaire steps barefooted into a glass shard torture chamber - YOU are going to be the 2nd person that they are going to call (you know that their attorney is going to be the number one!). The cool underlying surface of the glass is still at 65-70?, while the surface is 130-160?F! The glass simply cannot change temperature quickly enough throughout it's thickness, so something has to give. Yet, these tiles are marketed for use in showers! But there are no thermal shock standards for this material... these are cases where the government needs to establish standards to protect the consumers. Like the exploding Ford Pinto - bad designs & products need to be made safe! Broken glass is inherently dangerous around showers, bathrooms, swimming pools & spas, and pool decks.

In fact, these same tile can be made to crack & fissure, by merely laying the sheets of tiles out in the sun... now, how can an installer cause that????

Still, these manufacturers blame the installation procedures. Okay, for just a minute, let's assume that it is the installation. Then, why do I possess multiple factory assembled sample boards, that exhibit the same internal stress cracking that the installed product is exhibiting in the field? These are 1 foot square sheets of tile thinset to a 3/4" thick piece of plywood & grouted with a polymer fortified thinset - all assembled by the manufacturer in their factory controlled conditions. And guess what? They still cracked!

I know of a project in Southern California where the tiles had been installed, and were in the "thinset curing stage," when random tiles started to crack. And guess what? The factory blamed a faulty structure.... Failure of Glass Mosaic Tile - Cracks, Fractures, Fissures & Spalling (click on the image for an enlarged image and a closer look) But the commercial hotel developer, general contractor, swimming pool contractor, structural engineer, soils engineer, and materials testing laboratory hit back right between the eyes. And the factory took back the balance of almost 30,000 square feet of unmounted tile. Hmmm, do you think that the factory destroyed the returned tile...??? This is probably the very tile that you're going to receive in your next shipment! And then you're going to be blamed for your faulty installation!

Where am I going with this...

There needs to be a standard established for the manufacturing of glass mosaic tiles. Currently there is an ANSI Standards committee formulating these standards. But guess who is sitting on these committees? You guessed it - representatives from these very same manufacturers! Do you think that there is going to be any substantial thermal shock standard established that is going to protect the public from cracking glass tiles? Very doubtful. The fox is in charge of the hen house.

If they are not willing to subject themselves to this higher standard, then they need to disclose to the public, what extremes a particular product can safely handle. Maybe they need to establish a tiered rating system with temperature extremes based upon maximum rates of rise X a time variable. A consumer friendly A-B-C system would be ideal, with A tiles being the most shock resistant (on par with Pyrex) and C being the poorest quality. Every tile sold in the US (even imported tiles) would have to meet these standards. To maintain their thermal shock rating, a manufacturer would be required to submit samples for regular & periodic quality control checks by an independent testing laboratory (UL), to verify that the standards are still being met.

This brings us to the science behind the problems of utilizing recycled glass as a component of the raw materials. Mixing raw & recycled materials, results in a blend of materials (down to the microscopic level) with differential expansion indexes. Glass tile is very dense. The slightest thermal changes results will result in minuscule amounts of expansion. However, if this expansion is occurring at different rates within the matrix of the material (as what occurs with blended recycled materials), a stress crack may result.

Additionally, the manufacturing processes employed by a manufacturer may lend itself to "stressing" the tiles. Most manufacturers utilize a "press" much like a cookie cutter to cut the tiles out of sheets of molten glass. This process seems to render the fewest problems. These tiles are recognizable by their smooth edges, uniform size & thickness. The edges will often be tapered, being wider at the top of the tile. They may also exhibit slight marks on the edges from the press (these are not visible once the tile is set & grouted).

The second procedure is the actual cutting of the individual tiles from a hardened irregular shaped sheet of glass. The cutting procedure actually causes micro-fractures & stresses within the edges of the glass. Removing these stresses requires that the tiles receive an additional firing. These tiles are recognizable by an edge that is perfectly straight & vertical, without any marks from a press. If the tiles were re-fired, the edges will not be sharp like freshly cut glass, but very slightly rounded.

The third process is a hybrid of the press & cutting process, where the press stamps out the shape, but does not sheer the glass into individual tiles. The sheet is later "cracked" along the depressions in the sheet left by the press - resulting in a distinctive irregular edge. This "cracking" process also imparts micro-stresses into the tile. These tiles are readily recognizable by their irregular shape and oftentimes sharp edges. If the tiles were subject to re-firing to relieve the internal stresses, these sharp edges will have softened.

The final major process is the actual pouring of molten glass into molds. These tiles vary in thickness, even within an individual tile. A series of nozzles squirt molten glass in what looks like ice cube trays. The bottom of the mold forms the top of the tile. Some manufacturers follow this with a press, to stamp in a texture or stand offs into the back of the tiles. However, if the mold was not sufficiently filled, or the glass too cool, the glass will have not flowed level within the mold. They tend to be thicker than all of the prior methods, and therefore even more susceptible to exhibiting internal fissures.

An added issue is the cost of energy. It costs a lot of money to run a glass kiln & foundry. Many manufacturers do not follow proper annealing procedures - that is the slow controlled cooling of glass. The glass is transported through a temperature controlled linear kiln (called a Lehr), where the temperature zones within the kiln slowly decrease. Failure to properly anneal glass will result in the glass cracking or shattering when subject to the slightest temperature or mechanical shock - HEY DOES THAT SOUND FAMILIAR? There is no way by looking at glass tile with the naked eye, to see these inherent stresses. There is also no way to verify that the manufacturer is not "speeding up the annealing process" to save themselves some money. Remember, it's all about the Benjamin's!

So far the manufacturers that utilize virgin raw materials, and forgo the use of recycled glass in their products, have been spared the agony of their products cracking. My personal brands of preference include:,,,

While I am not fond of their color renditions and the silica speckles in their tiles, another brand that I have had success with is "Colorines Mosaicios" manufactured in Mexico. They are available exclusively through DalTile, as they were purchased by DalTile a few years ago.

To summarize the characteristics of glass mosaic tiles that tend to exhibit internal stress cracks:

  • Manufactured using recycled materials - they key commonality.
  • Manufactured in Asia (most Asian manufactured tiles are crap)
  • Improper annealing (how can you possibly know?)
  • Method of manufacture
  • Size & thickness (thinner & smaller mosaics seem to perform better)

Just because a glass mosaic tile is from a well know company, bears a prominent designer's name, is from a large company, or the product is in every tile showroom you walk into, does not mean that it is a quality glass mosaic. A lot of these glass tiles will perform wonderfully as a kitchen backsplash, but will fail miserably when subject to any climate changes or thermal shock.

Rules to live by:

1. By all means, follow the manufacturers installation instructions to the letter! Do not bootleg anything! Only follow the TCNA standards & recommendations.

2. Only use setting materials recommended by the manufacturer - if they do not specify brands & specific products, make the inquiry in writing! Keep all of your receipts. When you take delivery of the setting materials, note the lot numbers on the receipt.

3. Take lots of pictures. Digital pictures are free! be sure to track the dates specific areas were floated, set, and grouted. Be sure to follow the proper cure times before moving on to the next phase. Documentation is the key! It does not hurt to keep a color coding system, outlining areas with colored tape, so that they are readily identifiable in the photographs.

4. If it is an extremely large project (high risk & high gain), be sure to involve the manufacturers during the planning & installation process. Invite site visits & document the dates & progress on those visits. Follow up with a thank you letter & document any recommendations & comments.

5. Additionally, do not be afraid to send samples of the products to an independent testing lab for analysis and thermal shock testing. A few thousand dollars spent in advanced will save hundreds of thousands of dollars later.

6. Be an informed consumer.

7. Read the manufacturer's warranty before making your purchase.

8. Consider having the manufacturer post a bond or purchase an insurance policy to guarantee the product performance - if the project size warrants it.

9. Read the manufacturers warranty - some are so lame that they provide a warranty until you open the box or install the product! Read this joke from :


Limited Warranty Terms and Conditions

All products ("Products") sold by Hakatai, Enterprises, Inc., hereafter referred to as the "Company," are subject to this Limited Warranty.

Limited Warranty

The Company warrants that its Products, if properly stored and transported, will be free from defects in materials and workmanship from the date of sale until the date the product is installed ("Warranty Period"). THE PURCHASER SHALL EXAMINE ALL PRODUCTS FULLY PRIOR TO INSTALLATION. If a Company Product is found to be defective during the purchaser's examination, and the purchaser submits the written service request required herein, the Company will, at its option, replace the Product with a Product that is at least functionally equivalent or refund the purchase price..."

"...Warranty Limitations and Exclusions


WOW, they offer a complete warranty until I install it! And I have to declare any defects prior to installing it.... hmmm, that has "confidence in our product" written all over it doesn't it?! It should say "Warranty Scam"!

I doubt my clients will just let me stack the boxes in their backyard & collect my money. If they are not willing to stand behind their product - then this should set off alarms in your head... Warning! Warning Will Robinson! Warning! Aliens approaching! Run for safety (with your $ in your pocket!). They provide a taillight warranty, when the headlights are still in your eyes! TURN and RUN!

Remember, the manufacturer may have a strong warranty backing their product, but no one can force them to pay out, except you and your lawyer!

They will do everything they can to point the blame at YOU!

NOTE: In the accompanying images, some of the tiles appear to have white cracks across the surface. These are actually casting marks or imperfections that collected grout in them & became highlighted. Look inside the tiles for radial cracks. Click on any image to view a super-sized version.