Aquatic Technology Pool & Spa

Glass Tile Mosaics - Unexplained Cracking

Glass Tile Mosaics - Unexplained Cracking, Fissures, Spalling, or Failures

By Paolo Benedetti, FRIDAY, JANUARY 29, 2010

Glass Tile Mosaics - Tessellated StressInternationally renown pool designer Paolo (Paul) Benedetti presents an end users view into the failure of glass tiles (cracked, fissures, spalling). He has created spectacular glass tile mosaic knife edge perimeter overflow pools, infinity edge pools, vanishing edge pools, disappearing edge pools, negative edge pools, no coping pools, zero edge pools, no edge pools, and edgeless pools.

An Insiders Look

Over the past few years I have examined, studied, discussed or consulted on approximately 100 glass tiles failures. The installations ran the gamut from interior decorative walls & bathrooms, simple glass tile waterlines in pools, elaborate outdoor pools lined entirely with glass tile mosaics, to glass tile manufacture's own factory assembled & provided sample boards!

Following Directions

Let's face it, it's a guy thing... don't ask for directions when you're lost, and by all means don't read the instructions before you've started the assembly/installation!

A number of the installations (most) were installed by people who didn't even bother to read the manufacturer's installation instructions. These projects were destined for failure even before they "hitched a horse to their cart." Combine shoddy workmanship with defective glass tile mosaics, and you have a guaranteed lawsuit - the only ones who wins are the attorneys!

However, some of the installations were performed by individuals as anally retentive as me. They should not have had ANY issues... but they did anyway. These are the projects that I'm focusing on. People who did everything by the book, and still the projects experienced glass tile mosaic failures. These are the people who did nothing wrong. They used the proper setting materials, waited the correct amount of time for the various layers to cure, installed expansion joints in the right places, and documented exactly what they did.

Limiting your Liability with DETAILED Instructions

In order for a General Contractor, Tile Contractor, or Swimming Pool Contractor to minimize their liability they need to be sure that they have specific instructions from the tile manufacturer. You'll notice that I did not say eliminate the liability, as there is absolutely no way to prevent someone from "point the fingers" - and that's exactly the manufacturer's tactic! "It didn't leave our factory that way!" But read on... it probably did (they were just too stupid to know any better, or too deceitful to care!).

You want to find instructions that specify their approved setting materials, and outlining for neophytes the correct curing/waiting times between the installation stages. This is what you want from a set of instructions... details. If the instructions say "any commercially available thinset" (or worse yet "thinset"), or "sanded grout" (do they really mean plain unadulterated grout, with polymer fortifiers, or sanded & epoxy fortified?), be sure to get written clarification! I guarantee you that a they will deny that they ever spoke to you - if all you do call on the telephone. Oceanside Glass tile probably has one of the most detailed set of instructions that I have ever seen. They specify everything!


Did I mention that you should DOCUMENT everything? It is not difficult to note the lot numbers of the waterproofing, thinset, grouts & expansion joint filler when the delivery quantities are verified on the job site. It doesn't have to be anything formal, just a notation of the tracking numbers on the packing slip.

During the installation, the documentation of the curing times can be as simple as a digital camera that date stamps the images as they are taken. After an area is prepared, it can be marked with a marker as to the date finished & the date ready to start again. Then take a picture. When work resumes in this area (on or after the date written with the marker) take another picture. As work progresses to the finish layers, you can use a "china" or grease marker to label the tiles with this information. It'll clean off easily during the detailing stage.

Digital pictures are wonderful, as they can be enlarged, emails, & distributed easily. Be sure to encode the images, so that they cannot be manipulated with post-imaging software (Adobe Photoshop) before they are ever distributed. This same software allows the images to be documented in a manner which will reveal if someone in the future manipulates them. remember - a picture is worth a thousand words.


Out of the failures that I've seen, there is a resounding commonality.... the use of recycled glass. Granted anytime we can use recycled materials, it is great for the environment. But for some reason, in the manufacturing of glass tiles, it's use seems to be a problem. I have yet to see a problem with blanket failures from any manufacturer who uses ONLY virgin materials in their production process: Lightstreams, Cicis, Colorines, Bisazza, Interstyle. Over the years, I have personally used products from each and every one of these manufacturers, and have yet to experience any issues. I have many of them in my own home... and inspect them frequently!

Why all of the failures?

First of all, a large number of manufacturers have taken their manufacturing facilities off-shore. China has found itself one of the largest manufacturers of glass mosaic tiles. Do you really think that they perform any quality control on the "recycled" glass that goes into their tiles? If they had a single source of their recycled raw materials, they might have an argument. However, this is not the case, green glass is green glass, clear glass is clear glass... glass is glass. Grind up all of these different glasses, that have definitely have different chemical formulations. And Houston, we have a problem.

Name brand manufacturers and boutique designers, saw all of the potential profits in glass tile mosaics, and not wanting to miss a buck, placed their names on this crap. There are no quality control inspections... just delivery schedules and profit margins. Do they even understand the material science side of glass production? I seriously doubt it...

There are a few manufacturers that use a single source of recycled glass, and therefore claim that all of their recycled glass is the same & therefore (it must be) compatible. Let's say for instance, they rely on the use of ONLY clear soda beverage bottles from one brand of soda. We are all keenly aware that beverage companies do not have a single source for their glass bottles. In fact, shipping costs of containers both empty & full quickly eat into profits. Therefore bottling plants are situated around the globe, usually utilizing glass container vendors that are close by, minimizing overall distribution costs - "make it, where it is drank." Eventually, all of these bottles get a soda label applied and they get filled with soda. Does that make the glass containers from these various vendors the same in their chemical composition? Does someone somehow think that the contents of the bottles in some way will make these bottle harmonious? Corona bottles for instance, used to have the element cobalt in the paint on the labels. Any cullet (ground up recycled glass) that contained any hint of Corona bottles was routinely refused by companies or processors that uses glass cullet (source: Container Recycling Alliance).

Some of the manufacturers claim that they have "special chemicals" that they add to make everything homogeneous. But they have a problem - the person who controls the source of their raw materials is the one verifying that the raw recycled glass is "all the same." But how can they tell by just looking at it? Unless they actually take in, clean, sort, & grind all of their own recycled glass containers there is absolutely no way to know 100% that the cullet is all the same!

Many name-brand tile companies here in the United States, actually have their tiles manufactured in China (by someone else). Most of them do not even own their own manufacturing facilities. Instead, they rely on these Chinese companies to make their tiles for them. They have virtually no control over the raw materials or the manufacturing process. It is merely accepted if it is delivered on time & it cosmetically looks correct. You can find these glass tile mosaics in almost every Home improvement store. In tiny print somewhere on the box it says "Made in China." They conveniently left off the rest of the disclaimer, " people who don't give a rats ass about you & only want your yankee dollars."

Lack of Quality Control

Most manufacturers do not perform any type of quality control, other than maybe a visual inspection with the naked eye as it passes down an assembly line. Some might have automated systems that check for consistency in size & thickness. They may even go to the extreme of using a computer to check the color of the finished glass tiles against a production standard.

But few if any are using a polariscope, to perform a visual inspection of a random sampling of the finished products. Some of the manufacturer's that I've talked to didn't even know what a polariscope was! How the hell can they even perform this crucial inspection step, if they don't even own one?


What the hell is a polariscope you say? Well, it is actually a relatively simple and very inexpensive device. The polariscope is an important tool for determining strain & stress patterns that develop during the manufacturing process. It allows an inspector to immediately determine if strain or stress is present in almost any transparent material.

How it works...

The polarizing filters align the light into planes of polarized light. When the polarized light passes through that area of stress, the light becomes retarded. The amount of retardation observed is directly proportional to the amount of stress in a given area. A polariscope is merely a device that transmits light through the translucent material (from behind). The inspector looks through 2 polarizing filters, while slowly turning one of them 360ยบ to change the alignment of the planes of light. Any inherent stresses within the material will clearly highlight themselves. How obvious are these stresses within the material? Take a look for yourself - you be the judge:

Images courtesy of: yours truly

(Click on an image to enlarge it - again to shrink it).

This tile has obvious stresses horizontally across the top as indicated by the white line. The clouding on in the bottom of the tile also indicates an area of stress.
This tile shows a large internal stress down the center of the tile. This will most definitely manifest itself as a fissure or crack. once the tile is exposed to any environmental thermal expansion.

This small 1" x 1" tile shows a large area of inherent stress all across the top edge. To the unassisted eye under plain lighting conditions this looked like a perfectly good tile. The job that this batch of glass tile mosaics were installed in, had an installed failure rate of 25-30%.

Guess what percentage of uninstalled tiles from this batch exhibited indications of internal stress? Good for you, you're so smart - about 30%! Coincidence? Hardly! Now since this was never installed, how can the manufacturer blame the installation?

This tile is what a "good" piece of glass mosaic tile should look like under a polariscope.

The star actually "rotates" as the singular polarized filter is rotated. The small bubbles within the tile are acceptable, and should not affect it's performance.

So, how much do these complex testing apparatus cost? A measly $250-$1,500. At those prices there is absolutely no excuse for these multi-million dollar companies to not own at least one!

Tile showrooms, tile buyers, distributors, tile contractors, swimming pool contractors & designers, and "expert witnesses" should all own one... The industry needs to start rejecting these faulty defective materials, before these unscrupulous manufacturers get the opportunity to push the blame onto the "poor installer" one more time!

Come to think of it, I have never been asked by a glass tile factory to "send us a sample of some unmounted tiles, so we can test them." It has ALWAYS BEEN: "Something must have been done wrong in the installation..." WELL, THOSE DAYS ARE OVER! There is a smarter consumer emerging from the woods... and they are well armed (with a Polariscope)!

Imagine, receiving a shipment of glass mosaic tiles, soaking them in water to remove them from their facing paper, then inspecting a few square feet for these flaws. Then calling them up to come get their recycled crap off of your lawn (from the couch on the front porch, they're blocking your view of the pink flamingos).

The manufacturers will quickly change their ways, as the word got out that they are knowingly (or ignorantly) selling defective glass tiles. These defective tiles simply are not suitable for the purpose that they were advertised for!

We need the Consumer Product Safety Commission to get involved - maybe the Congress can do some good afterall!

Have you experienced a glass tile mosaic failure?

Go and buy yourself a polariscope - because the proof is IN the pudding glass!