Swimming Pool Glass Tile Mosaics Thermal Shock Testing ANSI A137.2

There is finally a method prescribed for the testing of thermal shock resistance of glass tile mosaics - ANSI A137.2 - 7.9.  This first ever standard is a good start.  However, it is still a far cry from where the standard needs to go.

The ANSI A137.2, Section 7.9 Thermal Shock  standard was developed by a committee that consisted primarily of, none other than... glass tile manufacturers.  Anyone else see a potential conflict?

Set themselves up for success

Manufacturers submit samples of their products for testing to a laboratory of their choice.  There is nothing preventing the manufacturers from providing specially selected, inspected or treated glass tiles for testing.  These may include inspections, testing, treatments or materials that are not utilized in their normal course of production.

The testing procedures only subjects 5 loose tiles to ten thermal shock cycles.  Five tiles simply are not statistically representative of tens of thousands of tiles that may be used in a swimming pool.

The testing lab does not perform any follow up testing of commercially acquired tiles.  There is no subsequent verification that production methods are generating compliant materials.  Again, a self- fulfilling prophecy.

Not Real World Tests

The five sample tiles are tested in a loose state.  They are not tested in the state in which they will be used by the consumer - that is installed.  You know - mounted and grouted.

Mounting and grouting glass tiles places constraints upon them.  They are adhered to on the reverse by thinset.  They are also constrained around the perimeter by grout and neighboring tiles.  Under thermal expansion, they have nowhere to go, especially if the setting materials are too constrictive.

Thinsets vary by their tenacity and shrinkage rate.  Some thinsets have a very high sheer strengths.  Some thinsets experience excessive shrinkage, placing the glass under compression.  Some do both.

Grouts vary in compressive strengths.  Some are more flexible, others more rigid.  Epoxy grouts are more flexible than in years past, and should not be immediately dismissed (as in CTIOA report 2008-8-12).

How SHOULD they be tested?

Glass tiles should be tested in their mounted and grouted state.  The way that they are intended to be used.

Acceptable thinsets and grouts should be specified by glass tile manufacturers, only after successfully completing thermal shock and sheer testing.  

Yes, this may require multiple tests with various combinations of manufacturer's setting materials to find compatible products.  Nothing precludes a manufacturer from specifying only one brand of setting materials.  But, this method may require multiple tests until one is found.

In fact, the thermal testing should be combined with the sheer testing procedures.  The sheer test is performed in a mounted & grouted state.  

Prior to performing the sheer test, the tiles should be subject to the thermal tests.  Excessive expansion may loosen or crack tiles - which will then fail the sheer test.  A REAL WORLD test.

Self-Serving Standards

Until test standards are instituted with the intention and purpose of protecting consumers and not manufacturers, what is a specifier or contractor to do?

Have any proposed tiles tested, in their mounted and grouted state.  Utilize setting materials from one manufacturer, adhering to the ANSI specified thinset and grout cure times - prior to any thermal or sheer testing.

Glass tile mosaics are the most beautiful and luxurious swimming pool finish available.  Properly installed quality tiles should last you a lifetime.

Paolo Benedetti - Aquatic Artist 
"Creating water as art."™ 
Aquatic Technology Pool and Spa ©www.aquatictechnology.com 
You may contact Paolo Benedetti at: info@aquatictechnology.com or at 408-776-8220

Swimming Pool Glass Tile Mosaic Cracking - Tile Edge Quality

Poor Edge Tolerances

There are many reasons why glass tiles crack.  The most common is damage to the tile - a chip, scratch or impact.  These traumatic events occur during the manufacturing, handling, shipping or installation process.

Manufacturing Processes

Glass tiles are made into small squares by a number of various processes.  Cast or pressed, individually cut or snapped are the three most widely used methods.

Cast Tiles
Cast tiles are created when molten glass is poured into molds, individually forming each tile.  The process may be inverted, when a cookie cutter style press stamps out individual and distinct tiles.

Cut Tiles
Cut tiles are formed by cutting the tiles from a larger sheet of glass.  The tiles are usually then re-fired in a kiln to relieve stresses imparted during the cutting process.

Snapped Tiles
Snapped tiles are a more rudimentary method of forming tiles.  These are made by one of two processes: 

• a cookie cutter style mold presses the tile shapes into molten glass.  The cutter does not separate the tiles into individual pieces, leaving them connected by a thin layer of glass.
• molten glass is placed onto a mold tray and allowed to cover the mold.  It is then pressed or allowed to fill the cavities.  The tiles are connected by the layer of glass that remained across the dividers.

After annealing, they are later "snapped" apart, creating the separate pieces.  The process of snapping imparts chips and stress along the edges of the tiles.  Unless the tiles are re-fired in the kiln, these stressed tiles are handed off to the consumer.

Hard to Detect

These chips and stresses are hard to detect.  Since the tiles are usually mounted on an opaque paper, inspections are difficult for the end user, if not impossible.

Resulting Cracks

The stress that concentrates around these imperfections from thermal expansion will cause the tiles to crack.  Because not every tile has these imperceivable flaws, the cracking will occur randomly and the manufacturer will blame the installation practices.


Paolo Benedetti - Aquatic Artist "Creating water as art."™ 
Aquatic Technology Pool and Spa ©www.aquatictechnology.com 
You may contact Paolo Benedetti at: info@aquatictechnology.com or at 408-776-8220