Sunday, December 8, 2013

Clouding and discoloration behind glass tile mosaics

With glass tile mosaics increasing in popularity, so have the complaints about dark spots, discoloration, clouding and color rendition.
Installation Practices

Proper installation practices for glass tile mosaics are time consuming and expensive.  The cost for labor and setting materials in a pool or fountain can run from $35-100 per square foot - not including the cost of the tile!

In an effort to bring the installation costs of glass tile in a swimming pool within reach of those with limited means, many installers take shortcuts.  These shortcuts include direct setting tiles, bonding them to incompatible substrates, using inferior setting materials or rushing the installation.

Published Standards

In 2005, in response to many consumer complaints and installation failures, the tile industry created minimum standards for glass tile installations.  This committee was comprised of glass tile manufacturers, manufacturers of setting materials and tile installation contractors.  The results were the 2005 ANSI Standards A108.14 - A108.16 - Practices for the Installation of Glass Tile Mosaics.

These standards were promptly adopted by the Ceramic Tile Institute of America (CTIOA) and the Tile Council of North America (TCNA).

In fact, CTIOA has since promoted the ANSI standards as the ONLY acceptable methods of installing glass tiles.

Some third world and foreign tile manufacturers publish installation instructions that conflict with these standards.  Installation contractors need to be aware that failing to follow accepted and published industry standards will make them liable in the event of any installation failures.

The bottom line is that the installer needs to follow the most stringent standards that apply to their installation.  YES, that is even if a manufacturer allows for a faster, cheaper and easier method.

Trapped Moisture and Voids 

Moisture, voids or blemishes behind translucent (see through) glass tile mosaics will show through the tiles as a discoloration.  The discoloration can be spot behind a single tile, a random assortment of tiles or an entire installation.  They are unpredictable, occur randomly and may only affect a small portion of a project.

Voids, trapped moisture and blemishes occur behind the tiles from the following installation errors and mistakes:
  • the bondcoat skins over before the tiles are set (poor bond, loose tiles & voids)
  • using the improper direct bond (two step) installation method
  • notches left in bondcoat
  • too thin of a bondcoat
  • utilizing dark colored grouts - which are visible through the sides of translucent tiles
  • insufficient embediment into bondcoat
  • too much water in the bondcoat 
  • ground water weeping into the shotcrete from the soil
  • grouting too soon after setting (the back buttering with grout method may in fact trap moisture)
  • insufficient curing of the mortarbed (leveling bed)
  • a bondcoat that experiences shrinkage (and results in voids)
  • utilizing grey cements -which darkens when wet and will be visible through the sides of the tiles if allowed to ooze up between them
  • failing to install a waterproof membrane
  • filling the pool too soon
  • failing to shade the tiles from the sun prior to filling the pool
  • failing to protect the pool from rain (or snow or irrigation water prior) to filling the pool
I am not going to discuss each of the above conditions and why they cause discoloration behind the tiles.  Individually or in combination they can lead to visible setting flaws.


There are tests that expert witnesses utilize when investigating complaints of discoloration behind translucent glass tile mosaics. These tests analyze the visible color variations, composition of the setting materials, sheer strengths (pull off resistance) and moisture contents.

Samples removed for testing must remain in the same condition as when they were installed.  If they were under water, they must remain wet.  Allowing the samples to dry out will change the characteristics of the sample, rendering their evaluation useless in determining the cause.

Learning Process

The final result of any project evaluation, should be the education of the party responsible for the installation.  Incorrect installation procedures, improper setting materials or a combination of them, are responsible for most complaints of discoloration.  

Installers have been known to blame minerals in the water, airborne mold spores and poor pool water chemistry for causing these discolorations... anything but owning up to their misgivings.

Through strict adherence to the published installation standards and practices, you can be guaranteed a flawless glass tile mosaic swimming pool.

Contact the author, Paolo Benedetti of Aquatic Technology Pool and Spa at: or 408-776-8220. 
Visit his website at: 
All Contents © Aquatic Technology Pool & Spa, 2013. 
All rights reserved.

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To contact the author, Paolo Benedetti of Aquatic Technology pool and Spa, email him at: or call 408-776-8220.
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