Random cracking of glass tile mosaics is rarely the fault of the installer. It is usually the symptom of inherent stresses within the glass tiles.
A consumer or installer cannot be certain that any individual piece of glass tile does not possess a preexisting stress or flaw from the manufacturing process.
The only way to be absolutely sure, is to inspect each tile prior to installation... Time consuming and costly for sure.
Failure to Inspect
I do not know of any manufacturers of glass tile mosaics that perform a visual inspection of every single glass tile, prior to shipment. Again, it would be too costly and time consuming.
I'm sure that there are computerized optical inspection systems that could be employed, but after all it is "only glass tile." The cost simply does not outweigh their liability for a few cracked glass tiles.
The best way to protect yourself prior to an after installing glass tile mosaics, is to closely follow the installation instructions.
Unmounted sheets from each lot, color and pattern should be stored in a safe, cool & dry location. Should there ever be a suspected failure, these samples can be tested at a materials testing laboratory for thermal shock resistance and inspected for preexisting stresses.
Paolo Benedetti - Aquatic Artist
"Creating water as art."™
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You may contact Paolo Benedetti at: firstname.lastname@example.org or at 408-776-8220