Join Date: Apr 2006
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No longer solid. Crazing is what it looks like, hundreds of fractures in the plastic. It is caused by three things: UV exposure, chemical exposure (petrochemicals in waxes and cleaners, etc.) and excess stress, caused by expansion and contraction in an unyielding frame.
Probably sound enough to keep walking on, just nowhere near their original strength. The only cure is to replace the glazing.