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Why not to use Glass for Underwater Windows

Float glass - even tempered glass - is not meant to bear weight loads. Acrylic panels on the other hand can be used as structural elements in building architecture. Once installed acrylic has proven to retain its stability over several decades.

The pictures shows the two best reasons why not to use float glass for underwater windows:

  1. The window is supposed to be transparent. Instead it is green like a water bottle. Note that float glazing needs to be very thick to withstand the water pressure. The transparency of float glas is lower than that of acrylic glazing, giving the window a greenish color
  2. See the cracks on the bottom of the window? Float glass is not meant to be used under pressure. It is not flexible. It shatters. People might tell you that this is true for normal float glass, but not for their "special" float glass. From my long experience with pressurized glazing, this is not true.

The examples show imprudent ways of using float glass. There are cases, where tempered glass is a good option for underwater glazing. However in most cases the use of cast acrylic is advised.

greenish tint of unsuitable safety glazing. The bottom part always bears the highest load - obvously it was to much for this window

shattered glazing. possibly brocken because of too high load.

Safety Glazing might "delaminate" while underwater. The top right edge of the window shown has suffered from water penetrating between the glass layers.

A savety glass that was used some years underwater. Replaced in 2020. The transparency is very low, especially compared to acrylic glazing in service for the same time.

Acrylic Windows vs Glass Windows