Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Steve" <alienrelics@y...>
wrote:
> My local plastics guy says plexiglass is not good for constant
contact
> with water. It will absorb some and swell, causing crazing.

This is true. Here's a simple but long duration experiment.
Fill a 8x10" (approximate) tray (polyethylene is good) with
water (half full) and place
a piece of acrylic plastic (3mm thickness is good) over it like
a lid. The acrylic sheet needs to cover the entire tray and should
overhang a little on all sides. The sheet is not in direct 
contact with the water. Note flatness of plastic at start of
experiment.
Leave undisturbed in a normal room environment for two weeks or
so. At the end of this period note warpage of acrylic plastic.

The observed warpage is due to water absorbtion on the bottom
surface.