Plexiglas

In one of our galleries, we mounted 3/16th inch thick acrylic plexi,
measuring 96 inches x 29 inches overall, to a solid rectangular
frame made of Medite board. This whole case is wall-mounted in
'landscape' orientation. The show has now been mounted for less than
two months.  We have checked the environmental records of this
particular gallery since the show opened, and they show no unusual
or extreme changes. The objects behind the acrylic plexi, gelatin
silver photographs, show no signs of being affected by environmental
changes.

What is confusing is that the plexi appears to have expanded,
especially within the last two weeks. There is evident buckling, in
the spaces between where the screws pass into the frame. There are
now 1/4 inch gaps between the plexi and the frame, where once it sat
flush.

And, on one side of the case, the screwholes in the plexi no longer
align with the screwholes in the frame, because of this possible
expansion. They are now 2mm to the left of where they were.  The
other possibility is that the painted Medite frame has contracted
(although again, not likely due to environmental changes), but none
of the other cases in the room have changed at all, which makes one
wonder.

Your responses to this will help us with this baffling situation.
Has anyone heard of dimensional change of plexi or Medite, when
situated in an environmentally stable environment?

David Stevenson
Restaurateur
Conservator
Centre Canadien d'Architecture
Canadian Centre for Architecture
1920, rue Baile, Montreal
Quebec H3H 2S6
514-939-7001 ext. 1204
Fax: 514-939-7020


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                  Conservation DistList Instance 25:23
                 Distributed: Sunday, November 6, 2011
                       Message Id: cdl-25-23-012
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