The heat of the
sun is often sufficient to bring the shellac to a sticky state. It would
probably answer as well to shellac the under side of the paper, and to
use but one sheet, but I have not tried this plan. Around the periphery
of the pad, there is laid a piece of rubber gasket about one and a half
inches wide, and about one-eighth of an inch thick. In order that the
gasket may not be too expensive, it is cut from two strips about three
inches wide. One of them is as long as the outside length of the frame,
and the other is as long as the outside width of the frame. Each of
these strips is cut into two L-shaped pieces, an inch and a half in
width, with the shorter leg of each L three inches long. When the four
pieces are put together a scarf joint is made near each corner, having
an inch and one-half lap. It is somewhat difficult to cut such a scarf
joint as perfectly as one would wish, and it is best to use rubber
cement at the joints. Over the gasket is laid a sheet of the thinnest
grade of what is called pure rubber or elastic gum. Above this, and over
the gasket, is placed a single thickness of cotton cloth, of the same
dimensions as the gasket, and yet above this are strips of ordinary
strap iron, an inch and a half wide and nearly one eighth of an inch
thick. These strips are filed square at the ends and butt against each
other at right angles.
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