Plan your Forms so there will be no difficult measurements to
understand. Make as few pieces of lumber do the work as you can, and
do not drive the Forms full of nails. If you do the Forms will be
difficult to take apart without splitting.
Forms must be strong enough to hold the weight of the concrete without
bulging out of shape. When they bulge, cracks open between the planks
and the water in the concrete, with some cement and sand, will leak
out. This weakens the concrete, and causes hollows in the surface which
look badly after the Forms are removed.
Forms which lose their shape after being used once can hardly be used a
second time. A part of the erection cost of Forms is saved if the Forms
are built in as large a section as is convenient to handle. This saving
applies to their removal, as well as to their setting. Consequently,
the lightest Forms possible, with the largest surface area, are the
most economical.