The selection of lumber is of importance. If the Forms are to be used
over many times, surfaced lumber, matched, tongued, and grooved stuff,
free from loose knots, is an economy. If, however, they are to be used
only once, almost any old plank will do. By nailing a board on the
outside of the cracks or over the bad knot, and filling with a little
clay, the Form is made tight.
Green lumber is preferable to kiln-dried or seasoned stuff. Seasoned
stuff, when wet (either by throwing water on the form before placing
the concrete or by absorbing the water from the concrete) warps, and
the shape and tightness of the Form are damaged.
[Illustration]
Originally only surfaced lumber was used for Forms, dependence being
placed on it for giving a finish to the work. While to-day other than
smooth surfaces for concrete are the fashion, surfaced lumber has some
advantages. The Forms fit together better and are easier to erect. They
are more easily cleaned. They are easier to remove. All these items
reduce the cost of the work. The saving effected will of course depend
on the difference in local price between finished and rough lumber.