Page 47 - Masonry and Concrete

Concrete Construction Techniques
46 CHAPTER THREE

3
5
4

PLUMB
BOB

REBAR
STAKE

FIGURE 3-7
Squaring corners.

the soil is stable, but most concrete work requires building forms to
shape and hold the mix until it hardens. Forms for concrete must be
strong, tightly fitted, and rigidly constructed.
3.3.1 Temporary Formwork

Most formwork is removed after the concrete has hardened enough to
support its own weight. The formwork materials can often be reused
several times. The sides of residential concrete forms are usually con-
structed of 2 lumber or plywood held in place by wooden stakes or
braces and stakes driven into the ground, depending on the height of
the form (Figure 3-9). Removable forms must be built in such a way that
the green concrete is not damaged by the form removal process.
Once the concrete size and shape have been laid out and the cor-
ners marked with the temporary reinforcing bars, the elevation of the
top of the finished concrete must be established and a string line
erected to set the form boards and supporting stakes correctly. The
string lines should be attached to stakes set just beyond the corners.
1
The strings themselves should be 1 ⁄2 in. outside the corner markers to
allow for the thickness of the 2 form boards (Figure 3-10). Stretch the

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