Formwork for Foundation
Formwork for continuous or isolated footing is usually made of wood boards (planks) or plywood supported by vertical stakes driven into the ground. The top of the vertical stake is supported by a diagonal brace driven into the ground. Bracing may be replaced by the piling up of dirt to support the sides of the form. The correct distance between the planks is kept by crossing spreaders. On small footings, steel straps are used to replace the spreaders. It is common practice to construct the forms higher than necessary and place the straps in the inner sides of the form at a height equal to the concrete level. Figure 2.3 shows typical formwork for isolated footing.
Large footings are formed similarly to small and continuous footings except that the sides are supported by studs and wales. Holes are drilled into the sides of the forms, and tie wire is passed through the sides of the forms and fastened to the studs. Lumber planks or steel strap spreaders are used to provide extra support. Figure 2.4 shows details of large continuous footing.