For laying cast-in-situ concrete structures, the concrete which is in a plastic state requires to be supported by temporary supports and casings of the desired shapes till it becomes sufficiently strong to support its own weight. This temporary casing is known as formwork or forms or shuttering. The term mould is used to indicate formwork of relatively small units such as lintels, cornices and so on. For circular work such as arch, dome etc., the term centering is used. When the concrete has reached a certain required strength, the form is no longer needed and is removed. The operation of removing the form work is commonly known as stripping. After stripping, the components of form work are removed and then reused for the forms of another part of the structure. Such forms whose components can be revised several times are known as panel forms.
The cost of formwork may be up to 20-25% of the cost of structure in building work and even higher in bridges.
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