Definition
Formwork (also called shuttering) is the temporary or permanent mold used to contain and shape wet concrete until it cures and becomes self-supporting. Formwork can be made from wood, plywood, metal, plastic, or stay-in-place insulating forms. The formwork must support the weight of wet concrete (approximately 150 pounds per cubic foot) and construction loads without excessive deflection or failure.
Formula
For a footing or slab, calculate the contact area between concrete and forms. Include waste of 5-10% for formwork materials. Plywood sheets (4x8 feet) provide 32 square feet per sheet. Allow for bracing, stakes, and form ties in your material calculations.
Example
Formwork Calculation Example
For a 24x24 foot slab that is 4 inches thick with 8-inch tall perimeter forms: Formwork area = (24 + 24) x 2 x 0.67 = 64 square feet. Using 4x8 plywood sheets (32 sq ft each), you need 2 sheets plus waste. Add 10-15% for bracing and stakes. For footings, include both sides and end forms.