Concrete Formwork

Introduction:

Formwork is the system/structure of boards, ties, and bracing used to create a ‘form’ (or ‘mold’) which wet concrete is poured into. After the concrete has cured, the formwork is removed and it leaves the resultant concrete form.

Materials

Formwork for concrete can be made out of a number of materials, but the most standard is ¾” plywood. Typically the plywood side facing the wet concrete is coated in a material impermeable to the wet concrete; such as oil, water-resistant glue, steel, or a hard plastic.

• The material and coating (if provided) on the formwork, drastically increases the ability for the formwork to be reused as well as last for multiple uses. In a more sustainable construction process, and especially on projects such as towers where the floors are repeated, the formwork will get reused multiple times in their lifespan.
• Prefabricated steels forms are common on high rise projects and used for their strength and durability.

Strength & Constructability

The main requirement is that the formwork structure needs to be strong enough to withstand the immense outward pressure the wet concrete creates. A secondary aspect is constructability, and that the formwork needs to be relatively easy to construct and easy to remove.

• In certain applications like lot line conditions, the formwork may never be removed and is instead abandoned in the space.

Tolerance

You can get tight tolerances with a great subcontractor, but concrete is a messy business and difficult trade to master. Forms can shift, weight can affect plumbness, and so on. The tighter the tolerances required, also will translate into more money as extra time is needed to re-verify heights, take surveys, etc. Therefore, dimensions and elevations should ideally be struck in ½” increments.