Formwork is used during the pouring of concrete to help hold the liquid form of the concrete in place as it sets. Several types of formwork design exist, from plywood forms to metal forms, and from temporary forms to permanent ones. Exceptionally large projects may require slip forming. Choosing the best formwork design starts with determining what type of project you will be undertaking. Very large projects may require a formwork carpenter who can make the best assessment as to the best pouring process. Small projects at home can generally be done with plywood forms.
For small projects, consider formwork design that is simple and easily managed. It is usually okay to create concrete structures in sections if the finished structures will not be exceptionally large; very large structures are often poured continuously to avoid creating seams that can lead to weakness. This process is known as slip forming and it requires a large amount of machinery and manpower. The amateur concrete worker will not use a slip form formwork design, since the execution will be exceptionally complex. Instead, small projects can be poured in sections, and the forms can be made of plywood or steel.
Plywood forms are usually made from a specific type of plywood that is resistant to water damage. The forms are held in place by temporary supports such as rods and connecting pins. These components are collectively known as falsework. Wood is lightweight and easy to manipulate, making it a good formwork material for most small projects, but it can bend or warp, which means imperfections and surfaces that are not completely flat are possible when using such forms. If this will be an issue, steel forms should be used. These are heavier, more expensive, and difficult to transport, but they will create a flat surface every time.
Choosing the best formwork design will often depend on the size, shape, and complexity of the project. It may be easiest to use permanent forms that will stay in place after the concrete sets, since it may be too difficult in removing the forms from exceptionally complex shapes. In other instances, removing the forms is not a difficult process and it will allow the forms to be reused for other projects. Choosing permanent forms can be advantageous for pouring complex shapes that need to be uniform when repeated; the same form can be reproduced easily to provide uniformity throughout a structure.