The process of pouring concrete involves creating molds into which the wet concrete can be poured. These molds hold the concrete in place as it sets so a specific shape can be created. The name for these molds is formwork, and various types exist. Metal formwork is generally used for heavy-duty applications, though some metals are lightweight and thin, and are therefore suitable for smaller jobs or lighter-duty applications. Metal formwork generally comes in two varieties: steel and aluminum. Steel forms are very stable and solid, but also quite heavy and difficult to handle, while aluminum forms are lightweight and easy to move, but not as stable or strong as steel.
Regardless of the type of metal formwork being used, the metal panels will be held in place with bars and couplers known as falsework. Once the concrete has set and the structure is stable, the falsework will be removed and the panels can be deconstructed. The set time for concrete can vary depending on the size of the project as well as the shape of the finished concrete structure, so it is likely that the metal formwork will need to stay in place for several days while the concrete hardens.
If the structure is large and the volume of concrete being used is quite high, steel formwork is most likely to be used because thick gauge steel will be relatively unyielding and strong enough to support the weight of all that concrete. Aluminum formwork can also be relatively durable and unyielding, but for larger projects, the more brittle aluminum may not be the most appropriate choice. Lightweight metal formwork made from aluminum is suitable for small or medium projects, and even then, steel falsework is often used to keep the formwork panels in place.
Both types of metal formwork are usually reusable as long as they are not damaged during the pouring process. This means the panels will need to be cleaned after each use to prevent concrete buildup on the faces of the panels. Aluminum is fairly easy to clean, and corrosion is less likely on aluminum than on steel. Rust and corrosion can be a problem with steel formwork, but if the panels are properly cared for and stored in a dry storage unit, steel forms can last a long time and can be reused on many projects. If a panel is damaged, steel can sometimes be reworked back into shape, whereas aluminum is more likely to break without chance for repair.