Choosing the Right Formwork

Formwork is an important part of concrete construction. It is an often temporary structure that gives concrete a desired shape when poured. Formwork is made from a variety of materials, including wood, metal, steel, and plastic.

Any concrete construction process usually begins with the installation of a formwork. Composed of panels assembled in the desired shape, the formwork forms a solid, watertight structure capable of supporting the weight of fresh concrete. Once the formwork is in place, all that is left to do is pour the concrete into it using a concrete pump and leave it to harden. Once the construction is completely dry, the formwork can be removed.

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Which material should you choose?
Formwork is available in different materials: wood, steel, and plastic. Here are a few points to help you choose the best material.

Wooden formwork

Wood is one of the most widely used materials for formwork construction, as it offers several advantages:
- It’s an easy-to-cut material, which makes it suitable for small, intricately shaped elements.
- It offers many compositional possibilities.
- Its texture makes it ideal for exposed concrete structures and complex, non-repetitive structures with varied textures.
However, there are several things you should bear in mind:
- The boards should be thick (27 to 40 mm) to prevent warping.
- The wood must be lightweight and free of cracks.
- Plywood panels are recommended for large, flat surfaces.
The main disadvantage of wood is that its characteristics change over time. It loses porosity and the surface wears away, which can affect the color and appearance of the concrete. Wooden formwork can therefore only be reused a limited number of times.
If you need to reuse your wooden formwork many times, choose waterproof marine plywood panels with a thickness of 16 to 19 mm. They make the formwork more durable.
Steel formwork

Metal formwork is the most widely used, as it can be reused many times over – 20 to 25 times more than wooden formwork. It is particularly suitable for floors and posts.

It also offers other advantages:
- It is sturdy and allows large concrete surfaces to be poured.
- It can be installed and dismantled quickly.
- It is recommended for circular or tall structures.
- For ease of transport, some metal formworks are available in foldable versions.
- Steel does not absorb moisture from fresh concrete, so steel formwork will not warp.
- Steel allows the heat released by cement hydration to be dissipated, which is an advantage in hot weather.
However, steel formwork has one drawback. In cold weather, concrete is less well protected against temperature drops. It is therefore advisable to add thermal insulation to the formwork.

Mixed steel and wood formwork is also available. The structure is metal (aluminum or steel) and the face is made of wooden plywood panels.

These mixed formworks have several advantages:
- Flexible assembly
- They can be moved manually
Plastic formwork

Plastics such as PVC or polyethylene are used to manufacture the outer surface of the formwork.

This type of formwork offers several advantages:
- It offers superior siding quality.
- It can be easily removed from the mold.
- It can be used to create a variety of reliefs.
- The plastic material can be used to create small modular formworks (0.5 to 1 square meter) that are easy to handle.
What type of formwork should I choose?
Formwork can be designed on-site or prefabricated.

On-site formwork

These are the traditional formworks used for various constructions such as walls, floors, or pillars thanks to their great adaptability.

Frame formwork is recommended for walls, as it protects the panel edges from mechanical stress. These formworks are strong, durable, and easy to assemble. Column formworks are designed with beams and are used in residential and industrial buildings. However, these formworks are time-consuming to install.

Prefabricated formwork

Prefabricated metal formwork is designed to withstand various casting pressures (> 70 kN/m², <>= 60 kN/m² and <= 50 kN/m²).

Self-climbing formworks are hydraulic systems mainly used in the construction of high-rise buildings.
What are the main characteristics of a good formwork?
Formwork design must meet several requirements:

Rigidity: Formwork must be sufficiently rigid and stable to withstand the pressure of fresh concrete. The aim is to ensure that the concrete remains stable until it hardens. It must also be easy to dismantle to avoid damaging the concrete during demolding. The formwork material must not be deformed by high or low temperatures.

Watertightness: It must be watertight to prevent laitance from leaking at joints, for example.

Surface texture: Formwork must achieve the desired surface texture to meet aesthetic and functional requirements. You must also consider the number of times it will be reused when choosing the material for your formwork. Wooden formworks are subject to deterioration over time, which can affect the final appearance of the concrete.