The appearance of reinforced concrete on construction sites has led to the use of formwork during the construction of buildings. It is used to keep the concrete in place until it is dry. After the earthworks, the formwork is an important step of the construction: well done, it allows you savings and to avoid that the concrete mixes with the ground.
Wooden formwork in which the concrete is poured
Principle of the formwork technique
The formwork is a temporary mold used in masonry for the concrete to take a specific form, to maintain it until its setting and to give it a surface (rough or smooth), important detail if the concrete is apparent.
Different types of formwork
The formwork is generally made of wooden planks but it is also found in metal, according to the constraints of the construction. It is not necessary to use new planks; we can opt for salvaged wood! In this case, they must be straight with sharp edges and the formwork is only used once.
If pine planks represent a cheap material for formwork assembly, plywood is more qualitative: its thickness is more resistant to thrust. In addition, associated with a resin coating, the use of plywood reduces the porosity of the planks and allows the reuse of the formwork.
Finally, metal forms are used by professionals on large construction sites or atypical forms.
For a long formwork or an outer slab is placed at regular intervals shims along the mold to prevent deformation. Once poured concrete, it must be reinforced by eliminating a maximum of air bubbles: it is the technique of vibrated concrete which involves striking the formwork filled with concrete with a hammer.
When the concrete has set and is stable, the form must be stripped. A delicate operation that owes a lot to the material used for the mold and the dexterity of the formwork.
Once dry, the concrete is fragile, especially in the corners and edges. You have to be thorough. The main difficulty is that boards adhere to dry concrete.
- First, remove all stakes or wedges installed along the formwork
- With a hammer, the formwork is struck gently: the vibrations of the wood will separate the mold from the concrete
- If the formwork boards are coated with form release oil, it is easier to remove them
- As soon as there is space between the wood and the concrete, the formwork can be removed
On the same topic:
The assembly of reinforced concrete walls.