What Is Formwork?
Formwork, commonly known as shuttering, is a temporary ancillary mold-like arrangement where fresh concrete is laid for casting different structural members such as beams, columns, slabs, etc. There are different types of formwork materials used in construction. In this article, such different materials are discussed.
The shuttering plates, also known as forms, are arranged in such a way that the material (concrete – RCC or PCC) takes the proper & required shape and size after it solidifies and matures over time.
The formwork does not only act as a mold to concrete but is also responsible for providing support, strength, and stability to the fresh concrete. After the concrete stiffens and matures, the formwork is removed carefully. This process of removal of formwork is known as Stripping.
Formwork is an essential job that requires some great skills and accuracy for its construction. So, usually skilled and experienced labours are hired for the construction of formwork. Lack of accuracy and skills while construction of formwork may lead to poor, inferior, and unsatisfactory quality of work, which at last results in loss of valuable resources like time and money.
While considering the total cost of the project, formwork contributes to 20% to 30% of the total cost of concrete structure. Sometimes the cost of formwork may go beyond the specified range (up to 60% in some cases) depending on the complexity of the concrete structure.
Requirements of a Good Formwork
i) A good formwork should be able to resist the amount of load exerted on it
during and after the process of concreting.
ii) There should stay no gaps between two forms when arranged adjacently so that
any kind of slurry leakage does not take place.
iii) The surface of a good formwork should be smooth and unwrinkled which results in a better quality & a smooth finished concrete product, when the formwork is removed.
iv) The formwork should be designed in such a manner that its installation and
removal can be done easily without putting heavy efforts.
v) A good formwork should be so durable that it could be re-used for a number of
times, while also preventing frequent maintenance.
vi) The formwork should be lighter in weight up to a possible extent so as to
eliminate complexity for laborers while its installation and removal.
vii) As stated above, a durable formwork can be used a number of times, which also
helps to achieve affordability, in terms of economy, in a long run.
Types Of Formwork
Formwork is mainly classified on the basis of different materials. The different types of formwork materials are as follows:
- Timber formwork,
- Plywood formwork,
- Steel formwork,
- Aluminium formwork
- Plastic formwork
1. Timber Formwork
Timber formwork is considered to be one of the oldest and most conventional types of formwork. Despite being one of the oldest in its category, it is widely used till date as it is considered to be one of the most flexible and low-cost materials. One of the major reason timber forms are widely used is that it is a low-cost material and also lightweight as compared to steel.
- Installation and stripping are easier due to their flexibility.
- Lower cost as compared to other types of formwork materials.
- Because of its flexible nature, it is preferred as it is easy to customize in terms of size.
- Timber is locally available.
- Because of its lower cost, it can be used in lesser repetitions (8-10 times) as compared to steel and plywood formwork.
- Timber attracts termites and hence they can damage the wooden sheets. So to prevent termites, the sheets shall be coated with an anti-termite coating chemical.
- The surface of timber form is rougher than plywood or steel. So the surface finish of the concrete element wouldn’t be that great.
- If the wood is not seasoned properly, it may not produce the desired results.
2. Plywood Formwork
Plywood is a man-made material. It is made up of thin sheets of plies glued up together to form a sheet of wood. This formwork material is an upgraded type of conventional timber formwork. Practically, plywood sometimes can be as cheaper as timber because of its more repetitive uses as compared to timber.
- Smooth finished concrete can be seen as the surface of the plywood sheet is smooth.
- Labor costs can be reduced by using plywood formwork as it can cover a larger area per sheet.
- The installation process is easier than that of steel formwork.
- Plywood formworks are more durable than timber as they are processed forms of wood.
- Comparatively economical material.
- Heavier in weight as compared to timber.
- Lesser repetitions of use as compared to steel formwork.
- It may get damaged if proper care of plywood forms is not taken at the time of installation or stripping.
3. Steel Formwork
Steel formwork is made up of panels fabricated out of thin steel plates fixed along the edges by small steel angles. Unlike timber and plywood formwork, steel shuttering is installed using suitable size clamps, bolts, and nuts.
Although steel panels have a high initial costing, it is a lot more durable as compared to any other type of formwork. So, in the long run, they turn out to be as economical as any other type of formwork.
- Due to its solidness, steel forms can withstand heavy load and pressure of concrete. So it can be used where the heavy concrete work is carried out.
- Steel formwork does not shrink or warp.
- Steel form plates have a smooth surface, so the quality of exposed concrete is excellent.
- Water absorption does not take place in steel formwork and so chances of honeycombing reduce to a great extent.
- It is possible to manufacture steel formwork in any required size and shape, such as curved or circular. So steel formwork is also used where circular columns and structures are to be constructed.
- Due to its strength, stiffness, and durability, the number of reuses is a lot more than that of timber and plywood formworks.
- High initial cost and high maintenance cost.
- The maintenance of steel formwork plates is complex unlike any other type of formwork. It needs to get repaired where and when required. For example – dent repairing, bend repairing, etc.
- Transportation and storage of steel formwork is complex.
- Due to its heavy weight placement of shuttering panels in its accurate position becomes tough at times where there is a use of larger sized panels.
4. Aluminium Formwork
Aluminium formwork is very much similar to steel formwork. It is, of course, made up of aluminium. The main difference between steel and aluminium formwork is that the aluminum forms are lighter in weight as compared to steel formwork. This is because aluminium has a lower density than that of steel.
- Aluminium forms are lighter than steel so its transportation becomes a bit easier.
- Like the steel form plates, these also turn out to be economical if used for more number of times.
- It has comparatively low strength. So it cannot be used for very heavy concrete work.
- Once manufactured, it is not possible to alter the formwork plates.
5. Plastic Formwork
In this type of formwork system special grade recyclable plastic, also known as geoplast (Acrylonitrile Butadiene Styrene – ABS), is used.
It does not allow any kind of chemical reaction to crop up between the concrete and the plastic form. Also, it does not let the concrete material stick on the plastic forms.
It is the latest advancement in its class. The built plastic formwork is so perfect that the gap between the two forms is very minute and hence does not allow any kind of slurry leakage. This type of formwork system is also available in various sizes like any other formwork.
- It can be used more than 100 times if proper care of forms is taken.
- Overall economic in the long run.
- Light in weight.
- Easy to install, strip and handle.
- Labour friendly.
- Smooth finish when concrete is hardened.
- Plastic formwork is said to have no effect on the environment (eco-friendly) as it is made up of recyclable plastic.
- The initial cost is high.
- The load-carrying capacity of plastic formwork is comparatively low.
Author – Harsh Ved