In concrete projects, one of the most important stages of structural execution is formwork. Formwork plays a key role in shaping and supporting fresh concrete until its final setting and directly impacts the quality, dimensional accuracy, and final surface finish of the concrete. Selecting the appropriate type of formwork from options such as timber, metal, plastic, and modular systems can lead to improved execution speed, reduced costs, and increased structural durability. In this article, we examine various types of formwork and comprehensively analyze the advantages, disadvantages, and applications of each.
What is Concrete Formwork?
In the construction industry, concrete and concreting are of utmost importance. Formwork is equally crucial in the concreting process and can significantly impact the strength of the concrete. Concrete formwork refers to a set of temporary or permanent structures used to hold fresh concrete until it hardens and gains sufficient strength. These forms must be able to withstand the weight of the concrete and lateral forces from vibration and other factors. Additionally, forms must be designed to provide the desired shape and dimensions of the structure and prevent the leakage of cement paste (bleed water).
What is the Purpose of Formwork?
One of the most critical stages and operations in executing concrete structures is formwork. Formwork can be considered the most impactful part of the concrete structure execution process in terms of economy and execution time. On the other hand, adherence to execution details, maintenance, execution quality, and employing the best type of formwork suitable for the project have a significant effect on the entire project. Formwork for buildings varies depending on the size of the structure. In small buildings, brick is often used for foundation formwork. One of the operations in executing foundations, columns, and concrete beams is formwork. Formwork is essentially a temporary operation carried out within a predetermined timeframe and in a specific part of the building. Formwork is executed for foundations, columns, beams, etc.
Formwork Requirements
- Forms must be constructed and installed in such a way as to achieve the intended shape, size, condition, and finish of the concrete.
- Forms must be sufficiently strong to withstand the pressure or weight of fresh concrete and other loads without warping, leaking cement paste, rupturing, or endangering workers. (Arka plastic concrete forms are very resistant and lightweight and significantly increase execution speed.)
- Forms should be designed and constructed to be easily and quickly installed and removed to prevent waste of time and money.
- Forms should be, as much as possible, portable and movable with available tools and facilities.
- Forms must be sealed to prevent leakage of cement paste.
Types of Formwork by Material
Types of Formwork Based on Materials
Timber Formwork: In timber formwork, forms are made from wooden planks. Due to high flexibility, they are used in small and complex projects. However, they have a shorter service life compared to metal forms. Timber formwork is the first type used in the construction industry. Before using this type of formwork, its condition must be carefully checked to ensure the wood is free of any cracks or rot. Its lifespan is short and it quickly becomes unusable. It is not at all suitable for large projects because it is extremely time-consuming. Generally, the use of timber formwork is recommended when labor costs are low or when complex concrete sections require flexible formwork.
Metal Formwork: These forms are made of steel or aluminum and, due to their durability and high strength, are used in large projects. Also, the final concrete surface is smoother and of higher quality using these forms. Metal formwork comes in two types: steel and aluminum. It is much heavier compared to other types of concrete formwork. Metal formwork is very expensive and the cost of using it is exorbitant.
Polymer Formwork (Plastic): These forms are made from plastic materials and, due to their light weight and ease of transportation, are used in various projects. Additionally, resistance to moisture and weather conditions are advantages of these forms. Plastic formwork is lightweight, can be cleaned with water, and is suitable for large sections and multiple uses.
Masonry Formwork: These forms are made from materials such as brick or cement blocks and are typically used as permanent forms in foundations. One type of concrete formwork is brick formwork, which is used due to its low cost and availability. It is very vulnerable due to water penetration. It does not have high strength, which is a major weakness. Concreting with brick formwork often disrupts the leveling of the concrete.
Types of Formwork Based on Building Components
Concrete formwork can also be categorized based on building components, in addition to the material used:
- Wall Formwork
- Beam Formwork
- Column Formwork
- Foundation Formwork
- Slab Formwork (Slab/Deck)
Types of Formwork Based on Application
Foundation Formwork: Used to hold concrete in footing and foundation work.
Wall Formwork: Used for constructing concrete walls in structures.
Column Formwork: Used to create concrete columns with various cross-sections.
Slab Formwork: Used to hold concrete in slabs and concrete decks.
What are the Characteristics of Good Formwork?
- It must be very robust to resist the pressures applied to it.
- Connections in the formwork must be tight against cement paste leakage.
- The formwork should be constructed so that its parts can be separated without damaging the concrete.
- Formwork materials should be inexpensive and accessible so they can be used multiple times.
- The formwork must be precisely adjusted to the desired location.
- It should have as little weight as possible.
- Formwork materials should not warp or be damaged when exposed to concrete.
- The formwork must be placed on a firm base.
Important Points for Foundation Stripping
For foundation stripping, you must also pay attention to the following points:
- If stripping is done after the curing period is complete, necessary concrete care must be performed after stripping.
- The stripping process should be done step by step, and any impact on it should be prevented. To care for the concrete, you must prevent any impact or pressure on the concrete.
- You should proceed to remove the forms when the concrete can withstand the applied forces without deforming.
- You should not proceed to remove load-bearing forms and props until the concrete members have gained adequate strength.
Advantages and Disadvantages of Various Types of Formwork
Advantages of Plastic Concrete Formwork
– Lightweight: Plastic forms are easy to transport and handle due to their low weight. This feature reduces labor costs and installation time.
– Resistance to Moisture and Corrosion: Unlike metal or timber forms, plastic is resistant to water and chemicals and does not rust or rot.
– Reusability: These forms have a long lifespan and can be used multiple times without loss of quality. This helps reduce costs over the project.
– Smooth and Polished Surface: Plastic forms give the concrete a smooth surface that reduces the need for final finishing.
– Thermal Insulation: Plastic, due to its insulating properties, transfers less heat and improves concrete curing.
– Recyclability: Some plastic forms are made from recycled materials and are also recyclable after their useful life ends, which helps preserve the environment.
Disadvantages of Plastic Forms
– Limitation in Carrying Heavy Loads: Plastic forms are not suitable for heavy structures and massive concrete pours and may deform.
– Relatively High Initial Cost: Compared to timber forms, the initial purchase cost of plastic forms is higher, although this cost is offset by their long lifespan.
– Sensitivity to High Heat: Plastic may deform or melt at very high temperatures, so its use in extreme temperature conditions is limited.
– Limitation in Large Sizes: Producing plastic forms in very large sizes is difficult, and they are typically better suited for small to medium projects.
– Need for Proper Maintenance: Although resistant to moisture, it may be damaged by severe impacts and UV rays and requires care.
Advantages of Timber Forms
– Timber formwork has a relatively low and more economical price.
– In timber formwork, construction is easier and shaping is more convenient.
– This type of formwork is suitable for small yet complex projects.
Disadvantages of Timber Forms
– The service life of these forms is short.
– In timber formwork, moisture absorption and the possibility of deformation exist, making it unsuitable for use in humid areas.
Advantages of Metal Forms
– Metal forms have a long lifespan and can be reused in subsequent projects.
– The smooth surface and final quality of concrete are higher with metal forms.
– Metal forms have high resistance to impact and environmental changes.
Disadvantages of Metal Forms
- Metal concrete formwork has a higher initial cost.
- Metal forms are heavier and require transportation equipment.
Which Formwork is Best? Choosing the Best Type for the Project
Choosing the best type of formwork depends on several important factors:
- Type of project
- Budget
- Execution speed
- Environmental conditions
Comparison of Various Types of Formwork
| Type of Formwork | Advantages | Disadvantages | Best Application |
| Timber Formwork | Low cost, flexible, suitable for complex designs | Short service life, moisture absorption, requires skilled labor | Small projects and special shapes |
| Metal Formwork (Steel/Aluminum) | Durable, reusable, smooth concrete surface | High cost, heavy weight | Large and repetitive projects like bridges and tall buildings |
| Plastic Formwork (Polymer) | Lightweight, moisture resistant, easy transport | Shorter lifespan compared to metal, size limitations | Small to medium projects, humid environments |
| Precast Formwork (Modular) | Fast installation, high quality, reduces execution time | Higher cost, limitation in custom design | Mass construction projects like housing and towers |
| Slipform or Climbing Formwork | Suitable for tall structures, continuous execution | High equipment cost, requires specialized labor | Towers, silos, chimneys |
Which Formwork is Better for You?
- If your construction project is small yet complex, timber formwork is the best option and is economical.
- If durability and concrete surface quality are important in the project, metal formwork is a suitable choice.
- If the project is in a humid environment or requires frequent movement, plastic or polymer formwork performs better.
- If project execution speed is important, we suggest modular or tunnel formwork systems suitable for mass construction.
- For tall and continuous structures, slipform or climbing formwork is excellent.
Combined Use of Formwork Systems
In many projects, using a single type of formwork alone is not efficient. Combining formwork systems helps you achieve the best performance and optimal cost.
Combining Formwork Systems
- Foundation (Timber Formwork) + Walls and Columns (Metal Formwork):
- For foundations, timber or plastic concrete formwork is typically used because they are simpler and cheaper.
- For main columns and walls that require a smoother surface, metal or aluminum forms perform better.
- Metal Formwork (for heavy structures) + Plastic Formwork (for details and light sections):
- In projects that require both strength and fine details (such as bridges or tall buildings), metal forms are used for main sections and plastic forms for smaller, more detailed parts.
- Modular Formwork + Masonry (Permanent) Formwork:
- In some structures like retaining walls, modular forms are used for repetitive sections, but parts of the wall remain as permanent formwork and become part of the structure.
Advantages of Using Combined Formwork Systems
- Cost Reduction: Using expensive forms (like metal) only in necessary sections, and cheaper forms (timber or plastic) in simpler sections.
- Increased Execution Speed: Lighter forms like plastic formwork can be moved faster, while metal forms are difficult to transport.
Concrete Formwork Training
For proper execution of concrete formwork, following these steps is essential:
1) Formwork Design and Planning
- Selecting the appropriate type of formwork for the project is the first important step. You must determine your strategy based on the project type, environmental conditions, and other factors.
- The second step is calculating the applied loads (concrete weight and lateral pressure).
2) Preparing the Project Site
- Level and prepare the surface under the formwork.
- Actions: Install bases, scaffolding, and supporting equipment.
3) Assembling and Installing the Forms
- Firmly connect the forms to each other to prevent concrete leakage.
- Precisely adjust the dimensions and leveling of the forms.
- Apply release agent to the internal surface of metal forms to prevent concrete sticking.
4) Concreting
- Concreting should be done slowly and in layers.
- Vibrating the concrete to remove entrapped air and increase density is also essential.
5) Formwork Removal (Stripping)
- Determine the appropriate time for stripping (based on air temperature and cement type).
- Separate the forms without damaging the concrete surface.
6) Cleaning and Maintaining the Forms
- Wash the forms after each use.
- Inspect and repair damaged parts.
- Store the forms under suitable conditions for future use.
Safety Tips in Formwork
- Inspection Before Installation: All formwork components must be checked for integrity.
- Use of Personal Protective Equipment (PPE): Such as hard hats, gloves, and safety harnesses.
- Continuous Supervision During Concreting: To ensure the stability of the forms and prevent settling or failure.
Important Points in Concrete Formwork
- Strength and Stability: Forms must have the capacity to withstand the weight of concrete and lateral forces.
- Prevention of Cement Paste Leakage: Form connections must be such that they prevent leakage of cement paste.
- Ease of Installation and Separation: Forms must be easily installed and, after the concrete hardens, separated without damaging the concrete surface.
- Resistance to Weather Conditions: Materials used in formwork must be resistant to moisture and temperature changes.
Order and Method of Formwork Removal
- First, vertical forms for platforms, walls, and large beams are removed because they do not carry any load.
- Then, slabs and bottom forms are removed.
- Finally, beams and safety props are removed after the permissible time has passed.
Equipment Related to Concrete Formwork
- Shore Jacks (Props): Used to support slab forms at the desired height.
- Scaffolding: Used for access to elevated points and holding forms in specific positions.
- Connections and Accessories: Include bolts, clamps, pins, and other components used for connecting and securing forms.
- Waterstop Tie Rods (Through-Ties with Waterstops): Used to prevent water penetration into concrete structures.
Appropriate Time for Formwork Removal (Stripping)
The time for form removal depends on the type of structure, environmental conditions, and the type of cement used. Generally, horizontal forms like slabs are removed sooner than vertical forms like columns and walls. Adhering to the appropriate timing for formwork removal is of particular importance to prevent deformation or cracking of the concrete.
By observing the above points and using appropriate equipment, quality concrete formwork in accordance with engineering standards can be achieved. The choice of formwork type depends on the project type, budget, and environmental conditions. Utilizing modern technologies can also help improve project quality and execution speed.
Choosing the Right Formwork
For many people, the price and quality of formwork are very key points, in which case they can benefit from plastic formwork (Arka polymer concrete formwork), which can fully meet customer needs.
Arka Engineering Company is the most reputable and experienced producer of polymer concrete forms (plastic decking) in Iran.
For more information and to receive specialized consultation, you can contact our experts.