A Formwork is a temporary structure used as mold for the original structure. There are different materials available to construct the formwork. Formwork Material is selected depending upon many factors like cost, requirement, type of structure etc.
- Different Formwork Materials
- 1. Timber as Formwork Material
- 2. Plywood as Formwork Material
- 3. Steel as Formwork Material
- 4. Aluminum as Formwork Material
- 5.Plastics as Formwork Material
- 6.Magnesium as Formwork Material
- 7.Fabric as Formwork Material
Different Formwork Materials
Different formwork materials and their advantages and disadvantages are discussed below.
1. Timber as Formwork Material
Timber is the most commonly used material for formwork. Timber logs, lumber etc. are used as bracing members from ancient times. So, the Timber formwork is also called as traditional formwork. It is most economical material used for formwork. This is used in sites as formwork material for number of years so, the method of constructing timber framework is well known to the workers.
- Timber can be cut into any required size easily.
- Timber is light in weight and it can be handled easily.
- Timber has good thermal resistance which prevents the damage of concrete in colder regions.
- It is easy to understand the construction method of timber formwork hence, skilled workers are not necessary.
- It is easy to replace the damaged parts of timber forms.
- Timber formwork can be easily dismantled.
- Dry timber may absorb water from wet concrete which result in the reduction of strength in concrete structure.
- Wet timber having high moisture content compress the wet concrete and forms cracks in the structure and grout may leaked through joints when shrinking occurs.
- Timber forms have limited usage. So, they cannot be useful for more times.
Fig 1 : Timber Formwork
2. Plywood as Formwork Material
Plywood which is a manufactured product of timber is also used for formworks. It consists number of veneer sheets or plies in layers. Now a days, the use of plywood formwork increases especially for facing panels. The reason behind it is that the plywood formwork provides smooth finish when compared to normal timber formwork. Hence, finishing cost may reduce by the use of plywood.
For formwork, special type of plywood called exterior plywood is used. The veneer sheets of exterior plywood are bonded with strong adhesive to make it watertight. The plywood boards are available in thicknesses from 7mm to 32mm.
In general, plywood of size 1220 x 2440 and 18mm thick boards are sufficient for most of the works. For curved structures, special types of plywood with sufficient thickness are also available.
- Plywood can also be cut into required size easily.
- Plywood Strong, durable and light in weight.
- Provides smooth finish on the surface.
- Very Large size plywood sheets are available which makes the construction of formwork quicker and easier.
- Curved formworks can also be prepared using plywood.
- When compared to timber, it gives more number of reuses.
- When compared to timber it is costly.
- Thin plywood sheets cannot sustain the weight of concrete they may bow out if proper thickness is not provided.
Fig 2 : Plywood Formwork
3. Steel as Formwork Material
Steel can also be used as formwork material. It is very costly but it can be used for more number of times than others. They provides excellent finish to the concrete surfaces. For mass strictures like dams, bridges, etc. steel from work is so strong and safe.
- Steel forms are durable and stronger.
- Provides uniform and smooth surface finish to the structure.
- Great reusability.
- Easy to fix the formwork and also easy to dismantle.
- Cost is very much higher.
- It is heavy in weight and requires lifting equipment for large structure formworks.
- Corrosion will occur when there is a frequent contact with water.
- The size and shapes of forms available are limited.
Fig 3 : Steel Formwork
4. Aluminum as Formwork Material
Aluminum formwork is used often for pre-fabricated formworks. It is getting more popular because of its light weight and good strength. It requires fewer supports and ties.
- Easy to fix and easy to dismantle.
- It can be handled easily because of its light weight.
- It can be re-used for many times.
- The walls and slabs of structures can be casted simultaneously.
- Monolithic crack free structures can be built using aluminum formwork.
- When the load reaches its maximum limit, the lighter sections may deflect.
- Architectural modifications are not possible when aluminum formwork is used.
Fig 4 : Aluminum Formwork
5.Plastics as Formwork Material
Plastic is another type of formwork material which is used for small concrete structures or for complex portions of the structure. It is light in weight and durable for long periods. For complicated concrete structures, Glass reinforced plastics (GRP) and vacuum formed plastics are used.
- Plastic is light in weight and can be easily handled.
- Formwork for complex shaped structures can be prepared easily.
- Good resistant against water.
- The damaged plastic sheets can be recycled and useful to make new sheets.
- Good quality plastic has great re-usability.
- Plastic is weak against heat.
- It is costly material.
- It does not take much load when compared with others.
Fig 5 : Plastic Formwork
6.Magnesium as Formwork Material
Magnesium is another metal element which is used for formwork. Magnesium is not directly used for formwork and is used with the combination of oxygen atoms which forms magnesium oxide, usually called magnesia or MgO.
Magnesium oxide boards or MgO boards are famous in some countries because of their multiple applications. MgO boards are available in required sizes and grades.
- Mgo boards are light in weight and easy to handle.
- They are fire proof and waterproof.
- Bio friendly boards cause no harm to the environment.
- They are strong to resist heavy loads.
- When Mgo boards meet wet concrete, the magnesium chloride present in MgO boards may dissolve and cause corrosion to the reinforcement.
- Skilled supervision is required for installation.
- MgO boards cannot sustain in humid conditions. They absorb moisture easily from atmosphere so, they are called as crying boards.
Fig 6 : Magnesium Oxide Boards
7.Fabric as Formwork Material
Fabric formwork is the modern technology in construction sector. Fabric can be mold into any required shapes which makes it more famous formwork for architectural purposes.
- It weighs very less when compared to any other formwork material.
- It is economical.
- Any complex shape can be constructed using fabric formwork.
- It is waterproof.
- Doesn’t affect the concrete properties.
- Easy to removal after the hardening of concrete.
- For installation skilled workers are required to form perfect and required complex shapes.
Fig 7 : Installation of Fabric Formwork