Questions You Should Know about Wall Formwork

Ten frequently asked questions about wall formwork (part one)

Industrialized vertical formwork has become a common part of the construction process on on-site concrete structures. They allow fast and well-defined production cycles, guaranteeing greater safety for operators during assembly, concreting and stripping than traditional formwork.

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Doubts or questions may arise during its use. Its use is simple, but some technical aspects must be taken into account.

Let's analyze the 10 most-frequently asked questions about wall formwork!

1.- What is the maximum admissible filling height?

The maximum height for concreting walls with industrialized formwork depends on many factors:

• Maximum design pressure: Each panel type has been designed for maximum resistance to pressure. Industrialized formwork is usually designed for maximum pressures between 40 and 80 kN/m².
• Fluidity of the concrete used: More liquid concretes generate higher pressures. Special attention must be paid when using self-compacting concrete 'SCC'. (See question #7).
• Filling time: A faster concrete filling speed generates greater pressure on the formwork. When using more fluid concretes at significant heights, it is essential to maintain a low filling speed, which the formwork supplier must indicate in dedicated tables.
• External temperature: influences the curing of the concrete: the lower the temperature, the longer the setting time and the greater the formwork's exposure to the load.
• Another factor to take into account is the concrete's vibration, which makes the concrete fluid, maintaining pressures and delaying its setting. Deep vibrations can subject the formwork to very large loads. E.g. Above 6 m in height, it is more difficult to vibrate the concrete with a needle vibrator normally used on site. External wall-mounted vibrators are therefore used, whose positioning must be studied correctly. (See question #9).

2.- What factor most affects the concrete finish?

Sometimes, once the panel has been stripped, stains with different shades or 'small holes' may appear in the concrete finish. There may be several reasons for this. Stains are usually caused by the use of a low quality or inadequate release agent, generating reactions with the concrete in some areas. Small holes or cracks are mainly due to poorly executed vibration or poor choice of concrete. Both effects can also be caused by inadequate formwork cleaning.

In general, for architectural or eye-catching finishes, it is advisable to use phenolic finish panels, since they have a glossy finish due to their very-low-porosity surface.

3.- Is it possible to manually handle vertical formwork?

Wall formwork is divided into three main families: manual, lightweight and robust.

• Lightweight formwork: These are metal-framed panels, with a weight that generally does not exceed 20 kg/m². These panels are manipulable, but have the disadvantage of being less resistant to concrete pressure 'around 40kN/m²', and having a shorter service life. They are mainly used in countries where the crane is still little used or for construction solutions where a crane is not available.
• Manual formwork: these panels are halfway between the Robust and the Lightweight panels, combining factors that define one and the other, usually weighing between 30 and 60kg/m², providing them with manual portability and usually resisting pressures between 40 and 80kN/m².
• Robust Formwork: 'Robust' panels are designed to be subjected to heavy loads, and can usually only be handled by mechanical lifting equipment. These panels usually weigh in excess of 60 kg/m².

4.- What is the standard vertical formwork equipment for a construction site?

Often when planning a new construction project, the well-known question arises: How many square meters of formwork do I need to execute my project?

It is difficult, if not impossible, to define equipment that is standard for every job site. Each project has its own unique aspects. However, it is possible to define the criteria for identifying the optimum equipment for each site:

• Number of operators: First of all, it is important to define the number of workers and crews that will handle the formwork. On large construction sites, more teams of workers are employed simultaneously, with formwork team needed for each team.
• Number of cranes: The formwork equipment should not be oversized in relation to the number of cranes on site. Sometimes there is a risk of slowing down production because the formwork equipment is larger than the handling capacity on site.

On-site production times: It is clear that for the execution of walls, times must be respected that, under standard conditions, can be controlled without problems. However, it is true that on some construction sites, the time required by the developer means that these deadlines need to be shortened, so the number of workers and formwork equipment on site has to be increased.

5.- What is the useful life of metal formwork with phenolic resin as formwork surface?

The durability of wall formwork basically on three variables:

• Formwork material: The service life of the frame is different depending on the material and its quality, the materials chosen to define industrialized formwork is usually aluminum or steel. Aluminum is a less impact-resistant material and therefore has a shorter service life than steel.
• Quality and protection: The quality and protection of the frame influences the service life of the frame. Galvanized steel frames guarantee a longer service life compared to painted or galvanized frames.

Use on site: On-site use is of course an important factor that has a direct impact on the service life of the material. The construction site is a place where the formwork is exposed to shocks and extreme weather conditions. The treatment, climate and maintenance have a decisive influence on the durability of the formwork.

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Ten frequently asked questions about wall formwork (part 2)

After having seen the first five questions about wall formwork, we complete the second part of the questions.

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Discover them with us!

6.- How many square meters of formwork can be transported with a lorry or trailer?

The amount of transportable square meters is extracted from a parameter called volumetric weight, which relates the weight to the volume of the equipment to be transported and is used to quantify transport costs.

7.- What should be taken into account when working with SCC (Self Compacting Concrete)?

Self Compacting Concrete is more fluid than other types of concrete usually used on site. It is used in cases in which a very good finish is required, or when concrete vibration is to be avoided due to time saving or because it is not possible to do it, for example in the case of some structural components that have little space between the reinforcement.

When using this type of concrete, it is important to be very careful with the pressures that the formwork receives, since this greater concrete fluidity implies a very significant increase in its pressure, by increasing its hydrostatic behavior. In case of elevated heights, such as to exceed the admissible formwork pressures, the following actions can be taken:

• Slow down and control the filling speed as indicated by the formwork supplier.
• Reinforce the formwork by means of a previous calculation, developed together with the formwork supplier's technical service.

8.- How many square meters of formwork can I handle at once with the crane?

The number of panels that can be handled with a crane depends on two factors:

• The load-bearing capacity of the crane at the point of handling;
• The weight of the equipment to be moved.

So the calculation to be performed is easy: It must be verified that the weight of the square meters of panels to be moved is less than the load-bearing capacity of the lifting equipment at that point.

Special attention must be paid to two aspects:

• The load-bearing capacity of the crane at the handling point; the greater the distance between the loading point and the base of the crane, the lower its load capacity.
• Lifting brackets: Panels or sets of panels should always be moved with at least two crane hooks: Safety during handling is a priority.

9.- Is it possible to use external vibrators on walls?

Yes, for concrete compaction, external vibrators are a possible alternative to ad ago vibrators. However, the following aspects must be taken into account:

• Require an ad-hoc Their positioning, the optimum quantity and the handling of the equipment during filling must be studied.
• They have a higher cost than the classic vibrators.

They require compressed air equipment (if pneumatic vibrators are used) or an electric generator (if electric vibrators are used).

10.- How often should the phenolic panel of the formwork be changed?

Also in this case, the change of phenolic formwork depends on the use that is made on site and the quality objective that is desired in the finish.

What does the durability of the phenolic depend on?

• The thickness of the phenolic resin, which usually varies between 15 mm and 18 mm.
• The correct use and application of the release agent before each concreting. If not properly applied, the risk is that the phenolic resin part will tear on contact, damaging it conspicuously.
• The care with which the panel is handled on site: sometimes phenolic resin panels are damaged by accidental blows that generate holes.
• Storage conditions: The panels should not be stored in humid places or under direct atmospheric conditions. This could generate excessive water absorption in the phenolic resin, or the wood might dry out (under the sun).

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Este artículo se sumerge en la definición, importancia, y los diferentes tipos de entibaciones, incluidas las innovadoras entibaciones deslizantes.

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