7 Things to Know About Concrete Forms

Apr. 29, 2024

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7 Things to Know About Concrete Forms

Poured concrete is a viscous solution that can take up to 48 hours to properly set. During the setting time, the concrete needs to be contained in a concrete form. Concrete forms or formwork are the supporting materials or molds that are used when working with concrete. They also determine the final shape of the concrete, because liquid takes on the shape of its container.

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However, not just any material can be used as a concrete form, as formwork needs to be able to hold the concrete’s weight and shape. For the formwork to be useful, it should have strong joints to prevent leaks, a rigid structure so that it doesn’t bend or break under the weight of the concrete, and it should also be able to be used with horizontal and vertical bracing. Keep reading for more details and important information about how to use concrete forms.

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1. Concrete forms are necessary to ensure that the concrete sets properly during a construction project.

Concrete is used regularly in construction projects. For example, it can be poured to create supports for a fence or gate or as a foundation for a new shed. However, when concrete is initially mixed, it isn’t a stiff compound that will hold a shape without help. It is a thick, viscous liquid that is difficult to mix, and it’s hard to manage without using concrete forms.

A concrete form or formwork is a support or mold that the concrete is poured into. Temporary or permanent, the formwork is built into the shape that the user wants the concrete to take when the liquid concrete begins to dry.

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2. Timber is the most commonly used material for formwork.

There are several different materials that are used to make formwork, but the most commonly used material is timber. This is because timber is cost-effective, lightweight, durable, and flexible, allowing the concrete to shift while it sets without pieces breaking off or putting strain on the formwork.

For the best results, invest in timber formwork that is easy to work with, lightweight, and dried thoroughly. Also, make sure the timber doesn’t have any loose knots that could pop out and allow the wet concrete to seep through the hole. While there is the chance that wood formwork will warp if it absorbs the water from the concrete, this effect can be limited by treating the timber forms with a sealant.

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3. While timber is most common, there are other materials that are used for concrete forms, including steel, plywood, and fiberglass.

In addition to timber, there are a few other common materials used to make concrete forms. Steel is regularly used in heavy civil construction to create thin steel plates, which can be held together with clamps or with fasteners to support broad concrete projects. This durable material is more expensive than timber, but it’s also stronger and can be reused or sold.

Another type of material used to make formwork is resin-bonded plywood. These sheets of plywood will typically be attached to timber frames to create large, inexpensive concrete forms. However, plywood is less durable and rarely reusable. Fiberglass concrete forms are best for projects with curved surfaces, though they are expensive and often need to be custom ordered.

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4. A good concrete formwork needs to be both strong and lightweight with a rigid construct that retains its shape under stress.

In order for a concrete formwork to be suitable for a construction project, it needs to be strong enough to hold the weight of the concrete without slipping, cracking, or bending. Any significant damage to the formwork will allow the concrete to pour out, or it may just ruin the intended shape if the concrete is partially cured.

However, the concrete forms also can be made with a lightweight material that are used without significant physical effort on the part of the user. Timber and plywood are great examples of material that is strong, flexible, and relatively lightweight, yet rigid enough that the concrete forms will keep the same shape, allowing the concrete to set in the desired form.

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5. Concrete forms are necessary to create high-quality concrete, but with careful planning, measuring, and cutting, users can save on the overall cost of formwork.

Many people either don’t know about concrete forms or they don’t want to have to pay for timber or plywood to set up formwork because the extra cost is too high. Unfortunately, without the use of formwork, it’s all too easy for construction projects to go awry, leaving the concrete slab for the new shed or workshop uneven and difficult to use as support. So, while it’s a bad idea to go without concrete forms, there are ways that can help save on the cost of these materials.

Plan out the project carefully so that pieces of the formwork can be reused for multiple sections and it’s also a good idea to limit the number of slender sections to avoid wasting small pieces of timber or plywood. By reducing the number of cuts that need to be made in the concrete forms, there is less timber or plywood needed in total. However, users should keep in mind that while formwork typically costs about $1.10 per square foot of the concrete area, a rounded or contoured framework is generally more expensive.

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6. One of the benefits of using steel is the long-lasting durability that allows it to be reused and even resold to help save on the cost of the project.

The initial cost and skill required to make steel concrete forms are higher than what’s needed for timber or plywood. Due to the impressive strength, durability, and resilience of steel, the steel concrete forms can be used on multiple projects without damage. For companies or independent professionals that regularly work with concrete, this is a way to cut costs on a project.

DIYers also can benefit from the long-lasting strength and flexibility of steel concrete forms by using this formwork on more than one project. If the steel formwork is just sitting in storage in the garage, consider selling it to another avid DIYer. A professional also may be interested in a bargain price for used concrete forms to help reduce the total cost of a project.

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7. Formwork helps to ensure that the concrete sets properly, so it’s necessary for a range of projects including building a fence, installing a gate, pouring a foundation, and constructing a home.

There are many different construction projects that utilize concrete and most of them require some type of formwork to ensure that the concrete sets according to plan. Goals can range from making a few simple steps to lead up to the porch to pouring a complex foundation to make insulating concrete forms for the home. Insulating concrete forms are essentially concrete walls that are poured between two layers of insulating material to create a strong and insulated foundation.

Other common uses for concrete forms include pouring a simple concrete slab to act as the foundation for a shed or workshop, securing the posts of a fence or a gate in the ground with a concrete base, or making simple paving stones for the yard with a shallow formwork mold.

Types of Formwork for Concrete Structures

Concrete is one of the most widely used construction materials, thanks to its exceptional properties. However, to create building elements with concrete, it must be poured into a specially designed mold. This is known as formwork or shuttering.

Formwork can use temporary or permanent molds, which hold the poured concrete in shape until it hardens and achieves enough strength to support itself. Formwork can be classified in many ways:

Type of material used
By the concrete element supported
Removable or permanent

Formwork has a fundamental role in concrete construction. It must have enough strength to bear all the loads present during casting operations, and must then hold its shape while concrete hardens.

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Which Are the Requirements for Good Formwork?

Although there are many formwork materials, the following are general performance features to meet the needs of concrete construction:

Capable of withstanding dead and live loads.
Retaining its shape with adequate props and braces.
Joints must be leak-proof.
If formwork is removable, the process must not damage the concrete.
Reusable material.
As lightweight as possible.
The formwork material should not warp or distort.

When selecting formwork it is important to consider the type of concrete and the pouring temperature, since both affect the pressure exerted. Also, formwork must be capable of resisting the loads of wet and dry concrete.

Formwork requires structures such as poles and stabilisers to avoid movement during construction procedures, and these are called falsework. To ensure high quality when working with concrete, a qualified workforce and adequate supervision are necessary.

The following sections provide an overview of some common formwork materials.

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Timber Formwork

Timber formwork was one the first types used in construction industry. It is assembled on site and is the most flexible type, bringing the following advantages:

Easy to produce and remove
Lightweight, especially when compared with metallic formwork
Workable, allowing any shape, size and height
Economical in small projects
Allows the use of local timber

However, before using timber its condition must be checked carefully, making sure it is free of termites. Timber formwork also has two limitations that must be considered: it has a short life span and is time consuming in large projects. In general, timber formwork is recommended when labor costs are low, or when complex concrete sections require flexible formwork.

Plywood Formwork

Plywood is often used used along with timber. It is a manufactured wooden material, which is available in different sizes and thicknesses. In formwork applications, it is mainly used for sheathing, decking and form linings.

Plywood formwork has similar properties as timber formwork, including strength, durability and being lightweight.

Metallic Formwork: Steel and Aluminum

Steel formwork and steel hardware is becoming more popular due to its long service life and multiple reuses. Although it is costly, steel formwork is useful for multiple projects, and it is a viable option when many opportunities for reuse are expected.

The following are some of the main features of steel formwork:

Strong and durable, with a long lifespan
Creates a smooth finish on concrete surfaces
Waterproof
Reduces honeycombing effect in concrete
Easily installed and dismantled
Suitable for curved structures

Aluminum formwork is very similar to steel formwork. The main difference is that aluminum has a lower density than steel, which makes formwork lighter. Aluminum also has a lower strength than steel, and this must be considered before using it.

Plastic Formwork

This type of formwork is assembled from interlocking panels or modular systems, made of lightweight and robust plastic. Plastic formwork works best in small projects consisting on repetitive tasks, such as low-cost housing estates.

Plastic formwork is light and can be cleaned with water, while being suitable for large sections and multiple reuses. Its main drawback is having less flexibility than timber, since many components are prefabricated.

Fabric Formwork

Fabric formwork is also known as flexible formwork. This system uses lightweight and high-strength sheets of fabric, designed to adjust to the fluidity of concrete and create interesting architectural forms.

This formwork type uses less concrete than rigid systems, which yields savings. It is an emerging technology in the shuttering industry, especially suited for constructions of irregular and complex shapes.

Stay-In-Place Formwork

This formwork is designed to remain fixed after the concrete has set, acting as axial and shear reinforcement. This formwork is made on-site from prefabricated and fibre-reinforced plastic forms. It is mainly used in piers and columns, and also provides resistance against corrosion and other types of environmental damage.

Another type of stay in place formwork is called coffor, which can be used in any type of building:

It is composed of two filtering grids, reinforced by stiffeners and linked with articulated connectors.
Thanks to its construction, it can be easily transported from a factory to the point of use.

Tunnel Formwork

Tunnel formwork is a common construction method used in residential apartments & hotels which involves producing repetitive structural elements for buildings with the same layouts. It employs a steel formwork system that is built on the construction site to pour concrete walls and slabs in a continuous cycle. This strategy is especially effective for tasks that require quick construction and consistent design.

Tunnel formwork is extensively used in high-rise construction projects when speed and efficiency are crucial. The advantages are faster construction, high quality control, and less labor cost. The approach allows the creation of long-lasting structures fast and efficiently, making it one of the popular choices in the infrastructure industry.

Permanent Insulated Formwork

This is one of the most advanced formwork systems, offering permanent insulation. It may also include thermal, acoustic, fire-resistance and rodent-resistance properties. Insulating concrete forms (ICF) are the most common type of permanent insulated formwork, where concrete structures are insulated with polystyrene boards that stay in place after concrete has cured.

Permanent insulated formwork offers energy efficiency and sustainability, contributing to a lower environmental impact from the building sector.

Classifying Formwork Based on Structural Components

In addition to being classified by material, formwork can also be classified according to the building elements supported:

Wall formwork
Beam formwork
Foundation formwork
Column formwork

All formwork types are designed according to the structure they support, and the corresponding construction plans specify the materials and required thickness. It is important to note that formwork construction takes time, and it can represent between 20 and 25% of structural costs. To mitigate the cost of formwork, consider the following recommendations:

Building plans should reuse building elements and geometries as much as possible to allow formwork reusing.
When working with timber formwork, it should be cut into pieces that are large enough to be reused.

Concrete structures vary in design and purpose. Like in most project decisions, no option is better than the rest for all applications; the most suitable formwork for your project varies depending on building design.

Nearby EngineersNew York Engineers has a MEP design track record of 1,000+ projects. Contact us via email (info@ny-engineers.com) or phone (786) 788-0295212-575-5300, and make sure your building systems meet codes.

Are you interested in learning more about concrete wall formwork? Contact us today to secure an expert consultation!

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