Whether you’re building a concrete patio or a skyscraper, you’re going to need concrete forms to get the job done. Without concrete forms, your concrete won’t hold its shape and will be at risk of cracking and losing its strength. Concrete forms go hand-in-hand with other concrete placing techniques to ensure your concrete remains strong and durable. So to guarantee your concrete construction projects go smoothly, order enough concrete products for the job and make sure you use concrete forms.
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Keep on reading and learn how to use formwork, the principles behind it, and why it is so helpful on the job site.
Formwork, also known as concrete forms, is a temporary or permanent mould used to create concrete slabs and structures. It’s a barrier that holds the fresh concrete in place and helps with shaping the concrete until the concrete is strong enough to hold its own weight and shape.
To work effectively at supporting the concrete’s weight and shape, concrete forms must:
Formwork is usually made from timber and plywood. But it can also be made from other materials, such as metals, ceramic, or glass fibre reinforced plastics.
Plywood formwork is also called shuttering. Shuttering is the most popular type of formwork and is created on-site using water-resistant plywood and timber.
When on the job site, concrete contractors will erect plywood, steel, or aluminium formwork to create the moulds of concrete slabs, walls, and other structures.
Concrete formwork includes the following components:
The formwork that comes in direct contact with concrete is called the formwork sheeting, or the formwork shell. This sheeting will mould the shape of the concrete and have the most influence on the finished concrete surface.
The formwork bearers, which are usually made of timber or steel beams and clamps, support the formwork sheeting. These distribute the concrete forces through the falsework, supporting structures, formwork ties, and soil.
Formwork ties are usually made of steel wire and are used to tie two formwork faces together to support horizontal pressure from vertical formwork.
The steel wire is slung around the formwork bearers, guided through boreholes in the formwork sheeting, and tightened by twisting the wire.
Once the formwork is constructed, concrete contractors will place rebar inside the formwork to reinforce the concrete.
Next, contractors will pour concrete inside the forms. Once the concrete hardens, they will remove (strip) the forms from the concrete structure if using temporary formwork.
To prevent damage to the concrete and difficulties when removing formwork, it’s important to consider the placement of formwork and the sequence in which the framework will be stripped.
Avoid using too many nails and supports (falsework) when building formwork, as this will be too difficult to strip later on. Only use as much as necessary to maintain the support of the formwork.
Temporary concrete forms should be left to support the concrete until the concrete has thoroughly dried and reached an ideal strength to support its shape. This usually takes about two days after pouring the concrete.
If you remove the formwork too soon, the concrete might begin to sag, crack, and collapse. Remember to be patient and let your concrete thoroughly dry before removing formwork.
Formwork is used for holding the shape of concrete while it dries. It is commonly used for building concrete for:
The type of formwork you use will depend on your project needs. A simple temporary plywood formwork, such as plank shuttering, is suitable for moulding concrete paths and driveways.
But if you’re building a concrete foundation for a home, you will want to use more sophisticated formwork, such as permanent insulated concrete forms.
Unlike traditional concrete forms, insulating concrete forms (ICF) are not removed once the concrete hardens. Instead, ICFs remain as permanent parts of the concrete structure.
While concrete creates the structure, the ICFs insulate the structure. Homes and buildings with ICF foundations are soundproof, airtight, and comfortable in all seasons. This insulation helps homeowners save on energy costs for heating and cooling throughout the year.
ICFs are often made from a combination of insulating materials, such as plastic foam beads and cement, or wood fibre and cement.
Another popular material for ICFs is expanded or extruded polystyrene. Expanded polystyrene is made by expanding plastic beads in a mould, similar to Styrofoam coffee cups.
Extruded polystyrene is made by expanding plastic resin and extruding through a die, similar to meat trays from grocery stores.
ICFs typically come in blocks or planks. ICF block systems are pre-formed with foam and metal or plastic ties. They are ready to stack and interlock when they arrive on site.
Plank ICFs are individual panels or planks of foam requiring assembly on site with ties.
Block ICFs save you time and labour costs, while plank ICFs save on shipping costs since they are more compact to ship.
These concrete forms usually provide at least two inches of insulation on both sides of a concrete wall.
ICFs are not only faster to place, but they also provide significantly better insulation compared to wood or steel frames. So if you’re planning to build a new home, consider using ICFs for a well-insulated foundation.
Formwork is necessary when there is no soil or other structural components to support freshly poured concrete and hold it in the desired shape.
Formwork is necessary for the construction of concrete and reinforced concrete structures, such as:
Vertical formwork is necessary for building concrete foundations, walls, and columns. Tie wires or tie rods are also used with this formwork to support the lateral pressure of concrete.
Vertical formwork must also be anchored to the subsoil to prevent lifting from buoyant forces in the concrete.
Horizontal formwork is necessary for constructing concrete ceilings and beams. This formwork must be supported against vertical and horizontal loads, using formwork load-bearers and columns, braces and struts, or a rigid connection to existing structures, such as walls and columns.
Concrete forms are an essential part of building sound concrete structures. When constructed correctly, formwork moulds concrete into the desired shape and supports the weight of concrete while it’s drying.
And most importantly, concrete forms allow concrete to reach its optimal strength and durability without sagging or cracking.
Unlike traditional formwork, engineered formwork is made of metal. They are prefabricated, not built on-site as the conventional ones. Engineered formwork consists of steel or aluminium, and since it is prefabricated using a more durable material, this option is often more cost-efficient and can be reused – up to 3 000 times! It is also more durable and reliable since a change in environment or temperature will not change its performance. Since you don’t have to spend time on setting up like the conventional ones, it makes the whole process faster, too.
It is clear that concrete forms are necessary for ensuring the concrete setting properly during a construction project, whatever the size of it. Even though timber is usually used for maintaining the form of concrete, there are different materials and types of formwork that can be used. However, prefabricated formwork is more useful for contractors, but you can easily sell them after finishing the project. A.L. Blair can help you with any project you have in mind, so don’t hesitate to reach out.
Concrete needs stability to cure properly, and proper curing will give it the strength it needs to withstand the pressures it will face.
Engineers have designed a variety of forms as the solution to create stable curing environments.
Each project will require proper form selection, installation, and form removal for the strongest concrete structures.
Let’s first get our bearings on concrete forms and the different types available to us.
Concrete formwork, also known as shuttering, requires solid molds to hold liquid concrete in place until it cures.
These forms are necessary to shape and strengthen the concrete. Without a form, the concrete would just end up in one big mound of hardened liquid with no real shape or use.
Formwork can turn concrete slabs into walls, foundations, and even floors. These forms can also add surface texture to the concrete for beautification.
Contractors have a choice to make when building concrete structures.
Which type of concrete form best suits the project?
Each of these eight forms has its uses, limitations, pros, and cons.
Wood forms are the most conventional type. The materials are readily available, and most contractors know the process.
To create a wooden form, wooden boards are nailed together into the desired shape. Wooden stakes are added at precise locations to help bear the weight of the concrete.
Experts recommend using boards less than six inches wide for wood forms as larger boards tend to warp.
The limitations of wood forms stem from the fact that most wooden boards aren’t strong enough to hold large amounts of concrete and cannot be used for heavy concrete construction.
ICFs are hollow blocks of insulation with steel reinforcement cages built into the form.
The concrete mix is poured and sandwiched by the insulation. These forms are permanent and never removed.
You don’t have to worry about timing or proper formwork removal with ICFs because they stay put, and the concrete will dry and strengthen with little to no adverse effects from exterior conditions.
Steel forms are the strongest type of concrete form, and you can reuse them multiple times. These forms are the most popular option for large industrial structures.
Another benefit steel forms offer is that they won’t absorb the water from the curing concrete. This hydration must evaporate from the concrete at the right speed for maximum strength.
Steel forms also present a lower risk of error after removal.
Concrete wall forms are pre-manufactured forms made from wood, steel, or both, all connected with anchors. This method is often used to build large and often intricate industrial structures.
Some require the use of cranes to install, while others are designed to be fast-paced and modular for easy setup and take-down.
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A decorative concrete form is used to create an artistic relief through the use of negative space as the concrete dries.
There is typically a melamine, acrylic glass, or laminated board with inserts that create the design in the mold.
Here are some things to consider when choosing your form:
Based on these factors, you can make a more informed decision. As already stated, larger projects require the use of steel forms, while wood can be used for smaller projects.
Steel is cleaner than wood, resulting in fewer bug holes in the finished product.
Wood is best for low-height structures, and steel is best for high structures where concrete can buckle under its own weight.
Of course, steel is more costly, so it’s best to reserve this form for when you need it.
The amount of time you should wait before removing your concrete forms is different for every project.
Here are some of the factors that affect curing times:
Let’s discuss these factors:
Frozen concrete will not dry, so if you are working in extremely cold weather, the curing process will take longer.
Rain also affects drying time, especially during the first few days when the air is still moist.
Heat aids the curing of concrete, but extreme heat can cause cracking. This can be prevented by using tarps or barriers to trap moisture.
Different types of concrete have varying drying times and reactions to outside factors.
There are five basic types of cement:
Each of these categories has subcategories with different uses and drying times.
The grade of cement used also affects drying times. We’ll discuss this more in the next section.
Larger sections gain strength faster due to the compaction of the weight of the concrete itself.
So, the structure’s size determines when the form is ready to be removed.
The removal of concrete forms is known as “striking-off” or “stripping off” the forms.
According to the American Concrete Institute (ACI 308), the drying times for each type of concrete are as follows:
According to the rules for Ordinary Portland Cement, these are the average drying times of various types of structures:
These drying times will differ for types 2, 3, 4, and 5.
Time is a critical issue in the construction process. If you are pressed for time, there are a few ways to speed up the drying process.
Here are some ideas:
Let’s talk about these ideas:
Admixtures can be created by adding certain chemicals or additives to the cement mixture to speed up the drying times.
Calcium chloride and silica fume are two such additives.
When weather conditions are causing an issue, you can use weather-resistant barriers to speed up the concrete drying process.
Plastic sheeting is good for trapping moisture when the temperature is high and protecting the form from rain.
Insulation blankets help to prevent freezing when the temperature drops.
If the air is overly humid, dehumidification can also aid the drying process.
Desiccant dehumidifiers use a chemical reaction to draw moisture out of the air. This is best for use in an enclosed area where the chemicals won’t dissipate in the surrounding air.
Condensation dehumidifiers cool the air to drop the dew point, then soak up the humidity from that process.
Heating dehumidifiers heat the air, raising the dew point and drawing the moisture off the surface of the concrete.
Not only is timing critical in formwork removal, but the proper techniques should be used to maintain the structure’s integrity.
Learning formwork removal is easier when you understand some common but detrimental mistakes — and avoid those at all costs.
Here are a few common mistakes that you should avoid in your removal process:
When you jump the gun and remove your forms too early, you will not be pleased with the results.
Your structure can slump to one side or bulge at the bottom. Multiple cracks can occur because it is not ready to bear the weight of the concrete on top.
Worse still, the structure can collapse due to multiple factors weakening the project’s structural integrity.
See also: How Precast and Custom Concrete Buildings Are MadeConcrete forms are a crucial part of the concrete construction process, and the information in this guide will ensure that proper formwork is used.
With the use of proper formwork, projects will go much more smoothly. There will be no need to repair or redo any structures with new concrete.
This will save money and reduce the amount of time it takes to complete a project, keeping you within budget and on schedule.
For more information, please visit concrete formwork systems.
Speaking of in budget and on schedule, we want to help you with your next construction project. If you’re looking for a contractor in the Colorado area, get in touch for a job quote!