Formwork is the name given to the structure or mould that holds freshly-poured concrete in shape while it hardens. There are many different types of formwork that have various applications in construction. The most common type of formwork is made from wood timber, but plywood, steel and fibreglass alternatives can also be used when needed.
Each of these materials has different strengths and are suited to different applications, such as pouring concrete slabs, beams, columns and precast pillars. Formwork is a temporary structure that can account for up to 25% of the cost of a project, so it is important to preserve the formwork when dismantling it so that it can be used again on future projects.
Good formwork should be strong enough to support the weight of the concrete while it dries. It needs to be rigid enough to retain its shape and not bend or warp. The joints in formwork also need to be tightly sealed so that wet concrete does not seep out. Good formwork also needs to be easily removable so that the concrete is not damaged in the process.
This is the most common type of formwork, especially for smaller construction projects. Timber is lightweight, strong, cheap and readily available, making it a cost-efficient material from which to create formwork. The disadvantage of timber is that it can warp, swell or shrink when used for concrete with high water content.
However, the timber can be treated with varnishes and coats of water-impermeable paint to reduce the effects of water on the wood. When choosing timber for use as formwork, make sure that it is light in weight, free from knots in the wood and easily workable with nails. The timber should have a smooth and even surface on the faces that will come into contact with the wet concrete.
Plywood can also be used as a low-cost formwork for small projects. It is cheaper than timber but plywood is not as rigid, which means that it is better suited to lightweight applications. Plywood panels can be bonded together and made to the exact dimensions of the concrete structure.
They also have the advantage of a wider surface area than timber, which means that fewer panels are needed to create the formwork. Plywood formwork can be reused up to 25 times, but it cannot support heavy loads of concrete. It is ideally suited to shallow concrete structures such as paving slabs and narrow beams.
Steel plates can be fastened together to create a strong and rigid formwork that is able to support heavy loads. These steel panels are held together with clamps or nuts and bolts. Steel formwork plates come in a wide variety of shapes and sizes.
They are quite a lot more expensive to purchase that timber or plywood formwork, but steel has a longer lifespan and can be reused almost indefinitely. Steel formwork is often used in large construction projects where heavy concrete beams and pillars need to be poured. Steel formwork can even be used to create curved and circular concrete surfaces.
Further advantages of steel over wood include a quicker installation and dismantling time and the fact that steel does not absorb water from wet concrete. This means that steel will not shrink, warp or bend while the concrete dries. Steel also creates a smooth finish in the concrete structure.
This material is quite strong and, like steel, can be reused many times over. Fibreglass is best suited to precast projects where the fibreglass creates a mould for the concrete. It allows contractors to pour decorative pillars and beams that ensure identical shapes and sizes in the finished concrete structure. Fibreglass moulds are often split into two halves that are fastened together with nuts and bolts.
Whether you are building a large, intricate structure or simply making some paving slabs for your home, formwork will be an important feature of your concrete project. Choose the right materials for the job and get the best results for your needs.
LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges.
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