What is Concrete Formwork?

Formwork is the moulding into which wet concrete is poured to give the user greater control over the exact shape of the finished, cured concrete. Formwork can be built with almost anything but is most often built with a combination of timber, plywood, and steel or aluminum hardware. Formwork can either be dismantled after the concrete has cured to an acceptable level, or it can be left to remain embedded on a permanent basis.

The various methods and types of formwork have their individual advantages, but unless you’re doing this as a business, the most common type mentioned above, is more than sufficient. Making small bits of formwork for shed or room foundations, walls, or even staircases, can be done with the simplest materials.

Sideview Example of Formwork for a Staircase

Home centers sell plywood for this purpose with a glossy finish on one side to prevent adhesion.

The basic concept of formwork is the creation of “walls” that will sand-which concrete poured between them. The height, width, and overall design-complexity of these walls are flexible so as to meet the needs of any given job. It can be as simple as a 1 foot square, 5 cm high deck-post base or a labyrinth of foundation pathways, walls, staircases, and almost anything imaginable.

One thing is for sure, and that is that formwork is responsible for some of the most intricate concrete structural designs around today. That said, for the most part as a DIYer, you’ll be working on considerably less complex formwork composition. You don’t HAVE to use the plywood with the “glossy finish”, but whatever you do use, remember that it will mirror the finished surface of the concrete.

Short walls won’t require all that much bracing and support, but as your walls get higher, it will be imperative that you don’t skimp on the support. Wet concrete behaves like any other liquid and will produce hydrostatic pressure. In other words, as with any substance in a fluid state, there will be more pressure at the bottom of the container and will lessen with height. This means you have to concentrate more support at the bottom.

There are various methods for attaching formwork together securely.

a. ply b. frame c. bolts d. steel pipes e. washers

Obviously, the thicker and taller the wall, the more support you’ll need. There is a variety of hardware available for individual specific tasks – such as for columns or walls. Wedges that are hammered into staggered slots in flat bars of steel are used for formwork with smaller perimeters, whereas long bolts threaded through sleeves cut out to fit within the formwork are used for larger projects.

The bolts are removed after the concrete has cured, but the sleeves remain. The holes are simply grouted up. This may explain why you often see slightly off-color circular tracings dotting a concrete wall. Of course, these types of hardware are not a must. You can also get by totally fine with only timber, it’s just a little more time-consuming not to mention harder to get accurate.

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