Formwork, also known as shuttering, is the mould for a concrete structure or element. The concrete workers set up the formwork and pour fresh concrete into it, letting the wet mixture harden into the shape needed for the project. The formwork can become a large temporary structure that the construction crew will dismantle after the concrete is strong enough to stand on its own, though in some cases, the formwork is left in place.
The material that makes up formwork must be strong enough to withstand all live and dead loads, while also standing up to the elements so that it can be reused after dismantling.
What Makes Good Formwork?
For shuttering to work, the form has to be well-constructed, with horizontal and vertical bracing that helps it retain the shape despite the weight of the concrete. The joints also have to be tight so that no leakage of the cement affects the final shape.
The material for the formwork has to be strong, with the right finishing so that it does not warp or distort under long exposure to the elements – and formwork will be exposed for a long time! Many different materials can make up a concrete project’s formwork, but the three most popular are timber, plywood, and steel.
Timber is the most common material used for formwork. It’s lightweight, inexpensive, and assembly is easy – when finished, nails won’t split the wood. All the timber formwork that comes in contact with concrete should have smooth, even surfaces, and it should be well-seasoned and free of loose knots.
The downside of some timber formwork is that the wood can warp, swell, or shrink from too much moisture. A layer of protection on the surface of the wood can decrease the chance of these weaknesses forming, though that can make the cost a little higher.
In plywood shuttering, sheets of resin-bonded plywood make panels that are the right size for the project. Contractors will then attach these panels to a timber frame. Most plywood panels made for shuttering have a smooth, finished surface that is great for different concrete projects, creating a fair-faced finish.
Plywood formwork can be cheaper than timber shuttering in the long run because the larger panels save on the costs of fixing, dismantling, and reusing the structure.
This type of shuttering uses thin steel panels stiffened along the edges by small steel angles. The panels are then assembled using strong bolts or clamps. Steel is great because it won’t bend or warp like wood, and it can store a large, heavy amount of concrete.
However, it is much pricier. Steel formwork is largely used in a large construction project or for projects where a large number of reuses are possible. This type of shuttering is best suited for curved or circular concrete structures.