Definition of a Form Work
Formwork is the term used for the process of creating a temporary mould into which concrete is poured and formed. Traditional formwork is fabricated using timber, but it can also be constructed from steel, glass fibre reinforced plastics and other materials. While formwork is a broad term that is used in relation to the forming process using a wide variety of materials, shuttering is a term that is often used to refer to the process of using plywood to form the mould. Shuttering is perhaps the most popular type of formwork and is normally constructed on site using timber and plywood. A special grade of plywood is necessary for shuttering, and it must be water-resistant. It is easy to produce, although it can be time consuming for larger structures. It is used when the labour costs are lower than the cost of producing re-usable formwork from materials such as steel or plastic. It also has the advantage of beingat a significant amount of concrete can be poured at once. Simple plank shuttering can be used for the construction of a path or hardstanding. The planks should be trimmed so they are level with the top surface of the slab, allowing a tidy concrete finish to be achieved.
When selecting formwork, the type of concrete and temperature of the pour are important considerations as they both effect the pressure exerted. The formwork sides must be capable of resisting the hydrostatic pressure of the wet concrete which will diminish to zero within several hours depending on the rate of setting and curing. The formwork base or soffit must be capable of resisting the initial dead load of the wet concrete and the dead load of the dry set concrete. Once the concrete has gained sufficient strength the formwork can be struck (removed). A minimum value of 5 N/mm2 is recommended in all cases when striking vertical formwork as so not to damage the permanent concrete in the process. High quality workmanship and inspection are necessary to ensure a high standard and appearance of the resulting concrete structure. Both shuttering and formwork in its various forms will be supported by falsework. This refers to poles, stabilisers, or other units that keep the shuttering or formwork in place as the concrete dries. For more information, see Falsework.