The concrete is contained in a timber or steel casing for a certain period after its placing. This cashing is known as shuttering, centering, formwork or moulds and it is to be removed when concrete has hardened sufficiently to support its own weight. Following precautions should be taken for formwork of concrete:
(1) The formwork should be designed in such a way that it can be easily removed and used again.
(2) The formwork should be fixed in such a way that the least hammering is required for its removal. Otherwise it may injure the concrete.
(3) The inside surface of formwork should be coated with crude oil or soft soap solution. This will make removal of formwork easy.
(4) The formwork should be sufficiently strong to bear the dead load of wet concrete as well as the impact of ramming or vibrating the concrete. The over-estimation of loads results in expensive formwork and the under-estimation of loads results in the failure of formwork.
(5) It is desirable to bring down the cost of formwork to a minimum consistent with safety. The various steps such as reduction in number of irregular shapes of forms, use of component parts of commercial sizes, putting the formwork in use again as early as possible, etc. may be taken to effect economy in the formwork.
(6) The formwork should be so arranged that there is minimum of leakage through the joints. This is achieved by providing tight joints between adjacent sections of the formwork.