For building an arch, a formwork of the same shape of its intrados needs to be used. This can be made of wood or metal and should be used in conjunction with a system allowing its easy removal.
For most arch forms, the formwork can be removed immediately after construction. The formwork can therefore be reused straightaway. This means that if there are a great many identical arches to be built, clearly it makes sense to prepare a precise and robust formwork to ensure that it can be reused and that the work will be of high standard and carried out quickly and economically. Building up bricks or blocks with dry joints and shaping the curve with a layer of mortar is a very economical way of making a formwork.
Corbelled arches are built using courses which each jut out further than the previous one. Cut out arches, and arches shaped with wooden reinforcement, are also built without formwork.
Vaults can be built in a similar way to arches.
Building can be done on a full formwork set up in place. This is mainly used for floors over basements. It is possible to use an integrated formwork. Being very heavy, this has to be assembled and dismantled in place. This technique is economical only if the vaults - and therefore the formwork - are light.