What is arch centering (a centre)?
Arch centering, often simply called a centre, is a temporary support structure on which an arch is built or on which bricks are stacked in an arch shape. Note: a centre is not a building style but a support.
How does arch centering work?
A masonry arch can only support itself once all the stones are in place, the keystone has been set, and the mortar has hardened. Until then, the stones must be held up. That is the purpose of the centring:
- The centre is made in the correct arch shape, usually from timber.
- It is set up beneath the future arch and propped.
- The bricklayer stacks the stones on the centre until the arch is complete.
- After hardening, the centre is removed; this is called striking or decentring the arch.
Only after striking does the arch rest fully on its own weight and on the hardened joints.
Application
Arch centring is used when laying arches over windows, doors, gateways, and vaults. It is also indispensable for relieving arches and masonry bridges. The shape of the centre precisely determines the final arch form, whether a round arch, segmental arch, or pointed arch. A carefully built and well-propped centre is therefore decisive for the quality and stability of the arch.
Related terms
- Arch
- Formwork
- Keystone
- Brick course (rowlock)
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