Centring, centre, centering"Centering 2, Centring 2" def. 1. Whitney, William Dwight, and Benjamin E. Smith. ''The Century dictionary and cyclopedia''. vol. 2. New York: Century Co., 1901. p. 885., or center is a type of

formwork Formwork is molds into which concrete or similar materials are either precast or cast-in-place. In the context of concrete construction, the falsework supports the shuttering molds. In specialty applications formwork may be permanently i ...

: the temporary structure upon which the stones of an

arch An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it. Arches may be synonymous with vau ...

vault Vault may refer to: * Jumping, the act of propelling oneself upwards Architecture * Vault (architecture), an arched form above an enclosed space * Bank vault, a reinforced room or compartment where valuables are stored * Burial vault (enclosure ...

are laid during construction. Until the keystone is inserted an arch has no strength and needs the centring to keep the

voussoir A voussoir () is a wedge-shaped element, typically a stone, which is used in building an arch or vault. Although each unit in an arch or vault is a voussoir, two units are of distinct functional importance: the keystone and the springer. T ...

s in their correct relative positions. A simple centring without a truss is called a common centring. A cross piece connecting centring frames is called a lag or bolst.Ching, Frank (1995). ''A visual dictionary of architecture''. New York: Van Nostrand Reinhold. p. 3. . Centring is normally made of

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin ...

timbers, a relatively straightforward structure in a simple arch or vault; but with more complex shapes involving double curvature, such as a

dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...

or the bottle-shaped

flue A flue is a duct, pipe, or opening in a chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors. Historically the term flue meant the chimney itself. In the United States, they are ...

in a Norman-period kitchen,

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class ...

bound by a weak lime mortar would be used. Shaping could be done by eye, perhaps with the help of a template, then stones or

brick A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured cons ...

s laid against it. On larger works like a 19th-century

pottery Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard and durable form. Major types include earthenware, stoneware and ...

kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay int ...

this was impractical. The structure would be built round a post acting as a datum, and each course of stonework would be set at a distance from the datum. When the centring is removed (as in "striking the centring"), pointing and other finishing continues.

Gallery

File:Small-arch-center.png, A simple arch centre suitable for single skin brickwork. File:Segmental-arch-center.png, A centre for a flat segmental arch. File:Arch-centering.png, The centring for a semicircular arch. File:Blackfriars02.jpg, Centring of trusses, not common centring Image:CatenaryKilnConstruction06025.JPG,

Catenary arch A catenary arch is a type of architectural arch that follows an inverted catenary curve. The catenary curve has been employed in buildings since ancient times. It forms an underlying principle to the overall system of vaults and buttresses i ...

under construction over centring

References

Construction Arches and vaults {{Architecturalelement-stub