Difference between Centering and Shuttering | Are these Terms Interchangeable?

Centering and shuttering are a type of formwork. Formwork is a temporary structure to contain and support the fresh concrete in its required shape and dimensions till it is hardened enough to support itself.

Centering and Shuttering Definition

Centering: It is a specialised formwork to support the soffit of arches, shell space structure. In such structures, the entire formwork is de-centred to avoid stress formation at any part of the structure.

Shuttering: It is a temporary structure to support the vertical stiffening members while the concrete is setting until it gains enough strength to become self-supporting.

Centering and Shuttering Meaning

Centering is used to support horizontal members. Hence, formwork for floor beams and slabs is known as centering.

Shuttering is used to support vertical members. Hence, formwork for columns, footings, or retaining walls is known as shuttering.

Requirements of Shuttering and Centering

• The surface of the form should be smooth
• It should be able to withstand all the loads coming on it
• It should be able to retain its shape (horizontal and vertical bracing is done for this)
• It should have minimum deflection under load
• It should be re-usable
• It should not be costly
• It should be water-proof so that it does not absorb water from the fresh concrete
• It should facilitate easy stripping during the time of removal

Centering and Shuttering Material

Steel and timber are commonly used as shuttering and centering material, former for its efficiency and later for its cost-effectiveness.

1. Steel

Panels are fabricated from thin steel plates and small steel angles are used along the edges to stiffen these plates. Clamps, nuts, or bolts are used to hold the steel panels together.

Steel is considered as the best material for centering and shuttering. The reasons are explained below:

• Steel provides a watertight formwork so that strength of the cement concrete is preserved
• It can bear the load coming on it easily
• It can be used for vertical, horizontal, or any type of formwork
• It provides a levelled surface of concrete. Desired appearance based on architectural recommendations is easy to achieve with the help of steel formwork
• As the bottom surface of the structural member is levelled, less thickness of plaster is required

2. Timber Planks

Timber is commonly employed by the contractors, as it is cheap and easily available.

Timber should be checked for following requirements for its use as centering or shuttering material:

• It should be seasoned
• It should be light-weighted
• It should not have loose knots
• It should have smooth and even surface, especially when used for exposed concrete surfaces

Some of the points of caution to be kept in mind while using timber planks for centering or shuttering are listed below:

• The size and thickness of planks may not be uniform. Because of this non-uniformity, timber planks do not have watertight joints. Water and cement slurry can flow from the joints which reduces the strength of the concrete and as a result structural member.
• The surface of the RCC member can be uneven. Thus, more thickness of plaster is required.
• If timber planks cannot bear the load of concrete coming on it, then deflection may occur in the planks. In some cases, it may even lead to breakage.

3. Temporary Brick Masonry

Temporary brick masonry should be avoided as far as possible.

It is sometimes used in mud for the vertical supports of the beam sides.

• The brick masonry soaks the cement slurry from the member. Thus, the strength of the member is greatly affected.
• Moreover, the brick masonry formwork cannot bear the weight of vibrator, so proper compaction of the structural member is not possible. This again reduces the strength.
• An uneven surface of RCC member is obtained requiring more thickness of plaster.

Difference between Centering and Shuttering

• Centering is used for horizontal concrete members while shuttering is used for vertical concrete members
• Formwork supporting slabs and floor beams is termed as centering while formwork supporting columns, footing, or retaining walls is termed as shuttering

Types of Shuttering

Beam shuttering and column shuttering are described below:

Beam Shuttering

The shuttering for beam is in the form of a three-sided box. It is supported by props so that it stands in the correct position and is levelled.

Column Shuttering

Column shuttering needs tight joints and strong ties as the column has smaller cross section as compared to its length. Braces are also provided to prevent deflection of the shutters. Ties are provided to hold the shutters in place.

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