In reinforced concrete construction, centering and shuttering are crucial processes that provide temporary support to freshly placed concrete. These systems help mold concrete to the desired shape and ensure structural integrity until it gains sufficient strength. Knowing the procedure, removal time, and precautions of centering and shuttering is essential for site engineers and contractors to ensure safety, quality, and project efficiency.
What is Centering and Shuttering?
Centering refers to the temporary supports used for horizontal surfaces like slabs and beams. Shuttering is the formwork or molds used for vertical or inclined surfaces such as columns, walls, and staircases. Together, centering and shuttering hold concrete in place during casting and until it hardens.
Importance of Centering and Shuttering in Construction
Provides shape and support to freshly poured concrete
Maintains dimensional accuracy as per structural drawings
Supports the load during setting and hardening of concrete
Prevents deformation, sagging, and honeycombing
Ensures quality finish and safety of the structure
Materials Used in Centering and Shuttering
1. Timber
Traditionally used, easily available, and lightweight. Suitable for small-scale works.
2. Steel
Strong, reusable, and gives smooth finish. Ideal for beams, slabs, and columns.
3. Aluminum
Lighter than steel and easy to handle. Used in modular systems and for speed construction.
4. Plywood
Used as sheeting with timber or steel frames. Provides smooth surface finish.
5. Plastic or FRP
Used in modern construction. Durable and suitable for curved surfaces.
Standard Components in a Shuttering System
Plates or panels – surface in contact with concrete
Soldiers – vertical supports for panels
Props or jacks – adjustable supports for height
Ledger beams – horizontal supports
Bracing – provides rigidity and prevents shifting
Ties and clamps – hold formwork together
Procedure of Centering and Shuttering
1. Planning and Design
Study structural drawings and determine the formwork layout
Decide formwork material based on design and reuse potential
Calculate the load on centering based on slab or beam thickness
2. Preparation of Formwork
Cut and assemble panels, props, beams, and support systems
Apply form release agent or shuttering oil to avoid sticking
Ensure formwork is clean, dry, and free from debris
3. Fixing and Erecting the Shuttering
Erect vertical and horizontal supports as per design levels
Align formwork accurately to achieve plumb, level, and straightness
Provide adequate bracing and spacers for stability
Install ties, clamps, and wedges for a tight fit
Seal all joints to prevent cement slurry leakage
4. Inspection Before Concreting
Check levels, plumb, alignment, and dimensions
Inspect tightness, rigidity, and support condition
Ensure cover blocks are placed for reinforcement spacing
Verify that form oil has been applied and pipes/conduits are in place
Removal Time for Centering and Shuttering
The removal time of centering and shuttering depends on the type of member, span, weather, and type of cement used. IS 456:2000 provides standard guidelines.
| Structural Member | Minimum Removal Time |
|---|---|
| Vertical formwork (columns, walls) | 16 to 24 hours |
| Slabs (props left under) | 3 days |
| Beams (props left under) | 7 days |
| Props for slab (under 4.5m span) | 7 days |
| Props for slab (over 4.5m span) | 14 days |
| Props for beams (under 6m span) | 14 days |
| Props for beams (over 6m span) | 21 days |
Note: Removal should be done only after concrete attains required strength, especially in cold weather conditions.
Factors Affecting Removal Time
Grade of concrete (M20, M25, etc.)
Type of cement (OPC gains strength faster than PPC)
Ambient temperature and curing condition
Size and shape of the member
Load on the element and construction sequence
Precautions While Fixing Shuttering
Use only seasoned and straight materials
Ensure all supports are placed on firm ground or planks
Avoid gaps in joints to prevent leakage
Ensure correct dimensions, slopes, and thickness as per drawings
Use adequate props to prevent deflection or collapse
Provide openings for pouring and vibrating concrete
Precautions During Concrete Pouring
Do not pour from excessive height (limit to 1.5 m)
Use vibrators to avoid honeycombing
Support walkways and platforms securely
Ensure shuttering does not shift or bulge during concreting
Maintain uniform rate of concrete pouring across the formwork
Precautions While Removing Centering and Shuttering
Remove only after approval by site engineer
Start removing from slabs and soffits, then beams
Remove supports gradually, not by jerks
Do not hammer or apply force on formwork
Avoid placing loads on newly de-shuttered concrete
Check for cracks or surface damage after removal
Common Issues Due to Poor Centering and Shuttering
Sagging of slab or beam
Honeycombing and surface defects
Leakage of slurry through joints
Bulging or collapse during concreting
Misalignment of structure or failure of elements
Tips for Efficient Centering and Shuttering
Use modular shuttering for speed and accuracy
Ensure timely oiling and maintenance of formwork panels
Label and reuse components for cost savings
Train laborers on safe erection and dismantling practices
Use mechanized tools for height work and heavy lifting
Keep inspection checklist before and after concreting
Role of Site Engineer in Shuttering Work
Prepare layout and plan formwork activities
Ensure safety during erection and dismantling
Check shuttering alignment, levels, and joint sealing
Coordinate between bar bending and shuttering teams
Verify curing and concrete strength before removal
Maintain records and formwork inventory
FAQs on Centering and Shuttering
What is the difference between centering and shuttering?
Centering refers to temporary support for horizontal elements (like slabs), while shuttering refers to formwork that gives shape to vertical or inclined concrete surfaces.
What is the ideal time to remove shuttering?
As per IS 456:2000, vertical formwork can be removed in 24 hours, while slab and beam supports may take 7 to 21 days depending on span and curing.
Can we reuse shuttering material?
Yes, steel and aluminum shuttering can be reused multiple times if maintained properly. Even plywood can be reused up to 4–8 times depending on quality.
What happens if shuttering is removed too early?
Premature removal may lead to deflection, cracks, or collapse due to insufficient concrete strength. Always check cube test results and curing status.
What oil is used for shuttering?
Form release oil or shuttering oil is applied to the surface to prevent sticking of concrete. Common types include diesel mix oil, emulsion-based oils, or synthetic release agents.
Is it safe to walk on the slab after shuttering removal?
It is safe only after concrete has reached sufficient strength. Light foot traffic is usually allowed after 7 days, depending on the slab type and curing.
