Deshuttering period of slab, also known as formwork removal, is a critical process in concrete construction that significantly affects the structural integrity of a building. The Indian Standards (IS) code provides guidelines for the minimum duration before formwork can be removed to ensure adequate strength development in the concrete. This article discusses the deshuttering period of slab as per IS Code 456:2000, the Indian Standard code for plain and reinforced concrete.
Table of Contents
Importance of Deshuttering Time
The deshuttering time is crucial for the following reasons:
- Ensures concrete has attained sufficient strength to support its own weight and any imposed loads.
- Prevents early removal, which could lead to structural failures, cracks, or deformities.
- Maintains the designed strength and durability of the structure.
IS Code Guidelines for Deshuttering of Slabs
According to IS 456:2000, the minimum deshuttering period of slab depends on factors such as concrete grade, curing conditions, and ambient temperature. The table below provides the recommended duration:
| Type of Formwork | Minimum Duration Before Removal |
| Vertical formwork (columns, walls, sides of beams) | 16-24 hours |
| Slab (props left under) | 3 days |
| Beam soffit (props left under) | 7 days |
| Removal of props under slabs Up to 4.5 m span More than 4.5 m span | 7 days 14 days |
| Props removal for beams and arches Up to 6 m span Span length beyond 6m | 14 days 21 days |
Factors Influencing Deshuttering Time
Several factors impact the deshuttering period of slab, including:
- Curing Conditions – Adequate moisture and temperature accelerate strength gain.
- Grade of Concrete – Higher-grade concrete gains strength faster.
- Admixtures Used – Accelerators and retarders influence setting time.
- Site Temperature – Warmer conditions speed up hydration, while colder temperatures delay it.
- Load-Bearing Capacity – Heavy load-bearing slabs may require a longer deshuttering period.
Precautions While Deshuttering
- Ensure concrete has achieved at least 70% of its design strength before removal of props.
- Gradually remove formwork to avoid sudden load transfer.
- Monitor for cracks or deflections and take corrective measures if necessary.
- Conduct cube tests to verify strength development before removing supports.
Conclusion
Proper adherence to IS 456:2000 guidelines for deshuttering slabs is essential to maintaining the safety and durability of structures. Following the recommended timeframes and considering influencing factors can help prevent structural failures and ensure the longevity of the construction. Always consult an experienced engineer before making deshuttering decisions on-site.