Introduction
Formwork plays a crucial role in concrete technology, where support freshly placed concrete until it gains sufficient strength to support its own weight and the loads acting on it. However, removing the formwork too early can lead to cracking, excessive deflection, or even structural failure, while delayed removal can slow down construction progress and increase project costs. Therefore, understanding the correct stripping time and procedure for formwork removal is essential for ensuring structural safety, quality construction, and efficient project execution.
The removal of formwork, also known as stripping of formwork or shuttering removal, must be carried out carefully and in accordance with standard guidelines such as IS 456:2000. The stripping time of formwork depends on several factors, including the type of structural member, concrete strength gain, span length, weather conditions, and type of cement used. Proper planning and inspection before removal help prevent damage to concrete elements and ensure long-term durability of the structure.
In this article, we will discuss the removal of formwork in detail, including recommended stripping time as per IS 456, step-by-step removal procedure, safety precautions, effects of early removal, re-propping requirements, and practical site guidelines used in construction projects.
What is the Removal of Formwork?
Removal of formwork, also known as stripping of formwork or shuttering removal, is the process of removing the temporary moulds, supports, and shuttering used to hold freshly placed concrete after it has gained sufficient strength to support its own weight and construction loads.
The formwork is removed according to specified stripping times and engineering guidelines to ensure structural safety and prevent damage to concrete members. Depending on the structural element, the formwork may include side forms for columns and walls, soffit forms for beams and slabs, and props supporting horizontal members.
The stripping time varies based on factors such as concrete strength gain, span length, cement type, weather conditions, and the type of structural member.
Why Proper Formwork Removal is Important
Proper formwork removal is essential to ensure the safety, strength, stability, and durability of concrete structures. Removing formwork at the correct time allows the concrete to gain sufficient strength to support its own weight and imposed construction loads without cracking, excessive deflection, or structural damage.
Premature removal of formwork can weaken structural members and may lead to sagging, edge breakage, honeycombing exposure, or even collapse in severe cases. On the other hand, excessively delayed removal may slow down construction progress, reduce formwork reuse efficiency, and increase project costs.
The proper stripping sequence and timing also help maintain the dimensional accuracy and surface finish of concrete members such as slabs, beams, columns, and walls. Therefore, formwork removal should always be carried out carefully according to standard guidelines such as IS 456:2000 and site engineering recommendations.
Importance of Proper Formwork Removal
- Prevents cracking and excessive deflection in concrete members
- Ensures adequate concrete strength before load transfer
- Reduces the risk of structural failure or collapse
- Protects concrete edges and surface finish from damage
- Improves durability and long-term structural performance
- Enhances worker safety during stripping operations
- Allows safe transfer of loads from formwork to the structure
- Improves construction quality and structural stability
- Prevents unnecessary repair and maintenance costs
- Maintains construction progress and efficient formwork reuse
Also, read: What is Formwork?
Also, read: Shuttering/Formwork for Structure Members for Building Construction
Factors Affecting the Removal of Formwork.
The main factors affecting the removal of formwork are concrete strength gain, type of structural member, span length, cement type, weather conditions, loading conditions, and curing quality. These factors determine how quickly the concrete can safely support its own weight and construction loads without external support.
1. Type of Structural Member
Different structural members require different stripping times because the load carried by each member varies. Vertical members such as columns, walls, and beam sides can generally have their side forms removed earlier since they mainly retain shape. However, horizontal members such as slabs and beams require longer support because they carry bending loads and self-weight.
2. Strength of the concrete:
Formwork should not be removed until the concrete achieves adequate strength. Faster strength gain allows earlier stripping, while slower strength development requires longer support periods. Concrete strength depends on mix proportion, water-cement ratio, curing, and cement type.
3. Span Length of Member
Long-span slabs and beams require longer formwork support compared to short-span members because they experience higher bending stresses and deflection. As the span increases, the stripping time and duration of props are generally increased.
4. Type of Cement Used
The rate of concrete hardening depends on the type of cement used in construction. Rapid hardening cement gains strength faster and allows earlier removal of formwork, whereas ordinary Portland cement and blended cements may require longer stripping periods. Read the complete guide on types of cement.
5. Weather and Temperature Conditions
Temperature significantly affects concrete strength development. In hot weather, concrete gains strength more quickly, which may reduce stripping time. In cold weather, hydration slows down, requiring formwork to remain for a longer duration to ensure adequate strength gain.
6. Curing Conditions
Proper curing improves hydration and concrete strength development. Poor curing may delay strength gain and increase the risk of cracking after formwork removal. Adequately cured concrete can safely support loads earlier than poorly cured concrete. Read our in-depth content on Curing.
7. Loading Conditions
The formwork removal time also depends on the loads expected on the structure after stripping. If heavy construction materials, equipment, or workers are expected to act on slabs or beams, the props may need to remain longer or re-propping may be required.
8. Quality of Concrete Construction
Poor compaction, honeycombing, segregation, or excessive water content can weaken concrete and delay formwork removal. The concrete surface and structural condition should always be inspected before stripping operations are started.
Also, read: What is Mass Concrete?
Formwork Removal Time as per IS 456
The removal of formwork should be carried out only after the concrete has gained sufficient strength to safely support its own weight and any construction loads. IS 456:2000 provides recommended stripping times for different structural members to ensure safety, structural stability, and proper strength development of concrete.
The stripping time specified in IS 456 is based on normal conditions using ordinary Portland cement and proper curing. In practice, the removal time may vary depending on temperature, cement type, concrete strength gain, span length, and site conditions.
Recommended Formwork Removal Time as per IS 456
| Structural Member | Minimum Removal Time |
|---|---|
| Vertical formwork to columns, walls, and beam sides | 16 to 24 hours |
| Soffit formwork to slabs (props left under) | 3 days |
| Removal of props to slabs: span up to 4.5 m | 7 days |
| Removal of props to slabs: span over 4.5 m | 14 days |
| Soffit formwork to beams (props left under) | 7 days |
| Removal of props to beams and arches: span up to 6 m | 14 days |
| Removal of props to beams and arches: span over 6 m | 21 days |
Vertical Formwork Removal Time
Vertical formwork, such as column forms, wall forms, and beam side forms, mainly supports the shape of concrete rather than structural loads. Therefore, these forms can generally be removed earlier, usually within 16 to 24 hours after casting, provided the concrete has hardened sufficiently.
Slab Formwork Removal Time
The soffit formwork of slabs may be removed after about 3 days if the props are kept in place. However, the slab props should remain for a longer duration, depending on the slab span, to ensure adequate strength gain and prevent excessive deflection.
Beam Formwork Removal Time
Beam soffit formwork and props require longer support because beams are subjected to bending stresses and carry significant structural loads. As per IS 456, props under beams and arches may remain for 14 to 21 days, depending on the span length.
Important Notes on Stripping Time
- The specified stripping time of formwork assumes proper curing and normal temperature conditions.
- Formwork should never be removed solely based on elapsed time without considering concrete strength.
- In cold weather conditions, stripping time may need to be increased due to slower strength gain.
- Early removal of props may cause cracking, excessive deflection, or structural damage.
- Re-propping may be required in multi-storey construction to safely transfer loads.
Also, read: What are Concrete Column Kickers? | Column Starter
Procedure for Removal of Formwork
The removal of formwork should be carried out carefully and systematically to prevent damage to the concrete surface and ensure structural safety. Before stripping operations begin, the concrete must gain sufficient strength to support its own weight and any imposed construction loads safely.
The formwork should never be removed suddenly or forcefully, as improper stripping may cause cracking, excessive deflection, edge damage, or structural instability in newly cast concrete members.
1. Inspection Before Formwork Removal
Before removing the formwork, the site engineer or supervising authority should inspect the concrete member to verify adequate hardening and strength development. The stripping operation should only begin after receiving approval according to project specifications and IS 456 recommendations.
The following should be checked before removal:
- Concrete strength and hardening condition
- Completion of curing requirements
- Surface defects, cracks, or honeycombing
- Stability of supporting props and members
- Weather and loading conditions
2. Removal of Vertical Formwork
Vertical side forms for columns, walls, and beam sides are generally removed first because they mainly support the shape of the concrete rather than structural loads. These forms should be loosened gradually without applying excessive force or vibration.
Workers should avoid using hammers or sudden impacts that may damage the concrete surface or edges.
3. Removal of Slab Formwork
For slabs, the soffit formwork should be removed carefully while ensuring that the supporting props remain in position if required. The removal process should proceed gradually from one end to another to avoid sudden load transfer and structural distress. Read the advantages and disadvantages of Flat Slabs.
4. Removal of Beam Formwork and Props
Beam soffit formwork and props should be removed only after the concrete gains sufficient strength to safely resist bending stresses and loads. The props supporting beams and arches are usually removed after the slabs because beams carry higher structural loads.
Long-span beams may require additional time and re-propping arrangements before complete stripping.
5. Sequential Removal of Formwork
The formwork should always be removed in sequence to minimise structural damage and improve worker safety. Generally:
- Side forms of beams and walls are removed first
- Slab soffit formwork is removed next
- Slab props are removed carefully
- Beam soffit formwork and props are removed last
This systematic stripping procedure reduces the risk of cracking, excessive deflection, and sudden load transfer to newly cast concrete members.
6. Cleaning and Stacking of Formwork Materials
After removal, the formwork components should be cleaned properly and stacked safely for reuse. Nails, ties, and loose materials should be removed carefully to avoid injuries and damage to reusable formwork panels.
Proper storage and maintenance improve the durability and reuse efficiency of formwork materials in future construction works.
Effects of Early Removal of Formwork
Early removal of formwork can seriously affect the strength, stability, and durability of concrete structures. If the concrete has not gained sufficient strength, premature stripping may lead to structural distress and surface damage.
- Cracking in slabs, beams, and columns
- Excessive deflection or sagging of members
- Collapse of unsupported concrete sections
- Damage to concrete edges and corners
- Surface defects and honeycombing exposure
- Reduction in structural strength and durability
- Poor load transfer and instability
- Increased repair and maintenance costs
Precautions During Formwork Removal
Proper precautions should be followed during formwork removal to prevent damage to concrete members, avoid structural instability, and ensure worker safety. The stripping operation should always be carried out carefully, systematically, and under the supervision of the site engineer.
Premature or careless removal of formwork may lead to cracking, excessive deflection, edge damage, or even collapse of newly cast concrete members. Therefore, adequate concrete strength and proper stripping procedures must be ensured before removal begins.
Important Precautions During Formwork Removal
- Follow the engineer’s or contractor’s instructions: The engineer or contractor will provide specific instructions for when and how to remove the formwork. Follow these instructions carefully to avoid damaging the concrete or putting workers at risk.
- Inspect the formwork: Before removing the formwork, inspect it for any signs of damage or wear. If there are any damaged sections, they should be repaired or replaced before the formwork is removed.
- Check the concrete strength: Make sure the concrete has reached sufficient strength before removing the formwork. This will help prevent damage to the concrete and ensure that the structure is structurally sound.
- Use proper equipment: Use the appropriate tools and equipment to remove the formwork safely and efficiently. This may include power tools, hand tools, and lifting equipment.
- Avoid damaging the concrete: Take care not to damage the concrete while removing the formwork. This may involve using pry bars or other tools to carefully loosen the formwork without damaging the concrete surface.
- Protect workers: Make sure that workers involved in formwork removal wear appropriate personal protective equipment, such as gloves, safety glasses, and hard hats. Workers should also be trained in proper lifting techniques and should use proper tools and equipment to prevent injury. Read out guid on Importance of PPE at Construction site.
- Reuse or recycle the formwork: If possible, consider reusing or recycling the formwork to reduce waste and save money. Proper handling and maintenance of the formwork can extend its lifespan and allow it to be used for multiple projects.
FAQs on Removal of Formwork
Q: When to remove formwork from slab?
Answer: Slab soffit formwork may generally be removed after 3 days if props are left in place. Props are removed after 7 to 14 days depending on the span.
Q: What is stripping time in concrete?
Answer: Stripping time is the minimum time before formwork can be safely removed after concrete casting.
Q: What happens if formwork is removed early?
Answer: Early formwork removal may cause cracking, excessive deflection, or structural damage to concrete members.
Q: What is the minimum strength before removing formwork?
Answer: Concrete should gain sufficient strength to safely support its own weight and construction loads before formwork removal.
Q: What does IS 456 say about formwork removal?
Answer: IS 456:2000 specifies recommended stripping times for slabs, beams, columns, walls, and props under normal conditions.
Conclusion
Removal of formwork is a critical activity in concrete construction that should be carried out only after the concrete gains sufficient strength to safely support its own weight and construction loads. Proper stripping time, careful removal procedures, and adherence to IS 456:2000 guidelines help prevent cracking, excessive deflection, and structural damage.
By following the recommended formwork removal sequence, safety precautions, and curing practices, engineers and site workers can ensure better concrete quality, structural stability, worker safety, and efficient construction progress.
References & Standards
- Bureau of Indian Standards. (2000). Plain and Reinforced Concrete: — Code of Practice (IS 456: 2000) . Bureau of Indian Standards, New Delhi, India.
- Bureau of Indian Standards. (1964). Code of practice for formwork for concrete (IS 14687). Bureau of Indian Standards, New Delhi, India.
- Neville, A. M. (2011). Properties of concrete (5th ed.). Pearson Education Limited.
- Shetty, M. S. (2005). Concrete technology: Theory and practice. S. Chand Publishing.
- Punmia, B.C (2006). A textbook of Building Construction. Laxmi Publications (P) Ltd.
