Precautions to be taken while removing Formwork / De-shuttering
When forms are stripped there must be no excessive deflection and no damage to the concrete due to the removal of supports or due to the stripping operations.
Where stripping time is less than the specified curing time, provide adequate curing and protection from direct sun and dry winds.
Do not remove supporting props and shores from beams and slabs until the concrete has attained sufficient strength to carry both the dead load and any live load that might be imposed , with a safety factor of 2.
Detail the forms and scaffolding in such a way that they can be removed easily and safely without impact or shock.
Remove the supports in such a way to permit the concrete to take its share of the load gradually and uniformly.
When test cubes are used to determine the stripping times, cure them under the same conditions as the concrete they represent.
Under ordinary conditions, forms and supports should remain in place for not less than the following periods of time IS 456-2000 - Clause 11.3 Amendment No 05 July 2019
Time period for form work removal
Note : In case of cement use other that OPC or in case of use of mineral admixture like flyash and slag, in lieu of the minimum period specified, the stripping of formwork may be done in accordance with the 2nd column (For OPC), provided concrete cube testing is done to ensure that the following minimum strength is achieved;
At 3 Days - 45 % of specified strength
At 7 Days - 60% of specified strength
14 Days - 85% of specified strength
Above strength criteria is given in IS 456 Amendment No 05 July 2019.
When forms are stripped there must be no excessive deflection and no damage to the concrete due to the removal of supports or due to the stripping operations.
Where stripping time is less than the specified curing time, provide adequate curing and protection from direct sun and dry winds.
Do not remove supporting props and shores from beams and slabs until the concrete has attained sufficient strength to carry both the dead load and any live load that might be imposed , with a safety factor of 2.
Detail the forms and scaffolding in such a way that they can be removed easily and safely without impact or shock.
Remove the supports in such a way to permit the concrete to take its share of the load gradually and uniformly.
When test cubes are used to determine the stripping times, cure them under the same conditions as the concrete they represent.
Under ordinary conditions, forms and supports should remain in place for not less than the following periods of time IS 456-2000 - Clause 11.3 Amendment No 05 July 2019
Time period for form work removal
| Type of Formwork | Minimum period before striking formwork for Concrete Made Using OPC | For Concrete made using cement other than OPC or Using Mineral Admixtures like Flyash and Slag |
|---|---|---|
a) Vertical formwork to columns, walls and beams | 16 to 24 hours | 16 to 24 hours |
| b) Soffit formwork to slabs (props to be refixed immediately after removal of formwork) | 3 days | 7 Days |
| c) Soffit formwork to beams ( Props to be fixed immediately after removal of formwork) | 7 days | 10 Days |
| d) Props to slabs | | |
| 1) spanning up to 4.5 m | 7 days | 10 Days |
| 2) spanning over 4.5 m | 14 days | 14Days |
| e) Props to beams and arches: | | |
| 1) spanning up to 6 m | 14 days | 14 Days |
| 2) spanning over 6 m | 21 days | 21 Days |
Note : In case of cement use other that OPC or in case of use of mineral admixture like flyash and slag, in lieu of the minimum period specified, the stripping of formwork may be done in accordance with the 2nd column (For OPC), provided concrete cube testing is done to ensure that the following minimum strength is achieved;
At 3 Days - 45 % of specified strength
At 7 Days - 60% of specified strength
14 Days - 85% of specified strength
Above strength criteria is given in IS 456 Amendment No 05 July 2019.
