WHEN TO REMOVE CONCRETE FORMWORK?

Removal of Forms

Forms should not be removed until the concrete has sufficiently hardened in order that it can carry safely its own weight and any other live loads it is subjected to.

The supporting period (period between placing of concrete in forms and removal of forms) differ according to the type of cement used and the design of formwork. In general structures carrying construction loads, side timbers shall not be removed within 7 days and supporting timbers within 28 days of placing of concrete.

In no circumstances shall forms be stuck until the concrete reaches strength of at least twice the stress to which the concrete may be subjected at the time of striking.

The strength referred to shall be that of concrete using the same cement and aggregates, with the same proportions, and cured under conditions of temperature and moisture similar to those existing on the work. Where possible, the formwork should be left longer, as it would assist the curing.

Removal of Formwork
Removal of Formwork

In normal circumstances (generally where temperatures are above 200C), and where ordinary cement is used, forms may be struck after expiry of following periods.

Type of Form Removal Time Period
Walls, columns and vertical sides of beams 24 to 48 hours as may be decided by the engineer-in-charge.
Slabs (props left under) 3 days
Beam soffits (props left under) 7 days
Removal of props to slabs (Spanning upto 4.5 m) 7 days
Removal of props to slabs (Spanning over 4.5 m) 14 days
Removal of props to beams and arches (Spanning upto 6 m) 14 days
Removal of props to beams and arches (Spanning over 6 m) 21 days

 

For rapid hardening cement, 3/7 of the above period will be sufficient in all cases except vertical sides of slabs, beams and columns which should be retained for 24 hours.

All formworks should be removed without shock or vibration as this would damage the reinforced concrete. Before the soffit and struts are removed, the concrete surface should be exposed, where necessary in order to ascertain that the concrete has sufficiently hardened. Proper precautions should be taken to allow for the decrease in the rate of hardening that occurs with all elements in the cold weather.

Reference

IS-456 – Plain and Reinforced Concrete – Code of Practice

Also Watch This Video on Increasing Repetition of Plywood

20 thoughts on “WHEN TO REMOVE CONCRETE FORMWORK?”

    • Hi, You should gently release the wedges to the arch centre the next day and keeping the arch centre in position lower it a few millimetres. This will allow the mortar between the bricks to compress and increase the bond strength with the surrounding masonry.

      Reply
  1. i am building a rcc tank 2 lakh litres. its height is 2.5metres. i am going first for its side upto 1.2m in the first step. can i remove the form work in a day and go for the next step.??8

    Reply
  2. I think there is a mistake in the striking time for Vertical formwork to Columns, walls, Beams is 16 to 24 hrs instead of 24 to 48 hrs as you have mention in your blog.

    best Regards
    Ali

    Reply
  3. While filling the RCC column (with Box) with concrete, should it be filled to the full height of the column in one stretch? The common domestic construction practice is the column box is mounted ti half the height of the column filled with concrete on one day, and box is dismantled after setting and again mounted up to remaining top half and filled with concrete on another day.
    Is it a correct practice?
    My doubt is that will there be proper bonding between the already set concrete layer with the concrete poured over that then.
    Request clarification from Civil Engineers please

    Reply
    • prithvi , I am civil engg. but as per my thinking you should go for single fill of column e.g 7 or 8 feet rather than two half fills if appropriate size firma is available and have longer vibrator reach. 4 feet firma plates are more commonly available and so are 1.5m (5 feet) vibrators. make sure the condition of firma plates is good and no broken backing strips so that you can get better vertically straight columns. cost of 5 feet vibrator is 3500 in Mohali/Punjab and 6m set is around 10,000.

      On joint front, you will always have joints here or there, the whole building will not be casted in single go. so avoid if possible but not to be feared.

      Reply

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