How Long Should You Wait to Remove Concrete Formwork?

The forms can be removed once the concrete inside the molds has hardened and cured. Deshuttering, striking off, and stripping are terms that are sometimes used to describe this procedure.

Formwork is frequently required when pouring concrete for a garage, wall, or other home improvement project since the concrete must be kept in place until it hardens. While some formwork is permanent, the majority of formwork is just temporary and should be removed once it is no longer required.

You may be wondering how to speed up the concrete formwork removal process if you are working on a project involving many forms. It is important to know how long you need to wait and under what conditions you can safely remove the form.

As a result, you can better plan removal on a timeline that doesn’t slow down your project. Every job site will have a different length of time the formwork should remain in place. The type of cement, climate, the admixtures, and the size of the forms and structure will all have an impact on the finished concrete structure.

when to remove formworks?
Deshuttering Forms

Guidelines for Formwork Removal

In general, the American Concrete Institute (ACI) recommends the following:

  • ASTM C 150 Type I Cement : 7 days
  • ASTM C 150 Type II Cement : 10 days
  • ASTM C 150 Type III Cement : 3 days
  • ASTM C 150 Type IV or V Cement : 14 days
  • ASTM C 595, C 845, C 1157 Cement : Varies

Moisture and temperature must be monitored and maintained in the formwork during curing. It is very important to leave the formwork in place for as long as possible. By keeping the formwork intact, it serves as insulation which helps in curing the concrete.

The engineer should be present during the removal process, and all state and local rules should be followed.

A closer look at some guidelines can be done for specific structures. Make sure the site engineer knows the exact timeframe required for your concrete form removal to cure properly.

Here are some general rules when to remove concrete forms for Ordinary Portland Cement (OPC):

  • Walls and columns vertical formwork can be removed after 24 to 48 hours
  • Typically, slabs with props under them can be removed after 3 to 4 days
  • If the props are left under the soffits, they can be removed after one week (7 days)
  • Props support for concrete slabs under 15 feet (4.57 meters) can be removed after one week (7 days)
  • Removing formwork for soffit and props supporting slabs over 15 feet (4.57 meters) is after two weeks (14 days)
  • Props attached to beams and arches under 20 feet (6 meters) can be removed after two weeks
  • For beams and arches over 20 feet (6 meters), the props can be removed after three weeks (21 days)
  • Formwork can be removed 10-7 of the above times when Portland Pozzolana Cement (PPC) is used.

Concrete does not reach its maximum sufficient strength when the moisture content is disparity during the curing process. If the water integrated into the original mix evaporates from the surface, cracking may occur because the balance between the interior and the surface of the concrete is not restored.

The concrete must also be poured at the proper temperature (greater than 50 degrees Fahrenheit is a general guideline), so ideal weather conditions and a good forecast are crucial.

Curing concrete is accomplished by keeping the concrete constantly wet, protecting the surface from evaporation, or by applying a chemical compound. For water curing, spray it with water after new concrete is poured and finished where the curing process begins.

Concrete Formwork: Safe Stripping/Striking off

Form removal is recommended only when the concrete strength is gained to carry its dead weight without the further help of formwork or any props.

Be sure to plan ahead before removing forms, since doing so can cause cracks, sagging, and structural instability.

Remember that concrete reaches 70% of its final cure strength in 7 days but will take about 28 days to cure completely.

When using wood formworks, treat it properly with a form release agent or commercial oil to easily pull them away after the concrete dries.

Concrete form oil is a mixture of special release agents and light-colored mineral oils that will react with the concrete to form a barrier preventing the concrete from adhering to either plywood or steel forms.

deshuttering/striking of formworks

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