When Should I Strip Concrete Formwork?
Being able to strip concrete formwork quickly offers the advantage of allowing you to cycle forms efficiently and reach project completion faster. Removing forms prematurely, however, can cause damage to concrete structures and result in costly rebuilds. In general, concrete formwork can be stripped at the point in which concrete becomes strong enough to support its own weight as well as the weight of any loads it will need to carry. The correct time to strip concrete depends on a number of factors, including the type of formwork, the type of concrete, and even weather conditions. Below are some general recommendations to help you determine when you can strip formwork.
Consider Load Strength
Concrete should be cured until it reaches its required load strength before formwork is removed. Keep in mind that larger concrete sections may cure faster than those of smaller sizes. Large concrete columns and walls may reach required load strengths within 24 hours, but small beams and slabs can take a few weeks. The grade of concrete should also be taken into consideration. Concrete of higher grades will typically reach necessary strength at an accelerated pace. The American Concrete Institute provides specific recommendations for certain grades of concrete that should be followed when determining the appropriate time to remove formwork.
Factor in Temperature
If it’s too hot outside, concrete may dry unevenly and cause structural problems. Likewise, challenges in the concrete curing process can also occur when temperatures are too low. It’s best to plan concrete pours around extreme weather and avoid them if at all possible when the temperature is too high or too low. The best temperature range for reliable concrete curing is between 50- and 90-degrees Fahrenheit. If you do a pour in temperatures outside this range, it becomes even more important to properly monitor concrete as it sets and test its load capabilities before formwork is removed.
Monitor and Test Concrete
A good way to assess concrete maturity to determine if formwork can be removed is to conduct cylinder testing. This involves curing a cube or cylinder of concrete separately from the main concrete structure and testing its composition and strength to help you estimate the composition and strength of the main concrete structure. A testing method like this can be very helpful in allowing you to determine if it’s time to strip formwork, especially if you are unsure about how factors like outside temperatures may be affecting the curing process. Just keep in mind the difference in curing times among concrete structures of different sizes.
Strip Formwork Properly
Once you determine it’s the appropriate time to strip formwork, take extra care to do so properly. Have a plan in place for formwork removal. It’s often best to use wood wedges rather than crowbars to detach the forms from the dried concrete. As you’re stripping formwork, inspect the concrete thoroughly to ensure that there are no issues that need to be addressed or repaired.
When formwork is removed, make sure to promptly remove any concrete residue and apply a release agent before you put forms in storage or continue to cycle them for your project.
Stripping formwork should be a relatively smooth process if you time it well. Keep our suggestions above in mind when figuring out when to strip and be aware of the specifics of the grade of concrete and type of formwork you’re using.
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