CSLB General Building (B)Site Work, Foundations and ConcreteHard
A contractor pours a concrete footing and needs to know when it is safe to strip the wooden side forms without damaging the concrete. Assuming normal curing conditions (moderate temperature, no admixtures), what is a generally accepted minimum time before form removal for non-load-bearing footing forms?
- A5 to 7 days
- B2 to 4 hours
- C28 days
- D12 to 24 hours
Show answer & explanationAnswer & explanation
Correct answer: D. 12 to 24 hours
For non-load-bearing side forms on footings under normal curing conditions, concrete typically gains enough initial set and strength within 12 to 24 hours to allow safe form removal without damaging the edges, though the concrete continues to gain strength for weeks afterward.
Why the other options are wrong
- A. 5 to 7 days is excessive for simple non-load-bearing side forms, though appropriate for structural formwork under load.
- B. 2 to 4 hours is too soon; the concrete has not achieved sufficient initial set.
- C. 28 days refers to the concrete's design strength curing period, not form-stripping time.
Formwork Stripping Time
The minimum time concrete must cure before forms can be safely removed, varying by whether the form is load-bearing.
- Non-load-bearing side forms: typically 12-24 hours
- Load-bearing/structural forms (beams, slabs): several days to weeks
- 28-day cure is the standard for reaching design compressive strength
Memory trick: Side forms come off in a day; structural forms wait and stay.