Between 3 and 9 days
Concrete should be allowed to cure from anywhere between three and nine days, depending upon the temperature and moisture levels, according to the National Ready Mixed Concrete Association. Lower temperatures and higher moisture levels result in a longer curing time.
Seven to 28 days
According to Concrete Network, concrete should be allowed to cure for at least seven days before it's built on. However, waiting longer will greatly reduce the risk of the concrete cracking. Concrete continues to cure up to 28 days after it is poured, at which point it reaches maximum strength.
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When a contractor or engineer is in charge of a project, follow the professional's advice, since the result of curing is his responsibility, according to Builder Bill. For small, nondocumented jobs, wait a minimum of three days—although seven days is better, Builder Bill advises.