What is the minimum time to read a calcium chloride test before installing carpet?

The correct answer is 24 hours because this time frame allows for an accurate assessment of the moisture levels in the concrete substrate. A calcium chloride test is used to measure the moisture vapor emission rate of concrete, which is crucial for determining if the slab is suitable for carpet installation.

By waiting 24 hours after placing the calcium chloride test kit on the concrete, the contractor ensures that the test results reflect the substrate's moisture conditions under typical installation circumstances. Testing for a shorter duration might not capture fluctuations or unusual moisture conditions, leading to potential failures in the flooring installation and subsequent issues such as mold growth or adhesive failure.

While the other response options suggest longer times, they exceed what is typically necessary for a reliable reading and could delay the installation process unnecessarily. Therefore, a 24-hour reading strikes the appropriate balance between accuracy and efficiency in preparing for carpet installation.