When should concrete blocks in a basement not be drilled and treated?

The correct choice indicates that concrete blocks in a basement should not be drilled and treated just after a hard rain because the soil is likely saturated, which can lead to increased water movement and moisture levels in the area. When the ground is wet, drilling into the blocks may cause moisture to enter the treated area, reducing the effectiveness of the treatment and potentially allowing water to flow into the space being treated.

In contrast, treating during dry weather would provide optimal conditions for the treatment to adhere properly and yield effective results. Drilling before a hard rain could also be problematic, but it is preferable to do so when the weather allows adequate drying and sealing. Winter months can pose challenges, primarily because colder temperatures can affect chemical treatments. However, the immediate effect of a recent heavy rainfall creates the most concern regarding moisture intrusion during treatment.