Why driveways end up striped
Cleaning a slab by hand with a lance means every pass has slightly different pressure, distance and speed. The overlaps clean more than the middle of each stroke, and once the concrete dries you get the tiger-stripe pattern that is more noticeable than the dirt was.
A rotary surface cleaner holds the nozzles at a fixed height and rotation speed, so the whole slab receives an identical amount of energy. That is the entire difference between a driveway that looks professionally done and one that looks scrubbed.
