Power washing concrete surfaces can cause real problems. Relatively inexpensive high-pressure power washing units are commonly available. Some of those units can deliver water at pressures well in excess of 6,000 pounds per second (psi)!
Moreover, it is not just high-pressure water that’s the problem. The water exits the nozzle at both a high pressure and a high velocity. The resulting momentum is great enough to dislodge not only dirt and debris but also to create flakes, popouts, and even concrete spalls. Good quality concrete will also experience accelerated wear from high-pressure power washing.