Wrong nozzle tip. A wide-angle nozzle spreads pressure too thin to cut through embedded grime. Concrete needs a concentrated 25° or 15° tip to actually lift dirt out of the pores.
No pre-treatment. Mold, algae, and oil stains need a detergent with dwell time before any pressure is applied. Skip that step and you're just pushing dirty water around the surface.
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Get a Free Pressure Wash QuoteMoving too fast. Rushing the wand without overlapping passes leaves visible stripe marks — the telltale "zebra" pattern of a rushed job.
Low PSI equipment. Consumer-grade pressure washers top out around 1,800 PSI. Professional concrete cleaning typically requires 3,000+ PSI to fully restore the surface.
Skipping the post-rinse. Detergent residue left on the surface dries cloudy and leaves a film. A proper job always finishes with a clean-water rinse.
In South Florida, the combination of limestone in the soil and hard water means mineral deposits will also streak the surface if they're not properly neutralized at the end of the wash.
A truly clean driveway should look 2–3 shades lighter than when you started. If it doesn't, the job wasn't finished right.