The most common question we get from San Mateo homeowners isn't how much — it's how often. The honest answer is that it depends on the driveway more than the calendar. Two houses on the same street can be a year apart: one sits in full sun with no trees, the other faces north under a redwood and sees fog until eleven every morning. Here's how we tell which one you have.
The baseline for a sunny, open driveway on the Peninsula is once a year. Dirt, tire marks and the light grey film that builds up over twelve months come off easily, and a yearly clean keeps the concrete from ever getting to the point where stains have set. Spring is the natural time — after the rainy season, before the yard gets used.
Shade changes everything. Concrete that stays damp grows algae, and on the Peninsula, with our marine layer, a north-facing or tree-covered driveway can stay damp most of the year. That's the black and green film you see on the shaded half of a driveway, the one that's slick when it's wet. Those driveways need cleaning every six to nine months, and they need the algae treated, not just blasted, or it's back by the next fog season.
Trees add their own problems. Redwoods and pines drop tannin-rich needles that stain concrete brown; oaks drop leaves that leave dark outlines when they sit wet; fruit trees drop fruit. A driveway under a tree canopy should be cleaned every six months, and it helps to blow the leaves off it between cleanings so they don't sit.
Oil is a separate clock. A car that drips will re-stain the same spot every few weeks, and oil that sits soaks in. If you have a dripper, the fix is a drip pan or a piece of cardboard, and a hot-water degrease of the spot when the driveway is cleaned. Cold water — a rented machine or a garden hose — spreads oil, it doesn't remove it. That's why a driveway can look worse after a DIY wash.
What happens if you wait? Algae and moss dig into the surface and take more pressure to remove, which is harder on the concrete. Oil that's been down for a couple of years lightens but rarely comes out completely. Tannin stains set. And a driveway that's been black for three years usually can't be brought back to a uniform color in one visit; it takes a clean, then a season of sun, then another clean.
The simple test: look at the driveway from the street after a rain. If the shaded half is a different color from the sunny half, or if there's a green or black tint anywhere, it's due. If you can see individual oil spots from the sidewalk, it's due. If it's just dusty and even, it can wait until spring.
Whatever the interval, the method matters more. A rotary surface cleaner on flat concrete gives an even finish without the stripes a wand leaves; the edges, the garage apron and the sidewalk strip get done by hand; and the runoff is kept out of the storm drain. Text AQ Professional Power Washing a photo of your driveway at (650) 274-6797 and we'll tell you whether it's due and what it would cost — free, usually the same day.