Clean Freaks Co. Paver cleaning in Los Altos Hills.

Los Altos Hills sits in the marine fog belt on the eastern flank of the Santa Cruz range, and that changes what grows on a paver field. Overnight fog drip and long, wet Peninsula winters keep the surface damp for hours after the sky clears, and damp masonry on a shaded grade is where black algae, moss, and lichen colonize the joints. On a graded driveway the problem compounds: water sheets downhill, so the lower courses and the base of every terrace step stay wettest and stain first, while sand-set joints slowly wash out along the fall line.

Then there is the oak canopy. Coast live oaks shed leaf litter, catkins, and a fine tannin-rich debris nearly year-round, and where that organic layer sits on porous pavers it leaves brown tannin bleed that a garden hose only spreads. Clay brick, tumbled concrete pavers, and natural stone each drink that staining at a different rate and tolerate a different jet — clay chips and stone spalls under the pressure that tumbled concrete shrugs off.

This is why a hillside paver field is its own category. It is not a pressure job, it is a reading of grade, joint condition, canopy load, and material porosity before a single trigger is pulled — and a plan for where the lifted debris and rinse water are allowed to go. Get the pressure wrong on a shaded, moisture-laden field and you strip the joints, etch the stone, and drive water into an already saturated base; get the chemistry and the runoff plan right and the field comes back clean without a hint of the growth returning by the next fog cycle.

1. The partner identifies the paver material and joint type first — clay brick, tumbled or smooth concrete, or natural stone — and matches pressure and nozzle to it, favoring surface-cleaner passes and soft-wash chemistry over a raw jet that spalls stone and blasts sand from the joints.
2. Black algae, moss, and fog biofilm are treated with a dwelling sodium-hypochlorite or biocidal solution before any rinse, so the growth is killed at the root rather than smeared across the field and left to regrow within a season.
3. Oak tannin and organic bleed get a targeted pre-treatment on the stained courses, worked with the grade so the lifted color rinses downhill and out rather than settling into the lower terrace joints.
4. Because the run is graded, the partner plans the rinse path and runoff first — protecting drains, planting beds, and the downhill slope — then re-sands the swept joints and, where wanted, discusses resealing once the pavers are fully dry.

• Late spring, once the wet season closes — the winter’s moss and black algae are at their peak and the pavers finally dry long enough to clean and reseal.
• Early fall, before the rains return — clearing biofilm and re-sanding joints ahead of the wet months keeps water moving and slows regrowth over winter.
• After the heaviest oak shed — once catkins and leaf litter have dropped and been cleared, so tannin does not bleed into the stone through a wet winter.
• When the joints on a graded run start washing out — a sign the fall line is channeling water and the field needs cleaning and re-sanding before erosion undercuts the base.
• Ahead of spring or autumn entertaining — when terraces and motor courts should read clean and dry for guests.