Clean Freaks Co. Pool deck care in Atherton.

An Atherton pool surround sits in a difficult microclimate. Mature redwood, oak, and bay canopy holds moisture against the deck long after the marine layer burns off elsewhere on the Peninsula, and that persistent damp is exactly what black algae, gloeocapsa, and slick biofilm need to colonize a horizontal stone surface. The problem is rarely visible dirt — it is a thin organic film that darkens grout lines and pooled low spots and makes wet travertine or flagstone genuinely hazardous underfoot, right where children and guests move barefoot around water.

Material makes the work unforgiving. A single deck often runs travertine or limestone coping into exposed aggregate, brick, and a poured-concrete apron, and each behaves differently under a wand. Travertine and honed limestone are soft, calcareous, and easily etched or flame-pocked by too tight a tip; exposed aggregate loses its cement matrix and sheds stone when overpressured; brick coping spalls at the face. Meanwhile the joints between pavers hold sand and mortar that a careless pass will blow out.

Then there is the chemistry layer specific to a pool. Chlorine and saltwater splash, sunscreen and body oils, plus leaf and pollen tannin from the overhanging canopy, all bond into the stone’s pores and behave nothing like patio grime. Lifting them without bleaching the surrounding planting or driving residue into the pool takes a controlled, deck-specific approach, not a driveway rig turned sideways.

1. The partner identifies every surface around the water first — travertine or limestone coping, exposed aggregate, brick, poured concrete — and sets a separate pressure and tip for each, because the soft calcareous stone at the coping cannot take what the concrete apron shrugs off.
2. Organic growth is killed with a dwell-time soft-wash step, not blasted. A controlled sodium-hypochlorite or oxygen-based solution is applied to break down black algae and biofilm at the root, so the stain does not simply return with the next fog cycle.
3. Rinsing is directed and metered to protect the pool chemistry and the surrounding planting — runoff is kept clear of the water and of the drought-adapted beds and mature root zones that define a Peninsula estate garden.
4. Grout and paver joints are cleaned at low pressure and re-sanded where the pass exposes them, and soft stone is finished to restore even tone rather than left with wand-track striping across the deck.

• Late April through May, once the wet Peninsula winter has ended and before pool season opens, to strip a full season of shade algae and set clean footing for summer use.
• After the marine-layer months (May through August), when weeks of morning fog under a redwood canopy have re-darkened grout lines and low spots faster than the sun can dry them.
• Late October into November, after oak and bay leaf drop but before the first sustained winter rains, to clear tannin and organic litter before it stains soft stone over the wet months.
• Before a spring or summer gathering, when barefoot guests and children will move across a deck that reads clean but is slick with biofilm in the shaded zones.
• When a soft stone surround shows uneven darkening or a prior contractor’s wand striping, and the deck needs a corrective, material-appropriate pass rather than another aggressive blast.