Lichen, algae, and organic staining removed from natural stone. Patios, walkways, pool surrounds — Palo Alto properties from Old Palo Alto to Crescent Park. Stone texture preserved. Free estimates.
★★★★★ 5.0 stars · 80+ reviews across Google and Yelp
Palo Alto's mature tree canopy — oak, redwood, liquidambar — creates shaded conditions that accelerate biological growth on stone surfaces. Flagstone patios and walkways on properties throughout Old Palo Alto, Professorville, Crescent Park, and Midtown sit in partial to full shade for significant portions of the day. That shade, combined with Bay Area fog, irrigation overspray, and seasonal rainfall, creates ideal conditions for algae, moss, and lichen to colonize porous stone. What starts as a slight darkening becomes thick biological growth that makes surfaces look neglected and creates a genuine slip hazard when wet.
Flagstone isn't a single material — Palo Alto properties have sandstone, limestone, quartzite, slate, and bluestone, each with different surface hardness and porosity. Blasting soft limestone with the same pressure used on concrete strips the stone face and destroys the material. We assess the stone type before touching anything and adjust PSI and nozzle angle to remove the biological growth without damaging the surface or blowing out mortar joints.
Algae — the primary cause of that slick dark film on shaded patios. Lichen — the gray-green crust that bonds to stone and is far more tenacious than surface-level algae. Moss — concentrated in moist areas, joints, and low-traffic sections. Organic staining from leaf tannins, dirt compaction, and irrigation buildup. The stone underneath is still there — a proper cleaning reveals it.
Ready for a free flagstone cleaning estimate in Palo Alto? Call or text — same-day response.
Stone type identified — sandstone, limestone, quartzite, slate. Condition of mortar joints, existing cracks, and depth of biological growth evaluated before any water or pressure is applied.
For heavy lichen or algae colonization, a pre-treatment solution is applied to break down biological growth before pressure washing — this reduces the pressure required and protects the stone surface.
PSI and nozzle adjusted to match the stone. Soft limestone cleaned at lower pressure. Harder quartzite and slate can handle more. Surface technique avoids blasting mortar joints or stone edges.
Mortar joints and stone edges cleaned without eroding material. Crumbling mortar is flagged and reported before we start — we don't mask pre-existing conditions.
Full surface rinse to clear suspended debris and cleaning agent. Surface inspected for missed biological growth, remaining staining, or areas that need a second pass before we call it done.
Walk-through with the homeowner. Any remaining staining noted — some deep tannin or iron staining requires specialized treatment separate from pressure washing. We tell you what's possible and what isn't.
Natural stone cleaned without damage. Call or text for a free Palo Alto flagstone estimate.
Palo Alto flagstone cleaning — lichen, algae, and organic buildup removed from natural stone surfaces. Stone color and texture restored.
Same result on your Palo Alto property. Call or text for a free flagstone cleaning estimate.
Straight answers for Palo Alto homeowners. Don't see yours? Call or text (408) 598-1857.
The main culprits are algae, lichen, and moss — driven by the Bay Area's mild climate and seasonal moisture. Flagstone in shaded areas, under tree canopy, or near irrigation builds up biological growth consistently. Left untreated, it becomes a slip hazard and accelerates staining deeper into the stone.
Yes — but pressure calibration matters. Natural flagstone varies significantly in surface hardness. We adjust PSI and nozzle angle based on stone type. Soft limestone gets treated at lower pressure than harder quartzite or slate. The goal is removing the biological growth without stripping the stone's surface texture or blasting out mortar joints.
Yes — any flagstone or natural stone exterior surface. Patios, front and back walkways, driveway aprons, pool surrounds, steps, retaining walls. If it's outside and it's stone, we can clean it.
We treat them carefully. Deteriorated mortar joints can be eroded at higher pressures. We use controlled angles to clean the stone face without degrading the joints. If mortar is already crumbling when we arrive, we'll point that out before we touch anything.
In most cases, yes — significantly. Lichen and algae staining can make flagstone look decades older than it is. Once removed, the original stone color comes back. Deep iron or tannin staining may require a specialized treatment — we assess on-site and tell you what's possible.
Yes. Bull Run Exterior Wash LLC is fully licensed and carries general liability insurance on every job.
Call or text (408) 598-1857. Estimates are free and scheduling typically runs 3 to 10 days out. We serve Palo Alto, Menlo Park, Los Altos, Mountain View, and the rest of the South Bay and San Mateo County.
> free estimate // palo_alto // same_day_response