The Quick Answer
- Green film and black spots are surface growth, not damage — they clean off with the right chemistry.
- Shaded, damp zones (north sides, under trees, by the pool cage) grow first; check them monthly in summer.
- High-pressure blasting strips joints and scars surfaces — soft-wash methods clean without collateral damage.
- A sealed surface through rainy season stays a rinse-clean; an unsealed one becomes a restoration project.
01
The summer watch list
Walk the shaded zones monthly June through September: the north side of the house, under oak canopies, the pool deck corners the cage keeps damp, and anywhere irrigation overspray lands. Growth caught as a light film is a maintenance rinse; growth left until October is embedded in the surface texture and needs professional chemistry.
02
When to call it in
Black algae speckling that survives a scrub, rust bleeding from furniture or well water, oil on the driveway, or tannin shadows under leaf piles — these are treatment jobs, each with its own chemistry, not more-pressure jobs. And if any surface has gone slick underfoot, treat that as urgent; algae on a pool deck is a genuine slip hazard.
How It Works
Why soft-wash beats blasting
Mold and algae are killed by chemistry, not pressure — a sodium-hypochlorite-based soft wash applied at low pressure kills growth at the root, rinses clean, and leaves joint sand and surface texture intact. High pressure just mows the growth (it returns in weeks from what's left behind) while blasting sand from joints and etching wand-stripes into softer materials.
Stain-specific treatment
Rust wants oxalic-acid-based removers; oil wants degreasers and sometimes poulticing; tannins bleach out; efflorescence needs specific salt-dissolving cleaners; irrigation staining depends on your water's iron. Matching chemistry to stain is most of the professional's value — the wrong cleaner sets some stains permanently.
Where It Goes Wrong
The pressure-washer scars
Wand stripes, etched swirls, and emptied joints — the signature of a rushed pressure job — are permanent on many surfaces. Travertine and softer stone mark especially easily. If a cleaning quote is dramatically cheap and leads with 'high-power pressure washing,' the discount is coming out of your surface.
Bleach mistakes around the landscape
Straight bleach dumped on pavers kills the growth and the flower bed downhill of it, and can lighten some surfaces unevenly. Professional soft-washing dilutes to effective-but-controlled strength, pre-wets and rinses landscaping, and neutralizes runoff. Chemistry with a plan beats chemistry from a jug.
Ready for the next step?
Bring the question to the crew that does the work.
Common Questions
