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Beoordeeld door Tom ReillySenior Editorial Reviewer — Roofing, Carpentry & General Contracting
Who to call · Hilversum

Green algae or mildew on sidingHilversum, Noord-Holland

Green or black streaks on vinyl, wood, or fiber-cement siding are usually algae (Gloeocapsa magma) or mildew colonies fed by moisture and shade. Left alone they trap moisture against the surface, accelerating rot in wood and degrading paint. A professional pressure washing ($200–$500 for an average home exterior) removes these growths in 2–3 hours using a soft-wash technique — low pressure (under 1,500 PSI) with a sodium hypochlorite or oxygen bleach solution that kills spores without damaging siding. Standard high-pressure washing can force water behind siding laps on vinyl and splinter softwood grain, so soft-wash is the industry standard for building exteriors.

Who to call

For this problem in Hilversum, call a: Schoonmaker

Vind een Schoonmaker in Hilversum

Symptoms to look for

  • Green, black, or dark streaks on siding that don't wash off with a garden hose
  • Siding feels slimy or slippery to the touch in shaded areas
  • Discoloration worsens on north-facing walls or under trees
  • Musty outdoor smell near the house foundation

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