Mold, Mildew & Algae: The Difference—and How Power Washing Removes All Three

Chelsey Smith • November 23, 2025

If you’ve ever noticed green, black, or white patches forming on your home’s exterior, you’re not alone. Hamilton’s humid summers and wet seasonal transitions create the perfect environment for mold, mildew, and algae to thrive.



While they may look similar, each has its own risks — and the right cleaning method matters. At Clean Start Exteriors, we specialize in identifying and removing all three using safe, effective power washing techniques.

Here’s what you need to know.

Mold vs. Mildew vs. Algae: What’s the Difference?

1. Algae

Appearance: Green or greenish-black streaks
Found on: Siding, decks, gutters, stone, rooflines
Cause: Sunlight, moisture, and organic buildup


Algae doesn't usually damage surfaces immediately, but it spreads quickly and makes your home look neglected.


2. Mildew

Appearance: Powdery, grey, or white patches
Found on: Shaded siding, fences, trim
Cause: Damp, poorly ventilated areas


Mildew is easier to remove but is often a sign your home needs a deeper clean.


3. Mold

Appearance: Thick, black or dark green patches.

Found on: Wood, siding, trim, under eaves
Cause: Moisture trapped under surface layers


Mold is the most serious of the three. It can cause structural damage over time and is harder to remove without specialized treatment.


Why Power Washing Is the Solution

Power washing isn’t just about blasting off dirt. When done properly, it:

  • Removes organic buildup
  • Kills the root growth
  • Prevents regrowth
    Restores a clean, fresh exterior

However, not all surfaces should be high-pressure washed. At Clean Start Exteriors, we use:

  • Soft washing for siding, roofs, and delicate surfaces
  • Power washing for concrete, stone, and durable materials


This ensures the contaminants are removed without damaging your home.


Why These Growths Form More Easily in Hamilton

Hamilton’s weather patterns create the perfect recipe for buildup:

  • High humidity
  • Heavy rain
  • Moisture trapped behind siding
  • Shaded areas that never fully dry
  • Pollutants from urban and industrial areas


This means most homes need annual or biannual exterior cleaning to stay ahead of mold, mildew, and algae.


Signs Your Home Needs a Professional Cleaning

You may notice:

  • Green streaks on siding
  • Black patches forming on trim
  • Slippery deck surfaces
  • White, powdery buildup
  • Musty smells near exterior walls

If any of these sound familiar, a deep clean from Clean Start Exteriors can make your home look new again—and help prevent long-term damage.


Why Hamilton Homeowners Trust Clean Start Exteriors

We remove mold, mildew, and algae using a proven process:

  1. Inspection – Identify what type of growth is present
  2. Surface Protection – Safeguard plants and landscaping
  3. Targeted Treatment – Apply specialized cleaning solutions
  4. Soft or Power Washing – Clean with the correct method
  5. Rinse + Prevention – Apply optional anti-growth treatments


The result? A spotless, sanitized exterior with longer-lasting results.


The Bottom Line

Mold, mildew, and algae aren’t just cosmetic issues — they’re signs your exterior needs attention. If you want your home to look its best and stay protected, trust the professionals.


For reliable, effective power washing in Hamilton, Clean Start Exteriors delivers every time.

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