What's That Black Stuff Growing on my House?

Understanding the dark streaks, algae, and organic buildup commonly found on homes throughout Southwest Louisiana and Southeast Texas.

One day you look at your house and suddenly notice black streaks under the gutters or dark green patches on the siding. Most homeowners don’t notice buildup happening little by little until it becomes obvious.


Like a growing child, you barely notice the child in your own home growing, but the children of the couple you vacation with occasionally seem to shoot up like weeds. Dirt and organic buildup on a home can happen the same way. Since we see our own homes every day, gradual changes often go unnoticed until the staining becomes hard to ignore.


In SWLA & SETX, our heat and humidity create the perfect environment for algae and organic growth. The good news is that this is extremely common in our area.

WHAT IS THE BLACK STUFF?

Usually, it’s a combination of:


  • Algae
  • Mold
  • Mildew
  • General organic buildup


One common culprit is a type of algae called Gloeocapsa magma, which is often found on roofs but can contribute to staining on other exterior surfaces as well.


Algae thrives in humid environments, and Southwest Louisiana and Southeast Texas certainly provide plenty of humidity. Dirt, moisture, pollen, and airborne debris all contribute to the problem. Over time, what starts as a light discoloration can eventually become noticeable dark staining.


The longer algae and buildup are allowed to remain on a surface, the more likely they are to leave lasting stains. In severe cases, permanent discoloration can occur or stronger cleaning solutions may be needed later, which can shorten the lifespan of certain surfaces.



The good news is that most buildup doesn’t immediately damage a home. However, allowing it to accumulate for years can shorten the life and appearance of exterior surfaces.

WHY DOES IT GROW MORE ON CERTAIN SIDES OF THE HOUSE?

If one side of your house seems dirtier than the others, there’s usually a reason.


In many cases, the north-facing side of a home receives less direct sunlight throughout the day. Without as much sunlight to dry the surface, moisture tends to linger longer. That damp environment creates ideal conditions for algae and mildew growth.


Trees can also play a major role. Large oak trees and other shaded areas common throughout SWLA & SETX trap moisture and reduce airflow around the home. Add in our long rainy seasons, high humidity, and heavy pollen, and exterior surfaces can stay damp for extended periods of time.



That’s why homeowners often notice more staining on shaded siding, fences, patios, sidewalks, and driveways.

IS IT JUST COSMETIC OR CAN IT CAUSE DAMAGE?

At first, most algae and organic buildup are mainly cosmetic issues. The home simply looks older, dirtier, or less maintained.


Over time, though, buildup can contribute to longer-term problems. Organic growth can trap moisture against surfaces, increase staining, and create slippery conditions on walkways, patios, pool decks, and driveways.



Allowing buildup to remain for years can also contribute to premature aging and deterioration of exterior surfaces. While it may not seem urgent at first, regular exterior cleaning helps maintain both the appearance and condition of your property.

WHY HIGH PRESSURE ISN’T ALWAYS THE ANSWER

Many people assume tougher stains require more pressure, but more pressure doesn’t always mean better cleaning.


Improper high-pressure cleaning can damage siding, force water behind surfaces, leave oxidation marks, strip paint, and even etch concrete or wood. In some cases, the cleaning process itself can create more problems than the dirt.


That’s why professional exterior cleaning should focus on proper techniques, correct spray angles, and the right cleaning solutions for the surface being cleaned.



At Bayou Blast Brothers, we use safe, property-protecting cleaning methods designed to deliver results without damage.

HOW OFTEN SHOULD A HOME BE CLEANED IN SWLA & SETX?

Every property is different, but most homes in Southwest Louisiana and Southeast Texas benefit from professional exterior cleaning every 1–2 years.


Homes with heavy shade, large trees, poor drainage, or constant moisture exposure may require more frequent cleaning. Properties near busy roads, wooded areas, or areas with heavy pollen can also experience faster buildup.



Routine exterior cleaning not only improves curb appeal but also helps prevent long-term staining and surface deterioration.

FINAL THOUGHTS

Organic buildup is simply part of living in the humid climate of SWLA & SETX. Most homeowners don’t notice it happening until the staining becomes obvious, but regular exterior cleaning can help protect your home’s appearance and maintain its value.


The important thing is cleaning surfaces correctly using safe, property-protecting methods rather than relying on excessive pressure.


If your home is starting to show black streaks, algae, mildew, or organic buildup, Bayou Blast Brothers provides professional exterior cleaning throughout SWLA & SETX.


We offer free quotes for:


  • House washing
  • Driveway cleaning
  • Patios and sidewalks
  • Storefronts
  • General exterior cleaning


Send us a photo or contact us today to get on the schedule.

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