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Those Stubborn Black spots on siding!

Ryan Cash

UAMCC Associate Member
What are those Black spots on the siding?
What is Artillery Fungus?,
How do I remove these black spots on the side of this home?

The first and most important step in cleaning anything is stain identification. Knowing what you are dealing with will allow you to properly clean and remove it. While in the field, we can never be 100% confident in our assessment, it’s absolutely vital to have an understanding of the most common things that will be found on a home.

If you’ve ever been to a home that has small black spots all over the lower siding, it’s most likely a type of fungi called Spharebulus Stellatus, or more commonly known as Artillery Fungus, Shotgun Fungus, or Cannonball Fungus.


It typically develops and thrives on rotting wood and dark colored mulch in moist environments. This specific species builds up liquid inside it’s flowering body until it bursts open, discharging spores up to 20 feet away. The discharged spores are extremely sticky and adhere to whatever surface they land on (siding, windows, cars, etc.)

As the spores dry out on the building, they begin to harden and become more difficult to remove the longer they sit. They eventually become so hard that they are almost the equivalent of super glue.

Unfortunately, there is currently no chemical solution/fungicide on the market to easily remove these fungi spores, so mechanical removal is the only option. While the use of Sodium Hypochlorite (chlorine bleach) may kill the spores, they will remain glued to the wall even when dead.

There are several options for removing the spores but none of them are easy. Because of this, most contractors choose to avoid this work and instead educate the customer about it's cause.

If you choose to attack the spores though, prepare for a very labor intensive job and charge accordingly.

A few tools that may help along the way:

  1. Razor blade (removal of spores on glass)
  2. 0000 Steel Wool (buffing remnants of spores off glass)
  3. Plastic Putty Knife- removing bulk of spores from siding
  4. Melamine Foam (Magic Erasers) for buffing out residue on siding

Avoid using high pressure on siding, as the pressure required to remove the spores will be strong enough to damage the siding as well. Hot water and a good surfactant will absolutely help with the removal as well.

Whether you choose to attempt this cleaning or not, it’s most important to talk to the customer about the stains, what causes them and hose to avoid them in the future.