Black Stains on Brick: 5 Causes and Solutions

Brick structures provide a rustic, timeless aesthetic. However, you may notice unsightly black stains forming on your brick walls over time. Depending on the root causes, black stains can harm your brick structure’s integrity, damage mortar, and even pose health risks. When left untreated, black stains tend to lead to more severe masonry problems, which result in more costly repairs. That’s why you should know these five reasons that cause black stains on your brick and how you should remove them.

1. Accumulated Moisture

Excessive moisture can discolor your brick and cause black stains to appear. Sometimes the stain might appear to be dark green instead of purely black. Be alerted: these are not simple discolorations but mold clusters growing.

How to Remove

The most effective method for removing mold from brick is dry ice blasting. Dry ice can “burn away” mold and prevent it from coming back by absorbing any residual moisture. Since dry ice turns into carbon dioxide upon contact, it won’t damage the brick surface compared to other blasting media.

2. Lichen, Moss, or Algae

If you notice dark greenish stains on your brick, they might be lichen, moss, or algae. These types of stains tend to appear on brick surfaces that don’t receive sufficient sunlight, as lichen grows in moist, dark, and cool environments. You may also find lichen stains near drainage pipes.

How to Remove

You can use a garden house to spray a vinegar and detergent mixture onto the brick, then scrub the surface with a hard-bristle brush. You can also power wash bricks with a lower setting so you remove the lichen without damaging the brick’s porous, brittle surface.

3. Carbon Black Stains

Carbon emissions from cars and industrial factories can leave black stains on your bricks. These types of stains are common in larger cities or on buildings near factories and form as carbon particles set on the brick’s porous surface. Visually, they may vary from pure black to dark grey.

How to Remove

Rainwater naturally removes carbon stains over time, although in busy traffic areas, the stains will form faster than rain can remove them. In such cases, power washing is one of the most effective ways to remove carbon stains.

4. Pollution Black Stains

Pollution in modern life can also lead to black stains on bricks. These stains are a combination of oil, grime, chemicals, and dirt. They often appear at the bottom of a building, where cars pass by and particles sink and settle.

How to Remove

Due to their oily and chemical contents, pollution stains are hard to remove with water alone. Instead, you can try a bleach-water solution with a garden hose, then scrub the surface with a hard-bristle brush.

5. Paint Stains

If you notice black stains around freshly painted, dark-colored windows or door frames, they might be paint splashes. Other times, you may be dealing with spray-painted graffiti.

How to Remove

You can try to remove paint stains from bricks yourself. It is doable but extremely time-consuming. Therefore, it might be a lot easier for you to hire someone to clean up the paint stains. 

When to Call a Pro

There are several reasons why you might want a masonry contractor to remove the black stains from your brick walls:

• Accessibility: If you’re dealing with stains more on higher floors or on chimneys, it’s much safer to have a contractor do the climbing and cleaning

• Health concerns: You should let a professional handle harmful black mold stains, chemical pollution stains, and lead paint stains.

• Convenience and efficiency: Removing black stains from bricks can be extremely time-consuming and labor-intensive. Why spend over 15 hours cleaning when you can put that time into something else?

• Bricks are brittle: the porous nature makes brick surfaces brittle, and improper cleaning methods can damage the mortar and the bricks, leading to higher repair bills. A professional masonry contractor knows how to clean bricks. In the worst-case scenario, they’re insured to cover their own mistakes.

How to Prevent Black Stains From Forming

Regular brick maintenance is the best way to prevent black stains from forming. Primarily, this means seasonal cleaning and inspection for damages. Many masonry companies offer seasonal cleaning services that will give you peace of mind. Masonry contractors typically charge $40 to $100 per hour for basic projects.