There are several things that cause brick to take on a black appearance. The most common factor is dirt and road dust. Homes that are located near factories are especially prone to blackening due to the level of heavy truck traffic and air pollution associated with industry. Brick can also appear black if it has been soiled with oil or if there are algae growing on the surface of the brick. Oil and algae require a little bit more effort than a standard cleaning for surface dirt. Look for tips on cleaning these substances in the "Tips" section of this article.
Spray down the brick with the water hose starting with the highest bricks and working your way down. Use long, sweeping motions to loosen the black dirt from the brick and flush it away. Continue spraying until the entire brick surface has been soaked.
Attach the detergent to the water hose and apply it to the brick liberally using the same sweeping motions outlined above. If your detergent cannot be applied with a water hose, simply spray it on the surface of the brick. Wait from five to 10 minutes.
Scrub any remaining black areas with the scrub brush, making sure to scrub in the direction of the brick texture.
Rinse the brick with long, sweeping strokes. Allow to air dry.
Inspect the brick for any remaining black residue. If black stains remain, repeat process or apply the techniques presented for cleaning oil and algae.
You can remove oil from brick by mixing up a paste of trisodium phosphate (TSP) and 1 gallon of water. Spread the paste over the oil, maintaining a thickness of about a ½ inch. Allow to dry. Scrape off the dried paste with a putty knife, and rinse the residue away with a water hose. To clean algae, scrape away the algae with a putty knife. Wet the brick with a water hose, and apply a solution of bleach and water. Wait one hour, and rinse. Repeat process until algae is completely gone. Scrubbing the surface with a scrub brush after soaking will help speed up the process.
Bleach may cause discolouration. Be sure to perform a spot test before using any cleaners or cleaning solutions that contain bleach. Power washing may cause brick to crumble.