Moss and mold will grow anywhere they find favorable conditions, so they're often found growing on brick walkways, retaining walls, patios and chimneys. Moss has a shallow root system, and both moss and mold produce thousands of tiny spores that are quickly distributed by wind and rain. This allows them to establish and spread easily on your brickwork.
When you see moss growing anywhere in your landscape, you’re seeing a mass of tiny plants called bryophytes. It will grow on almost anything, including bricks, tree bark and soil. Mosses prefer shaded, moist conditions and appear on bricks as yellowish, green, or greenish-brown tufts or mats. They usually remain dormant if conditions are dry, buy are revived during rainy cycles. Mosses growing on brick generally don’t cause serious damage, but in some areas it looks unattractive or has grown out of control.
Prune trees and shrubs that overhang your brickwork to let more sunlight and air in. Use a stiff-bristled brush to scrub away existing layers of moss. A pressure washer may also be effective, but test a small area first and spray at a low angle across the brick joints instead of straight into them. Pressure washers can do a lot of damage, particularly to old brickwork. You can also buy moss-killing sprays at hardware stores and garden centers. These come in bottles designed for use with a garden hose. Attach the end of your garden hose into the hose end on the sprayer bottle, and then turn on the water. Squeeze the trigger on the moss killer bottle to spray the brickwork. The water automatically mixes with the herbicide in the bottle as you spray. Thoroughly soak the area with the moss killer. Repeat treatment yearly, or when new moss growth appears.
Mold spores need only a small amount of moisture, nutrients and temperatures that range between 50 and 75 degrees Fahrenheit to thrive. Mold lives on dead organic matter that you can’t see, such as the dusts and vegetation on brickwork. If you find green, black or brown slime growing on your bricks, it is likely a combination of mold and algae. Mold is more common on porous materials such as drywall and wood because these offer more organic matter, but it will also grow on brickwork. Although it grows more slowly there than on other materials, mold can cover large surface areas of brick over time, particularly if there's inadequate airflow.
Remove any furniture and plants from horizontal brick surfaces, and prune away overhanging trees and shrubs from vertical services to allow more air and sunlight to the brick. Remove mold when it is dry to reduce the risk of spreading mold spores; wear a dust mask to avoid breathing in particles. Sweep the brick with a stiff broom or brush to remove as much surface mold as possible. Once you’ve removed as much of the surface mold as you can, mix a solution of 1 cup chlorine bleach per gallon of water and use it to kill any remaining spores on the brickwork. Bleach can discolor brick, so test a small hidden area before you apply. Alternatively, use 5 percent white vinegar, undiluted. Wash the entire area with either the bleach solution or the vinegar, and scrub joints with a soft-bristled brush. Rinse with clean water and let the brick dry thoroughly before replacing furniture and plants.