How to clean and control mold and mildew on exterior bricks
What You Will Need to Clean Mold and Mildew from Brick Surfaces
Cleaning Agent. The best cleaner for mold and mildew is household bleach. A safer and green alternative is an "oxygen bleach" like StainSolver. Oxygen bleach is a fume-free powder that is mixed with water. Chlorine bleach works faster than oxygen bleach, but oxygen bleach is safer when used near vegetation. Bleach will be mixed with water so an outdoor spigot and garden hose are needed. Powder or liquid laundry detergent, or grease-cutting liquid dish detergent used when hand washing dishes will lessen the fumes of bleach while adding cleaning potential to the mixture.
Tools. Cleaning bricks on a flat surface, like a patio, may be accomplished with a stiff broom, bucket, and garden hose. For large areas, consider renting or buying a pressure washer. Keeping on top of mold and mildew will be an on-going process that could make purchasing a pressure washer worthwhile. Stubborn build-up will require a utility brush with wire bristles. Tackling mold or mildew on tall, vertical surfaces, like the side of a house or a chimney, will require a ladder. If using bleach, a plastic tarp like that used to cover floors and furniture when painting will be needed to protect vegetation.
Before You Start
Dress appropriately. If working with bleach, be sure the clothes you choose to wear are some that you will not mind getting bleach stains (color fades). Working with a power washer creates a spray and you will most likely get wet so wear water proof boots or old shoes, like tennis shoes. For safety, wear goggles, rubber gloves and a hat.
Protect Landscaping. Whether using chlorine bleach or oxygen bleach, wet the ground around the area where you will be working before covering the vegetation. The wet ground will help to dilute any runoff from the cleaning process.
How to Clean the Bricks
Bleach Mixture. When using chlorine bleach, start with a ratio of one part bleach to three parts water. Use about 1 to 2 teaspoons of detergent (powder or liquid laundry detergent, or grease-cutting liquid dish detergent like Dawn) to each gallon of water/bleach. If using an oxygen bleach product, follow the instructions on the container.
Small or Low-Level Cleaning. When cleaning a flat surface or short vertical surface (like a brick wall), use the broom or wire brush and a bucket of water with bleach. Begin by spraying the surface to dampen the bricks. Dip the broom or brush into the bucket and apply light pressure as you scrub the bricks. Let the mixture remain on the bricks for at least 10 minutes and then rinse off with the garden hose. Some areas may need a second treatment. For intense build-up of mold or mildew, increase the ratio of bleach to water to 50:50.
Large or High-Level Cleaning. Add the bleach/detergent mixture and water to the pressure wash reservoir. Follow the manufacturer's directions for the angle to hold the spraying wand. For areas of build-up, adjust the wand to concentrate pressure; otherwise, a wider spray pattern can be used. Rinse the surface with water.
Remember the Landscape. Carefully fold the plastic used to cover foliage to contain the bleach solution. Carry the plastic to an area where you can unfold the plastic to allow it to evaporate, like on a driveway. Spray the foliage with water again to ensure no bleach solution is lingering and to further dilute solution that made it to the ground.
Control Mold and Mildew on Bricks
Keeping brick surfaces mold and mildew-free is an ongoing process. When the first signs of mold or mildew appear, use the same process to clear it away. After the initially cleanup, following application should require less effort and less bleach.