How to Pressure Wash Brick and Mortar Walls

Homeowners often take great pride in a brick house and want it to look like new. Brick has been a popular choice for generations because of its rich, timeless look. Yet over the years, dirt, grime, and even moss can cause discoloration and make a home's exterior unsightly. Luckily, a pressure washer can restore brick to its former glory. Following the steps below will have that old brick looking new once again. 

This article walks through the steps needed to properly clean and restore a home's brick exterior to keep it looking new. 

Before You Clean 

A home's bricks should be treated with love and care. The most important thing to consider before attempting to clean brick walls is the operating pressure (PSI) intended for use. Older bricks and grout are not as strong as newer construction materials, and using too much pressure will result in cracks in the bricks or grout, which can lead to other more serious problems, like interior water damage and the difficulty of fixing cracks in the walls. 

Power washing brick can be rewarding if done with care, and it is recommended to use 800 PSI or lower, which is more than enough pressure to clean bricks adequately without causing damage to exterior walls. The user should not hover or stop moving when cleaning either, as prolonged pressure in one spot is usually what causes damage. 

Step 1. Patch the Mortar Anywhere Cracks Are Visible 

At least a week before cleaning, the first task is to patch any damaged mortar joints between the bricks and let them harden for at least 7 days. This will prevent water from seeping behind the brick and causing mold to form in the walls. 

While it may be difficult to wait when the goal is pressure washing, it is very important to maintain the structural integrity of the brick and mortar. The instructions included in the packaging should be followed for the correct ways to apply the mortar to the bricks. 

Step 2. Cover and Protect Outlets and Windows 

In order to properly protect the home, it is very important to cover all exterior electrical outlets, including any exposed electrical ports such as connections for an air conditioning unit, a transfer switch box for a generator, and any other type of electrical component that could be sprayed with water. Plastic wrap or bags and some tape or rubber bands should suffice. 

Additionally, all windows, trim, doorways, and other exposed exterior openings should be covered in areas where the bricks will be cleaned. Homeowners will appreciate this precaution if the spray happens to cross over a window while cleaning. 

Step 3. Wet the Brick 

The surface of the home should be thoroughly soaked. It is important to perform this step prior to applying any detergents, as it prepares the brick for cleaning. 

• Pro Tip: To ensure an even soaking, water should be sprayed from the bottom to the top of the house. This bottom-up motion helps to evenly soak all surfaces without it running down in uneven streams. This is different from the recommendation for cleaning siding, which involves washing top-to-bottom to prevent water from getting into the folds. 

Step 4. Apply Detergent 

A detergent specifically designed for cleaning brick or exterior siding should be chosen. Using the incorrect kind of detergent can cause dirt to stick to the mortar. The detergent should be applied to the brick by spraying from the bottom up to the top. 

The solution should be allowed to work into the brick for 5–10 minutes. The key to cleaning brick is less pressure and more detergent. Because bricks and mortar are porous, the detergent and water will soak in slightly. Providing plenty of detergent and water helps cover all areas where dirt may reach. Letting the soap do its job of loosening and moving the dirt out of the brick will make it cleaner and brighter. 

Step 5. Brush Tough Stains 

For extremely dirty and stained brick, a rotary scrub brush can be used. This is a less abrasive technique than using water at high pressure. It helps work the detergent into the brick and breaks up tough stains. 

Grease, moss, tree sap, and grass stains around the foundation (often from mowing) are difficult to remove. Scrubbing these kinds of stuck-on messes with a quality brick and mortar detergent can help to break up and loosen them. 

Step 6. Rinse the Bricks 

Once the detergent has sat and had time to work into the brick, the user should switch to a delicate spray pattern. It is very important to use a delicate pattern, as using too much pressure can and will damage the brick. Again, it is recommended to start with a low-pressure setting below 800 PSI and adjust slowly to higher pressures only if needed. 

Unlike the initial wetting process, the bricks should be rinsed from top to bottom to remove the detergent and residue. The wand should move slowly but constantly; the pressure washer should not be held in one spot. Spraying in a circular motion over tough stains and continuing from top to bottom in mostly sweeping motions will evenly remove dirt. 

• Pro Tip: Wet bricks can be deceiving, so it is best to wait until they are totally dry to assess whether any tougher stains remain, if any spots were missed, or if there are uneven stripes that need a second treatment. This should be done before applying a sealant to ensure optimal results, which may mean waiting an additional day or two. 

Step 7. Apply Sealant 

Once the brick is clean and dry, the final step is to apply an approved brick and mortar sealant. This helps keep the bricks clean longer, much like a wax or seal coat on a vehicle after a premium car wash. 

The sealant helps prevent acids, oils, greases, and other harmful substances from penetrating the surface. These sealants leave the brick and mortar looking as though nothing has been applied, but when water or other liquids contact the surface, they bead up and run off instead of penetrating the brick.