Moss can appear as a benign green growth on brick surfaces, but its presence poses a genuine threat to masonry structures. It absorbs and retains significant amounts of moisture within its dense, mat-like structure. This constant dampness compromises the integrity of the porous brick and the surrounding mortar joints. When temperatures drop, the trapped water expands during the freeze-thaw cycle, which can lead to spalling, cracking, and a reduction in the structural lifespan of the brickwork.
Preparing the Area and Mechanical Removal
Begin by donning appropriate personal protective equipment, including safety glasses and gloves, to shield against debris and chemical solutions. You should first test any cleaning or chemical solution on a small, inconspicuous area of the brick to ensure it does not cause discoloration or damage.
Use a stiff-bristle brush or a plastic scraper to lift the thickest layers of moss from the brick face and the mortar joints. Dry moss is often easier to scrape away, making a dry day the ideal time for this manual process. For larger patches, a pressure washer can be used cautiously, but only on durable brick with sound mortar.
If using a pressure washer, select a wide-angle nozzle (such as a 25-degree tip) and maintain a distance of at least 12 inches from the surface to prevent etching or blowing out the mortar. The goal is to remove organic debris and expose the brick surface, not to blast away the mortar. This maximizes the effectiveness of the subsequent chemical application by allowing the solution to directly contact remaining moss spores.
Chemical Solutions for Killing Moss
Once the surface is mechanically cleared, a chemical application is needed to kill the residual moss and its rhizoids. Several common household items can be used as effective moss-killing solutions. A simple, non-toxic option is a 1:1 mixture of distilled white vinegar and water; the acetic acid disrupts the moss’s cellular structure. Apply this solution generously using a garden sprayer and allow it to dwell for 15 to 20 minutes before rinsing thoroughly with water.
Another highly effective, non-acidic treatment involves creating a baking soda paste mixed with water. Baking soda (sodium bicarbonate) is an alkaline substance that alters the moss’s pH environment, causing it to desiccate and die. Press the paste directly onto the mossy patches and leave it overnight before scrubbing off with a brush and rinsing.
For aggressive treatment on resilient moss, a diluted bleach solution (one part household bleach to ten parts water) can be sprayed on. This requires extreme care as it can discolor surrounding vegetation and some colored bricks if not rinsed quickly and completely.
If the moss infestation is severe, a commercial biocide designed for masonry provides a targeted approach. These specialized cleaners, often containing active ingredients like ammonium salts or benzalkonium chloride, are formulated to be safe for brick and mortar. Always follow the manufacturer’s instructions for dilution and dwell time, ensuring the product is applied on a dry, calm day to maximize contact time before a final rinse.
Strategies for Preventing Regrowth
Long-term moss prevention relies on addressing the environmental factors that encourage its growth: moisture and shade. Moss thrives in damp, poorly ventilated areas, so the initial strategy should focus on increasing airflow and sunlight exposure to the brick surface. Trimming back overhanging tree branches, shrubs, or dense vegetation allows more direct sunlight to reach and dry the brick faster after rain.
Improving drainage around the brick structure is important to prevent water from pooling at the base of walls or foundations. Addressing issues like clogged gutters or faulty downspouts that direct water onto the brick eliminates a constant source of moisture. The final defense involves applying a quality masonry sealer, such as a silane or siloxane-based product. This penetrating sealer creates a hydrophobic barrier within the brick’s pores, repelling water and reducing the ability of moss spores to anchor and retain moisture.