Algae thrives in damp and humid conditions, making your walls especially vulnerable during the rainy season. When rainwater continuously soaks into porous surfaces like concrete, brick, or stone, it creates the perfect environment for algae to grow and spread. These green stains aren't just unsightly—they can also degrade your wall’s surface and pose potential health risks over time. That’s why it’s important to act early. By keeping your walls dry and protected, you can stop algae before it tak