Eliminate tough mold, mildew, and algae stains from your outdoor surfaces with Outdoor for California residents. Use this outdoor and unscented stain remover on siding, walkways, concrete, wood, plastic, vinyl, aluminum or virtually any other outdoor surface. Simply mix with water and apply to the contaminated surface, that's it. goes to work with the wind and rain to gently breakdown the growth and wash it way over the next few weeks or months. There's no scrubbing, no rinsing and no power washing. gentle formula contains no bleach or acidic chemicals so it won't harm the surfaces being cleaned. properly cleans the surface so it stays cleaner, longer.