Mold Armor's Mildew Stain Remover Plus Blocker keeps surfaces cleaner Longer. Mildew Stain Remover Plus Blocker is no ordinary cleaner. Its safe, powerful bleach-free formula eliminates mold and mildew stains, soap scum and mineral deposits like calcium and lime. But, thats only the beginning. As it cleans, it leaves behind an invisible shield that works continuously for up to 3 months to protect surfaces and materials from odor or stains caused by moisture. And, its effectiveness is not diminished by washings or rain! Mildew Stain Remover Plus Blocker can be used indoors and out on: counters and sinks, shower curtains, tubs and toilets, doors, walls and ceilings, aluminum, glass, fiberglass, stone (except natural marble), cultured marble, acrylic PVC, vinyl, porcelain, rubber, chrome, Formica and more. Molds reproduce by means of tiny spores; the spores are invisible to the naked eye and float through outdoor and indoor air. There are approximately 10,000 mold spores on the head of a pin. Mold spores land on fabrics and surfaces that are wet and begin to grow. Mold Armor's Mold Blocker creates an invisible barrier to the growth of mold to keep indoor and outdoor surfaces mold free for up to 3 months.