ANj - We would like to get more information on how the product was applied to see why it did not work as expected. Spray and Forget House and Deck Outdoor Mold and Mildew Cleaner Concentrate must be applied when the surface is dry and there has been no rainfall for at least 24 hours before or after the application. Many factors, such as climate, surface composition, stain severity, weather and shading, can affect the stain removal time which takes several weeks or longer. Our product works to remove biological stains and the removal time can vary depending on the factors mentioned. When applied as directed, stains will be prevented from returning for years. Please call our Spray & Forget helpline at 1-866-641-0826 so we can get more details and assist you.