After clearing the copper gutter of any loose leaves, dirt, and debris, apply a mixture consisting of equal parts vinegar, salt, and flour using a scrub brush to polish the material. Focus on any tarnished parts, using a circular motion to brush the paste on. Afterward, rinse off the paste using low-pressure water applied with a recommended 25-degree nozzle tip.
Steel gutters tend to react negatively to cleaning solutions used on vinyl or wood surfaces. Mix 1/3 cup of laundry detergent for every 6 gallons of water, using a fan nozzle tip to apply the solution. For mold and mildew, mix household bleach with water in a 1:3 ratio and spray onto the steel gutter prior to pressure washing. Finally, it is recommended to wash down the cleaning solution using a 25-degree nozzle tip
To clean vinyl gutters, use a cleaning solution specifically designed for the material. Alternatively, a mixture of water and white vinegar can also work for mild mildew and mold stains. For more stubborn stains, combine one quart of liquid laundry bleach, 2/3 cup powdered household cleaner, 1/3 cup laundry detergent, and a gallon of water. A soft washing technique is preferred.