How to Clean an Oxidized Painted Metal Roof

Rust cannot form unless some type of moisture is present.

Oxidization — also called rust — will begin to develop on painted metal roofs when moisture present on the metal encounters oxygen. If left untreated, the oxidization will not only leave ugly stains on the surface, but it will also deteriorate the metal and compromise the structural integrity of the roof. To prevent extensive damage to the roof, remove the rust as soon as possible. In addition, the longer the rust sits on the painted roof, the harder removing it will be.

Things You'll Need

• Phosphoric acid–based cleaner
• Bucket
• Steady ladder
• Brush broom
• Water hose

Instructions

1. Mix a phosphoric acid–based cleaner with water in a bucket. Use a ratio of 10 percent cleaner to 90 percent water for small, surface rust problems. For a stronger solution, raise the ratio to 50 percent cleaner and 50 percent water mixture. When mixing the water and acid, add the acid to the water, not the other way around.

2. Set a steady ladder against the building or house that has the rusty roof. Have someone hold the ladder as you climb it. This will help steady and support the ladder, reducing the chance of injury.

3. Saturate a brush broom in the mixture and scrub the rust for several minutes until well saturated.

4. Leave the mixture on the rust for an hour for the highest phosphoric acid–based cleaner ratio and longer for the more diluted mixture.

5. Rinse the painted metal roof thoroughly with a water hose to remove all traces of the acid. Repeat the entire process if oxidization remains.

Tips & Warnings

• Always read and follow the directions printed on the phosphoric acid label.

• Wear heavy rubber gloves to prevent skin irritation.

References

• United States Steel: Cleaning Painted Metal Buildings
• Scale Model Exchange: Rust Removal