What are the best ways to prevent filiform corrosion on painted cast iron outdoor flower boxes?

Filiform corrosion is a common issue for painted cast iron outdoor flower boxes, but it can be prevented with proper care. Here are the best methods:

1. Surface Preparation: Ensure the cast iron is thoroughly cleaned and free of rust before painting. Use a wire brush or sandpaper to remove any existing corrosion.

2. High-Quality Primer: Apply a rust-inhibiting primer specifically designed for metal surfaces. This creates a protective barrier between the iron and moisture.

3. Durable Paint: Use exterior-grade paint formulated for metal. Epoxy or polyurethane-based paints offer excellent adhesion and resistance to moisture.

4. Regular Maintenance: Inspect the flower boxes annually for chips or scratches. Touch up damaged areas promptly to prevent moisture from reaching the metal.

5. Proper Drainage: Ensure drainage holes are clear to avoid water accumulation, which accelerates corrosion.

6. Protective Coatings: Consider adding a clear sealant over the paint for extra protection against humidity and salt air.

By following these steps, you can extend the lifespan of your cast iron flower boxes and keep them looking beautiful for years.