Causes:         
    – Water comes in contact with the metal and causes paint film imperfections.
    – Rust is not completely removed before spraying.
   – Contamination of the surface before spraying: Finger marks, water which is 
   allowed to dry on the metal surface, delay between cleaning with a phosphoric acid
   based product and spraying, etc.

Note:
    Rust problems are much more noticeable in regions where salt is thrown on the
    streets during the snow reason.

Preventive measures:
    – Remove all rust traces before painting.
    – Avoid any contamination before spraying.

Remedy:
    Sand all the way through to the bare metal.  Place sander on rusty paints until
    surface is clean and brilliant.  Use Valox (based on phosphoric acid) or sand  
    blowing and repaint immediately.