The defects in a paint film, which can be traced to rust forming under the paint, are due mainly to insufficient preparation of the metal, including incomplete removal of millscale.

Breakdowns are usually initially seen as blistering or cratering. Complete breakdown leading to wholesale lifting and flaking inevitably follows.

Thorough removal of the paint corrosion and millscale is essential before repainting. The surface must also be dry. The priming paint should be applied immediately after preparation, ensuring that a suitable primer and adequate paint systems are used.