Rust Scale

Protective coatings are used in abundance to protect steel structures from the onset of corrosion. If rust is visible, then the coating has begun to deteriorate. The deterioration may be initiated by design, damage, incorrect coating system, under or over thickness etc. It is essential that the industry uses standards and guidelines on how to determine the extent of the rust (or rust scale).

The extent and locality can be vitally important when deciding the type of coating failure, the warranty/guarantee periods, future maintenance and recommendations for repair or refurbishment.

The two documents widely used in the protective coatings industry to determine the extent of rust on a coated surface are:

ISO 4628 -3 Paints and Varnishes. Evaluation of degradation of coatings, Designation of quantity and size of defects, and of intensity of uniform changes in appearance – Assessment of degree of rusting.

The pictorial standard shows coated steel, which has deteriorated to different degrees by the combination of rust broken through the coating and visible underrust.

The second document is the “European Scale of Degree of Rusting for Anticorrosive Paints” which was developed in the 1960’s and is still widely used today. This document shows photographs of various degrees of rusting on a steel substrate that was coated with an oil-based, air-drying, anticorrosive paint. The photographs are in black and white.

There are 10 photographs used in the booklet ranging from Grade Re 0 to Grade Re 9.

Note; ISO 4628 -3 uses the photographs from European Scale of Degree of Rusting for Anticorrosive Paints