Assessment of surface cleanliness is necessary for further work related to the application of paints, metallization, and hot-dip galvanizing. There are many methods and elements of assessing surface cleanliness. The simplest and most commonly used is visual assessment, which involves comparing the appearance of the assessed surface with the photographic patterns included in the ISO 8501-1 standard. Unfortunately, this assessment method does not detect many surface defects that have a significant impact on adhesion and many other defects of the applied coatings.

Examples of surface defects include:

• oil and grase
• dust

• water soluble salts