Painting is the application of a liquid coating to a metal to protect it. It is considered the oldest method of corrosion control and certainly the most recognisable to people outside the corrosion protection field. Painting’s simple premise – the application of a protective film to protect the underlying metal from exposure to the environment – belies the reality of the sophistication behind the technology that is required to do it effectively.
Although protective coatings have been in existence for many years, it was only in the mid 1900’s that the true protection mechanisms of paint coatings were understood. Prior to then, it was thought that paint coatings worked by providing a complete insulation between the protected metal and the environment. In fact, the reality was much more complex and led to improvements in the way paint was used to protect metal, most commonly steel.
It is now known that most paints to a certain extent allow moisture and atmospheric components to travel through them in varying quantities. Rather than being a problem, this property can actually assist in the paint’s corrosion protection of the base metal. Modern protective coatings are highly specialised and have unique characteristics depending on the type of protection required. These modern coatings protect in different ways, are made of different materials and require varied surface preparation and application. Specifiers need to be aware of the different properties available in the large range of protective coatings. Although many different types of metals are protected by painting, this discussion will focus primarily on steel and structural steel.