Corrosion

The fundamentals of a coating could refer to several things, depending on the purpose or use of the coating. As corrosion can compromise the integrity of a building, leading to potential safety hazards, understanding corrosion coatings is extremely important. 

An antifouling paint would have the fundamental property of inhibiting the growth of animal or vegetable organisms on the coating.  

A fire-resistant coating must resist burning, or at least retard the burning of the substrate.  

A coating to be applied over concrete must have a fundamental property of resistance to strong alkali. 

In its publication, Corrosion Exclusively, the Corrosion Institute of South Africa (CorrISA) explains the fundamentals of coatings. 

Anticorrosive coatings 

All corrosion-resistant coatings must resist the corrosive atmosphere and prevent it from reaching the basic structure. Thus, there are as many variations in the types of coatings as there are in the forms of corrosion. 

The design of an effective anticorrosive coating is a complex task, which requires an extensive knowledge of not only corrosion principles but of the science and chemistry of coating formation as well. Without such inclusive information, the development of effective corrosion-resistant coatings would be impossible. 

Corrosion

All corrosion-resistant coatings must resist the corrosive atmosphere and prevent it from reaching the basic structure.

Coating systems 

A coating is not a self-supporting structure. It is part of an overall system, which includes the basic structure that supports the coating. 

Although it is always on a substrate of one kind or another, a coating can be thought of in the same light as a building. In order to be strong, a building must have a heavy, carefully constructed foundation. A coating must also have a carefully designed (formulated) and constructed (applied) foundation (substrate and primer). 

Functionality and purpose 

A building consists of several interlocking parts – the foundation, superstructure and roof – and each one has a different function. The corresponding parts of a coating are the primer, intermediate coats and topcoat. 

In the case of a small building with a relatively short, useful life, the foundation and superstructure may be minimal. The same is true of a coating applied only for decorative purposes, where the surface preparation, application and long life may be easily overlooked. However, in the instance of a substantial industrial structure, durability, reliability and long life are required. 

The same is true for an industrial corrosion-resistant coating. It must, likewise, be engineered with a properly prepared substrate, a sound foundation coat or primer, a strongly reinforced intermediate coat and long-lasting weather and corrosion-resistant topcoats. 

Corrosion

A coating system may employ one or more of the basic coating concepts of impermeability, inhibition, and anodic or cathodic pigments, or a combination of two.

Fit for purpose 

In constructing a building, the substrate (soil or ground) indicates the type and extent of the foundation since sand, clay or rock all have different foundation requirements. 

The same, of course, is true of coatings. The primer must be designed specifically for the substrate, whether it is steel, aluminium, concrete, plastic or wood. In fact, the surface over which a coating is applied may be more important from the standpoint of long life and durability than the design of the coating itself. 

Fundamental concepts 

The fundamental concepts involved in corrosion-resistant coatings include: 

  • Coating protection. 
  • Component design. 
  • Component function. 
  • Coating formulation.  

Many coatings contain as many as 15 to 20 ingredients, each of which has its own function in the overall performance of that coating. 

A coating system may employ one or more of the basic coating concepts of impermeability, inhibition, and anodic or cathodic pigments. While many coating systems employ only one of these concepts, some of the most successful anticorrosive systems combine two of the concepts into one coating system.  

 

Issue: Why do buildings need corrosion coatings? 

Solution:  Corrosion can compromise the integrity of buildings or infrastructure, leading to reduced load-bearing capacity, potential safety hazards and expensive repairs.  

 

Full acknowledgement and thanks go to the Corrosion Institute of South Africa. This article is adapted with thanks from Corrosion Prevention by Protective Coatings, Third Edition, Charles G Munger, Louis D Vincent, assoc. ed. (Houston, TX: NACE International, 2014), p. 63. 

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