If a single coating could do it all, coating selection would be limited to color and gloss, and specification writing would be simple. Because that mythical coating does not (yet) exist, we are left with various options. Many coatings can perform multiple functions and have a wide range of applications. These are then extremely popular. Real-world situations, on the other hand, frequently necessitate more specific performance requirements, resulting in the selection of a more appropriate coating or coating system.
This review will outline the factors that influence coating selection. These factors will revolve around "requirements"- Performance requirements, application requirements, budget requirements (restrictions), and other (special) requirements to discover and define the "needs." We will approach the coating selection process with a series of four basic questions to which the specifier, engineer, or owner must help us to answer. Only in this manner can the proper selection be made, narrowing down hundreds or thousands of coating options to the “best fit”, assuming one exists. However, there are times when a specific need or requirement exceeds the capabilities of existing coating technology, and compromises must be made to ensure proper application.
1. What is being coated and why is it being coated?
The question appears simple, but the answers can be deceptive. In one case, the reason for painting a vessel could simply be that the president will be visiting the factory next quarter. When appearance is everything, no one cares about the benefits of a 25-year corrosion resistant coating system. The answer to this question reveals the true reason for painting, the scope of the project, and the owner's expectations.
2. What's the service environment?
This is possibly the most important question to be answered. It describes the actual end use environment to which the coating will be subjected. This question has many subcomponents, some of which are as follows:
- Is the item exposed to an outside (weathering, marine, or industrial) or inside (mild, moderate, or harsh exposures such as shower rooms or food processing areas) environment?
- Is there a possibility of high temperatures?
- Are there going to be any harsh chemical fumes or chemical splashes and spills?
- Is the coating going to be covered with insulation?
- Is there going to be thermal cycling/shock?
- How frequently and with what chemicals will the coating be cleaned?
- Will the coating be subjected to abrasion? What kind?
- What is the substrate's current state (new steel, contaminated steel, rusted steel, old coatings)?
- What is the state of the existing coating?
3. When, how, and where will the item be painted?
The answers to this question will determine how the coatings project will be handled logistically; whether it will be shop applied, field applied, or on site at a working plant. It may reveal the requirement for a coating to withstand early moisture exposure or minimum temperature cure. Certain coating systems will perform better in the shop than others and will have less shipping damage to deal with later. If spraying the coating is not possible due to overspray issues, coatings that can be easily brushed or rolled must be chosen. If the project's completion time is critical (which it almost always is), faster curing products will be preferred. In many operating plants, open abrasive blasting for optimal service cleanliness and profile requirements may not be possible. While this restriction is fairly common, products that have surface tolerant properties must be selected. And while these products are technologically advanced, products that require higher degrees of cleanliness are preferred for longer service life. Compromises must be made depending on what can or cannot be done.
In the end, it is best to discuss your coating needs with a coating professional, preferably one that will walk you through the basic needs analysis outlined here and match the right coating system with your set of circumstances and expectations of service life. CONTACT US today to discuss the specifics of your project.
Check out these related resources
Does Formulation Matter?
Abrasion Resistance ASTM D4060
QUV Exposure ASTMD4547
Permeability ASTM D1653
Accelerated Weathering ASTM D4585
The Science Behind High Performance Coatings
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