“Selecting the Right Coating – The 4 Basic Questions”
If one coating could do everything, coating selection would be limited to color and gloss choices and specification writing would be relatively simple. Since that magic coating does not (yet) exist, we are left with hundreds of selections to choose from. Many coatings will indeed perform multiple functions and are quite versatile in their many uses. These then become very popular. However real-world situations often demand more specific performance requirements that necessitate the selection of a more appropriate coating or coating system.
This article will address the key elements that influence coating selection. These elements will center around “needs” … Performance Needs, Application Needs, Budget Needs (Restrictions), and Other (Special) Needs. To uncover and define the “needs” we will approach the coating selection process through a series of four basic questions that the specifier, engineer or owner need to provide answers. Only in this way can the proper selection be made that will narrow down the hundreds of coating choices to the “best fit” options (assuming one exists). Sometimes however, the specific need or requirement exceeds the existing coating technology and compromises must be made to ensure a proper application.
What is being coated and why is it being coated?
The question sounds pretty basic, but answers can be surprisingly deceptive. In one example, the reason for painting a vessel could simply be because the CEO of the company is making a plant visit next month. Appearance then means everything and no one is really interested in the benefits of a 25-year corrosion resistant coating system. The answer to this question exposes the real reason for painting, the scope of the project and the expectations of the owner.
What exposure will the item see?
This is perhaps the real “meat and potatoes” question to be answered. It tells us what the real environment the coating will be exposed to. There are many parts to this question which include;
- Is the item exposed to an exterior (weathering, marine, industrial) environment or inside (mild, moderate or harsh exposures such as shower rooms or food process areas)?
- Are there any elevated temperature conditions?
- Are there any harsh chemical fumes or anticipated splash and spills of chemicals?
- Will the coating be covered up with insulation?
- Will there be any thermal cycling/shock?
- How frequent will the coating be cleaned and with what chemicals?
- Will the coating see any abrasion? What type (cutting or small particulate)?
- What is the existing condition of the substrate (new steel, contaminated steel, rusted steel, old coatings)?
- What is the condition of existing coatings?
How, when and where will the item be painted?
Answers to this question will define how the painting project will be handled logistically; whether shop applied, field applied or in-situ at an operating plant. It may uncover the need for a coating to handle early rain exposure or cold temperature cure. Certain coating systems will handle shop application better than others and will have less shipping damage to deal with later. If spraying the coating is not possible (overspray problems) then coatings that can be easily brush or rolled must be selected. If the speed of completion of the project is critical (most of course are) then fast dry/fast cure 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 lives. Compromises must be made depending on what can’t be done.
What are the owner’s expectation in terms of service life?
On its face value, one would think that the answer should be “as long as possible”. This is not always the case; especially with limited budgets. In the earlier case where the CEO was to visit the plant, the need to “freshen-up” a vessel could be done rather inexpensively using a coating system with a minimal design life at minimal cost. The argument makes even more sense if the vessel is to be dismantled in say 5 years. It makes no sense to select a 30-year paint system for that vessel. On the other hand, it may indeed make perfect sense to select a long-term service life system for say an elevated water tank with a design life of 90 years … and one that has the local high school mascot painted on its exterior. Long term corrosion protection and long term appearance are vitally important. In the end, one can choose a 3-5 year system, a 10-15 year system or a 25-30 year coating system. The longer service life systems will cost more in terms of material costs and labor (surface preparation and application).
In the end, it is best to discuss your coating needs with a coating professional; one that will walk you through the basic needs analysis outlined here and match the right coating system for your specific set of circumstances and expectations of service life.