McElroy UniversityMetal Roofing Substrates and Coatings

The Importance of Quality Substrates and Coatings

The performance and long-term service life of a metal panel is widely dependent on two components - the substrate and the coating. Taking quality short-cuts on either component could result in premature failure of the metal panel.

Substrate and Coating Facts

When shopping for metal roofing, purchasers must be vigilant to ensure the substrate and coating on the metal panels they choose will match their long-term performance expectations. There are a variety of steel substrates and coatings available in the marketplace and the wrong selection could result in disappointment and reduced service life.

For long-term customer satisfaction and performance, McElroy Metal recommends panels with a Galvalume® substrate and Kynar 500® (PVDF) coating. McElroy Metal has created a video series to help educate our customers on the importance of selecting the optimal substrate and coating.

Substrate and Coatings Videos

Medallion-Lok Standing Seam Roofing System Installed

Galvanized VS. Galvalume Substrates

The most popular steel substrates in the metal roofing and siding industry are Galvanized and Galvalume. Galvanized substrates are coated in zinc, while Galvalume substrates are coated with an alloy of zinc plus aluminum. Both Galvalume and Galvanized are good substrates for metal panels.

Galvanized G90 Mar Rural sized

Galvanized Substrates

With Galvanized substrates, the greater the amount of zinc the greater the protection against panel corrosion. Two commonly used Galvanized substrates are designated as G100 and G60. These designations relate to the total amount of zinc contained on both sides of the panel surfaces. G100 contains 1.0 ounce of zinc for every one square foot of panel while G60 substrates contain 0.6 ounces of zinc. The important fact to consider is that a G100 substrate contains 66% more protective zinc than a G60 substrate. This difference will have a direct correlation to panel longevity and long-term aesthetics of your project.

Galvalume Sheet Mar Rural-sized

Galvalume Substrates

For most applications, Galvalume substrates offer the best long-term solution, and Galvalume's superior performance has been proven in the field. Over four decades of testing has shown that Galvalume delivers superior corrosion resistance compared to Galvanized panels. In fact, Galvalume's performance in the construction industry has been so superior, that steel mills warranty it against rupture, perforation, or failure due to corrosion. Similar warranties do not exist for Galvanized.

In one test, shown in the photos above, unpainted Galvalume and Galvanized panels were placed in four different types of outdoor environments, including normal marine and a rural setting. The harsher the surroundings, the better Galvalume performed. After 23 years of side-by-side comparison in all areas, Galvalume was two to four times more durable than Galvanized.

Download Our Galvalume Brochure to Find Out More


The coating system, or paint, for metal panels is just as important as the substrate. For the life of the panel, the surface, or coating, will be exposed to environmental elements - ultraviolet sun rays, acid rain, dirt, etc. Over time, these environmental conditions will break down the coating resulting in panel fade and chalk. Fade and chalk are not pleasing to the eye, and the degree of fade and chalk is directly related to the coating system. The most popular coatings for metal panels are Kynar 500® (PVDF), Silicone Modified Polyester (SMP) and Polyester. Of the three, Kynar 500® (PVDF) coatings provide the best protection against fade and chalk and are proven to provide the best long-term performance. 

coating chart

Still not sure which coating is right for you? Let’s look at some examples to help it make more sense. Both Kynar 500 (PVDF) and Silicone-Modified Polyester (SMP) panels were installed on a project in Louisiana. On day one, the colors were an identical shade of green. However, this project included a combination of materials, some with a Kynar 500 paint system and some with a SMP paint system. The photo below, taken only eight years later, tells a powerful story of the differences between the paint systems as it highlights both chalk and fade of the SMP paint system. Note that no fade or chalking on the darker Kynar 500 (PVDF) panels is present during the same eight-year window.

Kynar 500 vs SMP

Learn more about coatings


The next example also dramatically illustrates the superior performance of Kynar 500. This building was built in two phases, nine years apart. Note that there is no color difference between the original roof and the addition.
addition building vs. original
With examples like these, it’s obvious that Kynar 500 (PVDF) coatings are the “Best” option when long service life, color retention and chalk-resistance are important. Yet, uninformed homeowners still often select a Silicone-Modified Polyester paint system. Why? It’s often because not every panel manufacturer or contractor offers Kynar 500 paint as one of their standard products. In those cases, installers may feel forced to sell the product they have available to them and oversell it as “just as good” as Kynar 500. Plainly put, there is no paint system that is presently equal to or better than Kynar 500.

Benefits of High Performing Substrates and Coatings

As indicated above, high performing substrates and coatings are important when long-term performance and aesthetics are important. Warranties are also a consideration when selecting a metal panel. Consumers often associate warranty with dependability and performance.

This is not necessarily the case. Just because a warranty has an extended time frame (45 years or even a “lifetime”), it does not necessarily mean that the warranty is better or that the product offers better performance. We encourage you to fully read and understand your supplier’s warranties. 

Learn more about roofing warranties

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