In this episode of Building with Metal, McElroy Metal teams up with Sherwin-Williams to uncover what’s really behind the paint. From formulation to field performance, we explore the chemistry, testing, and technology that make modern coatings last for decades.
Discover how color science, durability testing, and application techniques come together to create beautiful, long-lasting metal roof and wall systems that stand the test of time.
Notable Quotes
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Michael Lewis: "The small miracle that we accomplished is that we do apply our coatings on flat coils of sheet metal and then downstream from that event it's then formed into final products... the average thickness of a human hair is roughly one hundred microns and our coatings are being applied at twenty microns sometimes thinner."
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Michael Lewis: "The major benefit to PVDF is the very fundamental strength of the carbon-fluorine bonds, from a chemical perspective. It's one of the strongest molecular bonds that we can engineer into a coating. And that's what makes it extremely robust as far as the field performance and its resistance to long term degradation goes."
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Michael Lewis: "Delivering a world class roof coating is not simply a function of the coating itself and the manufacturer of that coating, although we play a huge part in it. It requires excellence from every contributor in this industry, from raw material supply to deliver consistent, reliable performance."
What You'll Learn
- The four fundamental families of ingredients that comprise metal coatings and how each contributes to performance
- How coatings applied at just 20 microns thick—one-fifth the thickness of human hair—maintain color, gloss, and adhesion through extreme physical deformation
- The unique chemistry behind PVDF coatings and why carbon-fluorine bonds create superior long-term durability and color retention
- The difference between accelerated laboratory testing and real-world exposure studies, including Sherwin-Williams' 50-year test fence in Fort Myers, Florida
- How polymer structure affects coating properties, balancing flexibility versus hardness through molecular chain length and branching
- Recent environmental innovations, including the complete elimination of PTFE-containing ingredients from WeatherXL silicone modified polyester platforms
- The critical role every industry participant plays in delivering world-class coating performance, from raw material suppliers through field installers
- How to properly select coatings based on end-use requirements, environmental conditions, and life expectancy expectations
Key Timestamps
00:00 Introduction to the Building with Metal Podcast and guest Michael Lewis, Group Leader for Sherwin-Williams Performance Coatings Group in Bowling Green, Kentucky
05:15 Michael Lewis's journey into coatings R&D, from water quality labs to discovering the unique world of coil coatings and pre-painted metal systems
10:30 The remarkable properties of coil coatings: applying paint at 20 microns thick (one-fifth of a human hair) that withstands extreme forming and maintains aesthetic properties
18:45 Overview of Sherwin-Williams Paint School program: year-round education for industry professionals covering formulation, application, and field performance
25:20 The four families of coating ingredients—resin, pigment, solvent, and additives—and how they interact to create performance characteristics
35:40 Testing methodologies: immediate performance tests (hardness, flexibility, solvent resistance) versus long-term durability studies using test fences worldwide
45:15 Environmental innovations and the industry shift toward eliminating PTFE ingredients while maintaining coating performance standards
52:30 Future of coating technology: warranty evolution from 20 to 45 years and what advancements may come next
58:00 Critical advice for specifiers: matching coating selection to end-use requirements and the importance of excellence throughout the entire supply chain
Mentioned Resources
Episode Deep Dive
Understanding the science behind metal roof coatings reveals a world far more complex than most people imagine. When Michael Lewis, Research and Development Director at Sherwin-Williams Performance Coatings Group, explains what goes into protecting metal roofs, the sophistication becomes immediately apparent. From microscopic film thicknesses to molecular bond structures, every element plays a critical role in delivering the decades of performance that building owners expect.
Lewis leads a specialized team in Bowling Green, Kentucky, one of several major Sherwin-Williams manufacturing sites worldwide. His group works within a broader network of formulating chemists and technical personnel, each bringing different areas of expertise to the table. Some focus on color matching, others on manufactured products, while staff chemists provide guidance on creative solutions across various projects. This collaborative approach proves essential when developing coatings that must perform under extraordinary conditions.
The Path to Coatings Chemistry
The path to coatings chemistry often follows unexpected routes. Lewis first encountered laboratory work as a student employee in a university water quality lab, working with chemical reagents and glassware in an era before modern scientific instruments dominated the field. His entry into the coatings industry came through answering a newspaper advertisement for a development chemist position at what was then Valspar. He admits he had no idea what he was getting into, but the manufacturing environment opened his eyes to how much development and production work goes into every consumable product we use.
What Makes Coil Coatings Unique
What makes coil coatings particularly unique is something Lewis finds himself explaining regularly to friends and colleagues outside the industry. The process involves applying coatings to flat coils of sheet metal, which are then formed into final products downstream. This might include appliances like refrigerators and HVAC units on the manufactured product side, or trim coil, gutters, downspouts, siding, and roofing on the building product side. The remarkable aspect is the amount of physical strain and deformation these coatings tolerate after being pre-painted on flat steel.
Microscopic Film Thickness and Performance Standards
The numbers tell an astonishing story. The average thickness of a human hair measures roughly one hundred microns. Sherwin-Williams applies its coatings at twenty microns, sometimes thinner—approximately one-fifth the thickness of a human hair. At this microscopic scale, the coatings must still deliver consistent color properties and gloss or sheen characteristics while sustaining challenging physical strains during the forming process. Maintaining coating adhesion, excellent hardness, and aesthetic properties through complex assembly formations requires intense focus on quality at every step, from the manufacturer through field installation.
Education and Industry Knowledge Sharing
Education plays a vital role in spreading knowledge about coating performance throughout the industry. Sherwin-Williams hosts Paint School at its Bowling Green facility year-round, with sessions held monthly from January through May and from September through November. The program aims to raise awareness among people who may not work directly with paint formulation about the factors that influence coating performance when applied and installed in the field. Attendees come from all walks of the industry—formulators, sales and marketing professionals, formers, coaters, end users—each bringing their own perspective and piece of industry knowledge.
A panel of instructors leads the school, each contributing expertise in a different subject. Formulators bring their chemical knowledge, technical service division representatives understand application variables at the coating line, and field investigators provide real-world feedback about weathering and durability. This combination of laboratory science and field experience creates a comprehensive learning environment. As Lewis notes, while laboratory testing provides valuable data, nothing compares to actual real-world environments where Mother Nature tests these coatings under conditions no lab can fully replicate.
The Four Fundamental Families of Coating Ingredients
Understanding what makes one paint formula last longer than another requires examining four fundamental families of ingredients. Resin, sometimes called the vehicle or backbone, forms the structural foundation. Pigment contributions provide aesthetic qualities like color while also affecting durability and UV resistance, influencing how well the coating maintains colorfastness over time. Solvent plays a considerable part in polyester and silicone-modified polyester coating systems, which are essentially solvent-borne. PVDF represents a league of its own—a thermoplastic dispersed in a co-resin and solvent to make it flowable for application, but yielding a very different structure and durability after cure compared to standard polyester or silicone-modified polyester formulations.
PVDF: The Flagship for Long-Term Durability
PVDF stands as Sherwin-Williams' flagship for long-term durability and performance, representing the state of the art in coatings chemistry. The technology originated in early DuPont research into fluorinated hydrocarbon chemistry. The major benefit stems from the fundamental strength of carbon-fluorine bonds, which are among the strongest molecular bonds that can be engineered into a coating. This makes PVDF extremely robust in field performance and resistant to long-term degradation.
When PVDF cures, it forms a somewhat crystalline structure. This lattice encapsulates pigments within the PVDF crystalline network, providing a protective shell that contributes to superior color retention and, to a fair degree, gloss retention in the field. This unique chemistry and cure process differentiate PVDF from other coating technologies and explain why it delivers exceptional performance over decades of exposure to environmental stresses.
The Role of Additives in Coating Performance
The fourth family of ingredients, additives, represents an area where research and development work proves crucial. Additives can do good things or bad things, and finding what works effectively often means discovering what doesn't work nine times out of ten first. Additives contribute to flow characteristics and surface lubricity, helping paint form at roll formers without scratching. While researchers continually look for new tools to apply in coatings, the industry relies heavily on tried and true additives that have proven their worth through extensive positive performance data.
Resin Chemistry and Polymer Structure
Resin chemistry itself represents a highly specialized segment of the coatings industry. Polyester and silicone-modified polyester resins are engineered with functional groups that determine their structure. Depending on how they're cooked or reacted, they can form long, linear polymers or shorter, more branched polymers. A long linear polymer terminates in a reactive functional group at each end of its molecular chain, while a more branched polymer includes reactive molecular branches across its length. Generally, more branched resins are shorter but offer more reaction sites.
This structural difference creates a sliding scale between coating properties. Long linear polymers yield very flexible coatings, while shorter, more branched polymers that can network extensively with other coating ingredients provide more complex surfaces. Formulators don't stop with one polymer, though. They effectively blend different polymers to combine functional elements based on end-use expectations, bridging the gap between flexibility and hardness to deliver coatings that are either harder or more flexible, depending on forming requirements before installation.
Testing Methodologies for Coating Performance
Testing methodologies divide into two main categories. Immediately after coating, practical tests assess hardness, flexibility, and solvent resistance. Hardness testing uses mechanical pencil lead as a practical benchmark, with different pencil grades serving as QC-controlled standards that graduate in hardness up the scale. This simple approach works in the laboratory, during manufacturing quality control, at coating facilities, and even in the field, providing quick verification that coatings have cured properly and meet physical criteria stated on technical data sheets.
Long-Term Durability and Corrosion Testing
Long-term durability testing addresses film integrity—how long the film continues residing on the substrate surface after extended environmental exposure. This includes resistance to fading and gloss loss, which results primarily from UV degradation, though climactic factors like atmospheric acidity or coastal proximity also play roles. Corrosion testing represents another critical battery of assessments, performed in-house using accelerated methods that show strong positive correlation to real-world performance. These tests evaluate how well coatings perform as barriers to water migration and substrate corrosion, and how effectively the coating system resists corrosive deterioration mechanisms.
Accelerated Testing Methods
Accelerated testing uses Cleveland condensing humidity cabinets and salt spray cabinets designed to be as stressful and harsh as possible. This approach delivers strong indicators through controlled variables, showing how new coating formulations might perform relative to proven formulas. Researchers always prepare control samples representing established coating compositions, then compare any new iteration's performance in relative terms to see if results are better or worse for specific criteria like corrosion or color loss with UV exposure.
Real-World Exposure Testing and Global Test Fences
While accelerated tests provide good indicators of expected long-term durability, real-world exposure data remains essential. Sherwin-Williams maintains a large installation in Fort Myers, Florida, where panels from around the world are subjected to a forty-five degree angle of solar exposure as near to the equator as possible within the United States. The humid South Florida environment provides one of the most extreme solar exposure areas available domestically. Some panels on this test fence have been exposed for more than fifty years, allowing researchers to examine very old product iterations for performance.
The company constantly cycles test panels to Fort Myers for benchmarking, then pulls them at given intervals to measure film integrity, color retention, and gloss retention. This process verifies whether experimental efforts should continue or reveals positive directions for development. Beyond Fort Myers, Sherwin-Williams accesses multiple test fences around the world to simulate other extreme climates, including coastal environments in both northern and southern hemispheres. Salt spray behaves differently in cold, damp environments versus warm, damp conditions, making this global network critical for understanding coating performance across various installation climates.
Managing test fences in hurricane-prone areas like Fort Myers requires significant effort. When storms approach, teams literally remove every clip from every panel, store them safely away from the hurricane, then reinstall them once weather clears. This labor-intensive process protects decades of valuable exposure data from being destroyed by extreme weather events. Panels must be firmly secured for normal circumstances while remaining manageable for emergency removal when needed.
Environmental Considerations in Coating Development
Environmental considerations increasingly influence coating development. Cultural shifts and regulatory changes drive innovation, though not always in ways that grab headlines. Public perception about forever chemicals and PTFE-containing ingredients has created sensitivity across many industries, not targeting coatings specifically but affecting them nonetheless. In response, Sherwin-Williams has successfully migrated their silicone modified polyester WeatherXL building products platform completely away from PTFE-containing ingredients. One ingredient in particular had provided good surface lubricity through the forming process, fitting conventional wisdom about PTFE's role in manufactured items. Through careful research, they identified an alternative yielding comparable performance without sacrificing anything the original material provided.
Solvent considerations also reflect environmental pressures. Some solvents face restrictions in certain countries, while purity levels or byproducts in solvent formulations cause concern requiring extra consideration. The broader environmental push aims to reduce hazardous air pollutants resulting from solvent-borne products and coatings. While companies look for these opportunities, they refuse to sacrifice product performance. This creates an inherent push-pull dynamic in the challenge of moving toward more environmentally friendly compositions while maintaining the extremely durable, high-performance coatings that current technology delivers.
The Evolution of Coating Warranties
The evolution of coating warranties tells its own story about technological advancement. When Lewis first entered the industry, twenty-year warranties represented the standard. Today, forty and forty-five year warranties have become common. Asked whether the industry has reached maximum capacity for life expectancy in the forty-five to fifty-year range, Lewis hesitates to commit. He reflects that the accomplishments that would have made formulators shake their heads or smile in wonder thirty years ago are now standard. Even though current platforms and technologies feel like pinnacles of achievement, he suspects today's formulators would be equally surprised by advances in the coming decades. The industry will continue innovating, even if what comes next remains difficult to imagine from today's perspective.
Selecting Appropriate Coatings for Specific Applications
Selecting appropriate coatings requires understanding that end use and performance requirements drive the selection process. The critical question always centers on what the coating needs to do during part formation, the physical strains it will face, whether it serves interior or exterior applications, and how much color stability and film integrity matter over time. The industry offers different grades—good, better, and best—between polyester, silicone-modified polyester, and PVDF lines. Over-engineering the coating for the end use makes no sense. The coating must be appropriate to the life expectancy and demands of the particular application.
The Importance of Industry Collaboration
Understanding the final product receiving the coating informs better decisions about coating selection and how to marry the best properties of coating, substrate, and pretreatment. This comprehensive perspective reveals an essential truth about coating performance. Delivering a world-class roof coating is not simply a function of the coating itself and its manufacturer, although they play a huge part. It requires excellence from every contributor in the industry, from raw material suppliers delivering consistent, reliable performance with every ingredient, to proper formulation and application of pretreatments onto substrate at the coater line, to coaters' commitment to quality while observing application properties during coating.
Critical factors include reaching the prescribed peak metal temperatures to yield the best results; confirming positive physical results when coated before products move further down the chain; how coils are stored and protected from moisture before forming into parts; and transit and storage of formed parts in the field before installation. Those running coils through roll formers and carefully handling products during installation also play critical roles. Coating integrity must be maintained throughout the entire process to provide the best substrate protection and maintain expected properties. Everyone who touches the process, from raw material supply through coding formulation, application, and eventual field installation, plays a critical role in delivering world-class results that remain durable and satisfying for years in the field.
Partnership Between Coating Manufacturers and Metal Producers
Partnerships between companies like Sherwin-Williams and metal manufacturers like McElroy Metal exemplify this collaborative approach. Decades-long relationships built on knowledge sharing and mutual support create the foundation for serving customers effectively. When specifiers need to determine appropriate systems for particular projects based on environment, building use, and life expectancy, these partnerships provide accessible technical expertise to ensure optimal solutions. Strong relationships across every leg of the industry, combined with a technical voice where needed and a willingness to address questions as they arise, help everyone succeed.
The science behind metal roof coatings extends far beyond simple paint application. It encompasses molecular chemistry, environmental science, accelerated and real-world testing, manufacturing precision, and collaborative industry relationships. From carbon-fluorine bonds at the molecular level to fifty-year test fences in South Florida, from twenty-micron film thicknesses to forty-five-year warranties, every element contributes to systems that protect buildings for decades. Understanding this complexity helps everyone in the construction industry—from architects and contractors to building owners—appreciate the sophisticated technology protecting structures from environmental exposure while maintaining aesthetic appeal year after year.
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