While metal roofing substrates are durable on their own, their ability to last up to 50 years relies heavily on their paint system. For metal roofing, the paint system is made from three basic ingredients: resins, pigments, and additives. Pigments add color to the paint system, and additives help those pigments attach to resins. In general, these ingredients do not affect the strength of a paint system.
Resins are arguably the most important part of the paint. They surround the pigments to improve the durability of the paint system. Resins most acutely distinguish finishing coats and often provide the name of the paint system. Of those available to metal roofing fabricators, the two most common resins are polyvinylidene fluoride (PVDF also commonly referred to as Kynar®1 or Hylar®2) and siliconized-modified polyester (SMP).
PVDF and SMP both have their pros and cons, which can make choosing between them difficult for roofing professionals. Knowing how PVDF and SMP compare in the following three categories can help fabricators and distributors identify the better material for each specific project.
Due to differences in their chemical structures, SMP will fade more quickly than PVDF. Because PVDF is composed of alternating carbon-hydrogen and carbon-fluorine bonds, it lends the highest resistance to UV exposure, oxidation, humidity and extreme temperatures of any resin to its metal roofing system. This not only protects the metal substrate it covers but also ensures the color of the finish will remain bright, fading 5 Hunter Units or less over 35 years. No matter the color, PVDF offers superior fade resistance.
SMP creates a harder finish, which can protect metal substrates from harsh weather and debris including broken or fallen tree limbs. For this reason, SMP may be a more economical choice when roofing an industrial building, where aesthetic concerns are secondary to impact resistance.
That said, PVDF does provide resistance to harsh weather including UV exposure and extreme temperatures. While it does have superior color stability, it can have a lower impact resistance than SMP. Accordingly, fabricators should consider the purpose and placement of a building before making a finish recommendation.
Chalking refers to the appearance of a powdery substance on the surface of a coating. Chalking contributes to the appearance of color loss—the more chalk that appears, the duller and older the color will look. Just as with fade resistance, a resin’s resistance to chalking depends on its chemical structure. Initially, both SMP and PVDF can appear to have similar chalking resistance. But over time, SMP will abruptly lose this resistance. PVDF’s strong chemical bonds offer stable chalking resistance for 35 years or more, making it a better finishing choice over the entire life of a metal roofing system.
Advances in coating have improved all finishes, including both SMP and PVDF. Both finishing coats will increase the lifespan and durability of a metal roofing system, and both will look great when first installed. However, due to its incredibly strong chemical structure, PVDF will resist fading and chalking under any condition for much longer than an SMP coating. This high-level color stability makes PVDF a better coating option for buildings that need to last a long time and look stunning for years to come.
Drexel Metals backs their PVDF coatings with industry-leading 35-year limited warranties to give building owners and fabricators peace of mind that their metal roofing systems will look great today, tomorrow and decades down the line. Further, as greater demand puts a strain on PVDF manufacturing, Drexel Metals will rely on longstanding relationship with Sherwin Williams to continue to secure a supply of this finish.
1. Kynar® is a registered trademark of Arkema Inc.
2. Hylar® is a registered trademark of Solvay
