Sunday, June 17, 2007
IT STARTS WITH THE FINISH
Just a hunch but I suspect that someone out there is itching to know more about the paint finishes used on metal roofing. Following is an article written with the help of my company's paint supplier, Valspar. And, of course, if you want to know more about metal roofing, CLICK HERE.
A critical part of any metal roofing system is its finish. While some exotic metals such as copper, zinc, stainless steel, and titanium are often sold with a natural or “mill” finish, most metals are sold with a paint finish which provides protection and aesthetic beauty. Galvanized steel and galvalume steel are sometimes sold without a paint finish, or with a thin clear coating but consumers should keep in mind that those products are the “economy” end of metal roofing with minimal benefits for residential application.
There are several types of paint finishes available on metal roofing today. In most cases, these coatings are applied to the metal before it is formed into roofing – while it is still in coil form. The fact that these coatings can then endure the forming process is strong testimony to their ultimate durability.
Paint systems consist of three parts: Pigment, Resin, and Carrier. Let’s take a look at each of these and how it impacts the overall paint chemistry.
Pigments provide paint with its color. There are various types of pigments -- principally “organic” (contains the element carbon) and “inorganic” (sometimes called “mineral” or “ceramic”.) Organic pigments generally are less opaque, more difficult to control for color fastness and may also be water soluble. For that reason, quality paint finishes use Inorganic pigments. Inorganic pigments can be simple (and inexpensive) such as Red (Iron) Oxide or they can be complicated mixtures of metal oxides. The latter type, such as Cobalt Blue, may exist naturally or, more commonly, may be industrially prepared. These complex oxide types have high heat resistance in addition to extreme resistance to weathering-and are referred to as Ceramic pigments. In developing a paint system the appropriate pigments are suspended in a material called Binder (or Resin).
Resin binds the pigment particles and forms the smooth and adherent surface that we expect. There are many types of chemistry suitable to prepare paint but only a few can withstand the rigors of roof exposure and the destructive UV rays of the sun. Three types are in widespread use today: Polyester, Polyester Silicone, and Fluropolymer. Let’s take a further look at each of these:
• Polyester An organic binder, polyesters are moderate price with moderate performance. As an exterior coating, these finishes are typically used on low-demand products such as residential rainware, soffits, fascia, or sometimes siding. Polyesters are often formulated in light colors such as white or beige. The Metal Construction Association (MCA) would rate the best examples of polyester paints as “Standard” meaning they pass 5-year Florida Exposure Fence testing.
• Polyester Silicone The addition of a significant amount (30%) of silicone to a polyester finish increases cost, decreases hardness/flexibility and most importantly increases color holding and chalk resistance. An important chemistry, polyester silicone provides long term durability especially for sidewalls. Use on roofing, especially for high visibility applications such as residential or consumer commercial is a little questionable for these finishes, especially in Southern locations. They also meet the MCA criteria for Standard Performance.
• Fluropolymer-aka Kynar or Hylar When it comes to metal roofing, this is the best known and best performing finish category. These finishes offer top performance in terms of flexibility and maintaining color. They are ready for the most challenging needs. They are definitely the answer for the types of “difficult” that are usually used residentially such as dark earthtones, low gloss finishes, metallics and even “saturated” colors such as intense reds or blues. These are the only coatings that satisfy the MCA criteria for Premium System including 10 years Florida actual data.
Carrrier-This is the part of a paint system that you never see! The carrier gives proper fluidity, assists with adhesion to the substrate, and adjusts the speed of evaporation / drying. When the metals used for roofing are painted, the carrier disappears during the heat curing, or “baking,” process.
In many cases, distributors and contractors handling metal roofing are completely unaware of the various paint systems. As a result, they may anecdotally make performance claims which are unrealistic and misleading. Homeowners considering a metal roof should always know and understand the chemistry, attributes, and expected performance of the finish on the product they choose. Manufacturers and contractors who care about the metal roofing industry will gladly explain and guide homeowners through this process.
A critical part of any metal roofing system is its finish. While some exotic metals such as copper, zinc, stainless steel, and titanium are often sold with a natural or “mill” finish, most metals are sold with a paint finish which provides protection and aesthetic beauty. Galvanized steel and galvalume steel are sometimes sold without a paint finish, or with a thin clear coating but consumers should keep in mind that those products are the “economy” end of metal roofing with minimal benefits for residential application.
There are several types of paint finishes available on metal roofing today. In most cases, these coatings are applied to the metal before it is formed into roofing – while it is still in coil form. The fact that these coatings can then endure the forming process is strong testimony to their ultimate durability.
Paint systems consist of three parts: Pigment, Resin, and Carrier. Let’s take a look at each of these and how it impacts the overall paint chemistry.
Pigments provide paint with its color. There are various types of pigments -- principally “organic” (contains the element carbon) and “inorganic” (sometimes called “mineral” or “ceramic”.) Organic pigments generally are less opaque, more difficult to control for color fastness and may also be water soluble. For that reason, quality paint finishes use Inorganic pigments. Inorganic pigments can be simple (and inexpensive) such as Red (Iron) Oxide or they can be complicated mixtures of metal oxides. The latter type, such as Cobalt Blue, may exist naturally or, more commonly, may be industrially prepared. These complex oxide types have high heat resistance in addition to extreme resistance to weathering-and are referred to as Ceramic pigments. In developing a paint system the appropriate pigments are suspended in a material called Binder (or Resin).
Resin binds the pigment particles and forms the smooth and adherent surface that we expect. There are many types of chemistry suitable to prepare paint but only a few can withstand the rigors of roof exposure and the destructive UV rays of the sun. Three types are in widespread use today: Polyester, Polyester Silicone, and Fluropolymer. Let’s take a further look at each of these:
• Polyester An organic binder, polyesters are moderate price with moderate performance. As an exterior coating, these finishes are typically used on low-demand products such as residential rainware, soffits, fascia, or sometimes siding. Polyesters are often formulated in light colors such as white or beige. The Metal Construction Association (MCA) would rate the best examples of polyester paints as “Standard” meaning they pass 5-year Florida Exposure Fence testing.
• Polyester Silicone The addition of a significant amount (30%) of silicone to a polyester finish increases cost, decreases hardness/flexibility and most importantly increases color holding and chalk resistance. An important chemistry, polyester silicone provides long term durability especially for sidewalls. Use on roofing, especially for high visibility applications such as residential or consumer commercial is a little questionable for these finishes, especially in Southern locations. They also meet the MCA criteria for Standard Performance.
• Fluropolymer-aka Kynar or Hylar When it comes to metal roofing, this is the best known and best performing finish category. These finishes offer top performance in terms of flexibility and maintaining color. They are ready for the most challenging needs. They are definitely the answer for the types of “difficult” that are usually used residentially such as dark earthtones, low gloss finishes, metallics and even “saturated” colors such as intense reds or blues. These are the only coatings that satisfy the MCA criteria for Premium System including 10 years Florida actual data.
Carrrier-This is the part of a paint system that you never see! The carrier gives proper fluidity, assists with adhesion to the substrate, and adjusts the speed of evaporation / drying. When the metals used for roofing are painted, the carrier disappears during the heat curing, or “baking,” process.
In many cases, distributors and contractors handling metal roofing are completely unaware of the various paint systems. As a result, they may anecdotally make performance claims which are unrealistic and misleading. Homeowners considering a metal roof should always know and understand the chemistry, attributes, and expected performance of the finish on the product they choose. Manufacturers and contractors who care about the metal roofing industry will gladly explain and guide homeowners through this process.
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