#25 – Different Types of Coatings on Metal Roofing

February 28, 2017 | Filed under: Metal Roofing 101 Series, Roofing Help Videos

Whereas high end natural metals like zinc and copper do not need any coatings, there are four basic coating options available for steel and aluminum roofs. Three of those four are paint finishes which I will review here in a bit. The other type is a stone coating.

Stone coatings incorporate granules similar to those on asphalt and fiberglass shingles but they are glued to steel. These finishes are beautiful but they are prone to two of the common asphalt shingle problems that we often hear folks want to avoid. They lose granules over time, much like standard shingles, and they also are quite prone to black streaks of algae and mildew growth.

The painted products do not have granules to wear off and they are far more resistant to streaking but there are quality options available with painted finishes as well. At the very low end of finishes are clear coatings. Commonly applied to galvalume steel for a natural metal look, these acrylic clear coatings are primarily to provide lubricity and protection for the metal while it is being formed, transported to the jobsite, and installed. These coatings wash away over time – usually in less than 10 years.

The next step up in terms of paint finishes are coatings that use polyester as the resin to hold the paint to the metal and also to bond the pigment – or coloring – in place. There are several grades of polyester coatings and you will hear words like siliconized, modified, and super polyester. While the high end polyesters out perform the lower end products, these are still mid-level coatings in terms of longevity and fade and chalk resistance. The polyester resin will break down over time, allowing the pigment to be released through chalking. The breakdown of the resin also allows UV rays to begin to cause the pigments to change color.

The highest quality architectural coatings today are known by the chemistry name polyvinylidenefluoride or PVDF for short. They are sold under the trade names of Kynar and Hylar. These unique coatings use the mineral fluorite for their resin, creating a very tight molecular bond that is similar to Teflon. They resist dirt and hold their integrity for the long term, allowing the metal roofing industry to give the best fade and chalk warranties for these finishes. There is no better finish even on the horizon at this point. For this reason, we strongly encourage these PVDF coatings for residential metal roofs.

Kynar 500® is a registered trademark belonging to Arkema Inc.
Hylar 5000® is a registered trademark belonging to Solvay

4 responses to “#25 – Different Types of Coatings on Metal Roofing”

  1. bomi says:

    Thanks for your informative post about coating and paints. PVDF in particular. We are looking to replace our old shingled room with a metal roof, in the greater toronto area. Would you happen to know of any metal roofing companies that utilize PVDF in their finish? Once again thanks for the educational read, much appreciated.

    • Todd Miller says:

      Most larger manufacturers of metal roofing will offer a PVDF finish option. Only a few of the smaller, more regional players will not offer it. The PVDF coatings are promoted and sold under the names of Kynar 500 and Hylar 5000. Some of the manufacturers with products being sold in the GTA that I am sure offer PVDF include: EDCO Arrowline, Kassel & Irons, Classic Metal Roofing, Ideal Roofing, and Vic West. I am sure that there are many others. Again, some of these companies will offer a couple of different quality levels of coatings, with PVDF being the highest quality. Feel free to contact me anytime. If you’d like to send me photos of your home for my input, my email is todd@asktoddmiller.com.

  2. Jim Friis says:

    Todd, we have recently repainted our house with a new color scheme and now the red metal roofing on two porches doesn’t work well with the new color of the house. Is it possible to field coat the metal with a new color (natural alum/steel) or should we consider replacement?

    • toddmiller says:

      Repainting should be possible if the current finish is well adhered. Keep in mind that a field applied coating will never have the durability of the original finish. Also, repainting will probably void any remaining warranty on the roof. Repainting would consist of cleaning the roof, applying a primer and allowing it to dry, and then a top coat. Sherwin Williams has a paint system they recommend. Above that, you could look for an air-dry PVDF for enhanced fade and chalk resistance from Tnemec or Aquatec. Contact me anytime.

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