02 Dec Buying A Metal Roof Part 3: Coatings
In most cases, the coatings on metal roofing are applied before the manufacturer or contractor ever even sees the metal. The finishes are applied at roll-coating facilities where the metal is cleaned, chemically etched, coated, and baked. In some cases, a “print coat” is involved as well, allowing for these finishes to have an attractive multi-hued appearance. After coating, the coiled metal is shipped off to the manufacturer who fashions it into the various profiles. The finishes used in the metal roofing industry consist of three main components: 1) the pigment (also referred to as “solids”), which gives the coating its color, 2) the solvent, which is the liquid medium that is baked off after the coating has been applied, and 3) the resin, which binds the pigment to the surface after the solvent is gone. The finishes used in the metal roofing industry are classified by the quality of their resins.
There are three main types of coil-applied baked-on metal finishes used in the North American metal roofing industry today. Water-based acrylic emulsions are one of the most common and most environmentally-friendly coatings. They are typically two-coat systems consisting of a primer coat followed by a topcoat. They do not carry a warranty for fade or chalk. (Older aluminum siding was known for its chalking. Like the blackboard at school, if you rubbed your hand on old siding, you would end up with a fine white powder on your palms, shirt and pants.)
Another coating type is polyester coatings including a number of formulations such as siliconized modified polyester (SMP). Like acrylics, polyesters are lower cost finishes and also subject to fade and chalk over time. SMP finishes are higher quality than more generic polyester paints, but still won’t achieve the performance of the standard for today’s metal roofing industry: polyvinylidene fluoride (PVDF).
PVDF coatings are usually sold and applied to metal as the trade names Kynar and Hylar. These are two-coat systems with a primer coat followed by a topcoat. If the formulation is made up of the standard 70% Kynar or Hylar resin, it can use the full Kynar 500 or Hylar 5000 trade names. These trade names are used so that consumers, contractors, and architects can tell for sure that the finish on the metal roof system they are selecting is of the highest quality possible. There is no substantive difference between Kynar PVDF resin and Hylar PVDF resin, except that they are manufactured by two different companies, and thus marketed under two separate trade names. Kynar 500 / Hylar 5000 finishes usually carry a 30 year fade warranty up to five Delta E units. A Delta E unit is the smallest recognizable color shade shift seen by the naked eye. PVDF represents the highest quality coatings available for use on metal roof systems. Most metal roofing manufacturers and contractors would never recommend selecting a residential product that uses something other than a PVDF – Kynar 500 / Hylar 5000 finish.
In addition to these base coating options, some steel shake, shingle and tile profiles include an extra layer of coating to add both beauty and functionality to the products. This type of coating is applied “post-forming,” which means after the profile is fashioned by the manufacturer. The advantage of these post-forming coats, in addition to creating a gorgeous look, is that they can help seal off any cracks or fissures in the zinc or zinc/aluminum coating over the steel that may have occurred during the fashioning of the profile.
The two main options here are stone-coatings and Kynar powder coatings.
Stone coated steel products (also called “aggregate” or “granular” coated) are used very extensively for residential applications, primarily on the West Coast and in the Southwest. These coatings present a multi-hued, textured appearance and are primarily used on shake and tile profiles. The coatings consist of ceramic-coated sand or stones, which are bonded to the base steel and then covered with a clear acrylic coating.
The other post-forming coating option, the Kynar powder coat, is so far a Classic Metal Roofing exclusive and perfect for creating roofs for North Carolina homes. This coat is an electro-statically applied Kynar powder coat that is then baked into the base Kynar coat. The result is a beautiful, long-lasting, scratch-resistant, multi-hued coat that represents the pinnacle of modern coating technology. We call this coat the ThermoBond Textured Finish.
The newest development under the “coatings” headline is probably the most exciting due to its potential impact on the entire roofing industry: reflective pigment technology. These specially formulated pigments, which were first developed by the military in order to help camouflage tanks against infrared detection, are able to reflect a much larger percentage of the sun’s rays even in darker colors. This means that less heat is absorbed into the attic space, and therefore less energy is required to keep the home at a comfortable temperature during the hot summer months. The end result is a reduction in the home’s energy bills! Classic was the first specialty residential roofing manufacturer to incorporate this technology into all its product lines. Classic calls this technology Hi-R, for highly reflective. Other manufacturers are marketing their versions under various names, and the stone coatings are developing this technology as well.
Please note that all galvanized steel, galvalume, and aluminum roofs should have some sort of protective coating on the backside of the metal as well. It is acceptable for this to be a low cost coating. In many cases, it might be colorless.
So, that’s a lot of information about metal roof coatings. But if you’d like to know more, check out Classic Metal Roofing Systems’ process for manufacturing metal roofs.
Expert Advice and Free Estimates for A Metal Roof from A – W in North Carolina
And when you’re ready to talk to a contractor, McCarthy Metal Roofing Systems is here with expert advice and free roofing estimates for Apex, Burlington, and Cary, NC metal roofs…to Wake Forest, Wilmington and Wilson, NC…and the entire Triangle Area.
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Next Up in the Buying A Metal Roof Series: Sound Transmission