I know you had a 30-year warranty, but—after 15 years—those shingles simply must be replaced. Anyone can call a roofer, but why not take a shot at making your own shingles? But first you need a formulation—the recipe—and I’ve got just the one for you. And while we’re at it, let’s compare shingle manufacturing to metal roofing manufacturing.
In a U.S. News & World Report article on January 6, 2015, according to the National Association of Home Builders, you can expect to replace your:
- Air conditioning system every 10-15 years
- Water heater every 10 years
- Appliances every 10-15 years
- Asphalt shingles about every 20 years
In a blog post by McGarry and Madsen Home Inspection, they set the approximate lifetime of three-tab asphalt shingles at 15-18 years, while metal roofing is set at 30-45 years.
The Metal Roofing Alliance studies the market share of metal residential roofing vs. asphalt shingles and estimates that split to be 14% for metal roofing and 73% for asphalt shingles. All other materials make up the difference. Many have compared the properties of shingles and metal roofing, but in this blog I thought that it would be interesting to compare the formulation chemistry of each. Let’s first consider substrate.
The substrate for shingles is often a fiberglass web. For metal roofing, the common substrates are aluminum and metallic-coated steel, usually hot-dipped galvanized steel or Galvalume®. Both shingles and metal roofing are produced using a web-based coating process—but more on that later. Let’s first discuss the chemistry of these materials.
When discussing coatings technology, we often use the term “binder,” which is synonymous with the term “resin.” As the name implies, a binder “binds” together components in the formulation. For asphalt shingles, the binder is asphalt, a high-boiling (>900 °F), high-distillate fraction of petroleum. By comparison, gasoline is a light-distillate material, and kerosene and diesel fuel are middle-distillate materials. Asphalt is a mixture of many classes of chemicals, but primarily is composed of (according to Wikipedia):
- Naphthalene aromatics, consisting partially of hydrogenated polycyclic aromatic compounds
- Polar aromatics, consisting of high-molecular-weight phenols and carboxylic acids
- Saturated hydrocarbons
- Asphaltenes, consisting of high-molecular-weight phenols and heterocyclic compounds
By comparison, the binder (resin system) for coil coated metal residential roofing falls into two general classes:
- PVDF, a polymer made from vinylidene fluoride monomer
- Polyester and silicone-modified-polyester resins, polymers produced from purified isophthalic acid, hexanediol, and several other pure monomers
Each of the polymers for metal residential roofing start with pure chemical monomers, reacted under carefully controlled conditions to a well-defined endpoint at which the polymer properties are at an optimum level of performance.
For a shingle, the asphalt binder portion is a mixture of resin (the asphalt) and solid material, often termed “filler.” For a coil coating, the binder (the PVDF or modified-polyester/polyester-resin system) also encapsulates solid material, primarily in the form of colored pigments. The following generic recipes provides a helpful comparison:
|Asphalt Binder System||Coil Coating Paint System|
|PVDF, polyester, modified-polyester||0%||70%
(depends on the color of the coating)
|Filler (usually naturally occurring minerals)||60%||0%|
|Synthetic silica flattener||0%||2%
(depends on the gloss of the coating)
(the colored granules are sprinkled on top of the asphalt coating, and are not contained within the asphalt binder)
(depends on the color of the coating)
For those readers familiar with the coil coating process, you will recognize this example of a typical coil coating line:
But look at the similarity of the fiberglass web coating process for asphalt shingles:
In this rendering of a laminate shingle processing line, the entry end is to the far right. Here the fiberglass web enters a dry looper (we call this section the accumulator), and the processing moves toward the left. As in coil coating, a number of process steps are combined in this continuous process.
The distinguishing difference between the two processes is that the coil coating process ends with painted metal coils, which are then packaged and shipped to fabricators who roll form or stamp the coil coated metal into various shapes for use in metal roofing.
In this post we have discussed many similarities between shingles and metal roofing. Both are born of oil refining. Both can be formulated to be IR-reflecting with the use inorganic pigments. Both utilize a substrate, although the fiberglass mat in shingles hardly contributes to the material properties of the shingle, whereas in a metal substrate, the metal itself provides all the mechanical properties. Another big difference is the binder. Asphalt is a naturally occurring material that happens to have suitable properties for roofing and roads. The binders used in metal residential roofing coatings are formulated polymers, designed to provide outstanding properties such as resistance to degradation when exposed to heat and sunlight.
Residential roofing is a vast market, but just two products have a major share of the market: metal and asphalt shingles. While they share many attributes, longevity favors metal roofing because of the combination of a mechanically robust metal substrate coupled with coatings having exceptional resin (binder) chemistry.
Still want to make your own shingles? Or have I given you the real recipe—some “food” for thought?
David Cocuzzi, NCCA Technical Director