A common question we always have, when looking at a material we don’t personally work with, is “what’s that made of”. This is an especially common question roofers get, in relation to shingles. They’re referred to as “asphalt shingles”, but to non-roofers, asphalt is a more or less solid pacing material also commonly called “blacktop”. How can flexible, moderately-light-weight roofing components possibly be made of street-paving material?
Well, the truth is, they’re not just slabs of pure asphalt, but layers of specialized materials the topmost of which happens to be a specialized formulation of asphalt. The makeup of asphalt shingles is actually quite fascinating, so today, we’re going to take a closer look at them. Understanding the makeup of these materials will empower you to make the most informed decisions about your roof that you possibly can. Knowledge is power.
The exact makeup of roofing shingles varies from one manufacturer to the next, though there’s an overarching set of quality and fabrication standards they must comply with. Naturally, any given company is protective of their precise formula, but thanks to those standards, you can expect them all to be made of backing materials upon which there is a layer of asphalt coating. Most of these backings are reinforced with fiberglass or another flexible material with a high tensile strength, further enhanced by specialized resins and binding agents.
The Makeup of Asphalt
The first place to start is with the actual composition of asphalt itself. It’s a strange material. One of the reasons it’s so commonly-used for streets, parking lots, and driveways is the fact that, even once it hardens, it remains somewhat flexible. This reduces its ability to crack, crumble and erode when spread across long distances. It also, when applied conservatively, makes a good light-weight, weatherized coating.
Asphalt is, itself, a mixture of tars and rock, with additional additives to make it bind better, and harden more effectively, while remaining flexible. When applied to shingles, this is furthered even more by oxidation (blowing hot air through the shingle), which catalyzes all of this bonding even more. This extra process is not done to paving asphalt. The result is a coating that’s very resistant to temperature extremes, precipitation, and very good at absorbing and then radiating solar heat and UV once the sun sets.
The Surfacing of Shingles
The quickest way to spot an asphalt shingle is the slightly rough, granular surface, which is a bit different from other uses of asphalt. This is due to an extra, thin layer of crushed stone (usually lime stone), pulverized to a specific standard of size variation. Colorization of this stone is done either through special firing processes, or by adding an additional, thin layer of pigment polymer. The polymers are generally used in shingles designed to resist things like moss or algae in climates where such pests are exceptionally prevalent, with firing (a more affordable approach) done on less specialized shingles.
Of course, shingles must be resistant to water. Even in the desert, it can rain and even snow from time to time, and without bonding/laminates in place, they would become soggy, because asphalt is naturally semi-permeable. They would decay quickly when they became wet.
These bonding agents are very specialized compounds (and this is where a lot of companies are protective of their formulae), applied to the top, bottom, both sides, or throughout the many layers of a shingle. Since most shingles today are multi-layered, these laminates and bonding compounds are applied to each layer at the time of creation, which lets them not only resist water, but helps to unify the layers more effectively. These bonding agents are activated through heat and/or pressure, depending on the manufacturer.
The top layer of a shingle is commonly referred to as the “dragon tooth” given it has a somewhat toothy appearance, while the bottom is called the “shim”.
Shingle ingredients tend to be sticky, even if they don’t always feel like it to a passing touch. When packaged together, they’re under pressure, and often exposed to hot environments. To prevent them from sticking together, and to keep any adhesives/sealants from prematurely activating, a backsurface material is added. This powder is made of limestone generally. Finally, a one-sided tape, called release film, is added, to further prevent them from activating or sticking together.
Some shingles have an adhesive layer under this film, which is activated by pressure, chemically, or by heat. Others do not.
So, we can see that shingles are actually an intricate feat of chemistry, material sciences, and engineering. To learn more about them, and the other sciences of roofing, fill out our contact form today.