Coal Tar Roofing:

Until the late 1970s, coal tar was the technology of choice for flat and low-slope commercial roofing. Its unique structure, with closed rings of atoms linked to form a stable molecular configuration, makes coal tar highly impervious to the natural enemies of roofing: water, ultraviolet (UV) rays, atmospheric oxygen, and chemicals, such as airborne salts or the corrosive agents found in urban pollution.

The last several decades have seen the introduction of alternative organic technologies, including asphalts; modified bitumen systems, in which asphalts are modified with polymer chemistry to improve their performance properties; rubber technologies, such as EPDM; and composites comprised of plastic-like polymers. In addition, metal technologies have seen significant improvements in the last two decades, with the introduction of unique fastening methods and innovative aesthetic detailing that have improved their performance while widening their appeal.

Although each of these technologies has an appropriate use in the commercial roofing arena, today’s coal tar technologies continue to offer unique benefits for challenging applications, particularly those that are subjected to occasional ponding. If you own commercial properties with low slope or flat roofs — and you plan to hold on to those buildings for 20 years or more, it’s time to revisit the many advantages of advanced coal tar roofing technologies.

Performance Advantages
The traditional coal tar system is a built up roof that is manufactured on site, with layers of felts adhered to the roof using hot-applied coal tar pitch. It is the coal tar that protects the roof from the elements, while the felts act as reinforcement. Simple though this sounds, the impregnability of coal tar, even in this basic configuration, ensures lasting protection against the elements.

Coal tar's molecular structure provides the extraordinary benefit of actually healing itself as it begins, like all organics, to succumb to natural degradation. Specifically, any cracks that might be formed by impact or rapid drops in temperature, reseal when surface temperatures rise and the coal tar softens. These self-healing properties provide a long-term roofing solution that will require less maintenance than most roofing systems.

To counteract its low softening point, coal tar roofing requires surfacing with gravel, which provides a durable surface for roof traffic. Coal tar's unique chemical properties allow it to remain insoluble in water, explaining why many coal tar roofs are preferred for roofs with ponding water. Unlike most roofing materials, coal tar shows good resistance to attack from most organic compounds. Hydrocarbons, gasoline vapors, exhaust fumes, and cooking oils and fats do not affect coal tar, making it ideal for applications that require some chemical resistance. Attributes such as these have made coal tar roofing a long-term solution for flat and low-slope roofs for decades.