Asphaltic and modified bitumen roofing membranes comprise one of the largest segments of the low slope roofing market. The asphalt used for roofing is usually blended with reinforcing agents such as calcium carbonate to increase strength and decrease flow. If the material is modified bitumen, the asphalt is blended with a polymeric modifier such as atactic polypropylene (APP) to create APP-modified bitumen or styrene-butadiene-styrene (SBS) block copolymers to create SBS-modified bitumen. Two variants are SEBS (styrene-ethylene-butadiene-styrene) and SIBS (styrene-isobutylene-styrene) block copolymers.
Asphalt is a by-product of the crude oil refining process. After the "lighter fractions" are distilled off, (gasoline, kerosene, diesel fuel, grease) the remaining crude oil, called flux, is the basic building block for asphalt and modified bitumen. While asphalt has excellent waterproofing properties, it is extremely susceptible to attack by UV radiation. The deterioration that is observed as cracking and chalking is a direct result of this attack. The underlying mechanism is twofold. Chemical analyses of asphalt have shown it to be composed of hundreds of different chemical components. Some of these components are liquids at room temperature, but when dispersed in the asphalt matrix, appear to be solids. Over time and with the addition of heat (IR), these light fractions leach out. This has two effects. First, the loss of this material slightly reduces the size of the roofing material (i.e. volume reduction). This loss of dimension, or shrinkage, may cause stress on the seams and fasteners, reducing the service life of the roof. Moreover, these light fractions also act as plasticizers, making the membrane more flexible, especially at low service temperatures. Some of the stone granules that protect the bitumen cap sheet may become dislodged and collect in the gutters and low spots on the roof. This is a result of the loss of these asphalt fractions that act as "glue" to adhere the granules to the asphalt surface. As the granules become dislodged, more asphalt is exposed to the harmful effects of the sun's UV and IR radiation. This, in turn contributes to a more rapid degradation of the asphalt membrane.
An additional weathering related reaction is that of oxygen in the air with some of the components of the asphalt. This chemical reaction causes the asphalt to become less hydrophobic, as hydroxyl radicals are created on the component chains. This reaction can be observed by wetting aged asphalt with water and checking for a soapy feel. The soapy "feel" is the result of the asphalt reacting with oxygen.
Understanding the fundamental mechanism for asphalt deterioration now enables us to identify methods for extending its service life. If the asphalt can be protected from the harmful effects of UV, keep it cooler, and prevent its contact with oxygen, it will last longer. This can easily be accomplished through the use of white, UV blocking roof coatings, such as those of the AcryShield product line.
National Coatings AcryPly Roof Restoration System and AcryShield Roof Maintenance Systems are ideal for renewing and restoring your existing Asphalt, BUR, or Mod Bit roofing membranes. These systems allow you to gain a brand new, leak-free, monolithic roofing system without the extra cost, time and stress of a traditional roof replacement/roof tear-off system. Restoring your aged asphalt roof saves you time, money and allows for a cleaner environment. These systems are ideal for businesses that cannot afford to be closed during construction and application. For more information on our non-intrusive roofing systems, download our FREE Benefits Brochure or contact us at 800-423-9557.