Commercial properties use different types of materials for their roofing, one of which is modified bitumen or asphalt. It was first used in Europe in the early 1960s and in the US in the mid-1970s. Today, it remains one of the top choices for flat and low-sloped roofing. Modified bitumen roofing is composed of polymer-modified bitumen reinforced with one or more layers of fabric. This could be polyester, glass fiber, or a combination of both. This type of roofing can be installed using conventional methods such as hot or cold application or self-adhered. Withstanding the test of time, bituminous roofing products bring a proven track record to low-slope roofing. Bituminous roofing systems are known for their long service life, dependability, and exceptional waterproofing. There are two main types of bituminous roof systems, built-up roofing (BUR) and multi-ply, polymer-modified bitumen. The two-main polymer-modified bitumen membranes on the market are SBS and APP membranes.
Built-Up Roofing (BUR) BUR systems have been used for more than 100 years in the United States. BUR systems are composed of alternating layers of oxidized bitumen and bitumen-coated membranes, often called felts or ply sheets. Ply sheets are generally reinforced with a dimensionally stable, high tensile strength fiberglass mat. BUR systems are surfaced with an aggregate or roof coating to improve the weathering capability of the system, and the redundant, multi-ply approach ensures the system provides dependable waterproofing for many years. Modified Bitumen (Modbit) Systems Modbit systems consist of base plies and a cap sheet, sharing the main dependable waterproofing benefits of a BUR system. Modbit systems are highly customizable. sheets in modbit systems are surfaced with a mineral granule to increase the weatherability of the system, and cool roof granules and coatings can be used to reflect UV rays, increasing the long-term performance of the roof, and lowering energy costs for the building. SBS Membranes SBS membranes are constructed with bitumen that has been modified with elastic Styrene-Butadiene-Styrene (SBS) polymers to form a “rubberized” asphalt coating. The coating is applied to a reinforcing carrier of fiber glass for high tensile strength and dimensional stability, polyester for superior elongation and tear strength, or a composite of the two. SBS membranes offer excellent flexibility, especially in cold weather. SBS membranes can be self-adhering but are generally installed with mopping asphalt or cold adhesive.
APP Membranes APP membranes are constructed with bitumen that has been modified with plastic Atactic Polypropylene (APP) polymers, resulting in a coating with the highest temperature range and enhanced durability and toughness. The coating is usually applied to a polyester carrier mat, but a small number of fiberglass products also exist. APP membranes are mainly torch-applied due to the plasticized bitumen’s ability to melt. Modified bitumen is manufactured in factories and sold in sheets. It is specially made to have equal thickness and physical properties throughout the entire sheet. A finished roofing membrane can have one or several bitumen sheets, but it can also have a combination of built-up roofing felts and one or more modified bitumen sheets. Modified bitumen is recommended for roofing because of the following features:Longevity – This type of roofing can last up to 20 years without the need for too much maintenance. Strength – Both types of modified bitumen roofing can withstand both high and low temperatures due to polymer modification. The number of sheets also improves durability. Waterproof – The adhesives used to attach modified bitumen provide protection against water damage.Energy efficient – This type of roofing material comes with an insulating layer that limits the flow of heat throughout the system. Another use for modified asphalt in roofing applications is in waterproofing underlayment. Underlayment is a layer of material placed between the roof deck and the exterior surfacing material (typically shingles, wood shake, metal, tile, slate, or cap sheet). It is critical, though often overlooked, a component of any complete roofing system.
The underlayment helps keep the deck dry during installation until the surfacing material can be applied. On a finished roof, it will provide secondary protection from wind-driven rain, ice dams, and other types of moisture penetration. It can also help a roof system meet required fire ratings and minimize picture framing, which is the visible outline of deck panels caused by irregularities in roof decking thickness. Underlayment can be divided into two broad categories based on the technique by which it is affixed to the roof deck. Mechanically attached membranes rely on staples, nails, screws, or other types of fasteners to hold them in place. Self-adhered underlayment is comprised of an integrated adhesive layer, usually a polymer-modified asphalt, which bonds directly to the deck beneath it. Self-adhered materials are generally used in valleys, eaves, and rakes (sloped sides) where water can back up due to clogged gutters or the accumulation of snow, ice, leaves, and other debris. Mechanically attached sheets are used in the field of the roof. However, in certain areas where storms and high wind are prone to lift or remove the roof surface, building codes may require the self-adhered underlayment to be used on the entire roof deck. Self-adhered underlayment must perform in a wide range of environments. The adhesive should remain pliable and adhere to the roof deck during installation at temperatures as low as 40°F (4°C) while maintaining thermal stability at conditions above 200°F (93°C). Furthermore, the material should remain completely waterproof, even after penetration by fasteners used to attach the roof surfacing material. Asphalt modified with a small amount of styrene diene block copolymer (approximately 3-12% by weight) has been used extensively in the industry to achieve the desired performance. Specifically, these mixtures exhibit the small thermal susceptibility needed to provide low- temperature adhesion and high-temperature cohesion, as well as strength, toughness, and elastic recovery. The compound most commonly used in this application is a styrene-butadiene-styrene (SBS) block copolymer. Combinations with vinyl and acrylic olefins or other polyolefins are also used. The exact blend will depend on the desired physical properties and applications.
Many factors must be considered when formulating these blends. The chemistry of both the base asphalt and polymer strongly affects the efficacy of polymer modification. Both the extent and stability of polymer dispersion in the asphalt matrix can be established with ultraviolet microscopy (qualitative), and/or with “cigar tube” separation tests and creep-recovery measurements on a rheometer or quantitative. Regarding the choice of styrene polymer, molecular structure (radial/ branched vs. linear), coupling efficiency, molecular weight distribution, degree of hydrogenation, and vinyl content can be optimized to improve blending and yield the necessary attributes in the finished product. Other additives may be combined with the styrene polymers to further enhance adhesion, improve the compatibility of the asphalt-polymer blend or reduce the viscosity of the mixture to facilitate manufacturing. Self-adhered underlayment is integral to a roofing system and must meet many requirements to ensure suitability for use. Polymer-modified asphalt is a key component of this composite material, and careful selection of both polymer and asphalt is essential to certify sound performance throughout the service life of the roof. In conclusion, asphalt or bitumen are the best materials to be used in roofing systems. With the correct modification, they will be unbeatable. Our company is proud to be one of the biggest suppliers of natural and synthetic bitumen. contact us for more inquiries or any further needed information.