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Alu-zinc is an aluminium-zinc coated steel sheet that can be used unpainted up to corrosive class C3. The name AZ150 indicates the coat weight of 150 g/m2 per double side. The surface has been treated with SPT (Surface Protection Treatment) to prevent stains during handling and to ease shaping.
The surface is initially glossy metal with a rose pattern but after some time it turns greyish, and eventually it becomes matt grey.
Normally, the trimmed edges do not need to be painted but in corrosive environments in which the trimmed edges are aesthetically prominent a protective paint is recommended to be applied
It is customary to separate between the aesthetic and technical lifetime. The aesthetic lifetime is a measure of the time it takes for the top coat to change to such an extent that the appearance no longer meets the requirements. The technical lifetime is the time it takes until the sheet no longer can protect the supporting constructions or foundations of the building. The layer of Alu-zinc has a thickness of approx. 20 μm (0.020 mm) per side for AZ150.
The corrosive speed, i.e. how much of the coating that disappears each year, is a maximum of 0.2 μm in a normal environment (C2) in which Alu-zinc is freely exposed. Due to corrosive and appearancerelated reasons, the following combinations should be avoided to prevent them from affecting the aesthetic and technical lifetime:
Alu-zinc in combination with copper, brass or lead can cause galvanic corrosion. Avoid drainage from constructions and roofs that contain these metals. In particularly aggressive environments, even stainless steel and nickel can increase the corrosive speed of Alu-zinc.
Alu-zinc in contact with highgrade woods, damp wood or wood with waterproofing containing copper can cause black rust or corrosion.
Alu-zinc in combination with bitumen products without a UV stabiliser.
Alu-zinc in combination with wet concrete, cement and plastering that are very alkaline can cause discolouration or black rust.
Alu-zinc has an ability to repair itself which makes the material resistant to corrosion caused by scratches. The long lifetime is due to the fact that the aluminium-zinc coating provides the steel sheet with a double protection against corrosion. The first protection factor is the coating on the steel sheet that forms a passivating barrier against general corrosion. The other protection factor involves the formation of a galvanic element when the sheet is exposed to moisture (electrolyte), resulting in zinc ions flowing over and protecting the exposed steel against corrosion in scratches or trimmed edges.
The Manufacturing Process
The manufacture of asphalt roofing products is a continuous process performed on a roofing machine that begins at one end with a roll of core material and concludes at the other end with the finished product. This sequence of operations builds the product up in stages, adding materials along the way and monitoring their operations. The graphic below illustrates the sequence of events.
The Advantages of Asphalt Products
The dominance of asphalt roofing products through the years has not evolved as a matter of chance. It is based on proven product performance that goes beyond the basic roofing requirements of providing a covering that shields the building’s inhabitants from the weather. The characteristics have earned asphalt roofing its leading position include the following:
- Weather Resistance. Asphalt roofing products are proven to resist sunlight, heat, cold, water and ice.
- Fire Resistance. Asphalt roofing products are manufactured to comply with ASTM International and/or Underwriters Laboratories (UL) standards for fire resistance.
- Wind Resistance. Asphalt roofing products comply with the wind-resistant standards of Underwriters Laboratories.
- Efficient, high-volume production plus relatively low cost of application result in economies that are difficult for competing roofing materials to match. Moderate installed costs combined with long service life gives asphalt roofing products a very low annual or life-cycle cost.
- Ease of Application. Asphalt roofing is considered to be the easiest of all standard roofing materials to apply.
- Because of their flexibility and strength, asphalt roofing products can be applied on a wide variety of roof styles.
- Asphalt roofing is available in many appealing colors, shapes and dimensional depths that provide bold roof appearances. The wide range of asphalt roofing products introduced in recent years offer much greater flexibility in choosing the appearance of a building’s exterior than is available with most other types of roofing material.
- Style Suitability. Asphalt roofing is completely “at home” with most architectural styles, whether contemporary, modern or traditional.
- Low Maintenance. Properly chosen and applied, asphalt roofing products require little or no upkeep and are easily repaired, if damaged.
How long have PVC, or vinyl, roofs been around? Are they among the leading systems for commercial roofing?
Originally introduced in Europe in the early 1960s, polyvinyl chloride (PVC) roofing systems were among the first single-ply commercial roofing materials. Today, reinforced PVC roofs – also called vinyl roofs – account for 65 percent of the European commercial roofing single-ply market, and North American growth has outpaced the commercial roofing industry as a whole for more than 10 years. In 1985, PVC roofing systems were the first single-ply roofing products to obtain a standard designation from the American Society for Testing and Materials (now ASTM International): ASTM D4434 – Standard Specification for Poly(vinyl chloride) Sheet Roofing – which is regularly updated. Today, PVC is an increasingly popular thermoplastic roofing membrane worldwide.
What makes PVC roofs so special?
PVC roofing systems have witnessed tremendous growth in recent years due to a variety of standout characteristics, notably: longevity; durability in harsh weather and temperature extremes; low life-cycle costs; energy efficiency; heat and solar reflectance; flame resistance; chemical and grease resistance; ease of maintenance; ease and flexibility of installation; and inherent recyclability/re-use, among many other benefits. Often referred to as the first “cool roofing” system, PVC is energy-efficient, environmentally sustainable, long-lasting and costeffective.
How are PVC roofs energy-efficient?
Lots of ways! White PVC roofing systems not only reflect sunlight and solar energy to save building owners up to 40 percent in annual electricity costs, they also improve the performance of the underlying roof insulation by 25 to 50 percent; extend the useful life of the roof by as much as 75 percent; enable rooftop cooling equipment to run more efficiently; contribute to better indoor air quality and comfort; and collectively help mitigate the effects of urban heat islands and the air pollution they cause.
Environmental groups seem to think that PVC is one of the most hazardous products ever created – dangerous to human health and the environment. How do you answer that?
During the last 35 years, there have been literally dozens of scientific studies and more than 26 full-scale LCAs relating to the safety and environmental impact of vinyl production, use and disposal. Study after study by a wide range of scientific, governmental, academic, and industry groups has confirmed that vinyl production in the United States today is very safe, and that finished vinyl products, including PVC roofing membranes, are inert, posing no risk to human health and very little impact on the environment. In fact, many PVC products – including reflective PVC roofing systems – often make a decidedly positive contribution toward sustainability.
According to Dr. Patrick Moore, a co-founder of Greenpeace in 1971 and current chairman and chief scientist of Greenspirit Strategies: “It’s completely unacceptable for these activists to call PVC ‘toxic’ when PVC’s effects on health and the environment have been investigated at every stage from manufacture through use and on to final disposal – in all cases vinyl has been shown to be safe and environmentally sound.”