Unpainted Galvalume� Sheet in High Visibility Applications

The premier choice of designers and builders for high-visibility architectural projects is very often prepainted Galvalume steel sheet. It is extremely durable, very cost-effective, easy to install and available in a wide range of finishes, colors and panel configurations.

Unpainted Galvalume sheet is most often specified for low-slope roofing applications where functional performance is the primary consideration and cosmetic appearance is secondary. Galvalume sheet has clearly demonstrated its outstanding performance in these applications for over 20 years.

In some case, unpainted Galvalume sheet is being specified for high-visibility applications. The very attractive spangled appearance of the product, along with its excellent long-term durability, has contributed to this trend.

As with any materials used in high-visibility applications, extra care should be taken to maximize the desired appearance. End-users and specifiers should be aware of the following characteristics of unpainted Galvalume sheet which may affect cosmetic appearance.

Handling:

Just as care should be exercised in handling prepainted materials to avoid damage to the organic finish, care should be take when handling unpainted Galvalume sheet to avoid marring the metallic coating finish.

Surface Scratches/Abrasion - When the Galvalume sheet surface is abraded or burnished by agents such as hard-soled shoes or objects sliding over the surface, the coating becomes darkened. Although they might be apparent visually, these dark areas are not defects in the material and will not limit the useful life of the product.

Removal of the darkened area is generally impractical once the coating has been abraded, but cleaning with a mild detergent or gentle wiping with mineral spirits (and a thorough rinsing) may help in some cases. Most importantly, care during material movement and installation will help avoid the potential problem before it becomes one.

Fingerprints - Oils, such as the natural oils on one's hands, can cause unpainted Galvalume sheet to darken or smudge from handling. The use of clean gloves is recommended to minimize this marking of the product during handling and installation.

Should handling marks occur, they are best removed promptly with mild detergent or alkaline cleaners.

Harsh alkaline or abrasive cleaners should be avoided. Thorough rinsing after any cleaning is important. Even with these cleaning steps, however, uniform appearance may not be fully achieved and is not guaranteed.

Non-Uniform Weathering:

It is not uncommon for unpainted, metallic-coated sheet panels to exhibit some degree of darkening, or "weathering", on exposure to the atmosphere. Occurring on galvanized, Galvalume, aluminum-coated and other sheet materials, this darkening can occasionally appear non-uniform. Panel manufacturers and building owners have accepted this phenomenon for years as it does not compromise the quality or long-term durability of the product.

The change in visual appearance is strictly a surface phenomenon and is related to the passivation treatment applied to the sheet after the metallic coating has been applied. This treatment produces a film that protects the coated sheet from developing "wet storage stain", which might otherwise occur if coils or nested panels get wet during shipment or storage (see TB-206B, Preventing Wet Storage Staining of Galvalume Sheet).

This passivate film retards the natural weathering, or darkening, exhibited by the coated sheet surface. The darkening effect is normally uniform. However, it is possible for an uneven weathering response to occur due to variations in the type and amount of this surface treatment (as, for example, when material is obtained from different mills).

If non-uniform surface appearance occurs, it does not represent a deficiency in the material nor does it adversely affect any warranties which may be in place. However, for applications where high-visibility is of particular concern, the end-user can take precautionary steps. The materials supplier should be informed that the project is a high-visibility application and that cosmetic appearance is important. It should also be requested that material be supplied by the same mill. These steps should increase the likelihood of obtaining material which will weather more uniformly.

Critical Appearance:

While steps can be taken to improve the likelihood of obtaining uniform visual appearance on unpainted Galvalume sheet, it cannot be guaranteed. If uniform visual appearance is critical or mandatory as a condition of sale, then prepainted Galvalume or prepainted galvanized sheet should be ordered. A wide range of organic coatings and finishes is available, including polyester, siliconized polyester, fluorocarbon and plastisol formulations. In addition to enhancing the beauty and durability of Galvalume or galvanized sheet steel, these paint systems are designed to provide the uniform visual appearance demanded by such critical cosmetic applications.

Galvalume� is a registered trademark of BIEC International, Inc.

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