Steel Sheet, Metallic Coated by the Hot-Dip Process and Prepainted by the Coil-Coating Process for Exterior Exposed B...

A755/A755M- 15: Standard Specification for Steel Sheet, Metallic Coated by the Hot-Dip Process and Prepainted by the Coil-Coating Process for Exterior Exposed Building Products

When specifying materials for demanding exterior building applications, ensuring durability, performance, and aesthetic longevity is paramount. ASTM A755/A755M-15 provides an essential framework for engineers and designers to confidently select and utilize prepainted metallic-coated steel sheet, safeguarding their projects against the rigors of environmental exposure. This authoritative standard is the go-to resource for understanding the precise requirements for these advanced building materials.

What is A755/A755M- 15?

ASTM A755/A755M-15 is a comprehensive standard that defines the requirements for steel sheet that has undergone both hot-dip metallic coating and subsequent coil-coating with organic films. Its primary purpose is to ensure that these prepainted steel products are suitable for direct exposure to exterior building environments, offering a proven balance of corrosion resistance and finished appearance. This specification ensures consistency and reliability in the manufacturing and application of these critical building components.

Scope & Purpose

This industry-leading standard governs steel sheet supplied in coils, cut lengths, or formed configurations, specifically intended for exterior exposed building products. It covers the substrate's metallic coating (such as zinc, aluminum-zinc, or zinc-aluminum-magnesium alloys) and the applied organic coating systems, which can range from thin-film primers and topcoats to thicker, more robust systems utilizing various resin technologies like polyesters, silicones, acrylics, fluoropolymers, plastisols, and polyurethanes. The standard explicitly covers the performance characteristics of these coatings, including adhesion, flexibility, and resistance to weathering and corrosion, but does not extend to the structural design of the building components themselves.

Who Must Comply?

• • Primary audience: Materials Engineers, Product Engineers, Quality Control Inspectors, Procurement Specialists, and Construction Managers involved in the specification, manufacturing, or installation of exterior building products.
• • Industries affected: Construction, Steel Manufacturing, Building Product Fabrication, and Architectural Design.
• • Compliance nature: While often a voluntary standard, compliance is frequently mandated by project specifications, building codes, or contractual agreements, making it effectively required for many applications.
• • Enforcement: Compliance is typically verified through manufacturer certifications, third-party testing, and quality assurance inspections during material production and project execution.

Key Requirements Overview

The standard requires that the steel substrate be properly prepared and metallically coated according to specified ASTM standards for hot-dip coatings. Professionals must ensure that the organic coil coating system, comprising primer and topcoat(s), meets defined performance criteria for adhesion, film thickness, hardness, flexibility, and resistance to environmental degradation. Key provisions include stringent testing for color consistency, gloss retention, chalking, and corrosion resistance, often through accelerated weathering and salt spray tests. The specification also details requirements for the backer coat applied to the unexposed side for added protection and aesthetics.

Related Standards & References

ASTM A755/A755M-15 works in conjunction with several other proven ASTM standards. Complementary specifications such as A653/A653M (