ASTM A755 Standard Specification for Steel Sheet, Metallic Coated by the Hot-Dip Process and Prepainted by the Coil-Coating Process

Get Certified ASTM A755 for Reliable Prepainted Steel Performance 

The certification ensures the steel sheet is prepainted and coated with a metallic coating to comply with the substrate, coating, and paint standards in ASTM A755. The certified evaluation includes the type of metallic coating, coating weight, paint system, thickness of the paint, and the limits of lead before suppliers deliver the sheet to the customer. Buyers are thus enabled to compare the delivered sheet with their purchase order. This verification also provides durable roofing and siding performance.

The main purpose of ASTM A755 is to specify the steel sheet and coating system for exterior exposed building products. This specification is used by manufacturers, roll formers, and building designers to order, monitor, and select the product. 

• Material type: Hot-dip metallic-coated steel sheet, with a coil-coated organic finish. 
• Purpose: Describes the specification of substrate and coating requirements for exterior exposed building products. 
• Properties measured: Zinc-coated (galvanized), zinc-5% aluminum alloy-coated, 55% aluminum-zinc alloy-coated, aluminum-coated, and zinc-aluminum-magnesium alloy-coated steel sheet. 
• Method: Technicians confirm the coating, the coating process, the coating thickness limit, and the necessary coating properties.
• Coating system: A primer coat coated on top with a topcoat of polyester, silicone polyester, acrylic, fluoropolymer, plastisol, or polyurethane and a wash coat on the bottom side.
• Product forms: Coils, cut lengths, formed cut lengths.
• Building products: Corrugated sheet and roll-formed or brake-formed shapes.
• Units: Orders are placed in both inch-pound units (A755) and SI units (A755M), with no relationship between the two.
• Applications: Siding, roofing, and other exterior exposed building products.

What are the Uses of ASTM A755 Testing?

This specification enables the manufacturer and the buyer to order steel sheet that is prepainted to a specified level of substrate and finish. Roll formers and designers then use the sheet for products exposed to the outdoors. This standard-

• Designates steel substrate and metal coatings for exterior building products.
• Describes the system for the primer, topcoat, and washcoat on the sheet.
• Provides recommended minimums for coating mass ratings for exterior exposure.
• Sets a lead limit for the primer and washcoat.
• Requires color, pencil hardness, dry film thickness, solvent resistance, and T-bend performance evaluation during production.
• Covers coils, cut lengths, and formed cut lengths.
• Ensures the accuracy of the purchase order with clear ordering details. 

What Materials Are Covered Under ASTM A755? 

The specification covers steel sheet hot-dip coated with zinc, zinc-5 percent aluminum, 55 percent aluminum-zinc, aluminum, or zinc-aluminum-magnesium and coil coated with an organic finish. Common products include corrugated or formed building parts such as roofing panels and siding. The substrate also meets the required steel sheet specification, such as A653 for galvanized steel. 

Why is ASTM A755 Important? 

The specification provides a known means of specifying prepainted steel for exterior applications. The life span and appearance of the finished product are dependent on the substrate, the organic coating, and the forming method. Coil-coated steel also comes in finished product form; thus, it is most important to specify it correctly at the order stage. Furthermore, the amount of lead and the thickness of the layers allow the buyer to be sure of what they receive. 

ASTM A755 Evaluation Process and Data Collection

The evaluation starts with the technician’s review of the purchase order, which includes the identification of the substrate, coating, and paint system. Then the technician verifies that the sheet and its metallic coating comply with the specification of the substrate. The coil coating line then proceeds with the application of conversion coating, the primer coat, the topcoat, and the washcoat, and the technician verifies the lead limit. After that, the technician tests color, pencil hardness, dry film thickness, solvent resistance, and T-bend performance, plus any nonmandatory methods the parties agree to. Lastly, the analyst compares all the results with the order and reports conformance. 

Common Challenges and Troubleshooting

Accurate results require a complete purchase order and a properly identified substrate, followed by regular checks of each coating layer. Incomplete ordering information can disrupt the match between the provided sheet and the desired product. Thus, before ordering, buyers indicate the type of substrate, the type of coating, and the type of paint system they want, and they ask for a lead-free product on the order if they want one. Storage is also a concern, as water between building panels leads to corrosion failure. Crews store pallets off the ground at a slight angle and cover them with metal covers, never plastic bags. 

• Technicians record the type of substrate, coating type, and coating mass for each order.
• Technicians determine the paint system (primer and top coat).
• Technicians document the product form, thickness, and marking and correlate it with the lot that was evaluated.
• When interpreting results, technicians take into account the various factors of the exposure environment and forming method.
• Manufacturers and buyers use the results to support acceptance of the sheet for exterior building products. 

Link to ASTM A755