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Exterior Steel Coatings: Properties, Selection, and Application Methods

This webinar will discuss the properties of exterior steel coatings and the most common coating system used for ferrous metals on buildings. Topics covered include the basics of rust, the properties of a coating, the selection of a coating, and a typical exterior system.

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Exterior Steel Coatings: Properties, Selection, and Application Methods

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  1. D+D Specifiers Series Exterior Steel and High-Performance Coatings WALTER SCARBOROUGH CSI CCS CCCA SCIP AIA wscarborough@hbig.us 214.491.7385 Sponsored by

  2. Webinar Intentions To identify the properties of a coating and to discuss the most common coating system typically used for ferrous metals at the exterior of buildings

  3. Basics

  4. Why Coat Steel? Protection Aesthetics

  5. Basics of Rust Steel + Oxygen + Moisture RUST

  6. Mechanism of Protection • Barrier to protect steel from effects of its environment • Inhibitive by controlling the rate of corrosion • Sacrificial by deteriorating before the steel

  7. Properties of a Coating

  8. Properties of a Coating • Chemical resistance • Low moisture permeability • Ease of application • Adhesion • Cohesive strength

  9. Properties of a Coating • Tensile strength • Flexibility • Impact resistance • Abrasion resistance • Temperature resistance

  10. Properties of a Coating • Cold flow resistance • Dielectric strength • Surface tolerant • VOC compliant • Low odor

  11. Selection of a Coating

  12. Selection of a Coating • Type of exposure • Operating conditions • Substrate • Application ambient conditions • Environmental regulations

  13. Selection of a Coating • Budget • During operation or shutdown • Time constraints • New construction or maintenance • Shop or field application

  14. Selection of a Coating • Design or fabrication considerations • - Inaccessible areas • - Bolted connections • - Dissimilar materials • - Imperfections (welds, laminations, and gouges) • - Sharp corners

  15. Typical Exterior System

  16. Typical Exterior System One of the longest lasting systems includes following: Primer: Zinc-Rich Intermediate Coat: Epoxy Top Coat: Polyurethane

  17. Zinc-Rich Coatings • Binder, or resin, that is highly loaded with a metallic zinc-dust pigment • Binder holds zinc particles in contact with steel substrate to create a galvanic cell (zinc will deteriorate before steel) • Provides anticorrosion (galvanic) protection for as long as 20 years or longer

  18. Zinc-Rich Coatings • Requires clean steel substrates • Best method of application is in the fabrication shop

  19. Epoxy Coatings • Exceptional adhesion strength • Resistant to solvents and chemicals • Water-borne and high-solids are dominant technologies in use

  20. Epoxy Coatings • Have a fatal flaw - not UV light stable and thus requires a top coat

  21. Polyurethane Coatings • One of most versatile coatings available • Chemical and solvent resistant • Best color and gloss retention Light stable • Abrasion resistant • Long lasting

  22. Polyurethane Coatings • Acrylic polyurethanes are good for aesthetics • Polyester polyurethanes are good for chemical resistance, but weather resistance not as good

  23. Purpose of Coatings • Zinc-rich protects the steel by becoming sacrificial coating • Epoxy protects the zinc-rich • Polyurethane protects • the epoxy and provides • color

  24. Shop or Field Applied

  25. Shop or Field Applied • Shop coating steel is always far better than field applying a coating

  26. Shop or Field Applied • Cost is lower than field coating

  27. Shop or Field Applied • Safer for workers because there is not a large force of painters up in the air

  28. Shop or Field Applied • Short pot life of multi-component coatings • is a logistical challenge when field coating

  29. Shop or Field Applied • Reduced construction time

  30. Shop or Field Applied • More efficient use of resources • Less labor • Blasting media is recycled

  31. Shop or Field Applied Controlled application conditions

  32. Field Considerations

  33. Field Considerations Bolted connections require special attention

  34. Field Considerations Bolted connections in the lay-up-yard

  35. Field Considerations Bolted connections up in the air

  36. Field Considerations For quality control purposes, good if manufacturer can conduct field training classes for touch-up work

  37. Field Considerations Imperfection and damage touch-up

  38. Field Considerations Peeling paint due to overlap of primer at interior corners of H-sections

  39. Field Considerations Coating does not cover weld splatter

  40. Field Considerations Spot rusting due to proximity of paint booth and blasting area

  41. Conclusions • Coating selection should be based factors that are important to the application • Zinc-rich, epoxy, and polyurethane is high quality coating system that is useful for architectural applications • Shop coating will always be better than field coating

  42. D+D Specifiers Series Questions WALTER SCARBOROUGH CSI CCS CCCA SCIP AIA wscarborough@hbig.us 214.491.7385 Sponsored by

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