WALTER SCARBOROUGH CSI CCS CCCA SCIP AIA D+D Specifiers Series Sponsored by Exterior Steel and High-Performance Coatings

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 Webinar Intentions

Basics

Why Coat Steel? Protection Aesthetics

Basics of Rust Steel + Oxygen + Moisture RUST

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

Properties of a Coating

Chemical resistance Low moisture permeability Ease of application Adhesion Cohesive strength

Properties of a Coating Tensile strength Flexibility Impact resistance Abrasion resistance Temperature resistance

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

Selection of a Coating

Type of exposure Operating conditions Substrate Application ambient conditions Environmental regulations

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

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

Typical Exterior System

One of the longest lasting systems includes following: Primer: Zinc-Rich Intermediate Coat: Epoxy Top Coat: Polyurethane

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 Zinc-Rich Coatings

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

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

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

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

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

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

Shop or Field Applied

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

Cost is lower than field coating Shop or Field Applied

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

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

Reduced construction time Shop or Field Applied

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

Controlled application conditions Shop or Field Applied

Field Considerations

Bolted connections require special attention Field Considerations

Bolted connections in the lay-up-yard Field Considerations

Bolted connections up in the air Field Considerations

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

Imperfection and damage touch-up Field Considerations

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

Coating does not cover weld splatter Field Considerations

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

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 Conclusions

D+D Specifiers Series Sponsored by Questions WALTER SCARBOROUGH CSI CCS CCCA SCIP AIA