WALTER SCARBOROUGH CSI CCS CCCA SCIP AIA wscarborough@hbig 214.491.7385
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Transcript of WALTER SCARBOROUGH CSI CCS CCCA SCIP AIA wscarborough@hbig 214.491.7385
WALTER SCARBOROUGHCSI CCS CCCA SCIP [email protected]
D+D Specifiers Series
Sponsored by
Exterior Steel and High-PerformanceCoatings
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
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
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
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