Choosing Alloys for Architectural Applications

## Architectural Metals Overview | Material | Typical Life | Maintenance | Appearance Change | |----------|-------------|------------|-------------------| | 316 Stainless | 80-100+ years | Minimal | Retains brightness | | Aluminum (anodized) | 40-60 years | Low | Slight dulling | | Copper | 100+ years | None | Green patina (20-30 yr) | | Weathering Steel | 80-100 years | None | Uniform brown oxide | ## Stainless Steel **316**: Required for coastal, industrial, or polluted environments. The Chrysler Building's 304 cladding (installed 1930) remains excellent after nearly 100 years. **304**: Acceptable for inland, low-pollution environments. Not recommended within 1 km of coastline. Tea-staining (brown discoloration from surface contamination) is the most common defect. Prevention: specify 316 in marine environments and clean with nitric acid passivation after installation. ## Aluminum **6063-T5**: Standard curtain wall extrusion alloy. Good surface finish and anodizing response. Clear or color anodized finishes per AAMA 611. **PVDF coatings (Kynar 500)**: Maintain color for 30-40 years. AAMA 2605 specification. ## Copper Develops green patina (copper carbonate) over 20-30 years. Pre-patinated copper available for immediate green appearance. The Statue of Liberty's C11000 copper skin (1886) demonstrates 100+ year life. ## Weathering Steel (Cor-Ten) ASTM A588 forms a stable rust patina over 2-5 years. NOT suitable for continuously wet conditions, crevice-prone joints, or coastal environments. ## Life-Cycle Cost Maintenance-free materials (stainless, copper) often cost less over 50-100 year building life than coated materials requiring periodic refinishing.