Updated July 2026
Anodized aluminum is one of the most durable and long-lasting architectural finishes available. Its exceptional hardness, corrosion resistance, and low maintenance requirements make it a popular choice for storefronts, curtainwall, entrances, windows, sunshades, and other aluminum building components.
When specifying anodized aluminum, one of the most common questions is whether a project requires Class I or Class II anodize.
While both classifications provide the benefits associated with anodized aluminum, they are designed for different performance requirements and applications. Understanding the differences can help ensure the finish selected aligns with the project’s environment, durability expectations, and long-term performance goals.
What is anodize?
Anodizing is an electrochemical process that enhances aluminum’s naturally occurring oxide layer. Rather than applying a coating on top of the metal, anodizing converts the aluminum surface into a durable oxide finish that becomes an integral part of the substrate.
This controlled oxidation process creates a finish that offers:
- Exceptional wear and abrasion resistance
- Long-term corrosion protection
- Excellent color and gloss retention
- Minimal maintenance requirements
- A noncombustible, environmentally responsible finish option
Because the finish becomes part of the aluminum itself, anodize will not chip, peel, or flake like applied coatings can.
Why choose anodized aluminum?
Architects and building owners often choose anodized aluminum for projects requiring durability, longevity, and a refined metallic appearance.
Anodized finishes offer several advantages:
Architectural anodize creates an extremely hard surface that resists scratching and abrasion. This makes it well-suited for high-traffic applications such as entrances, storefronts, and public-facing buildings.
Unlike many finish options, anodized aluminum maintains its appearance for years with minimal maintenance. The finish is resistant to ultraviolet degradation and retains its color and gloss in a variety of environments.
Anodized aluminum is an environmentally responsible finish choice. Aluminum is 100% recyclable, and anodizing does not contain volatile organic compounds (VOCs). These attributes can support sustainable building initiatives and green building objectives.
Anodize offers a clean, sophisticated appearance that highlights the natural beauty of aluminum. Linetec’s environmentally friendly etch process produces a smooth, uniform finish with a distinctive matte appearance.
What does anodize look like?
Clear anodize preserves aluminum’s natural silver appearance while enhancing its durability and corrosion resistance.
Beyond clear anodize, coloring processes can create a range of architectural finishes, including:
- Champagne
- Medium Bronze
- Dark Bronze
- Black
Linetec also offers specialty Copper and Bordeaux anodize finishes. These unique architectural finishes are produced through a proprietary process that incorporates controlled copper deposition and precisely timed immersion sequences to achieve rich, warm metallic appearances.
Understanding AAMA 611
For architectural aluminum building products, anodized finishes are typically specified to meet AAMA 611, “Voluntary Specification for Anodized Architectural Aluminum.”
Published by the Fenestration and Glazing Industry Alliance (FGIA), AAMA 611 establishes performance requirements and references the Aluminum Association’s classifications for:
- Architectural Class I Anodize
- Architectural Class II Anodize
The primary difference between these classifications is anodic coating thickness.
What Is Class II Anodize?
Architectural Class II anodize has a minimum coating thickness of 0.4 mil (10 microns).
While it provides good durability and appearance, it is intended primarily for interior applications or environments where exposure and wear are limited.
Class II anodize may be appropriate for:
- Interior framing systems
- Decorative interior aluminum components
- Interior trim applications
- Areas receiving regular cleaning and maintenance
Because of its thinner coating, Class II anodize does not provide the same level of wear resistance or environmental protection as Class I anodize.
AAMA 611 requires Class II anodize to withstand 1,000 hours of accelerated salt spray testing.
©Crabtree, Rohrbaugh & Associates (CRA) – Architects
Abstract Photography, Inc.; Terry Wieckert
What Is Class I Anodize?
Architectural Class I anodize has a minimum coating thickness of 0.7 mil (18 microns), making it nearly twice as thick as Class II anodize.
This added thickness provides increased durability, corrosion resistance, and long-term performance.
Class I anodize is commonly specified for:
- Curtain Wall systems
- Storefront framing
- Entrances and doors
- Windows
- Sunshades and canopies
- Exterior architectural aluminum components
- High-traffic public spaces
AAMA 611 requires Class I anodize to withstand 3,000 hours of accelerated salt spray testing, making it well-suited for demanding environments and exterior exposure.
Class I vs. Class II Anodize Comparison
SPECIFICATION | CLASS I | CLASS II |
|---|---|---|
SOUTH FLORIDA WEATHERING: | ||
| Color Retention | 10 yrs: Fade = 5 Delta E | 10 yrs: Fade = 5 Delta E |
| Chalk Resistance | N/A | N/A |
| Gloss Retention | 15 unit variation | 15 unit variation |
| Gloss Range | 4 - 30 | 4 - 30 |
| Hardness | Excellent | Good |
| Dry Film Thickness | 0.7 mils minimum | 0.4 mils minimum |
| Effect of Poor Substrate | Significant | Significant |
ACCELERATED TESTING: | ||
| Salt Spray | 3,000 hours | 1,000 hours |
| Humidity | No specification | No specification |
| Warranty | 5 - 10 Years | N/A |
Which Class Should Be Specified?
The answer largely depends on where the aluminum will be used and the level of performance expected.
Specify Class I When:
- The application is exterior.
- The finish will be exposed to weather.
- Long-term durability is critical.
- The project is located in a coastal or high-humidity environment.
- The aluminum will experience frequent contact or heavy traffic.
Specify Class II When:
- The application is interior.
- Environmental exposure is limited.
- The finish is primarily decorative.
- Lower performance requirements are acceptable.
When in doubt, Class I anodize is often the preferred choice for architectural applications because of its superior durability and long-term performance.
One of the most common specification errors is selecting Class II anodize for an exterior application because the appearance is similar. While both finishes may initially look alike, their long-term performance differs significantly.
Anodize Frequently Asked Questions
While Class II anodize may be used in certain light-duty exterior applications, Class I anodize is generally recommended for exterior architectural aluminum because of its increased thickness and superior weather resistance.
Anodized finishes are known for excellent color retention. Properly specified and maintained architectural anodize resists fading and maintains its appearance for many years.
No. Because anodize becomes part of the aluminum surface, it does not chip, crack, or peel like applied coatings.
For storefront, curtain wall, window, entrance, and other exterior building applications, Class I anodize specified to AAMA 611 is the most common choice.
Partner with Linetec for Architectural Anodizing
Choosing the right anodized finish can have a significant impact on a project’s appearance, durability, and long-term performance.
As a leading architectural finisher, Linetec offers Class I anodize finishes in a range of standard and specialty colors, including Copper and Bordeaux anodize. Our team works closely with architects, fabricators, and glazing contractors to help ensure the right finish is selected for each application.
Whether you’re evaluating finish options, reviewing specifications, or requesting samples, we’re here to help.
Ready to discuss your next project?
Contact Linetec to learn more about our anodize finish options, request finish samples, or speak with a finishing specialist.
Send us an email