Part 2: Specifying Anodized Finishes

The Aluminum Association has developed a system of designation for anodized finishes on aluminum. Specific finishes of the various types are designated by a letter followed by a two-digit numeral. Each designation may be combined into a single composite designation to identify a sequence of operations covering all of the important steps leading to a final complex finish.

Almost all finishes used on aluminum may be subdivided into three major categories: mechanical finishes, chemical finishes and coatings.

Descriptions of the most commonly utilized finishes are as follows:

Mechanical: (M)

M10 – Unspecified as fabricated

Chemical (C)

C21- Fine matte (eco-friendly etch process)

C22 – Medium matte etch (caustic etch process)

Anodic Coatings (A)

Architectural Class II (0.4-0.7 mils thick)

A31 – Clear

A32 – Integral color

A34 – Electrolytically deposited color (two-step)

Architectural Class I (0.7 mil and thicker anodic coating)

A41 – Clear

A44 – Electrolytically deposited color (two-step)

All composite designations are preceded by the letters “AA” to identify them as an Aluminum Association designation.

Example 1: Aluminum Association (plus) Mechanical Finish (plus) Chemical Etching (plus) Anodic Coating translates to:

Class II Clear Anodized Finish AA M10 C21 A31 complying with AAMA 611

Example 2: An Architectural Class I medium bronze electrolytic deposition (two-step) would be designated:

Class I Color Anodized Finish: AA M10 C21 A44 complying with AAMA 611. Provide color as indicated.

Maintenance and Cleaning

As with any finished building material, anodized aluminum requires reasonable care prior to and during installation, as well as periodic cleaning and maintenance after installation. Although anodized aluminum possesses exceptional resistance to corrosion, discoloration and wear, its natural beauty can be marred by harsh chemicals, rough conditions or neglect. The marks resulting from such mistreatment may be permanent. For example, mortar, cement and other alkaline materials will quickly corrode anodic coatings if allowed to dry on the metal surface.

Surfaces exposed to the atmosphere will collect soil and dirt, the amount of which varies depending on geographic area, environmental conditions, finish and location of the building. More frequent cleaning may be required in heavily industrialized areas compared to rural areas. Seasonal rainfall can reduce washing frequency by removing water-soluble deposits and less adherent soil. In climates where rainfall is low, atmospheric washing of the surface is minimal. These areas may require more frequent cleaning than in areas where rainfall is more prevalent.

Never use aggressive alkaline or acid cleaners on aluminum finishes. Do not use cleaners containing trisodium phosphate, phosphoric acid, hydrochloric acid or similar compounds. It is preferable to clean the metal when shaded. Do not attempt to clean hot, sun-heated surfaces since chemical reactions on hot metal surfaces will be accelerated and non-uniform.