What anodic coating grade is recommended for exterior architectural applications?

Grade AC 15 is the minimum for outdoor use, but AC 20 or AC 25 is recommended for severe or coastal environments (Table 1).

How are the grades of anodic coatings designated?

They are designated by 'AC' followed by the minimum local thickness in micrometers (e.g., Grade AC 15 requires a minimum of 15 µm).

How is the thickness of the anodic coating measured?

Thickness is typically measured using the Eddy current method as specified in IS 6012.

How is the sealing quality evaluated?

Sealing quality is tested using methods specified in IS 5523, which include the dye spot test, measurement of admittance, or measurement of mass loss.

IS 1868

: 1997

Anodic coatings on aluminium and its alloys - Specification

CurrentFrequently UsedSpecificationMaterials Science · Aluminium and Non-Ferrous Metals

Archive.org BIS Portal Google

This standard covers the requirements for anodic coatings on aluminium and its alloys. It classifies coatings into different grades based on minimum local thickness and specifies criteria for sealing, appearance, and corrosion resistance to ensure durability in architectural and industrial applications.

Lays down requirements for anodic oxidation coatings on aluminium and aluminium alloys, specifying properties and test methods.

Quick Reference Values

Grade AC 25 minimum local thickness25 µm

Grade AC 20 minimum local thickness20 µm

Grade AC 15 minimum local thickness15 µm

Grade AC 10 minimum local thickness10 µm

Grade AC 5 minimum local thickness5 µm

Practical Notes

Always specify the correct coating grade based on environmental exposure; coastal or heavily industrialized areas require AC 25.

Poor sealing is a primary cause of fading or staining in anodized aluminium. Insist on sealing quality tests like the dye spot test or admittance measurement.

Ensure the base aluminium alloy is anodizing-quality, as metallurgical impurities can lead to visible surface defects after the coating process.