IS 1868:1997 is the Indian Standard (BIS) for anodic coatings on aluminium and its alloys - specification. 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.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Coating grades | By thickness (µm) — match to exposure | Grades |
| Exterior/coastal | Thicker grade ≈ 20–25 µm | Selection |
| Interior/decorative | Thinner grades | Selection |
| Sealing | Anodic film MUST be sealed (else chalks/stains) | Critical |
| Tests | Coating thickness + sealing quality + abrasion/appearance | Accept |
| Site | Protect from alkali/mortar & damage (no field repair) | Caution |
IS 1868:1997 is the specification for anodic coatings (anodising) on aluminium and its alloys — the controlled oxide layer applied to architectural aluminium (windows, doors, curtain-wall sections, louvres, railings, cladding) for durability and finish. It is the durability companion to the aluminium material/section codes.
It is read with the aluminium stack:
Anodising converts the aluminium surface into a hard, integral aluminium-oxide layer (then sealed) — far more durable than paint because it *is* the metal surface. IS 1868 grades it by coating thickness class, matched to exposure:
The key point: 'anodised' is meaningless without the thickness grade for the exposure + proof of sealing.
Scenario: aluminium curtain-wall / window sections for an external coastal façade.
Step 1 — exposure → grade: external + coastal → specify the thicker IS 1868 grade (≈20–25 µm), *not* an interior/decorative thin grade.
Step 2 — colour & finish: natural or specified colour, with lot uniformity stated.
Step 3 — acceptance tests: verify on delivered sections — coating thickness (eddy-current/microsection) meets the grade; sealing quality passes the dye-stain/admittance test; abrasion/appearance OK.
Step 4 — handling/site: protect anodised surfaces from mortar/alkali splatter and mechanical damage during construction (alkali etches anodising; scratches can't be 're-anodised' in situ).
Step 5 — verdict: reject sections under the thickness grade or failing the sealing test — unsealed/thin anodising looks fine on day one and chalks/pits within a couple of monsoons.
Result: a façade finish that lasts decades — provided thickness *and sealing* were both specified and verified, not just 'anodised'.
1. Specifying 'anodised' with no thickness grade. Interior-grade thin anodising on an external coastal façade weathers out fast — thickness must match exposure.
2. Ignoring the sealing requirement. Unsealed anodic film is porous and fails (chalking, staining, corrosion) — sealing quality is as important as thickness and must be tested.
3. No acceptance testing. Thickness and sealing are invisible to the eye on day one; accepting on appearance lets thin/unsealed material through.
4. Confusing anodising with powder coating / paint. They are different systems with different durability and repair behaviour; don't substitute silently.
5. Site alkali/mechanical damage. Mortar/alkali splatter etches anodising and scratches can't be field-repaired — protect during construction.
IS 1868 is reaffirmed; anodising remains a premium, durable architectural finish for aluminium (competing with powder coating and PVDF) because it is an integral, hard oxide rather than an applied film — but only if thickness grade and sealing are correctly specified and verified. The recurring, expensive façade failure is *thin or unsealed anodising* that passes a visual day-one check and then chalks, stains and pits within a couple of years on an exterior — by which time replacement is a re-cladding job.
The practitioner contract is exactly two things plus protection: specify the IS 1868 thickness grade for the actual exposure (thicker for external/coastal), require and test the sealing quality (not just thickness), and protect anodised surfaces from alkali/mechanical damage on site (it can't be field-repaired). Read with IS 733/IS 8147 for the section design — façade performance is the *combination* of an adequately stiff section (low E, deflection-governed) and a correctly anodised, sealed surface; getting one right and the other wrong still fails the façade.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Min. Thickness for Severe Exterior Use | 25 µm (Grade AC 25) | 25 µm (Class AA 25) | ISO 7599:2018 |
| Sealing Quality (Acid Dissolution Test) | Mass loss ≤ 30 mg/dm² (Test per IS 6012) | Mass loss ≤ 30 mg/dm² (Test per ISO 3210) | ISO 7599:2018 |
| Minimum Thickness for Hardcoat | 50 ± 10 µm (Grade HA) | 50.8 µm ± 20% (0.0020 in ± 0.0004 in) for Type III | MIL-PRF-8625G |
| Corrosion Resistance (Salt Spray) | To be agreed upon; no specific duration mandated for all grades. | 336 hours minimum, no more than 15 isolated pits (for Type II coatings) | MIL-PRF-8625G |
| Light Fastness (Exterior Colour) | Minimum rating of 7 on Blue Wool Scale (per IS 2454) | Minimum rating of 8 (using a different class system for fastness, per ISO 2135) | ISO 7599:2018 |
| Abrasion Resistance (Hardcoat) | Max 50 mg mass loss/1000 cycles (Taber, CS-17, 1000g) | Wear resistance specified by performance on specific alloys, typically verified by Taber test (ASTM D4060) as per contract. | MIL-PRF-8625G |