What is the difference between Type 1 and Type 2 coatings in this standard?

Type 1 is Aromatic Polyurethane, used as an intermediate coat. Type 2 is Aliphatic Polyurethane, used as a topcoat due to its superior UV and weather resistance (Clause 4.1).

What is the required adhesion performance?

The coating must achieve the best possible classification, Gt0, in the cross-cut adhesion test as per IS 24001 (Table 2).

Is this standard for single-pack or two-pack PU coatings?

This specification primarily covers two-component (two-pack) systems, consisting of a base and a hardener/activator (Clause 3.3).

What is the typical DFT for this coating?

The standard does not mandate a specific Dry Film Thickness (DFT). It should be as agreed upon between the purchaser and supplier, based on the required performance and exposure conditions (Clause 5.2).

IS 16503

: 2017

Polyurethane Based Coatings - Specification

CurrentFrequently UsedSpecificationMaterials Science · Painting, Coatings and Surface Finishing

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This standard specifies the requirements, sampling, and test methods for two-component polyurethane (PU) coatings. It covers two types: Aromatic PU (Type 1) for intermediate coats and Aliphatic PU (Type 2) for topcoats, intended for the protection of steel and concrete surfaces against corrosion, chemicals, and weathering.

Specifies requirements and methods of test for single and two pack polyurethane based coatings for various substrates.

Quick Reference Values

Gloss at 60° angle (for glossy finish)> 80 units

Adhesion by cross-cut testClassification Gt0

Flexibility and Adhesion on conical mandrelNo cracking or detachment

Hard dry time at 27±2°CMax 24 hours

Pot life of mixed material (min)4 hours

Resistance to Salt Spray (1000 hours)No blistering, rusting, or loss of adhesion

Practical Notes

The distinction between Type 1 (Aromatic) and Type 2 (Aliphatic) is critical. Aromatic PUs are tough but yellow with UV exposure, making them suitable for primers. Aliphatic PUs have excellent UV resistance and color retention, making them essential for final topcoats in exterior applications.

Surface preparation is paramount for performance. The specified adhesion values are only achievable if the substrate (e.g., steel) is prepared correctly, typically to Sa 2.5 blast cleaning standard.

For two-pack systems, the mixing ratio and pot life are non-negotiable. Inaccurate mixing or using material beyond its pot life will lead to coating failure.