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IS 2402:1963 is the Indian Standard (BIS) for external rendered finishes. This standard lays down the specifications and guidelines for external rendered finishes (plastering) on building facades using cement, lime, and sand. It details background preparation, mortar mix proportioning, and systematic application to ensure long-term durability, weather resistance, and prevention of cracks.
Code of Practice for External Rendered Finishes
Overview
Status
Current
Usage level
Frequently Used
Domain
Architectural — Flooring, Wall Finishing and Roofing
! Never apply a stronger (richer) plaster mix over a weaker background or a weaker undercoat, as this invariably leads to shrinkage cracks and delamination.
! Roughening of dense concrete surfaces (e.g., by hacking) is absolutely crucial before applying the render to ensure proper mechanical keying.
! Incorporating hydrated lime into cement plaster significantly improves workability, increases water retention, and reduces the likelihood of shrinkage cracking.
Design, preparation and application of external rendering and internal plastering. External rendering
Covers design, preparation, and application of external cementitious renders, directly aligning with IS 2402's scope.
ASTM C926 - 19ASTM International (US)
HighCurrent
Standard Specification for Application of Portland Cement-Based Plaster
Specifies the application of Portland cement-based plaster (stucco), which is the US equivalent of external rendering.
BS 5262:1991BSI (UK)
HighWithdrawn
Code of practice for external renderings
Was the primary British code of practice for external renderings before harmonization with European standards.
Key Differences
≠IS 2402:1963 prescribes a prolonged wet curing period of at least 7 days. In contrast, modern standards like BS EN 13914-1 focus on protecting the render from rapid drying (sun, wind) and consider continuous wetting potentially harmful.
≠Modern European standards (BS EN 13914-1) specify renders based on performance categories (compressive strength) and strongly encourage the use of lime for improved flexibility and workability. IS 2402 relies solely on prescriptive volumetric mix ratios with less emphasis on lime.
≠BS EN 13914-1 provides a more advanced approach to substrate preparation, detailing methods to assess and control suction using stipple coats or proprietary primers. IS 2402 recommends the more traditional method of simply wetting the background.
≠ASTM C926 specifies minimum waiting times between coats (e.g., 7 days drying for the brown coat), which are more defined than the general guidance in the much older IS 2402.
Key Similarities
≈All standards share the fundamental objective of providing a weather-resistant, durable, and aesthetic external wall finish using cement-based mortar.
≈Both IS 2402 and its international counterparts advocate for applying the render in multiple coats (e.g., undercoat and finishing coat) to achieve the desired thickness and minimize cracking.
≈All codes recognize that the condition, strength, and preparation of the substrate (background) are critical factors for the long-term performance and adhesion of the render.
≈The basic constituent materials for the render mix—Portland cement, sand (aggregate), and water—are common across all the standards.
Parameter Comparison
Parameter
IS Value
International
Source
Total Render Thickness (Typical)
15 mm to 20 mm
15 mm to 20 mm (for two-coat system on masonry)
BS EN 13914-1:2016
Finish Coat Thickness
6 mm to 8 mm (in a two-coat system)
Approx. 1/8 in (3 mm) for smooth trowel finish
ASTM C926 - 19
Undercoat Mix (Cement:Sand by volume)
1:4 to 1:6
1:3 to 1:5 (for brown coat)
ASTM C926 - 19
Finishing Coat Mix (Cement:Sand by volume)
1:3 to 1:4
1:1.5 to 1:3
ASTM C926 - 19
Curing Requirement
Moist curing by sprinkling water for at least 7 days.
Keep plaster moist with a fine fog spray for the first 24-48 hours.
ASTM C926 - 19
Use of Lime in Mix
Permitted, but less emphasized. e.g., 1:1/4:4 (cement:lime:sand).
Common and recommended. e.g., 1:1:6 (cement:lime:sand) for workability.
BS EN 13914-1:2016
Interval between Undercoat and Finish Coat
Not explicitly specified, but undercoat must be firm.
Brown (under) coat must be allowed to dry for at least 7 days.
ASTM C926 - 19
⚠ Verify details from original standards before use
Key Values4
Quick Reference Values
Thickness of undercoat10 to 15 mm
Thickness of finishing coat3 to 8 mm
Curing duration per coatMinimum 7 days
Time interval between coatsMinimum 2 days
Tables & Referenced Sections
Key Tables
Table 1 - Recommended Mixes for External Rendered Finishes