Gypsum plastering has transformed the Indian construction industry over the past decade. What was once used only in premium projects is now the standard for residential and commercial construction across South India. This guide provides a comprehensive technical overview of gypsum plastering — what it is, how it works, and why it has become the dominant interior plastering method.
What Is Gypsum?
Gypsum is a naturally occurring soft sulphate mineral. Its chemical name is calcium sulphate dihydrate (CaSO₄·2H₂O). It is found in thick beds within layers of sedimentary rock, formed over millions of years from ancient seas and lagoons where concentrated calcium and sulphate waters evaporated.
Gypsum has a chalk-like texture and is lightweight. In its natural crystalline state it is white to grey; once processed, it forms a fine white powder. Uniquely, when water is added to calcined gypsum powder, it re-forms back into its original crystalline structure — this property is what makes it so valuable as a plaster material.
How Gypsum Plaster Is Made
Raw gypsum rock is mined, crushed, and then heated at 100–120°C. At this temperature, approximately 75% of the chemically bound water evaporates, converting the dihydrate (CaSO₄·2H₂O) to a hemihydrate (CaSO₄·½H₂O). This calcined powder is what we call Plaster of Paris or gypsum plaster. It is then ground to a fine powder, packaged in 25–40 kg bags, and is ready for use.
At the construction site, the powder is mixed with clean water in the correct ratio (typically 0.6–0.7 litres of water per kg of powder) to form a smooth paste. This paste is applied to the wall surface and worked to a smooth, level finish. As it sets, the crystallised water re-bonds and the material returns to its original rock-like strength.
Properties That Make Gypsum Exceptional
Low Density
Gypsum plaster has a density of 700 kg/m³ — approximately 62% lower than sand cement plaster (1,860 kg/m³). This significantly reduces the dead weight of plastered walls, which is critical in high-rise construction and earthquake-resistant building design.
No Shrinkage
Unlike cement, gypsum does not contract during setting. The re-crystallisation process actually produces a slight expansion, which prevents the hairline shrinkage cracks common in cement-plastered surfaces. The result is a permanently smooth, crack-free surface.
Fire Resistance
Gypsum contains approximately 21% chemically bound water. When exposed to fire, this water absorbs heat as it evaporates — acting as a passive fire barrier for up to 4 hours. The material remains inert until temperatures exceed 1,200°C. This makes gypsum an excellent passive fire protection material for walls and ceilings.
Sound Insulation
Gypsum's composition and density provide better sound absorption than cement plaster. Gypsum-plastered walls and ceilings reduce sound transmission between spaces, making them valuable in hospitals, schools, hotels, apartments, and offices.
Thermal Properties
Gypsum has low thermal conductivity. When used in wall and ceiling systems, it helps maintain more stable indoor temperatures — reducing heat gain in summer and heat loss in winter. The air gap in false ceiling systems further enhances thermal performance. This directly reduces air conditioning and heating costs.
Setting Time
Gypsum sets in 25–30 minutes — compared to 60–120 minutes for cement. Walls are paint-ready in 3–4 days rather than 15–21 days. This dramatically reduces overall construction time and project overheads.
Types of Gypsum Plaster Applications
| Application | Description | Thickness |
|---|---|---|
| Wall plaster | Direct single-coat application to bricks, blocks, or AAC | 11mm standard |
| Ceiling plaster | Applied to RCC slabs — no putty or PoP needed | 8mm standard |
| Machine plaster | Spray-applied using plastering machines for large projects | 8–15mm |
| Gypsum board | Pre-manufactured boards for false ceilings and partitions | 9.5–15mm |
| Decorative moulding | PoP-based cornices, ceiling roses, and architectural details | Varies |
The Application Process
- Surface preparation: Clean the substrate — remove dust, oil, loose particles. Dampen the wall slightly if it is very dry (especially brick).
- Mixing: Add gypsum powder to clean water (not water to powder). Mix for 2–3 minutes to a lump-free, consistent slurry.
- Application: Apply with a steel trowel, working from top to bottom. For walls, apply at 11mm thickness; for ceilings, 8mm.
- Levelling: Use a straight edge (darby/float) to level the surface.
- Finishing: Once the plaster begins to set, use a wet sponge and finishing trowel to achieve the final smooth surface.
- Drying: Allow 72 hours minimum before applying primer and paint.
Applications Across Building Types
Gypsum plastering is now standard across all types of construction in India. Residential homes, high-rise apartments, commercial offices, retail spaces, hospitals, schools, government buildings, and industrial facilities all use gypsum for interior plastering. Kanish Plasters has completed projects from individual 800 sq ft homes to ISRO facilities and major township developments — demonstrating gypsum plastering's suitability for any scale or building type.
💡 Key Takeaway: Gypsum plastering is not just a material — it is a system that integrates material science, quality application, and process discipline. The best results come from using quality material, the right mixing ratio, properly prepared surfaces, and trained applicators with robust quality checks.
Ready to get gypsum plastering for your project? Contact Kanish Plasters for a free site visit and quote. Serving Chennai, Coimbatore, Bangalore, Madurai, Trichy, Kochi and all of Tamil Nadu.