Plastering is one of the most important finishing works in construction. It gives walls and ceilings a smooth surface, improves durability, and prepares the base for paint or other finishes. Whether it is done inside a building or on the outer surface, plastering plays a key role in both appearance and protection.
In this blog, we explain internal and external plastering in simple English, covering materials, methods, thickness, curing, defects, and best practices.
What Is Plastering?
Plastering is the process of covering rough masonry, concrete, or blockwork surfaces with a thin layer of mortar. This layer hides surface irregularities and provides a neat, even finish.
Plastering is mainly classified into:
- Internal plastering
- External plastering
Each type serves a different purpose and uses slightly different materials and techniques.
Internal Plastering
Internal plastering is the application of plaster on inside walls and ceilings of a building. Its main purpose is to create a smooth, clean, and level surface suitable for painting, wallpaper, or other interior finishes. It also helps seal surface pores and improves hygiene inside rooms.
Purpose of Internal Plastering
Internal plastering is done on walls and ceilings inside a building. Its main functions are:
- To provide a smooth and even surface
- To prepare walls for painting, wallpaper, or tiles
- To improve hygiene by sealing pores and joints
- To enhance the overall appearance of interiors
Materials Used for Internal Plastering
Common materials include:
- Cement and sand mortar
- Gypsum plaster
- Lime plaster (in traditional buildings)
Cement plaster is widely used due to its strength, while gypsum plaster is preferred for faster work and smooth finish.
Thickness of Internal Plastering
Normally, internal plastering thickness is:
- 12 mm for brick walls
- 6–10 mm for concrete surfaces
Maintaining uniform thickness is important to avoid cracks and uneven finishes.
Internal Plastering Procedure
First, the wall surface is cleaned and wetted. Then, plaster mortar is applied evenly using a trowel. After levelling, the surface is finished smoothly. Proper curing is done in cement plaster to prevent shrinkage cracks.
External Plastering
External plastering is the application of plaster on the outer walls of a building. It protects the structure from weather conditions such as rain, heat, wind, and pollution. External plastering also improves the building’s appearance and helps prevent water seepage and surface deterioration.
Purpose of External Plastering
External plastering is applied to the outside walls of a building. It is exposed to sun, rain, wind, and pollution. Therefore, its role is not only decorative but also protective.
External plastering:
- Protects walls from weather effects
- Prevents water penetration
- Improves thermal performance
- Enhances building elevation
Materials Used for External Plastering
External plastering usually uses:
- Cement and coarse sand mortar
- Waterproofing compounds or additives
- Polymer-modified plaster (in premium projects)
The mix is stronger than internal plastering to withstand harsh environmental conditions.
Thickness of External Plastering
The usual thickness for external plastering is:
- 15–20 mm, often applied in two coats
A thicker layer helps resist cracking and improves durability.
External Plastering Procedure
The surface is roughened and cleaned before work. A base coat is applied first and allowed to set. Then, a finishing coat is applied. Proper curing for at least 7 days is essential to avoid surface cracks and debonding.
Difference Between Internal and External Plastering
| Aspect | Internal Plastering | External Plastering |
|---|---|---|
| Location | Inside walls and ceilings | Outside walls |
| Exposure | Protected environment | Exposed to weather |
| Thickness | Thinner (6–12 mm) | Thicker (15–20 mm) |
| Durability | Moderate | High |
| Waterproofing | Usually not required | Highly important |
Common Plastering Defects
Even good plastering work can fail if proper care is not taken. Common defects include:
- Cracks due to shrinkage or poor curing
- Debonding caused by dirty surfaces
- Efflorescence (white patches)
- Uneven or wavy finish
Most of these issues can be avoided by using correct materials, proper mixing, and skilled workmanship.
Best Practices for Good Plastering Work
- Always clean and wet the surface before plastering
- Use correct mix proportions
- Avoid excessive water in mortar
- Ensure proper curing, especially for external plastering
- Do not plaster during extreme heat or rain
- Use waterproofing additives for external walls
Following these practices improves the life and appearance of plastering.
Importance of Plastering in Construction
Plastering is not just a finishing activity. It directly affects durability, comfort, and maintenance costs of a building. Poor plastering leads to cracks, dampness, and repeated repairs. On the other hand, good plastering improves the building’s value and long-term performance.
Conclusion
Internal and external plastering are essential parts of building construction. While internal plastering focuses on smoothness and appearance, external plastering provides protection and durability. Choosing the right materials, maintaining correct thickness, and following proper procedures ensure long-lasting results. When plastering is done correctly, it enhances both the beauty and strength of a building.
Frequently Asked Questions (FAQs)
1. Which is better for internal walls: cement or gypsum plastering?
Gypsum plastering gives a smoother finish and faster completion, while cement plastering is stronger and more moisture-resistant.
2. Why is curing important in plastering?
Curing prevents shrinkage cracks and increases strength, especially in cement-based plastering.
3. Can internal plastering be done without curing?
Gypsum plaster does not require curing, but cement plaster always needs proper curing.
4. How long does external plastering last?
With good materials and workmanship, external plastering can last 20–25 years with minimal maintenance.
5. Is waterproofing required in plastering?
Waterproofing is highly recommended in external plastering to protect against rain and dampness.