Yes, building sand is suitable for plastering, particularly for certain applications like backing coats and renders. Its fine, soft nature makes it highly workable, which is advantageous for creating a smooth and consistent base layer for various wall finishes.
Understanding Building Sand in Plastering
Building sand, also known as plastering sand or soft sand, is a versatile aggregate used widely in construction. It is characteristically soft and fine, making it ideal for applications where workability and a smooth finish are crucial, such as bricklaying, pointing, and, indeed, plastering.
When used in plaster mixes, building sand primarily contributes to the bulk and workability of the material. It helps to create a pliable mixture that can be easily applied and leveled, forming a strong bond with the substrate.
Key Characteristics of Building Sand for Plaster
- Soft and Fine Texture: This allows for a smoother application and a more consistent finish compared to coarser sands.
- High Workability: It mixes well with binders like cement and lime, producing a manageable paste that spreads easily.
- Good for Base Coats: Building sand is excellently suited for the initial "scratch coats" or "backing coats" of plaster, which build up thickness and provide a level surface for subsequent finishing layers.
Building Sand vs. Other Sands
Understanding the differences between sand types is crucial for selecting the right material for your plastering project.
| Sand Type | Primary Applications | Key Characteristics | Plastering Suitability |
|---|---|---|---|
| Building Sand | Plastering, Bricklaying, Pointing, Mortar | Soft, fine, high workability, good for smooth finishes | Excellent for backing/scratch coats, renders |
| Sharp Sand | Concreting, Floor Screeds, Block Paving | Coarse, angular, good drainage, less workable | Adds strength to cement renders; less common for plaster base coats |
| Washed Sand | Paving, bedding, general landscaping, concrete mixes | Clean, typically fine to medium, free from impurities | Can be used for specific mixes requiring very clean aggregates |
For more detailed information on sand types, refer to reputable building material guides.
Practical Applications of Building Sand in Plaster
Building sand is predominantly used in the initial layers of a plastering system, where its workability and ability to form a good key are beneficial.
1. Backing Coats and Renders
When applying traditional two or three-coat plaster systems, building sand is a primary component of the backing or scratch coat. These layers are responsible for:
- Building Thickness: Creating the desired depth over the wall surface.
- Leveling the Surface: Correcting any unevenness in the underlying masonry.
- Providing a Key: The textured surface of the backing coat allows the subsequent finish coat to adhere effectively.
For exterior rendering, building sand mixed with cement and often lime creates a durable and weather-resistant protective layer for external walls.
2. Mortar Mixes
While not strictly plastering, building sand is also crucial for mortar used in bricklaying and pointing, often serving as a binder for the base structure that will later be plastered. The soft texture aids in achieving strong, workable mortar.
Essential Considerations for Using Building Sand in Plaster
To achieve the best results when plastering with building sand, consider the following:
a. Correct Mixing Ratios
The ratio of sand to binder (cement, lime, or gypsum) is critical for the strength, workability, and longevity of the plaster. Typical ratios vary depending on the specific application and desired strength:
- Cement-Sand Ratios: Often 1 part cement to 3-6 parts sand for backing coats.
- Lime-Sand Ratios: For more breathable and flexible finishes, ratios of 1 part lime to 2-3 parts sand are common.
- Adding Plasticizers: A small amount of plasticizer can enhance workability and reduce the need for excessive water, improving the final strength.
Always consult product specifications for recommended plaster mix ratios.
b. Quality of Sand
Ensure the building sand is clean and free from impurities such as clay, silt, organic matter, or large stones. Contaminants can compromise the strength, adhesion, and appearance of the finished plaster.
c. Application Techniques
- Surface Preparation: Ensure the wall surface is clean, free from dust, and suitably dampened (but not saturated) to prevent the plaster from drying out too quickly.
- Layering: Apply plaster in thin, even layers, allowing each coat to set sufficiently before applying the next. This helps prevent cracking and ensures proper adhesion.
- Curing: Proper curing, especially for cement-based renders, is essential. This often involves keeping the plaster moist for several days to allow it to gain full strength.
Conclusion
Building sand is a highly suitable material for plastering, particularly for the essential backing and scratch coats that form the foundation of a durable and smooth wall finish. Its fine texture and workability make it an excellent choice for creating robust and even base layers, ensuring that your subsequent decorative finishes have the best possible surface to adhere to.
