Plastering is critical in building construction. It provides a smooth, durable surface for walls, columns, beams, and ceilings. It’s applied using plastic mortar, sand, cement, and water.
Plaster finishes are not just for aesthetics but also offer protection for interior and exterior surfaces. Depending on the required outcome, these finishes vary from smooth surfaces to textured designs.
In this article, we look at the different types of plaster finishes commonly used in construction projects.
Let’s get straight to the point.
Plaster finishes are crucial for aesthetics and construction protection. They are applied to walls, ceilings, columns, and beams. The materials and techniques used to achieve smooth or textured surfaces vary.
Common types include smooth coat, sand-faced, spatter dash, pebble dash, and stucco finishes. Special finishes, such as acoustic plaster, waterproof plaster, and exposed aggregate, are used for specific purposes, such as soundproofing, moisture resistance, or decorative effects.
Selecting the right plaster finish enhances a building’s appearance and durability, making professional guidance essential for optimal results.
What Is A Plaster Finish?
A plaster finish is the final layer applied to a surface to create a smooth, visually appealing, and durable finish. This process involves applying a mixture, typically made from lime, cement, or gypsum, to a surface after mixing it with water.
Depending on the desired effect, plaster finishes are commonly used on walls and ceilings to create different textures, patterns, or smooth surfaces.
What Is Finishing Plaster Made Of?
Plaster finishes can be made from various materials, including lime, gypsum, or cement. The plaster is mixed with water to apply a paste to a surface. When it sets, it hardens into a durable finish.
The choice of material depends on the finish required and the conditions the plaster will be exposed to.
Types Of Plaster Finishes
Several types of plaster finishes exist, each with distinct properties and uses. Here are some of the most common finishes used in construction.
1. Smooth Coat Finish
One of the most commonly used types of plaster is a smooth coat finish. It creates a flat, smooth surface, ideal for interior walls.
The mixture for a smooth-coat finish typically consists of one part cement and three parts fine sand, with water added as needed.
This finish is applied using a wooden float. It’s important to avoid using a steel float for exterior surfaces, as it can make the surface too smooth and prone to cracking when exposed to the elements.
2. Sand Faced Finish
A sand-faced finish requires two coats of plaster. The first coat is applied with a thickness of about 12 mm using a 1:4 ratio of cement and sand mortar.
This layer’s surface is often textured with zigzag lines. After seven days of curing, a second coat, 8 mm thick, is applied.
This layer is made from a 1:1 mix of cement and fine sand. A wooden float rubs the surface with clean, evenly sized sand particles to create a uniform texture.
3. Spatter Dash Finish (Rough Cast Finish)
The spatter dash finish, or roughcast, uses a 1:1:3 ratio of cement, sand, and coarse aggregate. The coarse aggregate, usually between 3 mm and 12 mm in size, gives the finish its rough texture.
A large trowel is used to throw the mortar onto the prepared surface, and a wooden float is employed to polish it lightly. This highly durable and water-resistant finish is ideal for exterior surfaces.
4. Day Dash Finish (Pebble Dash Finish)
A day dash finish, or pebbledash, involves applying a final coat of 12 mm thick plaster, similar to the mortar used in the smooth cast finish. Small pebbles, ranging from 10 mm to 20 mm, are pressed into the wet plaster.
These pebbles are embedded using a wooden float to create a decorative, textured surface. This finish is commonly used on exterior walls for aesthetic and protective purposes.
5. Depeter Finish
The deeper finish is similar to the pebble dash finish but uses small pieces of gravel or flint instead of pebbles. A 12 mm thick coat of plaster is applied, and while still wet, gravel or flint is hand-pressed into the surface.
This type of finish allows for creative patterns and designs, with different coloured flints used to add visual interest.
6. Scraped Finish
For a scraped finish, a layer of plaster, usually 6 mm to 12 mm thick, is applied and left to harden for a few hours. The surface is then scraped using a tool such as a steel straight edge or a saw blade to create a textured pattern about 3 mm deep.
This finish reduces the likelihood of cracking and provides a unique surface texture.
7. Textured Finish
Textured finishes create decorative patterns or designs on a plastered surface. They are typically applied using sketch plastering techniques, which involve using various tools to create textured designs.
These finishes are often used in stucco applications and offer endless possibilities for customisation. To create the desired texture, specialised equipment and skilled hands are required.
8. Stucco Plaster Finish
Stucco plaster finishes are known for their quality and versatility, making them suitable for interior and exterior applications. This finish is applied in three coats: the scratch coat, the brown coat, and the final white or finish coat.
The stucco plaster is highly durable and has a total thickness of around 25 mm. This finish is often used in high-end construction projects.
9. Waterproof Plaster Finish
Waterproof plaster finishes are specifically designed to protect surfaces from moisture. The plaster includes cement waterproofing compounds that meet the standards of IS:2645.
The compound must be thoroughly mixed with dry cement to ensure proper integration. This type of finish is commonly used in areas exposed to water, such as bathrooms or kitchens, and in exterior surfaces where moisture resistance is critical.
10. Exposed Aggregate Plaster Finish
An exposed aggregate plaster finish involves using marble chips, either white or coloured, that are 6 mm to 12 mm in size. These chips are made by crushing hard marble stones.
The finished plaster coat is at least 20 mm thick and is applied similarly to a sand-faced finish. The marble chips provide a distinctive and decorative surface, often used for outdoor walls and decorative elements.
Special Materials For Plastering Finishes
Special materials are sometimes added to the plaster mix to enhance the finish for specific needs such as soundproofing, fire resistance, or durability. Here are some examples of specialised plaster finishes.
1. Acoustic Plaster
Acoustic plaster is made by mixing gypsum with other materials to create a honeycomb structure in the final coat. This structure contains tiny holes that dampen sound, making this finish ideal for concert halls, auditoriums, and other spaces requiring sound absorption.
2. Asbestos Marble Plaster
This finish uses a mixture of asbestos, cement, and finely crushed marble. The asbestos improves the appearance and provides additional fire resistance. This type of finish is typically reserved for high-end applications.
3. Barium Plaster
Barium plaster is used in X-ray rooms to protect against radiation. The mortar mix includes sand, cement, and barium soleplate, which helps shield the room from radioactive particles.
4. Granite Silicon Plaster
This high-end finish involves mixing granite and silicon into the plaster. It’s often used in premium buildings because of its durability and quick setting time. The finish’s elasticity also helps to prevent cracking, making it suitable for use in areas with temperature fluctuations.
5. Plaster Of Paris (Gypsum Plaster)
Plaster of Paris is made by heating gypsum to around 160°C to 170°C. Once mixed with water, the plaster sets within a few minutes.
However, retarders can be added to extend the setting time. This lightweight, fire-resistant plaster is often used for decorative purposes.
It’s ideal for ornamental work but not recommended for areas exposed to water, as it dissolves when wet.
6. Keene’s Cement Plaster
Keene’s cement plaster is made by calcining Plaster of Paris with alum. This creates a plaster that hardens to a firm, white, glass-like finish within a few days. It’s mainly used for decorative purposes.
Conclusion
Plaster finishes play a key role in building surfaces’ appearance and durability. Each plaster finish has unique benefits, from smooth and polished finishes to decorative and textured designs.
By selecting the right finish for your project, you can enhance the aesthetics of your space while ensuring long-lasting protection against wear and tear.
For the best results, consult a professional wall plasterer who can guide you through the process and help you choose the most suitable plaster finish.
FAQs About Plastering
What Is A Troweled Finish, And How Is It Different From Other Plaster Finishes?
A troweled finish involves applying plaster with a trowel to create a smooth, handcrafted appearance with subtle texture variations. It offers a classic and elegant finish suitable for traditional and contemporary interiors.
Can You Explain The Difference Between A Lime Plaster Finish And A Gypsum Plaster Finish?
Lime plaster, made from lime, sand, and water, offers a breathable, durable finish suitable for historic restoration and eco-friendly projects. Gypsum plaster, made from gypsum and water, provides a smooth and quick-setting finish ideal for modern construction and interior applications.
What Is A Sand-Float Finish, And Where Is It Commonly Used?
A sand-float finish involves embedding sand into the surface of wet plaster to create a textured appearance. It is commonly used for exterior walls and stucco finishes to enhance visual interest and durability.
How Is A Dash Or Spatter Finish Achieved, And What Are Its Characteristics?
A dash or spatter finish is achieved by throwing or spraying small plaster particles onto the surface to create a random and irregular texture. It is commonly used for exterior walls to provide a rustic or decorative finish.
Are There Specialised Plaster Finishes For Specific Environments Or Applications?
Yes, specialised plaster finishes such as exterior insulation and finish systems (EIFS) are for energy-efficient exteriors, fire-resistant plaster finishes are for high-risk areas, and decorative finishes like frescoes or faux finishes are for artistic and architectural purposes.
