Roughcast and smooth lime render are both popular options for exterior wall finishes. Roughcast is a textured finish achieved by throwing a coarse lime render at the wall surface. On the other hand, a smooth lime render is a flat finish created by applying a lime render to the wall surface using a trowel.
Both roughcast and smooth lime renders have their advantages and disadvantages. Roughcast is particularly useful in exposed areas as its heavy texture creates a larger surface area that aids moisture absorption and evaporation. Additionally, the application method allows for the use of a mortar mix that is less prone to shrinkage during curing. On the other hand, smooth lime render provides a more uniform and cleaner appearance that can be painted over easily.
When deciding between roughcast and smooth lime render, it is important to consider the climate and location of the building, as well as the desired aesthetic. Roughcast may be more suitable for traditional or rural buildings, while smooth lime render may be better suited for modern or urban designs. Ultimately, the decision will depend on the homeowner’s or builder’s specific needs and preferences.
What is Roughcast Lime Render?
Roughcast lime render is an exterior wall finish made up of a mixture of sands, aggregates, and lime, either hydraulic or non-hydraulic. The final render coat is mixed and thrown at the wall to create a rough, textured surface. The texture is achieved by leaving the surface rough, which gives it a natural-looking appearance.
How is Roughcast Lime Render Applied?
For the best results, in terms of longevity and durability, the building/wall will need three coats. Firstly, coarse-haired lime render should be applied, followed by another coarse-haired render or coarse-unhaired, depending on the project requirements.
The last coat is the wet dash, also known as roughcast in England and harling in Scotland. This coarse material can contain grit, broken pottery, gravel and a number of other aggregates. It is thrown onto the wall, and this creates a textured surface that is ideal for areas that are exposed to the elements. The texture increases the overall surface area, which helps to absorb and evaporate moisture more easily.
The application method allows the use of a mortar mix that is less prone to shrinkage while curing. Early lime-based roughcast is becoming rarer and rarer, but it is still used today in heritage restoration projects.
When applied correctly, roughcast lime render can last for many years, making it a popular choice for new builds and restoration projects. However, it is important to apply the mixture correctly, as any mistakes can lead to cracking and other issues.
Related article: The Differences Between Lime Plaster, Mortar and Render
What is Smooth Lime Render?
A smooth lime render is an external wall finish applied to a substrate in a smooth, even layer. It is made from a mix of lime, sand, and water and is often used as an alternative to roughcast render. Smooth lime render is typically applied to buildings that require a more refined finish, such as stately homes and historic buildings.
How is Smooth Lime Render Applied?
Smooth lime render is applied in several thin coats, each one building up the thickness of the layer until the desired finish is achieved. The process typically involves the following steps:
- Preparing the substrate: The substrate must be clean, dry, and free from any loose material before the render can be applied. Any cracks or defects in the substrate must be repaired before the render is applied.
- Applying the base coat: A base coat of coarse lime render which sometimes contains hair, is applied to the substrate, typically at a thickness of around 10-15mm. This coat is left to cure fully before the next coat is applied.
- Applying the second coat: A second coat of lime render is applied to the substrate at a thickness of around 10mm. This coat is left to cure fully before the next coat is applied.
- Applying the finishing coat: The final coat of lime render can be coarse or fine, depending on the project, and is applied to the substrate at a thickness of around 3-9mm. This coat is left to cure fully before a finish such as limewash is applied.
Smooth lime render is a popular choice for buildings that require a more refined finish, providing a smooth, even surface that can be easily painted or decorated. It is also more durable than other render types and can last many years with proper maintenance.
Related article: Should You Paint Lime Plaster? Our Ultimate Guide
Differences Between Roughcast and Smooth Lime Render
Appearance
Roughcast and smooth lime render offer different visual effects. Roughcast has a textured, grainy surface that creates a rustic, natural look. It is often used in traditional or rural settings but also in modern designs to add texture and depth.
On the other hand, smooth lime render has a sleek, refined finish that looks clean and contemporary. Urban or minimalist designs often use it to create a smooth, unbroken surface.
Durability
Regarding durability, roughcast and smooth lime render have different strengths and weaknesses. Roughcast is more resistant to weathering and cracking because of its textured surface, which allows it to absorb and release moisture more easily. However, it can be more prone to staining and discolouration over time.
On the other hand, smooth lime render is less likely to stain or discolour but can be more prone to cracking and damage from weathering because of its smooth surface.
Cost
The cost of roughcast and smooth lime render can vary depending on several factors, such as the size of the area to be covered, the type of materials used, and the complexity of the application. In general, roughcast tends to be less expensive than smooth lime render because it requires less preparation and can be applied more quickly and easily.
Choosing Between Roughcast and Smooth Lime Render
Considerations
When choosing between roughcast and smooth lime render, several factors must be considered. One of the most important is the style and age of the building. Roughcast is a traditional finish often used on older buildings, while smooth lime render is a more modern option that works well on both new and old properties.
Another consideration is the texture and appearance of the finish. Roughcast has a more textured, natural look that can be ideal for properties in rural or coastal areas. In contrast, smooth lime render has a more uniform, sleek appearance that may be better suited to urban environments.
The cost of the two options is also a factor to consider. Roughcast is generally cheaper than smooth lime render, as it requires less preparation and can be applied more quickly.
Maintenance
Maintenance is an important consideration when choosing between roughcast and smooth lime render. Roughcast is a more porous material than smooth lime render, which may be more susceptible to water damage and staining. It may also require more frequent cleaning and maintenance to keep it looking its best.
On the other hand, smooth lime render is generally more resistant to water damage and staining and may require less maintenance over time. However, it is important to note that any render will require some level of maintenance to keep it in good condition.
Ultimately, the choice between roughcast and smooth lime render will depend on several factors, including the style and age of the building, the desired texture and appearance of the finish, and the budget and maintenance requirements. By carefully considering these factors, property owners can make an informed decision to ensure their property looks its best for years to come.
