External wall render

Types of External Wall Renders

The main types of external wall renders are traditional renders, cement-based renders, acrylic renders, silicone renders, monocouche renders, and others.

• Traditional renders: made with lime and sand. They let the water vapor escape the wall. This makes it less likely for dampness to build up inside. Because of this, traditional renders work well for older buildings that might have a lot of moisture on the inside.
• Cement-based renders: These external wall renders are widely used. A mix of sand, cement, and lime makes them up. They are strong and resist the weather well. Yet, cement-based renders do not allow water vapor to escape. This can trap moisture inside walls, especially in older buildings.
• Acrylic renders: These external wall renders contain a mix of traditional render and liquid acrylic polymer. The addition of liquid acrylic polymer enhances flexibility, durability, water resistance, and crack resistance.
• Silicone renders: Silicone renders are similar to acrylic renders. But silicone renders use a silicone-based resin on the outer layer. This gives extra weather resistance and breathability.
• Monocouche renders: Monocouche renders have all their colors mixed in before use. This means that even if the surface gets scratched, the color is consistent throughout. They come in different shades and need no painting.

Additionally, there are some other wall render types.

• Textured renders: Textured external wall renders look three-dimensional. This is because of the textures, patterns, or shapes that they create on the outside walls of buildings.
• Thin coat renders: Thin coat renders provide a neat and smooth finish. They are often used in modern buildings to give a streamlined look.
• Mineral renders: Mineral renders are made using natural materials like lime and aggregates. They are eco-friendly options and allow walls to breathe.
• Vegetation renders: These external wall renders promote plants or greenery to grow on them. They offer several environmental advantages. These include better air quality, natural insulation, and biodiversity enhancement.

Specifications & Maintenance

• Materials

  The average thickness of an external render is between 15 and 50 mm, depending on the material. Thin coats (less than 20 mm) use polymer-based materials, while thicker coats (more than 20 mm) use cement-based materials. Traditional renders are at least 50 mm thick and use natural hydraulic limes to achieve strength and weather resistance.

• Finishes

  An external render can have various texture finishes, including smooth, rough, ribbed, patterned, brushed, sponge, or pebbled. Renders with rough textures are usually made from lime, cement, hydraulic lime-cement mixtures, acrylics, or polymer cement.

• Colors

  Render hues include natural tones, whites, greys, blacks, yellows, greens, blues, reds, oranges, and browns. The color is often added to the mix before application, but some renders are painted after drying. Cement-based renders can be any color, but hydraulic lime-cement renders are limited to earth tones because of stains' natural pigments.

• Durability

  Durability depends on the material, thickness, and location. For example, hydraulic lime renders last up to 60 years in average conditions, cement renders last about 25 years, acrylic and polymer cement renders last 20 years, and lime plaster last up to 200 years.

Cleaning

Generally, external renders do not need maintenance, but dirt or biological growth may spoil their looks. Washing them with plain water is usually enough to remove dirt; other than that, it is recommended to avoid water on the surface because it can wash away the natural salts essential for drying.

Cleaning of the renders can be done by the following methods:

• Natural dry process: This is the best technique as per the maintenance manual because it prevents the surface from being cleaned. To support this process, ensure adequate sunlight and airflow around the area that needs to be cleaned.
• Cleaning with Water: It is only permissible to use water when natural drying is not possible. Always use distilled or rainwater to avoid mineral salt deposits on the surface of the rendering.
• Biological Growth Removal: If algae, fungi, or lichens grow on the surface of the external render, it is appropriate to use a biocide solution to clean it. The solution should only be used after natural drying and water cleaning. Choose a biocide which will not harm the rendering.

Repairs

If the damaged area is small, the entire area should not be recast instead only the damaged part or area can be repaired. If the area is large, then the whole area can be recast. The repair can be made by closely matching it and using a similar or compatible material to carry out the process but always before repairing thoroughly clean the area and remove any loose material from the area to be repaired.

Scenarios

The following are some of the common scenarios where the external wall render is applied.

• New Building Construction

  Newly constructed buildings often use wall renders to improve the aesthetics of the exterior wall. Typically, the wall renders are used to give the structure a uniform appearance while obliterating any wall imperfections. Different wall render materials can be used to achieve the desired look.

• Facade Renovation and Restoration

  In this case, the wall rendering completely transforms or restores the facade of the building. Usually, this applies to historical buildings and architectural monuments. At times, the external wall renders are used to modernize the look of older buildings and improve their aesthetic appeal.

• Extension and Addition

  When an extension or addition to a building is made, the new part usually needs to be rendered so that it blends in with the existing structure. A skilled contractor will usually assess the best type of render to use depending on the location and material of the wall being added.

• Commercial and Public Buildings

  Usually, public buildings and commercial structures like schools, hospitals, and office blocks use wall rendering for both functional and aesthetic purposes. The external wall renders improve durability and create visually attractive facades in urban environments.

• Retail and Hospitality Sector

  In the hospitality and retail industry, first impressions are critical. Aesthetics matters, and so, rendering improves the exterior of hotels, restaurants and retail spaces. It doesn’t just enhance the appearance, but also increases the value of the property.

• Industrial Buildings

  Industrial buildings may also require rendering on their external walls. Here, the renders improve resistance to harsh environments and protect the underlying structure.

How to choose external wall renders

When choosing external wall renders, several factors must be considered before choosing.

• Substrate compatibility

  Renders with good substrate compatibility should be considered. A substrate's physical and chemical properties are the surface on which something is applied. As previously said, various materials make up different external wall substrates, including concrete, blockwork, masonry, and timber frames. Compatibility is essential for effective bonding, performance, and longevity. Poor adherence might result in peeling, cracking, or other damage, making it essential for renders to interact with the substrate.

• Performance requirements

  Consider the climate of the site and choose renders that check the performance criteria highest on the list. Various performance demands are insulation, waterproofing, impact resistance, fire resistance, and others. The choice of renders will include the performance needs of the structures essential for the business.

• Installation methods

  Some renders call for specialized installation techniques, such as machine spraying or traditional hand application, leading to increased costs. Select rendering solutions with installation techniques to satisfy specific construction needs and budgetary limits. Make sure applicators are skilled in the chosen method, thus assuring the rendering project's success.

• Intended usage

  Take external factors into consideration carefully, such as the kind of building involved, whether it is residential, commercial, or industrial, and the desired aesthetic result. Choosing renders with properties adapted to the particular demands of various applications will maximize performance and value.

External wall render Q&A

Q: How thick should external render be?

A: The total thickness of external render is usually between 15 mm and 25 mm. It comprises three layers of undercoat, finishing coat, and scratch coat. The thickness may vary according to the wall surface texture and the thickness of the insulating material used.

Q: How long does external rendering take?

A: Depending on several factors, external rendering can take a few hours to a few days. Typically, it takes 1 to 3 days to complete the external rendering of an average-sized property. However, the time taken may be longer if the surface requires preparation or if crack and damage repairs take longer.

Q: Is rendering on a house worth it?

A: Rendering a house not only improves appearance but also provides weatherproofing, protection against algae and mould, longevity, and increased property value.

Q: What materials are used for external wall rendering?

A: Traditional cement-based renders are widely used but may frequently be replaced with polymer-based, low-cement, and cement/lime hybrid renders. Other alternative materials are the artificially manufactured material, the residue of the molten glass, and diatomaceous earth.

Q: Can one paint over external renders?

A: One can paint over external renders using water-repellent paints. This type of paint allows water vapor to escape from the render while preventing rainwater from penetrating the surface. Moreover, the water-repellent coating prolongs the life of the render and improves the building's aesthetic appearance.