When it comes to applying render on a building’s exterior, two main methods come to mind: spray rendering and hand application. Both techniques have advantages and challenges, making choosing between them a critical decision for both contractors and homeowners.
What is rendering?
Rendering is a construction technique used to apply a smooth or textured protective layer of plaster to the exterior or interior walls of a building. This layer, commonly made from a mixture of cement, sand, lime, and water, serves multiple purposes. It enhances the building's aesthetic appeal by providing a uniform or decorative finish, which can be painted or left as is, depending on the desired look. Rendering can also be adapted to include different colours or textures by adjusting the mix or application technique. Beyond aesthetics, rendering is crucial in protecting a building's structural integrity. It acts as a barrier against external elements like rain, snow, and changes in temperature, which can cause damage over time. Sealing the exterior and rendering help prevent water ingress, reducing the risk of dampness and structural decay. This is particularly important in climates that experience severe weather conditions. Moreover, rendering can significantly improve a building's thermal performance. The layer added to the walls helps to insulate the building, keeping it warmer in the winter and cooler in the summer. This can reduce energy costs, as less heating or cooling is required to maintain a comfortable indoor environment. The rendering process involves preparing the wall surface, mixing the render materials to the correct consistency, and then applying the mixture either manually with tools like trowels and hawks or mechanically using spray machines. The choice between manual or mechanical application depends on the project's scale and the required finish. The drying time for render can vary, but it typically needs to set and harden over several days, during which it must be protected from extreme weather conditions to ensure a smooth, durable finish.
Spray rendering
Spray rendering is a modern method of applying render that uses mechanical equipment to streamline the process, making it faster and often more cost-effective for large-scale projects. This technique involves using a spray machine that pumps the render mix through a hose to a spray gun, which is then applied to the wall in an even layer. Crucially, spray machines can also handle basecoat so that the retrofitting process can be accelerated. This approach is particularly favoured in commercial and new-build residential projects due to its efficiency and ability to cover vast areas swiftly.
Process
The process starts with preparing the render mixture, which typically consists of components like cement, lime, sand, and water, although proprietary mixes are also common. This mixture is then fed into the spray machine and kept under constant pressure. The machine delivers the render through a hose to a handheld spray gun, evenly distributing the render across the wall's surface. The spray nozzle atomises the render, which ensures even distribution across the surface. The operator will work in small circles to aid the even distribution of the render. Operators can control the thickness of the layer and the area covered by adjusting the machine settings and the technique used during application. Uniform coverage is one of the standout advantages of spray rendering, as it minimises human error and ensures a consistent finish across large surfaces.
Advantages
- Efficiency: Spray rendering significantly speeds up the application process, allowing for quick coverage of large areas, which can greatly reduce the time required to complete a project.
- Labour reduction: Using a machine to apply the render reduces the physical demand on workers, and fewer labourers are needed to cover the same area compared to hand application. This can lead to wage savings and potentially lower insurance costs due to the decreased risk of physical strain.
- Consistency: Spray rendering's mechanical nature offers a consistent mix and application rate, reducing the likelihood of human error and ensuring uniform quality across the entire project.
- Versatility: Modern spray rendering machines can apply different types of render, including those with special additives or properties, such as increased elasticity or thermal insulation. They can also handle different textures, which can be adjusted according to project requirements.
Disadvantages
- Initial investment: The cost of acquiring high-quality spray rendering equipment can be considerable. Additionally, the maintenance of the machines adds to the overhead, making it less economical for small projects.
- Training and skill: Operating spray rendering equipment effectively requires specific skills and training. The operators need to know the machine settings and techniques to achieve the desired finish, which can involve additional training costs.
Traditional hand application
Hand application of render is the traditional method that involves manually applying a plaster-like mixture to walls using tools such as trowels, hawks, and floats. This technique has been used for centuries and remains popular for its precision and adaptability, especially suitable for smaller projects.
Process
The process of traditional hand application will remain similar, irrespective of what type of render you choose. Some renders will require a different tool for finishing; for example, a monocouche render is cratched back with a monocouche scraper. However, the application process is similar. Silicone renders arrive ready to use; therefore, the bucket must be mixed gently with a paddle mixer to distribute the aggregate evenly. Once complete, you can use a scoop to add some render on a hawk. A hawk is essentially a large flat plate with a handle that helps you hold a small amount of render as you work. It can also catch the render that falls off as you apply it with a trowel. Once the render is applied, it must be rubbed with a plastic float to distribute the aggregate more evenly. Different types of render may require a secondary layer. For example, lime render often requires a first coat before a finishing coat. This adds to the time aspect of traditional hand application. Hand application also requires you to maintain a wet edge on the render; a wet edge ensures that the resultant finish has no trowel marks.
Advantages
- Precision and control: Hand application allows for meticulous control over the application, making it ideal for achieving specific finishes or working with intricate architectural features. Artisans can adjust the thickness and texture as they go, tailoring the application to the unique contours and details of the building.
- Flexibility in material mix: This method allows for on-site adjustments to the mix, accommodating different finishes and materials without needing specialised equipment. It’s particularly useful when dealing with traditional or heritage buildings that require specific materials to maintain their character.
- Lower start-up costs: Hand application does not require expensive machinery, making it accessible for smaller contractors or those undertaking DIY projects. The tools needed are relatively inexpensive and easy to obtain.
Disadvantages
- Labour-intensive: The method is physically demanding and requires a significant amount of manual labour, which can lead to higher long-term costs in terms of wages and potential health-related issues for workers.
- Time-consuming: Hand applying render is much slower than spray techniques, particularly on large surfaces. This can extend project timelines and may not be feasible for tight schedules.
- Skill dependent: The quality of the finish heavily relies on the skill and experience of the tradesperson. Inconsistent skill levels can lead to uneven finishes, requiring additional time and resources to correct.
What's the verdict - spray rendering or hand application?
Ultimately, this decision is down to you. Due to the lower costs, smaller projects, companies, and DIYers will likely stick to hand applications. You can attend the EWI Pro Training Academy and learn the necessary skills to apply the render manually. However, larger companies working on commercial projects will reap the benefits of investing in spray machines and spray rendering expertise. The time and wastage saved will pay off the initial investment in a shorter time.