What's the Difference Between Plastering and Rendering?

Plastering and rendering are both techniques used in building construction to cover and protect walls, but they're typically used in different contexts and can have slightly different compositions. Plastering is the process of coating interior walls and ceilings with plaster material. It can be used to smooth out surfaces, create decorative effects, and provide a base for painting or wallpapering. Plaster typically contains gypsum, lime, or cement mixed with water and sometimes sand. It's applied in thin layers, and the finish can be smooth or textured, depending on the desired effect. Rendering is essentially the exterior equivalent of plastering. It involves applying a mixture to the exterior of a building to protect it from the elements. The most common types of rendering use cement, sand, lime, and water, though acrylic and silicone-based renders are also used. Render tends to be more weather-resistant than interior plaster, and it's often thicker and more textured to help it shed water. Render can also be coloured or painted, providing a finished exterior look to the building. The techniques used in plastering and rendering are similar, and both require skill to apply evenly and create a smooth, attractive finish. The main difference is where they're used (inside vs. outside) and the materials that may be included in the mixtures. Also, the render is usually more durable to withstand weather conditions, while the plaster is typically smoother for interior aesthetics.

What is plastering?

Plastering is a process used in building construction to provide smooth, durable, and aesthetically pleasing surfaces for walls and ceilings.

1. Gypsum Plaster: A type of plaster for indoor applications due to its smooth finish and quick-drying properties. It's made by heating gypsum rock to remove the water content and then grinding it into a fine powder. When mixed with water, it forms a paste that can be spread onto walls and ceilings.
   • Plaster of Paris: For creating detailed decorations and finishes. It's also often used in mould making and casting.
   • Browning, Bonding, and Thistle: Types of undercoat gypsum plasters. Browning is used on absorbent surfaces, bonding on less absorbent surfaces, and thistle is a versatile type that can be used on most surfaces.
2. Lime Plaster: This is a traditional type of plaster that was widely used before the advent of gypsum plaster. Lime plaster is made from lime, sand, and water, and sometimes hair or other fibres are added for extra strength. The lime can be either non-hydraulic (it sets by reacting with carbon dioxide in the air) or hydraulic (it sets by reacting with water). Lime plaster is breathable, making it good for older buildings as it allows moisture to evaporate from the walls. However, it can take a long time to dry and is less resistant to impact than other types of plaster.
3. Cement Plaster: This type of plaster is more commonly used in outdoor applications or in wet areas of a house like a bathroom or kitchen. It's made from a mixture of sand, cement, and water. It's durable and water-resistant, but it doesn't give as smooth a finish as gypsum plaster. Depending on the required thickness, the ratio of cement to sand can vary. It also takes longer to dry compared to gypsum plaster.

What tools do you need for plastering and what's the process?

Plastering involves the use of a variety of tools, each serving specific functions. A plasterer's hawk is a handheld platform that holds the plaster during work, and a trowel is used to apply and smooth the plaster onto the surface. For further smoothing, a float is utilised. A corner trowel helps in forming clean corners, while a skimming blade is used for levelling and smoothing large areas of plaster. To assist the adhesion of multiple layers of plaster, a scratching tool is used to score the first coat before the application of the second coat. The plastering process includes several key steps, starting with the preparation, which involves cleaning the plastering surface and applying a primer if necessary. For plasterboarding, plasterboards are fixed to the wall or ceiling during this stage. After preparation, the first coat of plaster, or undercoat, is applied evenly using a trowel and then scratched to prepare for the second coat. The second coat, known as the skim or finish coat, is applied after the undercoat has dried. It is then smoothed using a trowel and float. Once the plaster has dried, it's polished to provide a smooth finish. The final step involves painting or wallpapering the wall or ceiling if desired after the plaster is fully dry.

What is rendering?

Render is a type of mortar applied as a decorative and protective coating to the exterior walls of a building. It provides an attractive finish, improves water resistance, and can increase the durability of the structure. Render typically consists of a mix of sand, cement, lime, and water, but it can also contain special additives for improved performance and durability. There are several types of render available, each with its own unique properties and advantages. Let's focus on silicone render and monocouche render:

Silicone Render

Silicone render is a type of through-coloured render, which means the colour permeates through the whole material. Its key ingredient, silicone, provides several benefits:

• Water Resistance: Silicone repels water, making it highly water-resistant. This characteristic prevents dampness from penetrating the walls, reducing the risk of structural damage over time.
• Breathability: Despite its water resistance, silicone render allows water vapour to pass through, so any moisture that does get into the walls can escape. This is beneficial in preventing dampness and mould growth.
• Self-Cleaning: Silicone render has self-cleaning properties, meaning it doesn't allow dirt to stick easily to the surface. When it rains, the rainwater washes away most of the grime, keeping the walls looking clean and fresh.
• Flexibility: Silicone render is flexible, which helps prevent cracking with changes in temperature or building movement.

Monocouche Render

Monocouche, from the French meaning "single layer", is a one-coat, through-coloured render. It provides a decorative and weather-resistant finish and is typically applied in a two-coat process (a scratch coat and a finish coat) but still is considered as one layer since it's part of the same system.

• Efficiency: Since monocouche render is a one-coat system, it can be quicker and more cost-effective to apply compared to traditional renders.
• Through-Coloured: Monocouche renders are pre-mixed with colour, eliminating the need for painting after application.
• Weather Resistance and Breathability: Like silicone render, monocouche render is water-resistant yet breathable, protecting the building from dampness while allowing any moisture that does get into the walls to escape.

Plastering vs rendering summarised

Plastering is typically applied on the interior of buildings, using materials like gypsum, lime, or cement to create a smooth surface on walls and ceilings. It offers a base for subsequent decorating, such as painting or wallpapering. The result is a smooth and aesthetic indoor wall surface that, being indoors and protected from the elements, usually requires less maintenance. However, it doesn't provide significant insulation and can be damaged by impact or indoor moisture issues. The mix used for plastering is generally finer and smoother compared to that of rendering. On the other hand, rendering is used on exterior walls. It employs a mixture of sand, cement, lime, and sometimes other additives for improved performance and durability. The result is often a more textured and robust finish that is weather-resistant and more durable, intended to withstand external conditions. Some types of render can add an extra layer of insulation to a building, improving energy efficiency. Render can also be textured or patterned, and can be pre-coloured, painted, or left as is. Given its exposure to weather, rendered surfaces may require maintenance like cleaning or repainting over time. The mix used in rendering is typically coarser and more substantial than plaster.