Render is a layer of material that is applied to walls and ceilings for decoration, waterproofing or insulation purposes. It typically consists of cement, sand, lime and water which are mixed together to form a paste-like substance that can then be spread onto the surface using an applicator. The render can then be finished with a trowel or similar tool to achieve an even finish.
Plaster is a much finer mixture than render and is usually comprised of gypsum or calcium sulphate hemihydrate along with water. This mixture creates a paste-like material which can be easily moulded into shapes when wet before drying hard when it comes into contact with air. Plaster is often used to provide a smooth finish on interior walls and ceilings as well as for ornamental purposes.
Texturing is the process of adding texture to render or plaster in order to create an interesting visual effect. This can be achieved by using a range of different tools such as trowels, sponges and rakes. The texture created will depend on the type of tool used and how it is manipulated against the surface.
Skim coating refers to the application of multiple thin layers (skims) of plaster over an existing wall or ceiling surface. It is commonly used when repairing damaged surfaces such as cracks or uneven areas, or when attempting to achieve a particular decorative effect.
Sand Cement Render
Sand cement render is a type of render that uses sand, cement and water as its main components. It is generally used on exterior walls and it provides a durable, waterproof finish that can be painted or left to weather naturally.
Acrylic render is a type of modern rendering system that utilises acrylic polymers to provide an attractive, long lasting and breathable finish. It is often preferred over other types of renders due to its flexibility and resistance to cracking, making it particularly suitable for older buildings or those in areas with extreme temperature variations.
Float and Set Finish
Float and set is a popular finishing technique for external and internal plaster work, whereby the first layer (the float) is applied with a trowel in an even, circular motion. The second layer (the set) is then added and gently smoothed out to create a uniform finish. This technique requires considerable skill to achieve an attractive and lasting result.
A scratch coat is the first layer of plaster that is applied to a wall or ceiling. It must be allowed to dry completely before further layers are added on top. The scratched surface provides grip for subsequent layers, helping them adhere properly and creating a strong bond between the original substrate and the plasterwork.
Patching refers to the process of filling small holes or cracks in a wall or ceiling with plaster. The patching should be done carefully and accurately in order to avoid any further damage to the surface. It is important that the patch is applied evenly and allowed to dry completely before any further work is carried out on the area.
Setting agent, also known as retarder, is a type of chemical additive used when rendering or plastering walls. It helps slow down the drying process, giving more time for smooth application and avoiding issues such as cracking or sagging caused by rapid drying. Once added to the mixture it will remain active for several hours, after which time it loses its effectiveness and needs to be replaced.
Damp Proof Course (DPC)
A damp proof course (DPC) is an impermeable membrane placed between two layers of masonry in order to prevent the rising of moisture. It is usually made from bitumen, plastic or slate and has a number of different uses including protecting against water penetration and increasing insulation efficiency. The application of a DPC should be completed before any other plastering or rendering work takes place.
Browning refers to the process of adding a small amount of pigment to render or plaster when it is still in its wet state. This helps create more subtle tones than those achievable with paint and it can also help bring out natural features such as textures and contours. Browning must be undertaken correctly in order to achieve a uniform and attractive finish.
Wall conditioners or primers are special solutions applied before the plastering or rendering process begins in order to improve adhesion and create a better bond between the original substrate and the fresh application of plaster or render. Primers should be carefully chosen to suit the specific requirements of the project, although most general purpose products will offer sufficient protection from moisture.
A float coat is the third layer of plaster applied to a wall or ceiling, following the scratch and set coats. This thick, even layer helps create an attractive and impact resistant surface that can be left to weather naturally or painted over. The application of a float coat requires extensive skill in order to successfully achieve a consistent and long lasting finish.
An adhesion coat is an important part of most external rendering systems as it provides a strong bond between the render and the substrate beneath it. It consists of two layers, typically composed of sand and cement mix with added chemical additives to help improve waterproofing qualities. Adhesion coats should be applied carefully and evenly in order to ensure that the render can withstand harsh weather conditions and remain durable over time.
Render Scratch Coat
A render scratch coat is a key component of external rendering systems. It is applied as the first layer to provide grip for additional layers and help ensure that the render adheres securely to the substrate beneath it. The scratch coat should be smoothed in order to create a consistent texture, which helps make subsequent coats easier to apply evenly.
The top coat is typically the final layer of plaster or render applied before decoration takes place. This layer provides an attractive finish that can be left exposed or painted over depending on personal preference. As with all other plastering and rendering work, careful application of the top coat is essential in order to create a smooth, attractive finish.
Jointing involves the application of small amounts of mortar to fill gaps between components or sections of plaster or render. The joint should be slightly recessed below the surface and filled with material that matches the surrounding area in terms of colour and texture. This helps ensure a consistent and attractive finish that is resistant to weathering and remains functional over time.
Curing refers to the process whereby freshly plastered or rendered surfaces are allowed to dry slowly in order to increase their strength and durability. During this period, walls should be kept moist by regularly spraying them with water for several days post-application. This helps prevent cracking and ensures that the finished render or plaster is as impact resistant as possible.
Dry dashing is a decorative technique used to add texture and colour to walls while also providing some protection from the elements. This involves throwing small stones, gravel or pebbles onto wet plaster or render and allowing them to stick in place. The result is an attractive finish with natural variations in tone and texture that can be further enhanced by painting or varnishing afterwards.
Skimming is the process of applying a layer of plaster to a wall or ceiling in order to provide a smooth and even surface. This technique is often employed to cover up any imperfections or blemishes that may be present in the original substrate, resulting in an attractive and consistent finish. Skimming can also be used as part of a decorative render job when combined with dry dashing or other techniques.
Modern rendering and plastering techniques have come on leaps and bounds over recent decades, allowing professional contractors to create stunning finishes for both interior and exterior applications. By understanding the different terms associated with these processes, you’ll be able to make more informed decisions about your own projects. With careful preparation, the right materials and a little bit of know-how, you can achieve amazing results with minimal fuss.