- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 16 May 2018
The main components of renders are cement, sand, lime and water. A common mix ratio used for rendering is 6 parts sand, 1 part cement and 1 part lime. Any general purpose cement can be used, although the sand should be fine and clean of impurities. Coarser sand is usually used as the base layer and slightly finer sand for the top layer.
Additives can be included in the mix that help with bonding or slowing the drying process, as well as pigments that alter the colour depending on the aesthetic requirements. By adding lime the render can be given a smoother texture, increasing its elasticity and making it less likely to crack after drying.
Render is usually mixed with a cement mixer which ensures an even mix with the addition of the correct amount of water. Render is then applied using a trowel in thin, smooth coats. A thin finishing top coat or finishing wash can be applied to achieve decorative effects. Depending on the surface texture finish required, top coats may be applied using a trowel, brush or sponge. There is considerable skill involved in achieving different textures, finishing styles and decorative effects.
Acrylic, pre-mixed rendering products have the advantage of superior water resistance and strength, allowing application to more challenging surfaces, such as concrete, cement sheeting or cladding such as expanded Polystyrene. Some types can also be applied using special spray equipment. Whilst traditional renders can take up to 28 days to fully set, acrylic renders can set in 24-48 hours.
A lime mortar (in which lime is used rather than cement) may be used for rendering older buildings, particularly if lime mortar was used in the original construction. This has greater flexibility and so is less likely to crack, and is ‘breathable’ allowing moisture to escape from the wall, but it takes longer to dry
Building regulations may apply depending on the extent of the rendering work to external walls. The Planning Portal states that where 25% or more of an external wall is re-rendered, regulations will normally apply.
 Related articles on Designing Buildings Wiki
- Brick veneer.
- Dry lining.
- Large-scale murals.
- Lath and plaster.
- Lime mortar.
- Parge coat.
- Wet trades.
 External references
Featured articles and news
Check out our list of the 90 most unusual buildings of all time.
The government is to set a personal consumption target to reduce water use.
BSRIA calls for more education to promote fuels that are fit to burn.
Michael Gove admits air pollution is making people ill and shortening lives.
BRE call for a clearer, focused drive for the delivery of sustainable, quality developments.
Proposals for a 140m high observation wheel next to the Tyne.
Consistently one of our most popular articles - so just how much do you know about BoQ's?
Significant updates encourage whole building life cycle assessment and recognise products with Environmental Product Declarations.
Gustavo Giovannoni’s role in integrating modern planning requirements into historic town centres.
Desipite Hackitt's recommendations, the government are to consult on combustible cladding.