- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 07 Oct 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
A more modern render which combines all of the above properties is a silicone enhanced render which is water repellant but where an acrylic render isn't breathable a silicone render is breathable like a lime mortar. In a range of colours and with its excellent breathable and water repellant properties, this is becoming a render of choice.
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.
 Find out more
 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
The focus is generally on the lime binder, but the aggregate is actually the most significant element.
The importance of communication, collaboration and simplicity when planning construction projects.
New working group is set up to consider options for raising standards across the property agent sector.
BSRIA provide a top 10 list of recent legislation and guidance affecting buildings.
Record third-time winner of the RIBA Stirling Prize - our profile of one of the world's most celebrated architects.
Foster + Partner's London Bloomberg HQ building wins the 2018 Stirling Prize.
A release schedule is prepared if not all required information has been prepared or issued when the contract is executed.
UKCW report shows industry changing on fire safety ahead of government regulation.
Formwork is the term used for the process of creating a temporary mould into which concrete is poured and formed.
CIOB, RICS and RIBA launch new digital tool to help enhance quality tracking.