Render is a coating applied to a building’s external walls – basically, the smooth, usually white surface on the outside of a house. Traditionally, a mix of lime, water and an aggregate (such as sand) created a flexible and breathable covering.

This method hasn’t been particularly popular in the last few decades, but has recently experienced a bit of a resurgence; it’s certainly still used for period property conservation.
 

Conventional render is made from a cement, sand and aggregate blend, but many modern products are cement free. These newer options sometimes contain products to help waterproofing and resistance to algae growth – you can even get renders pre-mixed with a colour for a vibrant finish and ones that work with external insulation.
 

Generally, modern render can be divided into three main types: monocouche, acrylic and silicone – but there are other options, as I’ll present later. Normally these need only one coat of 1mm-4mm thickness, but this is highly influenced by the substrate material used under the render.

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If chippings are being added to the surface once the render is in place, then it may need to be at least 6mm thick.

A basecoat of 8mm-10mm will be needed to level out a poor brick surface, sometimes using a mesh membrane to reinforce. For lighter weight construction – timber frame or steel studs – a proprietary backing board can be applied to act as the substrate, which is then covered in a reinforcement mesh, much like the levelling coat over masonry.

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One of the features making modern renders so popular is that they can be combined with External Wall Insulation (EWI) thanks to their light weights and thin coats. Normally there’s only need for one layer on the outside of the insulation, but still on top of a reinforcing mesh.

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With houses built using timber frames or steel studs, a cavity might need to be specified to ensure no interstitial condensation beyond the insulation in the panel. Details vary job-to-job, depending on the construction method and any restrictions in place.