Rendering

Rendering is the process of applying a coat of mortar-based or synthetic material to the outside of a building’s walls. It covers the underlying brickwork, blockwork, or stonework and provides both weather protection and a clean, finished appearance. Render is one of the most common external wall finishes, particularly on extensions, modern builds, and older properties where the original brickwork isn’t visually appealing.

Types of render

Cement render (traditional)

A mix of sand, cement, and sometimes lime, applied in multiple coats:

• Affordable and widely available
• Can be painted any colour
• Prone to cracking over time, especially if applied too thickly or without proper preparation
• Requires regular maintenance (repainting every 5-10 years)

Lime render

A traditional render using lime instead of cement:

• Breathable — allows moisture to escape from the wall behind
• Essential for older and period properties (pre-1920s)
• More flexible than cement render, so less prone to cracking
• Takes longer to cure and requires more skill to apply

Silicone/monocouche render

A modern, through-coloured render applied in a single coat:

• Low maintenance — colour is mixed through the material, so no painting needed
• Water-repellent but breathable
• More expensive upfront but saves on long-term maintenance costs
• Available in a wide range of colours and textures

Acrylic render

A synthetic, flexible render:

• Good resistance to cracking
• Can be applied over insulation boards (external wall insulation systems)
• Wide colour range
• Less breathable than lime — not suitable for all building types

When rendering comes up in renovation

Rendering is commonly needed when:

• Building an extension — new blockwork typically needs a rendered finish to match or complement the existing property
• Improving insulation — external wall insulation systems are finished with render
• Repairing or replacing old render that has cracked, blown (separated from the wall), or become unsightly
• Changing the look of a property — covering unattractive brickwork or updating the exterior

Key considerations

• Match the building — use lime render on older properties, not cement, to avoid trapping moisture and damaging the masonry behind
• Don’t cover the damp-proof course — render that extends below the DPC line can bridge it, causing rising damp
• Preparation matters — render applied to poorly prepared or damp walls will fail
• Building regulations may apply — particularly if you’re adding external insulation with render, which changes the building’s thermal performance

Tips for homeowners

• Choose the right type for your building’s age and construction
• Get a proper specification — thickness, number of coats, mesh reinforcement, and base preparation should all be agreed in the scope of work
• Check planning requirements — changing the external appearance of your property may need planning permission in conservation areas
• Budget for scaffolding — most rendering work requires full scaffolding access