What is External Render?

A wall coating of cement, lime or polymer mortar. Render is a material made of an aggregate, binder (cement or lime) and water, which is applied wet and hardens to finish the exterior, often the façade or front of buildings. The application of a premixed layer of cement or lime based mortar and sand undercoats and finishing coats to concrete block, brick or stone substrates is generally known as rendering. It is often textured, coloured or painted after application. Generally used on exterior walls, it can be used as a feature to an interior wall where desired. Depending on the 'look' required, rendering can be fine or coarse, textured or smooth, natural or coloured, pigmented or painted.

The rendering of brick, concrete, stone and mud houses has been used for centuries to improve the appearance (and sometimes weather resistance) of exterior walls. It can be seen in different forms all over southern Europe. Different countries have their own style and traditional colours, including the elegant Etruscan stucco reliefs of Italy and the traditional alpine finish (dragged travertine) of numerous Alpine resorts.

While rendering is a centuries-old technique, technology has improved and different types of systems are now available. Different finishes can be created by using different tools and techniques such as trowels, sponges, brushes or mechanical equipment. The art in traditional rendering is, (apart from getting the mix right) the appearance of the top coat. Different tradesmen will have different finishing styles and be able to produce different textures and decorative effects.

Why use External render?

New Build: The application elevates properties to give a pleasing finish to the eye and variation of finish when compared to neighbouring properties.

Renovations: Applying render over external walls gives your house a facelift, especially if the current exterior is unattractive or in poor condition. Render may be used to finish external structures or cover visually unappealing construction materials such as masonry substrates. It is also used to finish external insulation.

Is Planning Permission required?

Rules and guidelines Planning permission isn't necessarily required to apply render, providing the house isn't listed, in a conservation area or Permitted Development rights haven't been removed (visit: planningportal.gov.uk or check with your local authority).

Building Regulations Rendering work must comply with Building Regulations. In an older house it is likely that the walls could be insulated.

What preparation work is needed?

Before a building is rendered, the client/contractor should allow for the walls to be surveyed, then they can make any required repairs to structural defects and any movement stablised, ready for the new render finish.

Depending upon the nature of a project, access scaffolding may need to be erected. External fixtures may have to be removed, such as satellite dishes, alarm boxes, rainwater and soil pipes. Any vents will need to be extended, and sometimes window sills must be extended too. Where applicable and when appropriate, stop and angle beads can then applied around the window and door openings and corners (or the edges of a terraced property) to provide clean edges for the render. Doors, windows and surrounding finished surfaces etc. are then masked to protect against soiling or damage. The render system can then be applied.

How is the Render applied?

A glass fibre mesh (mesh cloth reinforcement) is bedded into the first coat of render. This mesh acts as a reinforcement against cracking. This is followed by one more thin coat of render.

Different proprietary systems are built up of different layers, using various forms of insulation, including expanded polystyrene (EPS), mineral fibre (Rock Fibre) and phenolic foam (more expensive but superior performance). Different types of render are also used with external wall insulation systems, depending on the application and the desired finish, including polymer cement, silicone and acrylic.

Many render systems are designed to be self-coloured so they don’t require painting. As well as a choice of colours, different finishes are also available, from smooth (scraped finish) to textured (roughcast textured finish).

Finally, the external rainwater and soil pipes etc. can be reapplied and following a few days drying time, the scaffold removed.

How long will it take?

The total process for the rendering process only can take from four hours to around two weeks. Naturally this is entirely dependent upon the required specification and size of the scheme.