Home health check

Many period properties have a rendered exterior made from lime-based materials, forming a durable coating that must be kept in good condition

Property expert Roger Hunt advises on exterior rendering

Protecting the exterior walls of a building and providing a unifying aesthetic, render comes in a variety of forms. Most commonly it’s applied to create a relatively smooth skin but, in the wetter regions of the UK, roughcast – or harling as it’s known in northern England and Scotland – is used. This offers good weathering properties and dries out more quickly as its increased surface area serves to maximise evaporation and protection against driving rain.

In Essex and Suffolk in particular, render was sometimes moulded or indented with patterns in a process known as pargeting.

Warning signs

Render sometimes deteriorates due to water ingress resulting from the failure of elements such as rainwater goods or poor detailing of roof overhangs and window cills. Repairs or re-rendering undertaken with an inappropriate material can exacerbate problems, causing considerable damage to the building’s fabric.

What to look for:

● Loose or delaminating render

● Inappropriate modern renders and finishes

● Staining, moss or plant growth

● Leaking rainwater goods

● Poor detailing of eaves, parapets and cills

● Bulges or cracks ➤

Material facts

Until modern cement-based products came into general use in around 1920, lime render was widely employed and the rendered surfaces were often protected with limewash. Traditional rendering techniques and the lime-based materials used allow old buildings to breathe while offering some flexibility that helps avoid cracking and failure of the surfaces. Lime renders and finishes age well, have an attractive texture and tend to provide soft, rounded edges to buildings.

Render: Based on lime mixed with sharp sand, render is applied in a number of coats (layers). Some renders contain clay, ash, hair, dung and other materials.

ROUGHCAST And HARLING: Lime mixed with pea gravel, roughcast is thrown onto the face of the building using a dashing trowel.

Pebbledash: Created by throwing dry pebbles or chipping on to a wet coat of smooth render, pebbledash was popular from Edwardian times.

LIMEWASH: Consisting of lime diluted with water and often coloured with pigments, limewash forms a durable protective coating while allowing the walling materials to breathe.