roughcast

Roughcast is a traditional exterior plaster finish formed by applying a lime- or cement-based render that contains aggregate such as gravel, pebbles, or crushed stone. After application, the render is dashed or thrown onto the wall, creating a rough textured surface that can be left exposed or treated further. When the aggregate is embedded but the surface remains smooth, the finish is often called pebble-dash or pebbledash.

Materials and technique: Traditional roughcast uses lime putty plaster with aggregate and sometimes horsehair to improve adhesion and crack resistance. The dash-on method involves throwing or dashing the wet render onto a prepared wall, then troweling or brushing to achieve the desired texture. Modern versions may use cement-lime or fully cement-based mixes. The texture can range from coarse to fine, depending on aggregate size and finishing method.

Regional use and variants: Roughcast has been widely used across Europe, especially in Britain and Ireland, where it served as durable protection for masonry and a decorative finish. Pebble-dash is a related finish in which stones are embedded in the wet render and often left visible, a variant still common on many urban and suburban exteriors.

Maintenance and considerations: Exterior roughcast, particularly cement-based forms, can be susceptible to cracking or moisture problems if not properly bonded to the substrate or if the wall lacks breathability. Lime-based roughcasts are more permissive of moisture movement but may require more frequent maintenance. Re-dashing or patching is common over time, and repainting may be needed to protect the render and underlying masonry.