Asbestos Render

Asbestos render is an external wall coating that was produced by mixing Portland cement, sand, lime, and asbestos fibres into a plaster-like material that was applied to exterior building surfaces. The addition of asbestos — typically chrysotile at 2 to 10 per cent by weight — improved the render's resistance to cracking, enhanced its weather durability, and gave it better adhesion to the substrate.

Manufactured and applied from the 1930s through to the mid-1980s, asbestos render is found on a wide variety of building types. It was particularly popular on system-built housing from the 1950s and 1960s, post-war council estates, schools, and commercial premises. In some cases, asbestos fibres were added to a sprayed render formulation that was applied using a machine, creating a rough-textured exterior finish.

Asbestos render presents an interesting risk profile. While it is applied to exterior surfaces where natural ventilation dissipates any released fibres, the material can deteriorate significantly over time due to weathering, frost damage, and building movement. Cracked, blown, or spalling render can expose loose fibres at the surface. The risk escalates dramatically during renovation, re-rendering, or demolition work, when large areas of render are hacked off the wall, generating clouds of asbestos-contaminated dust.

Sprayed asbestos render is of particular concern because it can be more porous and friable than trowel-applied render, with a higher asbestos content. Some sprayed render formulations used amosite or a blend of chrysotile and amosite, increasing the health risk.

Before any work that would disturb exterior render on buildings constructed before 1985, samples should be tested for asbestos content. If asbestos is confirmed, removal must be carried out by a licensed contractor using controlled methods including wetting, scaffolding with containment sheeting, and appropriate personal protective equipment. Over-rendering — applying a new coat over the existing asbestos render — may be an alternative in some situations, provided the existing render is stable and well-adhered.