Asbestos Stucco

Asbestos stucco is a cement-based exterior and interior wall finish that was formulated with chrysotile asbestos fibres to improve crack resistance, fire protection, weather durability, and workability during application. Applied as a wet-troweled or spray-applied coating over wire lath, masonry, concrete block, or existing cladding, asbestos stucco was a popular finish on residential and commercial buildings from the 1920s through the late 1970s, particularly in regions where stucco is a traditional exterior treatment.

The asbestos content in stucco formulations typically ranged from 1 to 10 per cent chrysotile by weight. The fibres served as micro-reinforcement within the cement matrix, reducing shrinkage cracking during curing and improving the long-term resistance of the finished surface to thermal expansion, settlement, and impact damage. Some stucco formulations also incorporated asbestos into the scratch coat or brown coat layers beneath the visible finish coat, meaning that multiple layers of the stucco system may contain asbestos.

Asbestos stucco is found on a wide variety of building types including single-family homes, apartment buildings, churches, schools, commercial storefronts, and industrial buildings. It is most prevalent in the United States, particularly in the Sun Belt states where stucco has been a dominant exterior finish for over a century, and in parts of Canada, Australia, and New Zealand. The material was typically applied in three coats, scratch, brown, and finish, with asbestos potentially present in any or all layers.

When intact and undisturbed, asbestos stucco presents a relatively low risk because the fibres are bound within the hard cement matrix. The material becomes hazardous when it is chipped, hacked, drilled, sanded, or demolished during renovation or repair work. Removing stucco from exterior walls generates large volumes of dust and debris, and if the stucco contains asbestos, this dust will contain respirable asbestos fibres. Pressure-washing, a common method for cleaning stucco surfaces, can also erode the surface and release fibres.

Before any renovation, repair, or demolition work that would disturb stucco on a building constructed before 1980, samples from each coat layer should be tested for asbestos. A licensed asbestos inspector can extract small core samples that capture all layers of the stucco system. If asbestos is confirmed in any layer, removal must be performed by a licensed asbestos abatement contractor using wetting, containment, and controlled demolition techniques. Patching or re-stuccoing over existing asbestos stucco may be an alternative where the existing material is stable and well-adhered.