Asbestos Mortar

Asbestos mortar is a cement or calcium silicate-based jointing compound that was manufactured with the addition of asbestos fibres to provide enhanced heat resistance, crack resistance, and bonding strength. Used from the 1920s through to the mid-1980s, asbestos mortar was employed in a variety of specialised construction applications where conventional mortar would fail due to high temperatures or thermal cycling.

The most common applications for asbestos mortar include chimney flue linings, furnace and boiler brickwork, kiln construction, fireplace surrounds, and some general masonry pointing in industrial buildings. The asbestos content varies from 2 per cent in general-purpose mortars to over 20 per cent in high-temperature refractory formulations. Chrysotile was the most frequently used fibre, though amosite and crocidolite were added to mortars intended for extreme heat applications.

Asbestos mortar is frequently encountered during chimney demolition, fireplace renovation, and industrial building refurbishment. It is an often-overlooked material because mortar joints are thin and visually indistinguishable from conventional mortar. Without laboratory testing, there is no reliable way to determine whether mortar in an older building contains asbestos fibres.

The risk from asbestos mortar is moderate to high, depending on the condition and the work being performed. When intact and undisturbed, the mortar presents a relatively low risk. However, demolition, repointing, or chiselling out old mortar generates significant quantities of fine dust that can contain respirable asbestos fibres. The confined spaces in which chimney and flue work is often carried out further increase the risk by concentrating airborne fibres.

Before any work on chimneys, fireplaces, furnaces, or old industrial brickwork, samples of the mortar should be tested for asbestos. If asbestos is confirmed, a licensed asbestos removal contractor must carry out the work, using wetting, controlled demolition techniques, and full respiratory protection. All mortar debris must be treated as asbestos waste.