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Recognizing and Controlling the Asbestos Hazard of Vermiculite Insulation in Construction

Vermiculite insulation was commonly installed as wall and ceiling insulation in a number of commercial and residential applications.  This material is now known to contain a significant asbestos contamination.  Contractors must ensure that any disturbance of vermiculite insulation is performed with appropriate precautions to protect their workers, comply with Ministry of Labour requirements, and avoid liability from the project owner.

Vermiculite is a mineral mined around the world and used in a variety of commercial and consumer applications.  After crushing and heating to about 1,000 oC, it expands like popcorn to produce fluffy particles.  The exfoliated material is fire-resistant, absorbent, light weight and a good insulator.  Vermiculite had a number of important applications in construction.  It was commonly added as a light weight component in concrete and plaster mixtures and in sprayed fireproofing.  Due to the binder systems present in these materials, they are unlikely to release significant asbestos during common disturbances.  However, vermiculite was also frequently used until the early 1990s as loose fill insulation inside masonry block walls, stove pipe and stack insulation, fire separations, cold rooms and in walls and attics of buildings, including homes.  These loose fill applications do pose a substantial risk of asbestos exposure to construction workers and require careful control. 

Many vermiculite mines contained varying amounts of asbestos minerals mixed in the vermiculite deposit.  Of particular importance to Canada was the Libby Montana mine owned by W.R. Grace, reported by the US Environmental Protection Agency as the source of as much as 70% of the world’s consumption (and likely 90% of the North American use) until it closed in 1990.  The Libby deposit was contaminated with an asbestos mineral usually identified as tremolite.  Although W.R. Grace took increasing measures through the history of the operation to reduce the asbestos content in their products, it is likely that most of their production contained at least a trace of free asbestos fibre.  Exposure to asbestos for prolonged periods or at high concentrations increases the risk of lung cancer and other respiratory diseases and many of the Libby workers and residents have become sick or died of asbestos disease originating from the mine and milling operations.

Vermiculite insulation can be readily identified as a light weight, silvery grey granular material, with granule sizes of about 2 to 10 millimeters.  The visual identification can be confirmed by testing by a laboratory who should be contacted for advice on testing and interpretation of results.  The laboratory should be accredited by one of the two US agencies that qualifies laboratories for the analysis of asbestos in bulk samples.

Obviously a contractor has to protect his workers and building occupants from any risk of asbestos exposure.  If undisturbed on a project, the material poses no risk.  However, even relatively minor disturbance may generate excessive levels of airborne asbestos.  Although the asbestos concentration in the installed insulation is relatively low, ranging typically from a trace to up to 5%, it still poses a very serious risk to health if disturbed.  Pinchin Environmental has performed hazard assessments of typical disturbances of loose fill insulation for the Department of National Defence and is aware of similar assessments performed in the US.  These show that under conditions that would be common on construction sites (removal of an insulated ceiling during renovation or demolition, manual removal of loose fill insulation) airborne asbestos levels may be up to 1700 times the maximum acceptable exposure level.  The owner of the project is required by the Occupational Health and Safety Act to provide a survey of all asbestos materials prior to a project.  However, contractors should be aware that the risk of asbestos-contaminated vermiculite has only recently been identified so that many building owners or their agent, and especially homeowners, may not be aware of the hazard.  In addition, the vermiculite might only be identified when a wall cavity or insulated chase is opened.  In any event, when loose fill vermiculite is identified, the contractor must put into place appropriate controls.  Because any disturbance of vermiculite will likely generate exposures in excess of the provincial limit, all such disturbance should be performed with Type 2 or Type 3 controls as required by the Ministry of Labour asbestos in construction regulation.  On most projects, this will generally require a qualified asbestos abatement contractor to carefully remove the vermiculite before the project can proceed.

Home renovation contractors may be the most affected by the vermiculite issue. The US EPA has estimated that up to several million US homes may have asbestos-contaminated vermiculite attic or wall insulation.  Although there are no available Canadian estimates, we would expect the Canadian number to be upwards to several hundred thousand homes.  Home renovators should carefully inspect their projects for vermiculite to prevent the serious liability that would result from asbestos contamination from an uncontrolled disturbance.

For more information on asbestos in vermiculite building insulation, visit the EPA website at or the Pinchin Environmental website,

Suggested byline:

Bruce Stewart CIH, ROH, is a Principal with Pinchin Environmental, a Mississauga-based consulting firm offering environmental and laboratory services across Canada, and a member of the TCA Environmental Committee.


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