Houses built before 1985 may contain siding made of plaster mixed with asbestos. This practice was widespread until the arrival of drywall, commonly called “gypsum”. In other words, if your walls are not made of gypsum, it is important to check if your walls contain asbestos.

An article published in La Presse*: ”Gypsum wallboard appeared at the end of the 1960s… Before that, most plaster walls contained asbestos. Asbestos is no longer used in Quebec since 1985, unless it is mixed with cement or asphalt… But in Montreal and elsewhere in Quebec, thousands of people are still exposed to it, most often unknowingly… This means that all renovation work in old houses is likely to have released carcinogenic asbestos fibres into the atmosphere… ” If you’re knocking down entire walls, you have to confine the entire job site in negative pressure, and obviously protect yourself adequately.”