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The first Decramastic roofs were made in NZ in the 1950s. These consisted of galvanized steel being pressed into a tile form and coated with a bitumen emulsion, known as mastic, and then covered with coloured aggregates or stone chip for decoration. Also known as Decrabond or pressed metal tiles, they were widely used in New Zealand during the 1970s and 1980s. Some versions of mastic or bitumen based pressed metal roof tiles produced prior to the early 1980s contain asbestos. The asbestos is found in the Mastic or bitumen used to adhere the stone chip to the metal. Only mastic or bitumen based pressed metal roof tiles are affected. There is no product formulations available to identify with any certainty when asbestos containing mastic or bitumen was used. And product information (such as manufacturing dates and batch data) was generally not included on tiles produced prior to the early 1980s, and is therefore not available to verify the presence or absence of asbestos in the tiles produced at that time. This means that all mastic or bitumen pressed metal roof tiles should be tested prior to works. Over time the stone chip wears and exposes the mastic bitumen and with weathering the asbestos can be released. High pressure water should not be used on asbestos containing roof tiles.
Results & Sampling: 70% of analysis and advice roofing samples submitted were positive for the presence of asbestos in 2020, similarly 74% were positive in 2019. When sampling, buildings may have a mix of asbestos and non-asbestos roof tiles, samples should be representative of the materials present and ensure sufficient bitumen mastic and stone chip is provided. Feel free to contact us at the Laboratory for any queries about your samples.
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