This heavy duty adhesive was found in a paste-like cement form. The manufacturers usually added a variety of different fibers to increase the products' flexibility and strength. To be able to resist extreme temperatures and increase its durability, asbestos fibers were added in the manufacturing process.
Applied mastic didn’t pose a serious threat to the nearby workers if it was left intact. Cutting, sawing or drilling through surfaces where mastic was applied onto would cause the asbestos fibers to be released in the near environment. You could have been exposed if: