This dry mix product was made in order to patch surfaces that presented imperfections. The paste that resulted from the dry powder being mixed with liquid was able to fill the holes produced from minor damage. Asbestos was added to spackle in order to improve its heat resistance.
Before it was even applied, spackle posed a serious threat to the workers that started mixing it as asbestos particles were being spread all around them. Worn out asbestos spackling paste was dangerous if interacted with it as the asbestos fibers were found in a friable state. You could have been exposed if: