Asbestos, a very resilient and durable material, was banned in the early 1980’s due to associated health risks in the removal process. The asbestos fibers, when frayed, can crumble and float in the air we breathe. When the pieces lodge in the lungs, they will not break down and can lead to long term illness.
It is important to know that the tiles will not become a health risk until they are removed or demolished. A professional asbestos abatement company should test and remove the asbestos from your home as needed.
The mortar used to seal the roofing joints will crack with any movement of the tiles. It is normal to have to replace these every few years. Water can leak through the cracks if large enough and create further damage to the roof if not repaired.