What is a ribbon slate?
Ribbon slates are Pennsylvania black slates that have small bands running through them. These ribbons contain a high amount of carbon that deteriorates much faster than the rest of the slate. This results in the slate becoming separated at the ribbon, allowing either the slates to fall out or water to penetrate the roof. Even so, ribbon slate roofs have still been known to last 50 to even 100 years if the roof is steep and well shaded. Once the ribbons become soft, the roof is virtually unrepairable and must be replaced.
