Experienced slate roofers know how to drive the nail in to hold the slate, what type of nail to use, and how to lay out the roof and starter coarse. The fasteners holding the slate on the roof have to be set correctly, not driven too loosely and not driven too tightly. The slate should just hang on the nail, with the head of the nail driven just into the recess of the pre punched nail hole. If the nail is driven too tightly, the slate wont hang loosely, and will break with the change of temperature, load, and other forces acting on the roof. Each slate must move independently of every other slate on the roof. If the nail is driven too loosely, the nail head will break the slate above it.
Using the wrong fastener is detrimental to a new slate roof. Many inexperienced slaters are quick to reach for the wrong nail when applying slate. A large head copper slating nail should be used in the correct length to match the thickness of the slate. A non-corrosive metal is a must. Copper should be used at all times, especially on low sloped roofs where water tends to shed slowly. I have seen a few roofs both repaired with the wrong fastener and installed with the wrong fastener. Corrosive fasteners disintegrate to the point where virtually nothing holds the slate in place – and the slate fall out!
