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!
Finally, among the most frequent problems encountered with new slate installation are inadequate side and headlap and the failure to install lathe strips under the starter equal to the thickness of the slate.
Slate is sold by the square. One square equals one hundred square feet of coverage using a 3" headlap. Shortening the headlap or trying to “stretch” the slate out over the roof using less than a 3" headlap is an unacceptable practice sometimes used to cover more square footage with fewer slate.