Slipped slates and nail fatigue
Slates are held by nails through the top or middle of each slate. Over decades the nails corrode and snap, and the slate slides down the roof. One or two slipped slates is a routine repair. Dozens slipping across a slope usually means the nails are failing everywhere, known as nail fatigue.
Cracked and broken slates
Slates crack under foot traffic, falling debris and storm damage. A cracked slate lets water straight through the lap to the felt below, so it should be replaced like-for-like in size and thickness.
Delaminating or soft slates
Poorer quality slate absorbs water and flakes apart in layers. If slates crumble at the edges or sound dull when tapped, they are reaching the end of their life and repairs will only buy time.
How slipped slates are re-fixed
A single slate cannot be re-nailed without stripping the slates above it, so roofers use a slate ripper to remove the old nails and secure the replacement with a hook or a lead or copper strap. Done neatly this is a sound, long-lasting repair.
Repair or re-slate?
- Repair when the slates are sound and only a few have slipped or broken
- Consider re-slating a slope when slates slip repeatedly across it
- Sound slates can often be reused on new battens and fixings, which keeps the cost down
- Always check flashings, valleys and ridges at the same time
