Nail fatigue
Each slate hangs on one or two nails. After decades of damp, the nails rust and snap, and the slate slides out. A handful over the years is normal on an old roof.
When it becomes a pattern
If slates are dropping across a whole slope every winter, the fixings are failing everywhere. Repairs will keep working for a while, but re-fixing the slope becomes better value.
How a slate is re-fixed
You cannot nail a slate back without lifting those above it. A roofer uses a slate ripper to cut the old nails, slides in a matching slate and holds it with a hook or a lead or copper strap.
Matching matters
Slates vary in size, thickness and colour. A good match sits flush and weathers in; a poor one stands out and can leave gaps.
Slates that are worn out
Slate that flakes, crumbles at the edges or sounds dull when tapped has reached the end of its life and should be replaced, not re-fixed.
