19 August 2026
Welsh slate laid on a Victorian terrace in Wandsworth or Balham in 1890 is very often still sound in 2026. It is a stone; it does not rot or perish. What fails is everything around it: the iron nails that held it, the battens they went into, and the lead in the valleys and around the chimneys.
Nail Sickness
The original nails were iron, and iron rusts. After a century they have rusted through, and slates start sliding on a roof that otherwise looks perfect. It shows as a few slips at first, then more each winter. At that point re fixing slates one at a time is a losing battle, because every slate on the roof is held by the same rusted nails.
How to Spot It
Slates in the garden or the gutter. A slate sitting lower than its neighbours. From the loft, daylight at the edges of slates. If you are seeing one slip a year on a roof over eighty years old, that is the beginning.
The Good News
Because the slate is fine, an old slate roof can usually be stripped, the slates cleaned and graded, and most of them re laid on new battens and breathable underlay with copper or stainless nails. You make up the shortfall with matched reclaimed slate. The roof keeps its look and a good part of its cost stays down, and it is good for another hundred years.
What to Do Now
If your slate roof is over eighty years old and has started slipping, get it surveyed before the next winter. We will tell you whether it is a few repairs or time to re lay it, with photographs of why.