How Are Broken Slate Roof Tiles Repaired?

How a Slate Roof Is Held On

Slates are laid in overlapping courses and each one is fixed with two nails, either through holes near the head or through holes at the centre depending on the exposure. The course above covers the nails of the course below, which is what keeps water off them and what makes the roof watertight.

That arrangement has a consequence that surprises people: once a roof is laid, the nail holes of any given slate are inaccessible. They are underneath two courses of slate. You cannot get at them without lifting a substantial area.

The other thing worth knowing is that good natural slate is close to permanent. A Welsh slate taken off a hundred-and-twenty-year-old roof is usually still a perfectly serviceable slate. What wears out is the iron or mild steel nail holding it, and the timber batten behind that.

So What Actually Happens When One Breaks

The broken slate is removed with a slate ripper — a long flat tool with a hooked blade that slides up under the slate and either pulls or cuts through the two nails holding it. That is a skilled use of a specific tool and it is the part that cannot be improvised.

The replacement slate is then slid up into place. It cannot be nailed, because the nail positions are covered. So it is held with a tingle: a narrow strip of lead or copper, nailed to the batten in the gap between the two slates of the course below, brought down over the face of the new slate and folded up over its bottom edge to hook it.

That is correct, standard, textbook practice on every slate roof in the country. It is not a shortcut and it is not a sign somebody has cut corners. A roof with a dozen tingles on it is a roof that has been looked after.

What it does mean is that a tingle is visible if you look for it, and that it is the one part of the repair that can be done badly. Copper and lead last; a tingle cut from galvanised steel will rust through and let the slate go again in a few years.

Matching the Slate

Slate varies enormously in colour, thickness and size, and a new slate dropped into an old roof shows. On a visible elevation, salvaged slate of the same origin is worth sourcing, and a reclaim yard will usually have something close.

Size matters more than colour for the water to work properly — the replacement has to give the same headlap as everything around it. A slightly short slate will look fine and leak.

Fibre cement slates and synthetic slates are a different product and should not be mixed into a natural slate roof. They weather differently and they will always be obvious.

When Patching Stops Being the Answer

Here is the honest test, and it is about rate rather than appearance.

Slates that slip intact, with no storm and no impact, are slates whose nails have corroded through. That is called nail sickness, and nails corrode as a population rather than one at a time.

So count them. One slipped slate a year on a large roof is normal ageing. One in 2023, two in 2024 and five last winter is a curve, and it only points one way. A roof that has had a slate refixed every few months is being kept alive rather than maintained.

A nail-sick roof can look immaculate from the ground right up to the year it does not, which is why the count matters more than the view.

The Option Between Patching and Replacing

Because the slate itself is usually still good, there is a middle answer that is not always offered: strip the slope, renew the battens and the underlay, and relay the existing slates with new non-ferrous nails, buying in salvaged slate to make up the broken ones.

It costs considerably less than a new covering because most of the material is already on the roof, it keeps the appearance of the building, and it resets the clock on the part that actually failed. There has to be enough sound slate left for it to work, which is why it is a judgement made on the roof rather than from the ground.

On a slate roof, ask about this explicitly before accepting a quotation for a new covering.