Finding reclaimed slate for period property restoration

Why reclaimed slate suits a period roof

Nothing gives away a restored period property faster than a roof that half-matches itself. A Georgian or Victorian slate roof was built around one particular slate — a certain size, thickness, colour and surface texture — and a modern interlocking tile or an 8mm Spanish slate laid alongside the originals will look like a patch for decades, not months. Reclaimed Welsh slate is usually the best answer, because for most of the nineteenth century north Wales supplied the majority of Britain's roofing, and that blue-grey material set the tone for thousands of terraces, villas, churches and farmhouses.

There is a practical reason too. Old slate is often thinner than new — commonly 4mm to 6mm against 8mm or more for a modern equivalent — which affects the weight on the timber, the depth of the lap and the way the roof sits over the eaves. Mix thicknesses carelessly across a plane and you get a roof that ripples in low sunlight. Consistency matters as much as colour.

Checking slates before you part with your money

Reclaimed slate is sold as seen, so the inspection you do in the yard is the only warranty you will get. Work through a sample of at least thirty slates rather than trusting the top of the pallet.

• Delamination. Slate splits along natural cleavage planes, and old slate that has been frozen and thawed for a century can be quietly coming apart. Tap two slates together: a sound one gives a clear ring, a failing one a dull thud. Then look at the edges — flaking layers, a chalky bloom or a "book" of thin leaves lifting at the corner all mean it is on its way out.
• Nail holes. Every slate on a stripped roof has been nailed once. A slate can be re-holed, but the new hole needs at least 25mm of sound material around it, ideally closer to 40mm, and it must not sit directly over or beside the old one. Slates carrying two or three sets of rust-stained holes are weak at exactly the point where the wind pulls hardest.
• Consistent sizes. Measure twenty slates with a tape. If lengths and widths wander by more than about 10mm, you will spend days sorting them into batches, and your gauge will be impossible to set cleanly.
• Chipped corners and hairline cracks. A small corner knock is fine on a bottom course or tucked under a flashing. A crack running into the exposed area is not, and neither is a slate that flexes when you hold it by one corner.

Buying the right quantity and grade

Most yards grade reclaimed slate as best, seconds and thirds. Buy "best" for the main field of the roof, where every slate is visible and every irregularity shows. Save the seconds and thirds for the bottom two courses, the under-eaves, the strip behind the chimney stack and any run tucked below a dormer or parapet.

Work out your numbers from the gauge rather than guesswork. A 500 x 250mm slate laid at a 100mm headlap covers roughly 20 slates per square metre. A traditional 400 x 250mm slate at the same lap takes nearer 27. Add 10 to 15 per cent for cutting, breakages and the inevitable handful that shatter in the hand. Where possible, buy the whole roof's worth in one go — a second batch from a different source will rarely match, and matching later is far harder than matching now.

Storage and handling on site

Reclaimed slate is brittle and heavy, and most of the loss happens between the yard and the scaffold. Stack it flat on a level pallet, off the ground, no more than about a metre high, covered against frost but open at the sides so air moves through. Never tip slates into a barrow or drop them from a height. Sort them into size batches on the ground, then carry up only what you need. Use copper or stainless steel nails of the correct length — long enough to hold, short enough not to punch through the slate above — and check that battens and gauge suit the thinner reclaimed material rather than the modern slate they replaced.

Maintenance beyond the roof

A sound slate roof is only part of keeping an old house dry. Clear cast iron gutters and downpipes twice a year, and repair them with metal rather than mastic where a joint has failed. Repoint chimney stacks in lime mortar, never cement, and re-flaunch the pot beds before water finds its way down the flue. Inside, traditional stone flooring — flagstones, York stone, limestone — prefers plain warm water and a soft brush; acidic cleaners etch limestone and most sealers trap moisture that the stone has always been allowed to release. If a slate or flagstone is loose, lift it, clean the bed and relay it on a lime or sand bed rather than cementing it rigidly in place.

Sourcing reclaimed slate sensibly

Reclamation yards, architectural salvage auctions, demolition contractors and roofers stripping a similar property are all worth approaching, and a local roofer will often know of a roof coming off before it reaches a yard. Ask for the provenance, request photographs of the actual batch, view it in daylight and take a sample slate from your own roof to compare colour and thickness on the spot. Agree in writing what happens if a pallet proves to be mostly seconds. And be patient: the right slate, at the right size and colour, is worth waiting a season for.