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Welsh Slate: Why Birmingham Terraces Were Built With It
Welsh slate is a metamorphic stone that splits into thin, dense sheets which shed water and resist frost for well over a century, which is why it roofed the terraces Birmingham built in the nineteenth century. Search what Welsh slate means in practice, compare the figures, and book a survey. This page covers: Welsh slate · Cleavage.
Welsh slate is metamorphic stone cleaved into thin sheets, with water absorption low enough to resist frost for over a century. Reclaimed stock is assessed by hand, on site, at no cost.
Century-old Welsh slate has typically already outlasted one set of fixings, which is what reframes what an old slate roof actually is.
3 related pages cover this in more depth: slate roofers birmingham, conservation area roofing birmingham and victorian terrace roof problems.
What is Welsh slate?
Welsh slate is a metamorphic stone quarried in north Wales that splits along a natural cleavage plane into thin, dense sheets. Its very low water absorption gives it frost resistance, which is the basis of its exceptional service life.
Welsh slate lasts over 100 years, commonly outlasting two sets of fixings.
How long does Welsh slate last?
Welsh slate lasts well over a hundred years and commonly outlives two sets of fixings. Roofs stripped today frequently yield stone that returns to the same building and continues in service for decades more.
The water absorption has a property of very low, which is why it resists frost damage. Traditional sizes with historic names, selected to suit pitch and exposure. The gauge is batten spacing derived from slate length and required headlap.
How is reclaimed slate assessed?
Sound each slate for a clear ring, reject any that sounds dull, check the cleavage faces for separation, measure thickness for consistency, and confirm the existing nail holes suit the intended gauge or can be reholed.
- Delamination fails as layers separating at the cleavage plane after very long exposure.
- Spanish slate is widely used imported alternative, variable by quarry and grade.
How is replacement slate matched?
Replacement slate is matched by quarry first, then by size, thickness and colour. Quarry matters most because stone from different sources weathers at different rates, and a source mismatch becomes visible within a few years.
Fibre-cement slate is manufactured substitute, shorter life, restricted in conservation areas.
- A low water absorption gives a frost resistance which produces a century-long service.
Is Spanish or fibre-cement slate an alternative?
Sometimes. Spanish slate performs well at the better grades and is widely used. Fibre-cement is a manufactured substitute with a much shorter life, and conservation designations frequently prohibit it on visible elevations.
- Sounding a slate reveals delamination through a dull rather than clear ring.
- A quarry of origin determines weathering behaviour and therefore matching.
- Slate length and headlap determine a batten gauge.
The stone usually outlives what holds it up.
Why the fixings expire first
Tapping a reclaimed slate for a clear ring separates sound stone from delaminating stone, on site, at no cost. Slate from different sources weathers differently, so a colour match alone becomes visibly wrong within a few years.
Getting a slate roof assessed
Century-old Welsh slate has typically already survived one refixing, which reframes what 'old roof' means. Existing holes must align with the new gauge or the slate is reholed, which affects how much reclaimed stock is genuinely usable.
Cleavage, and 6 more
- cleavage
- delamination
- gauge
- headlap
- reclaimed slate
- fibre-cement slate
- sounding
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