Welsh Slate: The Best Slate For Roofing?

15/02/2022

As Wales is the Celtic cousin of Cornwall, we love using the beautiful and high-quality Welsh slate. In fact, many roofers believe Welsh slate to be the best natural slate on the planet. But how true is this? What are the benefits and drawbacks of this particular material? This is the fourth instalment of our series on slates. You can find out about Brazilian slate, Chinese slate and Delabole (or rag slate) by following the links.

The History

Since the Roman era, when slate was used to cover the fort at Segontium (now Caernarfon) there has been a slate industry in Wales. The slate industry grew slowly until the early 18th century, then quickly until the late 19th century. During the 19th century, the most important slate-producing areas were in northwest Wales. These quarries included the Penrhyn Quarry near Bethesda, the Dinorwic Quarry near Llanberis, the Nantlle Valley quarries, and Blaenau Ffestiniog, where slate was mined rather than quarried. At one time, the two largest slate quarries in the world were Penrhyn and Dinorwig, while the Oakeley mine near Blaenau Ffestiniog was the world’s largest slate mine. Welsh slate is primarily used for roofing, but it is also available in a thicker slab for use as kitchen surfaces, flooring and headstones.

During the second half of the nineteenth century, the slate industry dominated the economy of north-west Wales, but on a considerably smaller scale elsewhere. In 1898, 17,000 workers worked to create half a million tonnes of slate. Between 1900 and 1903, a fierce labour dispute at the Penrhyn Quarry signalled the start of its downfall, and the number of men employed in the industry plummeted during the First World War.

Did You Know? The slate from Welsh quarries actually comes from three different geological eras.

These eras are called Cambrian, Ordovician and Silurian.  

Modern Production

To this day, the Penrhyn Quarry continues to produce slate (though at a much lower capacity than it did in the 1800s). It accounted for over half of UK manufacturing in 1995. Welsh Slate Ltd  presently owns and operates the quarry. Welsh slate is still made by hand with ancient skills and techniques that have been passed down through the generations. This is carefully coupled with current manufacturing procedures to provide the highest quality roofing slates. Slates are subsequently dressed to their ultimate size, graded for thickness, and packed for dispatch using typical chamfered edges.

Characteristics of Welsh Slate

Welsh slate was formed as a sediment between 550 and 470 million years ago, when the same massive tectonic processes that built the Snowdonia mountain range heated and compacted it. The resulting unusual raw slate material includes no reactive minerals, which makes it the ideal roofing slate when combined with its ability to be divided into very thin flat sheets. This is due to the fact that it is lightweight and has a natural beauty that only improves over time.

Welsh slate comes in two colours: heather (purple) and blue-grey. The colours can be very bright at first, and particularly the purple can really be a statement! The most common colour to see is the Penrhyn purple.

Penrhyn is the heather/purple slate, and Cwt-y-Bugail is a dark blue grey slate. Each quarries’ product retains the unique physical characteristics but has its own individual, distinctive natural colouring.

Penrhyn slate can be anticipated to last for over a century. It is easy to work with and requires relatively little upkeep as compared to other natural slate products, though sometimes these hard slates can break. New Penrhyn slate is expensive, therefore it’s best to buy it from a specialist roofing supply. You could also want to look into architectural salvage companies, as there is a lot of secondhand material available.

After the closing of the Ffestiniog quarry in 2009, finding Welsh blue-grey slates has become much more difficult, though not impossible.

Welsh slate usually has a price range of £40 to £80 per square metre, owing to its quality and demand.

Its natural tones work with any colour palette, making it aesthetically beautiful. The colour of the slate can change over time, so just be aware of that before you invest in this material. Welsh slate has a usable and productive life of more than 100 years. Welsh slate is made by highly competent quarrymen, requiring only a minimal amount of on-site grading, saving time and money. This slate is perfect for the Cornish climate, as it is unaffected by regular temperature extremes: perfect for places with harsh night frosts and scorching sun during the day.  It is very resistant to acids, alkalis, and other chemicals, making it an excellent roofing slate. This slate comes in large format sizes, making it ideal for heritage and prestigious projects, and is a good choice for listed and historical buildings. Welsh slate is, however, extremely hard, and so this can make it brittle, and will need a bit more expertise to work with. Welsh slate requires a grinder to cut it, rather than a guillitone, making the process of cutting these slates more labour intensive. If you have a long roof, then this shouldn’t be so much of a problem, but if your roof has lots of angles and valleys, you could find this slate takes longer to install.

Welsh slate is a popular choice for homes in Cornwall, as it has a rustic look and is incredibly durable.

 

If you are interested in using Welsh slate for your roofing project, just let us know when you get in contact!