In recent years, there has been a worrying influx of inferior quality slate into the UK and Ireland. Quite a few high profile cases have involved poor quality Spanish slate. But why is poor quality Spanish slate so rife in Ireland and the UK? And as a buyer how can you protect yourself?

The geology of Spanish slate vs Welsh Slate

In comparison to the more indigenous types of slate, such as Penrhyn Welsh slate, Spanish slate is a relative newcomer to the Irish and UK roofing market, having only been widely available since the 1980s. Looking at the geology of Spanish slate we can trace its origins back 400 million years ago. As impressive as this may seem, slate quarried in Wales dates from the Cambrian era (over 600 million years ago).
The formation of the Bangor Blue slate makes it far stronger, denser and more durable than its Spanish counterpart in the harsh UK climate. Spanish slate is also naturally susceptible to iron sulphide deposits, or pyrites as they are sometimes referred to. In the case of good quality slate these pyrites should not be an issue remaining dormant and unreactive. However, in cases where the slate is sub-standard, they can react, causing major damage, and failure on the roof after only a few years.

Explaining the influx

Numerous quarries exist in Spain, producing substantial amounts of slate for the international market. However, standards can vary widely from quarry to quarry, and there are often varying grades in circulation. Reputable suppliers such as LBS work with a select handful of Spanish Slate quarries to ensure that only the best slate makes it to Ireland. There are, however, unscrupulous individuals out there who will import below-standard material and pass it off as top grade. Be aware of guarantees making inflated claims on a slates lifespan (50+ years is not realistic). Always remember that the cheapest price roofing slate is not always the best.

A guide to buying Spanish slate

If you decide to opt for Spanish slate, how can you ensure that you are buying quality slates that won’t let you down?
The most important thing is to do your research and be sure to view the slate you are considering using on several properties. Try and find finished examples of the slate which have been up a number of years.

• Look at the shape of the roof and pay particular attention to see if you can spot signs of “rust” or delamination – this is a sure sign to stay away from it.

• Check the slate for visible pyrites. These are iron inclusions in the slate which can be visible to the naked eye and will “glisten” in the sun. Over time, these inclusions can “oxidize” and react with the atmosphere which can lead to rust staining and ultimately the deterioration of your roof. Nb!! Pyrites are to be expected to some degree in most Spanish slate offerings. What we would say is that where they are obvious – you must ensure they are backed by the relevant test certificates and guarantees.

• Be sure to give the slate a strong knock on the back and ensure there is a good hard ring to it and not a hollow “thud”

• Look for dimensional consistency. A common characteristic of lesser grade material is twists, warps etc. It is common for slates to have a natural “bow” which is fine as long as the nail holes have been punched on the face of the slate so that it bows down into the roof.

• Always look for CE marked slate for the BS EN 12326 which sets the standard for slate products (W1, S1, T1 is the highest rating)

 These are just a few of the common things to look for but perhaps the most important is to buy from a long established suppler which it is likely to be around in the future in the event that there ever are any problems. Be wary of 1 men companies offering 50 year+ guarantees. These guys generally have no worth in their businesses and will simply not be around in 5 years, let alone 50!
LBS are a trusted supplier of Spanish slate and offer the best options that can be found in Spain. Our selection criteria is based on quality and we work hard to ensure we have an excellent reputation in the marketplace.
So, whether your preference is Bangor Blue Slate or quality Spanish Slate - speak to LBS today .....