Roofing Why phyllite?

It’s slate’s older, lesser-known but more highly prized cousin - phyllite has graced the roofs, walls and floors of prestigious buildings all around the world. But what exactly is it? Where does it come from? And what makes it so desirable for architects and specifiers? Dora Kotzeva, SSQ Head of Marketing - and author of the firm’s upcoming CPD seminar - explains.

Of all the world’s roofing and building products, it has to have one of the most epic origin stories.

On the plains of South America, between the Pampas and the Andes, they found phyllite - the slate-like architectural stone that’s gone on to become one of the world’s most sought-after roofing, cladding and flooring materials.

But what makes it so popular? At SSQ, we’ve been sourcing it from our quarry in Argentina’s San Luis region for over twenty years - and in that time, we’ve built up an unparalleled understanding of just what makes it such an outstanding material.

500 million years in the making Phyllite is essentially the next step on from slate.

Over hundreds of millions of years of intense heat and pressure underground, sediment turns into shale. Shale turns into slate. And if those painstaking geological processes are allowed to continue for a few million years more, slate becomes phyllite.

The extremely gradual changes that produced today’s phyllite began between 560 and 640 million years ago in the Precambrian era, the earliest phase of Earth’s history.

And withstanding that almost unimaginable length of time has given it some outstanding characteristics.

Why is it so good? Phyllite is harder, denser and stronger than any of its competitor materials.

Those millions of years of heat and metamorphosis have given it exceptional durability and water absorption.

At SSQ, we’ve had our own Riverstone Phyllite extensively tested, with impressive results. Assessed to the US testing standard ASTM C406, Riverstone was awarded an S1 rating, indicating it will last a minimum of 75 years.

It’s also been tested to see how reactive the iron oxides on its surface are. Highly reactive iron oxides lead to discolouration and leaching over time. Riverstone, on the other hand, received T1 classification - meaning it’s highly unlikely than any leaching will occur.

All in all, we’re so confident in the quality and durability of our phyllite that we cover it with some of the most comprehensive guarantees in our industry.

With every Riverstone roof we supply, we give a 100-year Weathertightness guarantee, a 100-year Rust Free guarantee, and the opportunity to choose an Insurance Backed guarantee covering all materials, workmanship, and, in certain cases, the design, too.

On a par with any roofing material In our view, Riverstone is on par with any roofing, cladding or flooring material in the world, and suitable for almost any application.

But don’t just take our word for it. It’s been accepted for use on some of Britain’s most historic buildings, including many Grade II and Grade I listed buildings, many of them in Cornwall.

Today, Riverstone graces the roofs of Christ’s College in Brecon, Powys, the St Thomas Church in Exeter, Kresson Kernow Records Office in Redruth, and Devon’s Grade I listed Pig at Combe Restaurant and Hotel, among dozens of other historically significant buildings.

SSQ TEL: 020 8961 7725

Strong, stylish and versatile Riverstone is the ideal solution for new-build or refurbishment projects seeking to offer both outstanding aesthetics and exceptional robustness and longevity.

Add in the range of guarantees SSQ offer - including our industry-leading Ultra Cover scheme, which sees a Riverstone roof assessed at least twice during installation by independent surveyors, and checked by SSQ throughout - and you’re left with a material that’s head and shoulders above any of its competitors.

If you’d like to learn more about Riverstone - or are interested in our upcoming CPD, which will cover this and related topics in detail - please don’t hesitate to call 020 8961 7725 or email


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