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From Quarry to Job Site: The Processing of Natural Slate

Natural slate has been used for centuries as a reliable roofing material. Waterproof, fireproof, non-porous and eco-friendly, the rock has a lot of natural features that make it one of the more valued building materials on market. Most slate roofs have a lifespan of over 100 years, and can be removed and recycled to other projects should it outlast its parent building.

natural slate

What is it that makes natural slate such a hardy, versatile material? Keep reading to learn how slate is formed, and its journey from the quarry to the job site:

Formation of Natural Slate

Slate is a metamorphic rock, meaning that the first rock– the protolith— underwent a chemical transformation to become the finished product. It shares similar properties with sedimentary rocks such as shale– when compressed and heated over thousands of years, the clay within shale breaks down into what is known as mica. Mica, from the Latin word micare, “to glitter, allows the newly formed stone to cleave along flat planes. This is one of the properties that allows slate to be hand-crafted using a hammer and chisel. Slate also contains silicates and quartz, a high level of the latter helping contribute to slate’s shimmery appearance.

While the geological location and chemical makeup determines the different color and density of slate, all slates contain iron pyrites. Nicknamed “fools gold” for their misleading appearance, they are iron sulfides that are either “stable” or “unstable” in terms of slate makeup. Stable pyrites have undergone tremendous heat and pressure and thus crystalize, forming small clusters of gold in the rock.

natural slate
Unstable pyrites, however, have not been exposed to enough heat and pressure. Consequently, they have not crystalized, and remain vulnerable to the elements. Unstable pyrites will have a “bleeding” effect, creating a trail of ugly copper residue. Other than being an eyesore, these unstable pyrites will actually burrow a hole through the slate and compromise the roof, if left unattended.

Processing Natural Slate

The first step taken before quarrying slate is to remove the top layer of slate, or “overburden”, which is sometimes hundreds of feet deep. The overburden has been subjected to the elements for millions of years, and thus has been broken or otherwise compromised. Once this unusable slate has been removed, experts can come in an determine the quality of the rest of the rock underneath.

slatequarry
Once the quality of the slate has been determined, extraction can begin. Using diamond-beaded steel cables, large slabs of stone are cut out of the sides of the mountain, creating stair-like formations. While slate can be mined in the fashion of hollowing out mountains, as you would coal, slate quarries are typically massive, open-air endeavors.

These huge slabs are then transported to a factory where they are cut down into smaller, more manageable blocks, and sorted. Even though slate comes from the same place, there may be two or more different strains in the same quarry. Once sorted, the slate is again carefully evaluated for quality, and passed along to the slate splitters.
slate siding
Slate splitting is done by hand. Using a hammer and a chisel, skilled craftsmen split the rock into desired thicknesses. To finish the process, the ends of the slate are sawn to make them even.

Natural slate is considered one of the most eco-friendly building materials due largely in part to its minimal processing. Having been split by hand, and only using minimal factory sawing, harmful CO2 emissions can be avoided. The whole process uses barely any water, even less than the environmentally-hailed terra cotta, and no chemicals are added to the rock. Naturally waterproof and having a Grade A fireproofing rating, not needing to add chemicals ensures that harmful byproducts don’t run off into the environment. Plus, a lifetime of over 100 years lesses the overcrowding of landfills.

How Slate Tile is Pioneering Sustainable Architecture

With the health of our planet an ever-increasing concern, consumers are looking for ways to lower their carbon footprint and slow the impact they have on the environment. Sustainable architecture has been rising in popularity as a means to combat the destruction of our Earth— but “eco-friendly” does not have to mean “boring”.

slate tile
Slate tile is one of the most eco-friendly building materials on today’s market. Used as decades for reliable, gorgeous and long-lasting roofing, the slate siding trend has started to take root. Continue reading to learn 3 ways slate tile is pioneering the sustainable architecture trend:

Insulating

Heating and cooling systems heavily contribute to the eroding of our atmosphere, thus creating the “global warming” effect that has scientists and conservationists in a panic. Any building that is not properly insulated is subject to changing internal temperatures, which puts a strain on these harmful machines.
slate tile
Slate tile is both acoustically and thermally insulting. By maintaining a steady internal temperature, there is less of a demand for heating and cooling systems. So whether it is the dead of winter or the height of summer, occupants of slate tile buildings can remain comfortable without racking up the electric bill.

Processing

Thanks to its innate properties, slate tile requires very little processing from quarry to job site. Once the quality of the stone has been established, large slabs are cut out of the mountain and create massive stair-like formations. These slabs are then transported to a factory where they sorted, inspected, and cleaved into smaller blocks along their natural faulting points. Skilled craftsmen split these blocks into desired thickness by using a hammer and a chisel, and then the process is finished with the edges being “dressed” by a specialty saw.

slate siding
Slate tile is naturally waterproof, fireproof, resistant to hail and acid rain, and has an expected lifetime of 100+ years. The stone is never treated with any chemicals that can run off into the environment, and the minimal factory processing it requires eliminates almost all CO2 emissions that other building materials produce. The process uses even less water than terra cotta tiles, which has often been hailed as a premier eco-friendly material.

THERMOSlate

Solar panels have dominated the industry for years in terms of giving homeowners the ability to reduce their carbon footprint as well as lower energy costs in their homes. Their biggest downside, however, is how obvious they are. For high end homeowners, this could deter them from putting them on to their dream home, and they are not even an option for most historical preservation contractors.

slate tile
CUPA Pizzaras has come up with a unique solution. Their THERMOSlate panels utilize natural slate technology with a hidden thermal panel underneath. This panel, with an area of 15.6 sq ft, can heat up to 67 gallons of hot water per day. Taking into account the approximately 216 daily heated gallons the average American house of 4 uses, and the estimated 3-to-4 panels per roof, and it is easy to see how THERMOSlate saves both money and energy. Additionally, this technology can be used to heat swimming pools, significantly lowering the cost of this luxury addition.

Slate Roofing Restores the Episcopal Palace

When the original Episcopal Palace in Astorga, Spain, was destroyed by a fire in 1886, legendary architect Antoni Gaudi was assigned to reconstruct the structure. Gaudi, a modernist architect, built a palace reminiscent of the castles of royalty, complete with a moat and ornate gargoyles along its crest.

slate roofing
After decades of weathering the elements, however, the Episcopal Palace was in need of some repair. Recently, Spanish slate company Cupa Pizarras fitted the castle with gorgeous natural slate roofing.

slate roofing
Using 6mm thick slate tiles, the Astorga monument was restored to its former glory and continues to stand sentry over the Spanish landscape. It is currently home to the Museo de los Caminos, a museum dedicated to objects related to the Camino de Santiago, the pilgrimage routes to the burial place of Saint James.

Why Slate Roofing

Slate roofing was specified for a number of reasons. First and most obviously, slate roofing was first used on the roofs of castles and churches in medieval days. With its castle-like architecture, it was a clear choice of material, and remains so on many restorations.

However, this hardy rock is more than just a gorgeous and historically-accurate roofing material. Slate roofing is incredibly durable in any element– fireproof, waterpoof, and sturdy against hail, there are few conditions that can phase it. Even hurricanes have been defeated by this material. The typical lifespan of a slate roof is upwards of 100 years. In comparison, other popular roofing materials such as asphalt shingles are expected to be replaced every 30 years. Additionally, the gorgeous and durable nature of slate often ads market value to any property.

slate roofing
Slate roofing is also extremely eco-friendly. Although this was hardly a concern for the 1800’s architect who first designed it, sustainable design has become a focus for many architects. Thanks to its innate properties, slate roofing needs little more than to be cut out of the mountain and hand-carved to be ready to be fitted. This avoids the emission of ozone-eating CO2, and uses even less water than the environmentally-revered terra cotta tiles.

Whether it’s restoring a castle to its former glory, or constructing a high-end modern home for the generations to come, slate roofing is a reliable and gorgeous choice. Click on the gallery below to see some more gorgeous slate roofing projects:

Slate Tile: Strong enough to withstand Natural Disaster

This past weekend, Hurricane Matthew ripped through the Caribbean and southern United States, devastating much of what was in its path. The storm is responsible for taking over a thousand lives, 33 of them in U.S.. It is the deadliest hurricane since Stan in 2005, and the first category 5 Atlantic hurricane since Felix in 2007.

Tybee Island Damage (image via wyff4.com)
The storm felled trees, snapped power lines, and shredded the roofs off of buildings. Asphalt shingles still litter the streets, and property owners are left with the task of rebuilding.

Throughout it all, this slate sided home on Tybee Island, Georgia, survived without a single missing tile. Tybee was one of the first areas to evacuate and took the brunt of most of the damage, with winds reaching up to 96 miles per hour.

slate siding
Slate tile is an extraordinarily durable material that is renowned for its innate fire and water-proof properties. In freezing conditions, slate tile has also proven effective against hail. What is lesser-known about this popular roofing material is its resilience during natural disasters.

Saint Sylvester’s Church in Pensacola, Florida, has seen her fair share of destruction. Since being built, the slate-sided house of worship has endured 4 hurricanes. Through each one, not a single slate tile was lost.

Church-300x245
Although slate tile is often passed over for cheaper roofing options, homeowners in areas susceptible to natural disasters will likely spend more on repairs than the cost of a slate roof installation. On average, slate roofing is expected to live over 100 years— a sharp comparison when considering asphalt shingles, which need replacing in about 30 years.

Slate tile has a number of other properties that make it a solid choice for building material. Thanks to its natural properties, only minimal processing is needed from quarry to roof, eliminating much of the release of harmful CO2 and saving water. It also has a timeless, classic beauty. Many structures that have added slate tile increase in market value.

While slate tile has typically been used as a roofing option, slate siding has become more and more popular. Click here to view some more slate siding projects.

Vermont Slate Company expresses deepest condolences to those affected by the storm. To help the victim’s of Hurricane Matthew, click here.