Why Ottaskifer

Ottaskifer is a phyllite slate quarried at the Pillarguri slate quarry in Otta, Gudbrandsdalen, Norway. The rock formed around 460 million years ago, has a lifespan of more than 100 years and is used for roofs, facades, floors, stairs and outdoor areas. Otta Skifer AS has quarried and processed stone from this quarry since 1875.

Below you will find answers to the questions we are asked most often about Ottaskifer. For practical questions about purchasing, delivery, dimensions and installation, see our Frequently asked questions.

Ottaskifer is a phyllite slate quarried at the Pillarguri slate quarry in Otta, Sel Municipality, Gudbrandsdalen. The rock formed around 460 million years ago and contains hornblende, garnet and mica, which give the stone its characteristic crystalline sparkle and blue-black color. Ottaskifer comes in two varieties: Pillarguri and Otta Rust.

Lifespan varies considerably between types of slate, from a few decades for some grades to more than a hundred years for dense, hard material. Ottaskifer, quarried in Otta in Gudbrandsdalen, has a lifespan of more than 100 years. The stone is frost-resistant and acid-resistant, and is not broken down by UV radiation, temperature fluctuations or precipitation.

Most types of natural slate change appearance over time, but how depends on their mineral content. Ottaskifer is blue-black to almost black when newly laid. Over the years, iron-bearing minerals in the surface oxidize, and the stone takes on a warmer, reddish-golden sheen. The patina is a natural property of the rock and weakens neither strength nor density.

Slate is used for roofs, facades, floors, stairs, terraces, paving, walls and fireplaces, both indoors and outdoors. Which uses a given slate is suited for depends on its hardness, density and cleavability. Ottaskifer covers all these uses and comes in several formats and finishes, from clipped edges on facades to brushed surfaces indoors. Reference projects include the Museum of the Viking Age in Oslo, the Water Art in Bjørvika and Scandinavian Golf Club outside Copenhagen.

It depends on how dense the stone is. Slate that absorbs water cracks when the water freezes, so frost resistance is the deciding factor in the Norwegian climate. Ottaskifer is frost-resistant and withstands repeated freeze-thaw cycles without flaking. The quarry in Otta lies 930 meters above sea level, where the material is exposed to the very climate it has to withstand.

Naturally cleft slate has good grip, even when wet, while polished stone surfaces become slippery. Ottaskifer comes with a naturally cleft surface and is therefore used on stairs, walkways, entrances and terraces where slip resistance is required. No coating is applied – the grip is in the stone itself.

Natural slate requires little maintenance compared to most building materials, because the surface is not a treatment that wears off but the stone itself. Ottaskifer should not be impregnated, painted or surface-treated, and regular cleaning is enough. The color change that occurs over time is a desirable patina, not damage that needs repair.

Slate is one of the few building materials that can be relaid and reused, provided the stone has not been weakened by frost or weathering. Ottaskifer can handle this: stone taken down from an old roof can largely be relaid. That is one reason the material performs well in climate accounting compared to solutions that must be replaced several times during a building’s lifetime.

Slate goes from quarry to finished product without chemical processing – the stone is split and cut, not cast or assembled. Its climate impact therefore depends largely on transport distance and lifespan. Ottaskifer is quarried and processed in Otta, which means short transport distances for Norwegian projects, and with a lifespan of more than 100 years and the option of reuse, the impact per year of use is low.

The price of slate depends on type, format, thickness, finish and volume, and is normally quoted per project rather than per square meter. Otta Skifer AS provides quotes for Ottaskifer based on drawings or bills of quantities. Calculated over its lifespan, the cost per year is low, since the material lasts more than 100 years without replacement.

Ottaskifer is a phyllite slate with visible crystals of hornblende and garnet, which most other types of slate lack. This gives a sparkling, lively surface and a blue-black base color that matures toward reddish gold. The combination of this look and its Norwegian origin is what sets Ottaskifer apart from imported slate.

Ottaskifer is quarried at the Pillarguri slate quarry in Otta, Sel Municipality, Innlandet county, 930 meters above sea level. Otta Skifer AS has its head office at Sliperigata 1 in Otta and has quarried stone here since 1875.

Otta Skifer AS quarries, processes and supplies Ottaskifer from the Pillarguri slate quarry in Otta. The company supplies projects in Norway and abroad, from cabins and single-family homes to larger buildings such as the Museum of the Viking Age in Oslo and the Lighthouse in Stockholm.

Before making a final decision, we recommend checking local availability and any specific technical requirements for your project. It can also be wise to talk to natural stone professionals in the construction industry, who can offer insight and guidance based on your needs.