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How slate ages

En skiferhelle av Ottaskifer som står på et bord. Den har en sort og brun gyllen patina

All buildings have a waterproof membrane – a bit like the shell jacket you put on as the last layer after your wooden sweater before you go on a hike. A building’s membrane protects the insulation in walls and roofs and must be weatherproof all year round.

Preferably, it should protect the building forever without changing and without requiring much maintenance.

This is a very tall order.

We know that shell jackets that have not been weatherproofed or have been exposed to wind and weather for 20 years will change, as will our own skin if we don’t protect it with sun cream and other healthy nutrients!

An architectural drawing of a modernhouse with a slate facade and slate in the garden as stepping stones, flagstones and drywall.
Slate is a natural material used in a number of environments, both indoors and outdoors. It is a beautiful and sustainable building material with a long history.

Love patina and embrace visual change!

If a façade, roof or terrace should be able to withstand the ravages of time, you need to choose materials that work with the weather. Time always leaves its mark and materials should not fight nature’s forces and always look new; on the contrary, they need to wear and change.

Natural materials like wood, linen and metals become weathered and bleached and change colour. Some natural materials change a lot, and others not so much.

Scandinavian slate is a group of natural materials that have existed for several hundred million years. In functional terms, these materials do not change, but they will develop a patina. In contrast to most other materials, slate’s protective ability remains the same. Slate remains unchanged, in technical terms, in the same high quality through many generations.

To have a maintenance-free home that you find more beautiful for every year that passes, you need to accept change and that time will leave its mark and have faith that patina gives slate its unique character.

Technical specifications and test results: Datasheet Offerdal slate, Datasheet Oppdal slate, Datasheet Otta slate.

A close-up of brown and black slate used as a stepping stone and on a foundation wall. The slate is a reuse of roof slate from Otta.
A close-up of brown and black slate glued to a foundation wall of a cottage. The slate is a reuse of roof slate from Otta.
A close-up of a slate slab of light Oppdal quartzite slate.
Photo: Marianne Vigtel Hølland

How slate ages

The ageing process begins when the slate is split and its appearance is governed by the surrounding environment.

Oppdal and Offerdal

Our quartzite slate from Oppdal and Offerdal can become lighter over time, sometimes with light blurred spots. This is due to the mica that forms the split surface of the slate becoming bleached, while certain chemical elements in the shiny mica are leached out. When this happens, it is a change that is confined to the outermost surface of the slate.

Otta

Like other types of slate, Otta slate is built up of multiple layers, where hard and resistant minerals such as quartz and feldspar are intersected with less resistant mica. This structure (foliation) defines the slate and forms the layer where the slate can be split/sawn into profiles. In Otta slate, shiny mica, which primarily comprises the mineral muscovite, is transparent, in a light silvery tone. Over time and as it weathers, the surface structure undergoes an expected, natural process. This makes the grains of mica less transparent, which heightens the silvery appearance. How rapidly this takes place, or how much the colour changes, depends on a number of factors such as the thickness of the mica layer, its mineralogy and the environment in which the slate tile is fitted. This silvery nuance is often perceived to give the slate an even glossier and more unique appearance.

Otta slate also contains small amounts of minerals such as iron oxides and sulphides, which change naturally to create areas of golden patina or rust. This only happens when the slate is laid outdoors.

Technical quality is unchanged

The above processes are all natural changes that only occur in the uppermost layer of the slate. This means that, as it ages naturally, the slate retains all of its good technical properties. It also gives the slate an incredibly long lifetime in which it can be used over and again.

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