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FAQ – Frequently asked questions

Generally about the slate

It has an unlimited lifespan. For a natural stone to have a long lifespan, it must have a mineral composition that makes it weather-resistant. Our slate consists of highly durable minerals. In addition, they have a mineral structure that is dense and thus strengthens its technical properties. Our three types of slate are positioned within the top 10 in the world in terms of durability.

Our slate is from Norway and Sweden, and all production is done locally by our stonemasons. Slate is split by hand into its natural layers, unlike marble and granite, which are cut mechanically into sheets using a multi-blade saw. However, with a lifespan of > 100 years, slate is often a cheaper alternative in terms of lifespan. The installation cost is largely the same, whether you choose slate or an affordable material.

Slate is a 100% natural material. Our slate from Otta, Oppdal and Offerdal consists of highly durable minerals such as quartz, felt spat and mica. The minerals have a favourable structure that is dense and further strengthens its qualities. Through pressure and temperature, the deposition of sand and clay in rivers and on the seabed has been transformed into rock slate for hundreds of millions of years.

You save the environment from a more than 700% increase in CO2 emissions compared to a ceramic copy. Genuine slate tiles can be supplied with falling lengths that create a beautiful floating look. This format cannot be achieved by using ceramic copies. Choosing local genuine slate also supports sustainable production and local value creation.

The quality of Scandinavian slate is unrivalled. There are old types of rocks where time, pressure, temperature and transformations have developed the slate types into solid materials. The ice ages also contributed to removing much of the younger and weaker rocks that were originally above the slate sites we have today. Most types of slate from other parts of the world are younger, they have not been exposed to temperature, pressure and transformation in the same way as the Scandinavian slate types. Norwegian slate is also local and has a high degree of handicraft – which combined give it a record low environmental footprint.

Minera Skifer has three slate quarries, two in Norway and one in Sweden. Oppdal slate is light grey, the slate from Otta in Gudbrandsdalen is black or rust-coloured, and the slate from Offerdal in Jämtland is deep grey.

Yes, slate is a 100% natural material. Hundreds of millions of years ago, sediments of sand, clay and gravel sank to the bottom of the sea. There it was pressed together into layers, before it became slate under high pressure. Our slate is extracted from Norwegian and Swedish mountains and refined by local stonemasons right at the foot of our three slate quarries.

Yes, local slate from the Scandinavian region has an extremely low climate footprint. It is a 100% natural material that is largely processed by hand, requires minimal maintenance, is everlasting, and can be recycled and reused.

Light Oppdal slate is a medium-grain, rock-speckled gneis mica quartzite slate. Otta slate is a dark slate from the type of rock called Phyllite slate. Offerdal slate is a quartzite from the rock type felt spat metasandstone.

No, our slate must not be impregnated. However, for some applications, it would be advisable to recommend impregnation, as it provides protection against stains and dirt while also facilitating cleaning. For example, it is a good idea to impregnate worktops that are exposed to grease spills, etc.

Yes, slate has very good breaking strength and flexibility. For driving on slate laid in cement mortar or on concrete slabs, the slabs should be at least 2 cm thick. If the slate is laid in gravel, the surface should be stable, well compressed and frost-free, and the slate should have a minimum thickness of 4 cm.

No. Our three slate types in natural surfaces are 100% non-slip (with the highest classification) and are therefore very suitable for external areas such as terraces, staircases and the like. We also supply slate in finished surfaces that are non-slip. All our slate surfaces have been tested and the slip resistance has been documented with an R number, which is a standard for testing slip resistance and is used for ceramic tiles, among other things. See our product datasheets for test results.

Yes. Our slate from Oppdal, Otta and Offerdal is all 100% frost-proof and therefore very suitable for use in a tough Nordic climate.  The porosity of a material is calculated by measuring the maximum amount of water that it attracts. In general, porous materials with high water uptake are the least strong and durable. All of our slates have water uptake far below what the European standard states as a limit for frost protection (NS-EN 12326-1: water absorption ≤ 0.6). See more in our product datasheets here

Yes. Our slates are water-resistant and can be installed in pools, fountains and the like. With a very low level of water absorption, they are therefore also 100% frost-proof.

Yes. Our slate is non-slip and can withstand moisture and chlorine from a pool. Offerdal slate is particularly suitable for this (test-documented), and has been widely used for this purpose in Europe for decades. Our three types of slate can all be used both in the pool itself or around the pool. Otta slate and Lys Oppdal slate should be avoided in the actual zone transition between water and air.

Yes. It is a good idea to lay outdoor heating cables under slate that is glued on concrete or laid in gravel.

This is contingent on insulation under the heating cables. There are, among other things, heating cables mounted on insulating mats intended for this purpose.

 

No. Slate in its natural surface can withstand studs and have no unfortunate consequences. On floors where the surface of the slate is either brushed or sanded, we do not recommend the use of studs.

Yes, Minera Skifer’s three types of slate can withstand salt. However, over time, large quantities in humid climates can affect the minerals and cause a colour change in the surface– a patina. This has no impact on the technical quality of the slate, i.e. the function, durability and lifetime remain unaffected.

For a slate to have a rust colour, a slate type that can develop a rust patina must be used. In Scandinavia, only Otta slate from Gudbrandsdalen in Norway has a mineral composition that provides this property. Rust develops naturally over time due to weather and wind, and becomes increasingly beautiful over years. Read about Otta slate’s development of a beautiful rust patina here.

Flagstones

As the Norwegian saying goes, “beloved children have many names”.  Flagstones, crazy paving slate slabs and paving slabs are the same. Characteristic for the slabs is that they have an irregular organic shape and are available in sizes from small to extra large. They can be laid outdoors as well as indoors.

Yes! Our three types of slate are old Nordic rocks that are non-slip, frost-proof, have a high breaking strength, and thus withstand a tough Nordic climate very well. Crazy paving can therefore be used both outdoors and indoors.

Flagstones can be laid in mortar, glued onto concrete slabs, laid in crushed stone/gravel or on pedestals. See our detailed guides and videos for customizing and laying flagstones.

Flagstones from different suppliers vary a lot in terms of size, shape and quality. When comparing prices, one should map the actual slate slab size (number of slabs per m2), shape requirements, frost protection and surface smoothness. As an example, Light Oppdal slate from Minera costs between € 29 – 34 per m2.

Yes! Our slates are non-slip and can withstand the Nordic climate, and are perfect for stairs. Flagstones can be glued to the surface of a concrete staircase and then grouted.

Slate tiles

Definitely! Slate is ideal over electrical or hydronic floor heating due to its high heating capacity (ability to store heat) and conductivity (ability to conduct heat). A slate floor with heating cables will retain heat and distribute it evenly – providing a very comfortable indoor climate.

Yes. Our slate is hundreds of millions of years old and has survived many ice ages. It is therefore very resistant to water and is well-suited for use in bathrooms when the installation is carried out right and correctly in relation to falls and run-off against drains, etc. See our installation instructions for the glueing of slate.

Yes, slate tiles can be glued directly onto walls of suitable substrates such as plaster, concrete, Leca, etc. both outdoors and indoors. They can also be screwed onto walls horizontally or vertically, and where the slate tiles overlap. See our installation instructions for how to lay slate tiles.

Yes. One of the many excellent properties of slate is its ability to store and distribute heat. A firewall can usually be clad with slate by gluing tiles or flagstones directly onto an approved firewall by Leca or on a firewall board (the slate itself is not an approved firewall material).

Yes, all our slate types have properties that make them stay nice for years to come, even in our harsh climate, even without any maintenance other than rinsing/washing. On a terrace with a grill/outdoor kitchen, an impregnation can further facilitate cleaning by avoiding stains. Read more about how to maintain slate here.

Slate tiles can be laid loosely in gravel. Slate tiles can be glued onto cast concrete slabs. Slate tiles can be laid directly on pedestals that are either placed loosely on a concrete slab or in gravel. This is a very simple installation that requires no glue or joints. Learn all about laying slate with our films and installation instructions.

Slate roofing

The roof tile isscrewed or nailed onto wooden laths laid horizontally and vertically, with distances adapted to the size of the roof tile. The laths ensure that the slate roof is well ventilated against the suspended ceiling. Roof tiles from Minera Skifer have pre-drilled holes adapted to the slath distance. See our installation instructions for roof tiles.

Prices vary depending on the type of roof tile and the complexity of the roof (angle, gutter, etc.). The installation of slate slabs including laths costs from around € 70 per m2 of roof surface. The slate itself is an additional cost. As an example, Otta square slate in a fixed thickness and with fixing holes costs € 170 per m2 of roof surface, including slate overlap. A slate roof of 100 sqm laid with this type of Otta slate costs a total of around € 24.000.

A slate roof laid with Norwegian slate rarely needs repairs due to its high breaking strength and frost protection. It can withstand Norwegian winters and the weight of large amounts of snow. Replacing loose or broken slabs is a simple matter for professionals.

Yes, you can. The snow traps are attached to the laths at the same time as the slate is installed, and in exactly the same way as on roofs with other tile types (Zanda, etc.).

As a rule, it is not necessary to clean a slate roof. If a person lives somewhere where climatic conditions provide a breeding ground for moss, this can be removed from the slate roof for aesthetic reasons. The moss is cleaned away with a broom and water or a high-pressure cleaner.

A well-laid slate roof with slate from Norway is almost eternal and usually lasts longer than the actual lifespan of the building. Minera Skifer’s roof tiles are made of natural stone of solid Norwegian rock that does not weather, and it is therefore very common for old roof tiles to be reused on new buildings.

The traditional method is to finish with a higher ridge stone on one roof surface, creating an overlap that covers the ridge. Ridge fittings in steel are also used on slate roofs, as gutters, snow traps, etc., already break with the old style where only slate is visible. The ridge fitting is attached to a wooden lath on the ridge. The fitting itself must be pre-adjusted in the same profile as the lath it is going to cover.

Slate bricks

Yes, absolutely! There are few materials that create such a beautiful brickwork as slate, with its shaded colours and textures. Our slate brick has parallel, straight layers that make it very suitable for drywalling. We have six different types of bricks in our standard range – from the most rustic look to more modern designs.

A drywall is constructed by stacking the bricks on top of each other dry, i.e. without placing grout between the stones. The wall is anchored and supported by continuously putting casting compound behind the stones while stacking. In the case of high altitudes, additional anchorage to the underlying structure must be considered. See how to make a drywall using slate here. See film and installation instructions for how to make a drywall using slate  here

Natural brick is a type of stone brick that has 100% natural edges as a result of cracks occurring in the rock millions of years ago. Often these edges are almost smooth and have great colour variations in soft shades of red, green, black and white.

Yes, this is the classic of all classics when it comes to slate brickwork. Natural brick (also called drywall) is available in different sizes and is very suitable for both drywalling and general masonry with mortar joints.

Facade panels

Yes! Our facade slates from Oppdal, Otta and Offerdal are all maintenance-free and require no treatment other than rinsing/cleaning if necessary.

The price will vary according to installation method, type of slate, and the complexity of the facade (windows, corner endings, etc.). As an example, a slate facade fitted with an overlap of light Oppdal slate will cost from € 175 per m2, including the actual suspension system (rails and hooks). A finished facade of 50 m2 costs a total of approximately € 8700. This is a durable and beautiful “do-it-yourself” system that does not require a craftsman. See how quickly and easily you can clad a wall with facade slate yourself with this ingenious system.

Yes, it can. Slate for facade cladding is available in many different finishes. Most mounting methods can be used both outdoors and indoors. An indoor wall can also be covered with slate tiles that are glued to the wall.

No, but you are welcome to dress a firewall with facade slate by gluing it directly onto an approved firewall made of Leca or another firewall slab. One of the great properties of slate is its ability to store and distribute heat.

Yes, Minera Skifer’s three types of slate can withstand salt. However, over time, large quantities in humid climates can affect the minerals and cause a colour change in the surface– a patina. This has no impact on the technical quality of the slate, i.e. the function, durability and lifetime remain unaffected.

For a slate facade to have a rust colour, a slate type that can develop a rust patina must be used. In Scandinavia, only Otta slate from Gudbrandsdalen in Norway has a mineral composition that provides this property. Rust develops naturally over time due to weather and wind, and becomes increasingly beautiful over years. Read about Otta slate’s development of a beautiful rust patina here.

Installation

Glued slate will not come loose if the installation is done correctly. By using glue intended for slate, and following the manufacturer’s instructions (e.g. for temperature, substrate, glue layer, open time for ready-mixed glue, etc.), you will get a long-lasting result. Read more in the installation instructions for glueing slate.

For slate tiles with said edge, the same applies as to ceramic tiles. In principle, there is no difference in their installation. A joint width of approx. 5 mm is often used. When gluing slate slabs with a rustic cut edge, a larger joint width is required. As a rule of thumb, it should be half the thickness of the slate slab itself. E.g. a cut slab with a thickness of 30 mm should have a joint width of min. 15 mm.

It is not recommended. A hard cement-based grout will not give a durable result when the slate tiles are laid in loose masses (joints crack and loosen).

Slate can be glued on concrete both indoors and outdoors, e.g. on terraces. Slate can be laid directly on pedestals (without glue/ joints) in an outdoor area/terrace. Outdoor areas in the garden can be made using slate laid in gravel on a surface that is stable and frost-free. Slate slabs can be laid directly in the lawn with a layer of gravel underneath. See our films and installation instructions for how to shape and install slate.

Yes, slate can be glued directly onto walls with suitable substrates such as plaster, concrete, Leca etc. both outdoors and indoors. They can also be screwed onto walls horizontally or vertically, and where the slate tiles overlap. Slate can also be used for walls using mortar joints or without mortar joints (drywall). See our films and installation instructions for how to shape and install slate.

Our slate can be cut with an angle grinder or sawn with a stone saw with a water-cooled saw blade. Slate flagstones and slabs can be shaped with a hammer and/or slate knife, or cut to the desired shape using slate cutters (to be rented from our dealers). Light Oppdal slate can also be scratched and cracked in the same way as glass panes are broken. See different methods for adjusting slate in this installation guide.

Only a few and simple tools are needed, including a hammer, scriber, chisel, slate knife, or angle grinder. To shape slabs, a hammer goes a long way. A slate knife can be used to fine-tune the edges. Slate can also be easily customised with slate cutters that can be rented/borrowed from our dealers.

A slate scissors is a manual cutter used for shaping slabs. It is very easy to use, does not require electricity, and makes fitting faster, easier and neater. The ascissors allow both straight and curved edges to be easily cut. The thickness of the slate can be up to approx. 20 mm. You can rent a slate scissors from our dealers. See how to cut slate with scissors here.

The advantage is that the actual installation is simpler, cheaper, and that it is easier to make subsequent changes if necessary. The disadvantage is that the coating can become more unstable and that grass can grow in the joints.

Installation is more extensive than installation in gravel. The joints can be jointed with a cement-based grout, and the coating will withstand greater point loads and greater torsional forces.

Maintanance

Yes. Slate worktops can be impregnated with an oil-based impregnation agent that protects against greasy and oily stains. We recommend products that are invisible, i.e. that do not change the colour and gloss of the slate, and are approved for use with foodstuffs, such as Akemi Natura Impregnator or Steinfix 100+.

No, slate must not be impregnated. However, for some applications, it would be advisable to recommend impregnation, as it provides protection against stains and dirt while also facilitating cleaning. For example, it is a good idea to impregnate worktops that are exposed to grease spills, etc.

Slate requires little – both indoors and outdoors. Outside, rinsing with a water hose is usually sufficient. Clean water may be used indoors, possibly with a mild, neutral soap (avoid using common green soaps that often have a PH value that is not appropriate for natural stone). Once in a while, the surface can be coated with a coarse cleaning agent for natural stone. Read more about slate maintenance and stain removal here

Stains are easily removed with special agents which are supplied by several manufacturers. Akemi oil and grease remover paste removes tallow, grease and oil. Organic stains from wine, blood and plants can be removed using Akemi Good-Bye Stain cleaning agent. Follow the manufacturer’s instructions and neutralise the slate by rinsing with clean water after treatment. Read more about slate maintenance and stain removal here

Removing grass with boiling water from a kettle is both easy and environmentally friendly. This kills the roots and prevents rapid growth. One can also burn it off using a propane burner. It can also be removed mechanically with a rake (Fiskars) or using chemical weedkillers.

Removal of moss on a slate roof is done with water and a broom, or with a high-pressure cleaner. Moss only grows on the surface

Joints can be topped up with the same mass used when installing the slate slabs. For joints with a large width, gravel or single grit 2-4 mm can be used. Narrow joints can be topped up with a dry and fine-grained grouting sand. Weeds in joints can be removed using chemicals, be burned with a propane burner, or removed using boiling water, which is the easiest and most environmentally friendly method.

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