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A fire pit is an interesting addition to the garden, property or cottage in the woods and is easy to set up yourself. Of course, not only a foundation that protects the floor under the fireplace from the heat is important, but also the right stones. They are decorative, keep the fire under control and can be used to store all kinds of barbecue utensils. Only coated, heat-resistant natural stones are used for this purpose.
Refractory natural stones
Are there refractory natural stones?
Choosing the right stones for the fireplace is essential, as not every stone is suitable for permanent use as a fireplace. While most naturally occurring rock is solid and heavy, making it appear refractory, this is far from the case. Depending on the density and porosity of the selected stone, the possible use varies from slightly heat-resistant to more heat-resistant and almost fireproof. Limestone, like marble, for example, only withstands low heat and bursts if exposed to too much pressure, while the volcanic rock porphyry is almost heat-resistant due to its composition. If exposed to heat for a long time, the following problems can occur with many natural stones.
refractory natural stones for a fireplace
- Stone shatters, bursts or even explodes
- Cracks form, stone loses stability
- Discolouration occurs, for example with sandstone
- Heat is dissipated to the environment through the stone
The biggest problem here are the pores of the stone. These absorb moisture and the temperature often fluctuates between hot and cold with rising and falling moisture, the stone changes in volume, which can make it unstable. In itself, this is the case with every rock from nature and for this reason there are heat-resistant natural stones, but in themselves refractory stones that can withstand any heat. However, there are ten types of stone that are extremely heat resistant, making them perfect for a fireplace.
- sandstone
- porphyry
- basalt and basaltic lava
- granites
- soapstone
- trachyte
- tuff
- greywacke
- gneiss
- quartzite
Since a fireplace is not a building or structure that is essential to human life, the stones mentioned can be used as a border around the fireplace. Here, however, internal insulation from the direct heat effect is necessary, which is made possible by two refractory stone products.
- firebricks
- brick and clinker
Barbecue area in the garden
These are special blends of heat-resistant materials that can withstand even the heat of a blazing fire. They act as a layer that absorbs the heat of the fire directly and only gives off the residual heat to the natural stones. This is important, because only in this way can even the stones with the highest heat resistance withstand being used as a fireplace and allow you to spend pleasant hours in the garden over the long term. In the following paragraphs you will find detailed information on the individual natural stones.
Please note: Never collect stones from the forest, especially not from rivers or streams, and use them as a basis for the fire pit. Since you don't know what type of stone it is, after a few hours at the fire, it could fly dangerously around your ears.
Natural stones in the oven with embers
sandstone
Sandstone is one of the oldest sedimentary rocks that man has used for structures such as the pyramids. Due to the composition of at least 50 percent sand grains, mainly quartz, and other elements, the natural stone is extremely resistant to heat and also insensitive to frost. If the sandstone has high amounts of feldspar, i.e. silicate minerals, it becomes more resistant and can still be used effectively as a fireplace. Sandstone was not only used for the construction of buildings, but was often used for stoves, especially in ancient times in the Mediterranean and the Middle East. Sandstone is therefore perfect for Mediterranean gardens.
Tip: If you choose a sandstone fireplace, you have a wide range of colors to choose from. Yellow and red are the most common variants, followed by grey, white, brown and even green (Anröchter Stein), which can discolour when exposed to heat.
refractory natural stones, sandstone
porphyry
Porphyry, which means purple in ancient Greek, refers to various stones of volcanic origin belonging to the so-called igneous rocks. Igneous rocks are extremely heat resistant because, as the name suggests, they are formed from cooled magma. Porphyry has a high number of feldspar and crystals, which make the natural stone almost 100 percent fireproof. Above all, porphyry with large amounts of quartz should be mentioned here. The stones can even withstand very hot fires of up to 1,000°C and are suitable for a variety of garden projects due to their simple style.
refractory natural stones, porphyry
basalt and basaltic lava
Basalt and especially the basalt lava are also magmatites and have been known since ancient times. Basalt is striking in jet black, gray, or blue-gray in color and has a high density that makes the rock a perfect candidate for the fireplace. Especially the basalt lava is recommended here. It has a particularly rough look that is often used for facades and other structures such as bridges, while conventional basalt is more used for tiles. Because of its formation, splintered basalt has a so-called flow direction, which shows how the lava flowed.
refractory natural stones, basalt
granites
The various granites are also magmatites, but these belong to the plutonites, i.e. the deep rocks that, unlike basalt or porphyry, do not rise as lava. They are mostly underground and quite coarse-grained. They mostly consist of the following parts.
- quartz
- field spade
- Mica (layered silicate, is often used in cosmetics and as an insulator in electrical engineering)
Granites come in a variety of colors and can easily withstand fires up to 600°C, but are not among the rocks that can withstand extreme heat. They suffer primarily from direct fire exposure and should therefore only be used in conjunction with insulating materials. They are extremely popular because of their decorative uses.
refractory natural stone, granite
soapstone
At first glance, soapstone does not appear to be heat-resistant due to its soft surface and low weight, but it was used for stoves and cookware in the past. Soapstone consists of talc and is the best natural stone for fireplaces, as it is also almost fireproof. A special highlight of soapstone are the different color variants, which range from pure white to pink to black and blue and are therefore suitable for every type of garden. Modern garden projects in particular benefit from the shine of the stone.
refractory natural stones, soapstone
trachyte
Trachyte is one of the oldest building materials in Germany that was used for oven bricks. They are a plutonite, similar to granite, but are identical to syenites and are therefore much more resistant to fire and heat. Their sober grey-white color makes these stones suitable for a variety of gardens and plots. Since they are also very frost-resistant, you can easily light a fire over the winter to warm yourself up. They retain heat very well, which is precisely why they are so valuable for historic stoves. Many stoves in old houses are still made of trachyte.
refractory natural stones, trachyte
tuff
Similar to trachyte, tuff is used for the construction of ovens and is also a volcanic rock that is also popular around the world because of the numerous color variants. Depending on the region, different colors are created here, which are caused by volcanoes. Tuff is either solidified volcanic ash and fragments of rock or cooled lava thrown several kilometers after an eruption. Due to the quite porous condition, they were used for masonry in the past and the natural stones present themselves aesthetically in the garden.
refractory natural stones, tuff
greywacke
Greywacke is a natural stone that is mainly used as a basis for paving stones. Their dark color and high heat resistance make these extremely old stones a good base for a fireplace. A special feature of greywacke is its age. Dating from the Paleozoic Era, dating back about 500 million years, these rocks are an extremely dense compound of sandstone and feldspar. As the name suggests, greywacke is a natural stone in different shades of gray that can be easily put together with mortar and thus leave a very rustic impression in the garden.
refractory natural stones, greywacke
gneiss
Gneisses are metamorphic rocks that are formed as a result of pressure changes in the environment, for example due to plate movements, and contain at least 20 percent feldspar. The name of the stone comes from the Saxon miners' language of the 16th century and means "spark". This is to indicate the sparkling of the stones when rotated in the light. Their structure is similar to granite, but they are much more resistant to heat and frost and come in many colors that conjure up a wonderful character in the garden. They can easily be polished and thus present the color spectrum even more strongly. The typical colors of the stones are grey, white and black.
refractory natural stones, gneiss
quartzite
Quartzite are natural stones that consist mostly of quartz and can be used as colorful stones for the fireplace. They are extremely resistant to all forms of environmental influences and are therefore also resistant to frost and heat. It comes in all sorts of colours, from classic shades of gray to rich red and rainbow colours, which can be used fashionably for your own fireplace in the yard or garden.
refractory natural stones, quartzite
chamotte
Firebricks are not directly natural stones, but artificially manufactured stones made of clay and aluminum oxide (Al2O3), which are 100% fireproof. Fireclay bricks are an essential component for all forms of stoves and hearths as they can withstand any form of temperature. For this reason, they are used as protection against the heat of the fire by representing the first ring of the hearth, so to speak. They are the insulation and keep the above stones from the heat so they don't crack and stay more durable.
In terms of heat resistance, a distinction is made between:
- acidic fireclay with an Al2O3 content of ten to 30 percent
- normal fireclay with an Al2O3 content of 30 to 45 percent
The bricks are used with a special fireclay mortar, which is also fireproof and heat-resistant. It also protects the other natural stones in the fireplace from the heat, so you can easily create interesting projects without worrying about the heat resistance of the other stones.
refractory natural stones, chamotte
brick
Bricks or bricks are fired from clay and this gives them their refractory properties. Bricks can also be made from fireclay or sintered, making them clinker. Clinkers were burned so hot that the actual pores close and neither heat nor cold can harm the stones. For this reason, they are just as suitable as fireclay bricks as heat protection that you want to use for your fireplace. Bricks can be laid easily and made even more heat-resistant with fireclay mortar.
refractory natural stones, bricks