The choice of stove stones
Importance of Stones
The quantity and quality of stones for the sauna stove play an important part in the whole sauna experience. The choice of stones depends on the type of stove and its use. The stones should be carefully selected for their durability and salubrity. The characteristics of good stones include, among others, high thermal capacity and purity. The stones should not produce dust or form harmful gases.
In the past the most commonly used stove stones were made of granite or stones found by lakes or rivers. Granite rock, however, has a tendency to crumble at a relatively low temperature of 300 degrees. The thermal capacity of lake stones is fairly low and the heat conductivity is poor. The temperature in the sauna can reach high enough levels but the stones cool down relatively quickly. The lake stones are also prone to crumble away. It is worth using the well researched and recognized stone types.
The stones deliver the steam
The best sauna stones are the deep igneous rocks. These dark and heavy plutonite stones are excellent due to their thermal capacity and are particularly suitable for traditional type stoves. The heat-storing stoves require dense stones due to their superior thermal conductivity qualities. Deep dark rocks include: olivine, diabase, chrome ore and peridotite.
Types of stove stones:
- Olivine diabase: The most traditional and the most common stove rock. It is robust and has good heat storage capacity. The crushed natural stone can potentially discharge dust and gases into the air when hot. They have been used in all types of heaters. The bigger stove types require larger stones.
- Soapstone: Good heat storage and thermal conductivity. Soapstone is particularly suitable for traditional heaters. Not all electric stove manufacturers recommend the use of soapstone and advise these to be used only as surface stones. Regular-shaped stones should not be stacked too tightly around the heating elements.
- Rounded olivine diabase: Delivers a soft steam bath. Water flows easily onto all of the stones i.e. there is a plenty of stone surface to create steam. This rock does not crumble as easily as the cut, jagged rock. It has a well-proportioned appearance and is suitable for all heaters. This type is also used on top of ordinary stones.
- Heat-treated olivine diabase: Heat-treated at 1000°C, allowing for more resistance to deterioration than ordinary stone. As a result of this treatment the stones also have small micropores in which the water gathers and humidifies the steam. It is suitable for all heaters but also for demanding applications such as for stoves at public saunas.
- Kerkes stove stones (ceramic stone): Extremely durable, it is advertised to be "almost indestructible". The indentations on the surface collect water, and are intended to increase the moisture in the sauna. They are odourless and do not produce stone dust. They are suitable for all stoves and often used in public saunas. The most common mistake with these stones is that they are packed too tightly into the stove. This means that the air cannot circulate properly and damage to the stove can occur.
- Tiileri (ceramic stone): Porous surface which absorbs water and produces a moist steam for a longer duration. Their heat storage capacity is not as good as natural stones. They are durable and do not shed stone dust or emit fumes. They are designed to add moisture into the steam, especially in electrically heated saunas. Not all electric stove manufacturers, however, recommend this stone, because there is a danger that the stones are placed too tightly, which can break the stove.
New Stove Stones
Initially some dust may come loose from new stones, therefore, before installing, the stones should be washed thoroughly. Pay careful attention when placing the stones into the stove by following the stove manufacture’s instructions. A general guideline is to avoid stacking the stones too tightly, which would prevent proper air circulation.
Heating the Stove
The stove should be heated so that the surface temperature of the stones becomes very hot, the hotter the stones, the better and faster the water will evaporate and the steam will feel pleasant. The hot stones are also burning off the possible impurities in the water and the resultant steam will be pure water vapour.
The Stove maintenance
It is important to keep an eye on the stove and the condition of the stones at regular intervals. The top layer of the stones may seem in good condition, but further down the stones are exposed to much higher stress and temperatures. Crumbled stones block the flow of air through the heater and this may shorten the stove’s lifetime.
It is a good idea, at least annually, to change the position of the stones and replace any broken pieces. At the same time the heater can be cleaned of any residue and dust that may have gathered inside.
It is recommended that in normal use the stones should be changed either annually or every two years. In practice, the frequency for replacing the stones depends on the amount of use and the stone quality. When the sauna is used only occasionally, the stones do not need to be replaced as frequently, but in public saunas the stones should be changed several times a year.
Keywords: Stove stones, stove maintenance, heating stove, heater stones, stove stone types