Like the kitchen is the heart of the home, the heater is the heart of the sauna, and the stones determine the quality of heat and steam.
The size, density, heat resistance, and chemical composition of sauna rocks play a major role in a good sauna experience.
A good sauna rock has three main characteristics:
- It must efficiently accumulate and retain heat
- It must be heat resistant so that it won’t crumble
- It must not contain sulfur minerals; otherwise, the steam may become toxic
The best way to recognize sulfur-containing stone is the rusty look on the rock surface, so make sure you don’t use them in your sauna. Not only do they produce toxic heat, but they can also darken the wood and metal parts of the sauna.
How to determine a good sauna rock?
A straightforward way to determine a good sauna stone is the color. Darker rocks are usually better suited because they accumulate heat more efficiently.
A stone made up of only one dark mineral will hold up best on the heater. This type of stone is usually heavy and completely black. An exception is a pure white flint, which is suitable as a material for stove stones.
Another characteristic to look for is density and porosity. A good sauna stone is dense, heavy, and non-porous. It should not have flaws, holes, or pores to keep water from entering.
What types of rocks are best suited for my sauna?
Dark igneous rocks such as vulcanite, gabbro, peridotite, basalt, and granite are excellent choices. Mixed type such as the gabbro-diabase is also very common and found in nature. Vulcanite is good for its high metal content, which helps it store heat very efficiently.
Artificially made ceramic stones can also be very good, but they are much more expensive.
There are many choices available and each has a different strong point so it’s impossible to pick just one, so I suggest experimenting a bit to find out what works best for you.
You can also mix different types of stones and create your own unique sauna experience this way.
Rock types to avoid
Avoid sedimentary and metamorphic rocks like sandstone, quartzite, slate as they’re too soft and can easily pop when heated up because they have falts or moisture trapped inside.
Generally, I would avoid light-colored rocks because they tend to crumble more quickly. However, there are exceptions to the rule, such as artificially made (ceramic) stones or those made of pure white flint. Definitely avoid rusty-looking rocks when sourcing from nature as these contain sulfur content and can create toxic steam.
How often should sauna stones be replaced?
It is necessary to replace the stones periodically, as they tend to crumble and lose their properties over time. If your sauna starts to heat up more slowly, it’s time to re-stack your stones.
I would suggest replacing the stones at least once a year, or after about 300 hours of usage.
Before you you do so, make sure to wash the stones and stack them up in such a way that there are sufficient air gaps in between the stones. This will allow the hot air to circulate more efficiently in the heater.
To allow hot air to accumulate better in the stones, it is best to stack smaller stones more densely on top of the heater.
Harden your stones before the first use!
Harden your stones in order to make them last longer.
It’s a very simple process. Just heat them up to the normal operating temperature or a bit higher, and let them cool down naturally. The important part is to not throw water on the stones during hardening. That’s it!
Choosing the right sauna stones is a lot of fun experimenting and the final choice is highly subjective. You can’t go wrong with darker rocks made of gabbro, basalt, or peridotite, but don’t hesitate to try out different types and find yours!
Stay safe when experimenting in your sauna!
If you’ve been dreaming about getting your very own sauna, take a look at our outdoor sauna kits and let us know if you need any help choosing the right size and type.