7 things you may want to know about your sauna stones

Guest post series continues.  Welcome Dick from Scandia, Minnesota.  Dick works in Research and Development at the Andersen Corporation (Windows)   He has worked in Design, Project Management and Materials Research for 33 years.

Enter Dick:

7 things you may want to know about your sauna stones

  1. You can collect your own “rocks.”

“The best choice for sauna rocks are the ones closest to home that are of suitable composition.”

 -Dick Waskey

If you are still with me I know you probably have a wood burning sauna.  Someone who would wonder about collecting their own sauna rocks would probably burn wood.  There is a certain person who cuts wood and dry’s it, carefully splitting and stacking it in preparation for taking sauna-  It’s the “Gestalt” Principle, in action!   The preparation is just as important as the Sauna and when combined together give us an exhilarating experience.   That same person is likely also to search out and find their own “Sauna Stones” enriching your experience further.

Free sauna rocks

(Or you may just be a good Swede like me and you’re too cheap to lay out your hard earned cash for a pile of rocks…)

If you are wondering why I switched back and forth from rocks to stones I think of them as rocks when they are in the wild and they become “Stones” once they are placed in my sauna heater.

A word of caution!. Gathering stones for your sauna is not the same as Rock collecting.  Everyone grabs a pretty agate from the restaurant landscaping or even at a city park.  Taking an entire 5 gallon pail of rocks from public beaches, parks and private places is not alright.  Take a care and only collect rocks with permission or from land you own.  You might want to try a local landscape company or nursery supply business.  Mine lets me even sort through the pile and pick just the “Perfect” ones.

“All men are created equal; but no place more than in sauna.”

— Author Unknown

  1. Importance of Stones

The stones deliver the steam.  Stone size density, porosity, and surface all play a role in transferring heat from the fire to you.  If we use too small of stone it doesn’t  hold enough heat to last very long.  Too large and it takes longer to heat up.  A stone with a nice rough fracture is nice because it has a little more surface area to hold on to the water and gives off more heat.  Some stones might stack too close together and prevent the free flow of heat and water through the pile.  Too loose and too much water passes through too quickly.

I use stones about the size of my fist with a few larger and smaller to fit just right when I lay them in my stove.

Note that folks with those new fangled electric stoves need to be careful about their stones because stone size and placement can shorten the life of the elements… 

READ your instructions warnings!

  1. Black Rocks Matter.

I had to shamelessly say it. Now that I’ve got that out of the way let’s move on.

Darker rocks give off heat quicker.  It’s a physics thing. The “Finnish” stones for sale are all dark.

Look up Absorbtivity, Emissivity, Reflectivity, Transmissivity,
T=(αϵAAcϕσ)1/4T=(αϵAAcϕσ)1/4 and  AcAc: Ein=Acαϕ

(If you want to know more… I say “Nerd”.)

  1. Types of stove stones: (structural integrity)

Sedimentary- Metamorphic – Igneous, Oh my!

I noticed some companies tend to say things like “the only correct stones”, “the only real sauna rock” or “the correct type”…These are written by “Ad men” and are simply trying to convince you that they have the very best rock for your money.    Now be assured, proper sauna rocks are a safety concern.  But any igneous, structurally sound  rock will work in a sauna and you will be hard pressed to appreciate the differences unless you are 100% Finnish.

Without getting into a geology class let’s just say if you can scratch material off the rock with a nail, DO NOT USE IT!.

Sedimentary rocks (sandstone, shale, limestone, etc) and Metamorphic rocks (slate, marble, Quartzite, etc…) all are too soft, have faults in them or have moisture in them and should not be used.  These rocks with moisture in them can “POP” when subject to heat…

We want an igneous rock (Vulcanite, gabro, peridotite, Basalt, Olivine, Granite,  etc…) Note I did not include Obsidian and Pumice, both bonafide igneous rocks but they have issues.  Obsidian is so smooth that the water will run off so quick it will not have time to evaporate much.  Pumice is so light and porous that it will cool too quick and not have enough mass to give you the sustained heat a sauna needs.

If you are having trouble identifying your rocks.  Do an internet search for igneous rocks and that should help you.  You can also search for a map of your area showing what the predominant rock type is in the area.  Some folks might have to wait until vacation to find suitable rocks and depending on who’s with you… you might have to only bring a bucket full at a time home.

  1. Loading of Sauna Rocks-Stone can be dirty.

Before loading your stones in the Rock Chamber,  wash and rinse them to get off anything that might soil your floor or impart an off Oder when heated. Next depending on your heater, start with the largest stones first and then use smaller and smaller, stack them in and around the Rock Chamber until it’s full and heaping.  You do not want them so tight that air has a hard time getting through but you want them close enough that when you pour water on, it doesn’t run quickly off and doesn’t have a chance to turn to steam.

  1. Rock Replacement

Some rocks will last longer than others.  I’ve heard that some only last less than a year.  Whoa!  Those are not rocks we want to use…  But after a while rocks will crack and get smaller and smaller.  Usually the hottest rocks next to the fire pot degrade first.  They are subject to more thermal expansion due to the heat / cold cycle.  You might want to use room temperature water rather than cold to limit this stress on the rocks and also use only a cup of water at a time to limit the stress also.  It’s better to dump a cup on a few minutes apart than 2 cups all at once…

When your rocks are cracked and getting small, some are ending up on the floor.  It’s time to replace them.  Simply remove them all and combine the old useable good ones with your new rocks.  .  . See #3 above.

  1. The Spiritual Side

“A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral sauna.”

Antoine de Saint-Exupery

The secret to walkin´ on water is knowing where the rocks are”.

Bootsy Collins

“Rocks are more co-operative than people.” 
― Barry WebsterThe Lava in My Bones

“We often throw rocks not realizing that they’re going to land somewhere.” 
― Craig D. Lounsbrough

“It’s not an old book, or a treasure map. Nope. Staring up at me was a pile of rocks.” 
― Wendy MassJeremy Fink and the Meaning of Life

(Few people know she was also thinking about her sauna)

“Adieu to disappointment and spleen. What are men to rocks and mountains?” 
― Jane AustenPride and Prejudice

“I’m allergic to rocks hitting me in the face.” 

(Never throw rocks in your sauna)
― Mike Rowe

I will conclude with this great quote from Constance Malleson from her book, “In the North: Autobiographical Fragments of Norway, Sweden, Finland: 1936-1946.”

“The sauna… Is an apotheosis of all experience: Purgatory and paradise; earth and fire; fire and water; sin and forgiveness. It is lyrical ecstasy. It is resurrection from the dead. It is eternal new birth… You are healed, you are made new.”

PS- Here’s a fun thing to do.  When you are at a Chinese restaurant and you get a fortune cookie.  Always add “In a Sauna”  to the end of you fortune.  It makes them much-more-funner…


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23 thoughts on “7 things you may want to know about your sauna stones”

  1. I always equate Sauna with Fire and Ice.
    Game of Thrones – NO
    The Finnish winter war-MAYBE
    Coming out of the sauna to jump in a cold northern lake or roll in the snow-YES!!!!

  2. Hi Guys, at Glenn’s suggestion I’m posting this as a comment rather than a separate story.

    ******Be Careful when Scrounging Sauna Rocks – A Cautionary Tale******

    This is a grea post by Dick. Rocks are one of the least understood aspects of good sauna gear, and Dick’s article is really helpful. I definitely support sourcing your own rocks if you know what to look for, following Dick’s guidelines.

    Dick also mentioned cleaning, saying:

    “Before loading your stones in the Rock Chamber, wash and rinse them to get off anything that might soil your floor or impart an off Oder when heated.”

    But friends – this is a point I want to push further. Much further, in fact.

    Here’s a story I heard recently, which should stand as a lesson to all about the importance of sauna safety as a holistic concept.

    Last year, I met the head of one of Australia’s leading sauna companies. We spoke for a few hours about sauna culture and sauna technology, and at one point we started talking about rocks. We were standing next to a few ton of sauna rocks at the time (sitting on wooden pallets).

    I asked why he imported rocks – could he not source them locally? He explained that in the end it was much easier to from his supplier (one of the major Finnish sauna companies), due to the large quantity he traded in, as well as the need for consistent quality. And safety.

    He explained to me that several years ago, he wanted to see what other sauna suppliers in Australia were selling for rocks.

    Some were fine, but some of the rocks he received were clearly harvested locally, and were poorly selected for size.

    He went a step further by sending everything for chemical sampling. This is where things get scary.

    One day he got a call from the lab doing the test, and they said is was real lucky they were wearing safety suits, because one of the samples was covered in asbestos.


    WTF? How did this absurd situation come about?

    Investigation revealed that it was a shonky dealer who was known for other dubious standards and even more dubious practices. It turns out that apparently, this idiot had been picking up rocks from the train tracks. I’m not sure what the rocks on train tracks look like in other parts of the world, but in Sydney, they generally look like they would be excellent sauna rocks – hard, dark, and not too large.

    See here for some examples:
    * http://bit.ly/2fevuke
    * http://bit.ly/2w4gHU4
    * http://bit.ly/2y1f8TS

    Looks great, right?

    But this idiot – this cheapskate, tight-ass, irresponsible idiot – decided he would use these rocks to sell with his other sauna gear.

    Why is this a problem? Because the old generation of trains had brake pads made of asbestos. So every time they creaked on the brakes (generally near a station in exactly the type of place someone would sneak on to), they would rain down asbestos dust onto the rocks.

    Imagine you haven’t heard this story, you find these rocks (maybe someone even sells them on ebay after never using them), but you don’t wash them properly, so instead of a beautiful cloud of löyly, you also get a big blast of asbestos cascading around the air.

    Imagine how many people he actually sold these rocks to.

    Honestly, it makes me shudder.

    Moral of the story – dirt is not the only problem. If you scavenge rocks, always wash them really carefully unless you are quarrying them yourself. You never know where they have been.

    Stay safe, saunafolk!

  3. Before reading this I had never thought about collecting my own rocks fearing that the rocks would crack or shatter, or, worse, that I could irreparably damage my sauna. Thank you for helping me get passed my fears!

  4. Jack Tsonis
    Thank you for that article. I was wondering what the difference between train track rocks, basalt and vulcanite rocks were = they are none.

    However, now I’m equally concerned as to how much that shoddy dealer has sold, that’s still waiting in storage somewhere when I buy it from a supplier.

  5. Hello, is there a lot of Olivine stone in Minnesota and other northern states? It is by far the best stone for smoke saunas.
    If you have a lot of it around let me know!

    A new portable smoke sauna (stove) is coming to Minnesota next year! (prototype is almost ready)

    It will bring happiness to all for those who enter in….

  6. Hi there
    I am based in Dublin and myself and my friends go sea swimming a lot. It has just started to get cold. In one of our sea swimming places we have discovered two abandoned fishermen huts. They are basically stacked rocks to shelter from the wind and rain.
    To get to them you have to do a bit of cross country walking and transporting materials is not that easy. they are about 4mtr x 6 mtr.
    We want to turn them into saunas what advice would you have.

  7. Gareth: My advice is to get it going. Unlike a canoe trip, you’ll only have to transport your materials in one direction, so remember that as your trudging it along.

  8. A roof. You always need a roof. And fuel, so a wood shed. Fuel nearby or it makes no sense. You can get by without a metal stove if you have a smoke hole, and so on. Rock walls will be hard to heat. Good luck!

  9. Glenn; Great info for new sauna user.
    We bought a house with a electric Finnish sauna. Seems to work fine but the rocks do not generate any steam when water is put on them with a ladle. The temp was 180 degrees.
    Are the rocks worn out? Can they be? Should I replace?
    It seems a pretty simple process to generate steam over the rocks…but mine are “dead”
    Also..the water falls onto the floor under the heater…is there suppose to be a water catch basin? or is the presumption that the water evaporates so fast that it is unnecessary?
    Any help appreciated. Thanks

    PS We live in AZ are of course have a very dry climate.

  10. Hi Katie: Well, it’s great that you have a Finnish sauna, and yet totally weird how your rocks aren’t producing steam. I have experienced electro saunas the ship with lava rocks (probably because they are light) but those kind of rocks are lame. I am a tad perplexed, however, how your hot room can get up to 180f but those rocks don’t emit any steam. A crazy thing.

    Yes, for sure, replace your rocks. I have really good sauna rocks i’m going to start selling, but don’t have them built yet on the shopping cart. If you want to email me, [email protected], I can help you out.

  11. Sounds like something wrong with Katie’s thermometer or thermostat. I’d bring in a different thermometer and see if it reads 180. My guess is that the room is not really 180F. Maybe the rocks are, though, and that explains no steam

  12. She may be confused by the term “steam”. Sauna loyly, as we know, does not produce steam like a steam room. On the upper bench in my sauna you feel the loyly but you don’t see it!

  13. I understand this article is regarding actual rocks to be placed in the heater..but what about stone on the walls of a sauna? I am thinking about using limestone for two of the walls of the sauna (5×5 sheets bust down to 84″ total height) and then the remainder of the walls and ceiling will be cedar. Any thoughts? I’m just wondering if the limestone can handle the heat up cool down + water, etc… thanks in advance!

  14. Dan:

    Stone walls in sauna offer a great attribute: lämpömassa. Yet the price for this is heat up time. (stone being a conductor of heat).

    So, there’s an optimal mix: not too much stone in our saunas, but enough, especially in the surround, for safety (distance to non combustibles) and heat retention.

    I’m not sure about limestone specifically as a material to hold up to heat. I’d suggest contacting a stone company, like kitchen counter guys. Please let us know how you make out. Walls behind a quality sauna stove can get to 280 – 300f.

  15. Tough to answer without seeing them, Carlos. Mainly you are looking for hard rocks with no fissures or cracks of any kind, as the article describes.

  16. Hi, I am building my sauna. I found second hand Helo heater, which suits the size of the sauna. However it holds about 30 pounds of rocks maximum. I am wondering if it would be worthwhile to add the wire net with more rocks and mount it on the wall above the heater? Thank you. Igor, Montreal.

  17. Hi Igor:

    You can add a wire mesh atop a stove that holds a small amount of rock, but it may be like trying to haul an Airstream trailer with a moped.

    Your heater oomph may not be powerful enough to be able to support the added rock density. And these additional rocks may never get hot enough to create “aaaaaaahhh” steam.

  18. Hello,
    I have a Finnish electric sauna heater with original stones that I have been using for 10 years. Seems to work ok – good steam & good temperature. The stones by now have a lot of mineral deposits on them from the hard water that we have here. Should I worry about that?

  19. Hello, I have purchased 3″-6″ rounded granite from my local landscaper. With granite, do I need to ‘season’ the rock by putting it in an open campfire to ensure there isn’t internal moisture that could cause a safety hazard during first use? I am thinking not, but worth an ask.

  20. Derek:

    I’ve used and continue to use lots of “rounded granite” for sauna stove application. This is the core essence of the revered Lake Superior rock that we sauna nuts in Minnesota aspire to – golf ball to softball size. Instead of seasoning the rock in an open campfire, i’d be thinking of adding them to your sauna stove and get it rocking for a couple few hours. Then, while wearing military gear and shields, douse some water on the rocks, with the hot room door open and ready to high tail it out of there if you here a “pop.”

    As this article details, the key with good sauna stones is very hard rock, and no fissures or cracks, as you know.

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