Is there a better way to seal our sauna floor?

I’ve done it every which way ’til Tuesday. Rubber mats, Red Guard, etc. etc.

But I like this method the best. The three “F’s” of skim coating:

FRUGAL: $50 all in. Durarock is relatively inexpensive, easy to cut and lay down. $8.00 – $9.00 for a 3’x5′ sheet. A bag of vinyl cement is well under $20.00.

FORGIVING: Well mixed vinyl cement is easy to trowel and works its way into cracks and mistakes like nobody’s business.

FAST: All this takes about 20 minutes (and is actually kind of fun!).

Here’s how we prep our cement:

Here’s how we prep our floor:

Here’s how we lay it down:

Here it is “Finnished.”

This has worked great for me for about 10 sauna builds. My cabin sauna is 23 years old. I found a crack in my floor and simply mixed up a little vinyl cement English milkshake consistency, poured it on, and filled the crack. And that was 7 years (and 348 saunas) ago.

Once skim coated, our floor is ready for duckboards or a suspended wood step.

All good on this Western front.

If there’s a better way to Finnish off our hot room and changing room floors, i’d like to know about it!

Stepping inside Michael’s German backyard sauna

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23 thoughts on “Is there a better way to seal our sauna floor?”

  1. Love the idea!
    I’m curious if you use water in your sauna or is it electric? Wondering how this would hold up to water being on it.

  2. I use a lot of water in both my sauna hot rooms that each have this floor solution. I’m a big fan of how it seals off and makes waterproof.

  3. Hello Glenn,
    The skim job looks great! Easy too. I have 2 questions post reading your ebook a few times now.
    1. My build is coming along and I was just introduced to Extreme Green sheeting. It’s a magnesium oxide board that works like dura rock but is smooth , I bought all the needed 4×8 sheets, did the trever square tapered sleeper s and am perplexed on how to seal it. Sorta new product with not much inside tips yet. Question is do you think The vinyl crete coat seal job above mentioned will work on the Mag/oxide board.
    2. Bigger question is My Kuuma stove is on the way, it has an 8″ throat which will be fed from changing room, I already built pedestal in hot room for stove being in the corner (with heat shields) and it will be 11″ off the wood framed wall, with 2 layers of the extreme green board (1″ air gap between) for a final distance off finished wall of 7-9″ per Kuumas’ details. Problem is the through wall for throat which is now wood, soon to be metal studs with Extreme green (fire proof) on both sides and throat hole of 18.25″ wide. Im told we need 16″ non combustible around throat but all other dimensions including pad were built around the closer numbers. Is there a creative solution to not have to eat up more hot room floor by moving the stove away from side wall. As it is I can easily get 11″ inch offset from wood wall but the 16″ is gonna make for a bunch of tear out and redo and worse than all it will eat up hot room bench space. Sorry for the mouthful, hoping you have a creative solution. Thanks!

  4. Timothy:

    1. i’m not familiar with extreme green. I’d say test out a remnant piece with the skim coat. i’m an old dog with the durarock, and just love how it sucks up the vinyl cement, so hopefully you’ll have same results with your product.

    2. I hear you on the rip up, but I want to say, it’s ok to go one step forward and one back and then another forward in another direction. it happens all the time with everything and may as well happen with our sauna builds. You are needing to have clearances to non combustibles big time if you’re going to go with the outside feed/throat extension. It’s critical you do it right. And you’re going to feel tons better when you get your stove rocking and you can whisper ‘lampomassa’ three times as you toss water on the rocks.

  5. Greetings, Glenn. I hope you and yours are enjoying a wonderful sauna season. I have a question about the floor method you describe above, using the combination of concrete board and the vinyl cement patch product. Just to be sure–Does this create a final surface that is waterproof? Lastly, does water “bead up” on this floor surface and if does not, then is the water soaking into the flooring below? Or should it be treated with a concrete sealer product?
    Many thanks for all you do for the world’s sauna traditions!

  6. Hi Dustin:

    When mixed and applied properly, the vinyl cement is waterproof. The trick is to trowel it along the face of durarock that is sloped to the drain.

    You’re welcome! Keeping the tradition alive.

  7. Glenn,

    I am considering going up the sides of my hot room 6-12 inches of cement board and sloping the floor from that and bypassing the drip edge. I would then skim coat after that. Is this reasonable?

  8. Hi Glenn:

    Totally reasonable to run your cement board up the wall a bit. One thought is to skim coat your cement board before screwing to your wall, keeping gravity on your side.

    You can always use more vinyl cement or sealant as a second coat or patch job after it’s applied to the walls. I’ve done this several times and it works great. Even a car wash sponge to rub on the cement, then trowel after for that smooth clean finish.

  9. Hi there, am considering a sauna build, I have a 6×7 shed built on a concrete slab that I hope to use. This shed is rotting out and I will have to replace some siding and the treated wood sill plates at the bottom. This is in large part due to the slab—water runs under the shed, the wood soaks it up etc. From what I can tell unless I jack the shed up on bricks or something there is no way around the issue.

    My question is—is a drain and sealed floor necessary if water is going to come and go under the sill plates regardless? I’ve thought about grading the floor towards a corner and drilling a hole through to the gravel pad. My worry is if I seal the floor water will get trapped under the sill plate anyway. I’ve read that caulking/sealing along the sill plate is worth a try but I figure water will still end up getting through. Would love to hear your thoughts!

  10. Here’s a crazy thought. Maybe jack up the building and replace the sill plate/bottom plate with a double green 2x with gaps along the perimeter. Fill the gaps with good wire to keep rodents out, and you’ve created a breathable hot room. “That which blocks our path creates a new path?”

    This may not be your answer, Andy, but it may help bring you to the answer.

  11. That is a great idea and similar to one of the solutions I was thinking of. Perhaps I am confused—is a ‘green’ a #2 PRIME PRESSURE TREATED WEATHERSHIELD per the item list? Thank you for feedback!

  12. Garth: Yes, exactly. Seal everything on the floor up to the drip edge. This has worked great for me. The floor of my cabin sauna has held up for 24 years now and counting (and with heavy use) as well as my backyard sauna, 17 yrs now and also counting, with also heavy use.

  13. I have been working on my sauna for the last two years. It’s in the corner of our 32′ x 40′ steel shed just outside Pella, WI. Used white cedar from blow-downs harvested in our cedar swamp. 880 board feet sawn for just $80 locally; then milled/ T&G for $237. What a bargain! I’ve used Glenn’s E-book all through the process. I used stringers on my sauna floor in a pattern starting with 3/4″ against the wall down to 1/16″ at the drain. Nailed and glued. Then dura rock with vinyl cement patch. After that dried, I bought a Rust-Oleum epoxy product at Menards ( a little pricey, but not too bad) with copper-metallic color and anti-slip additives. It is spectacular! And…….even more waterproof than just vinyl cement patch. Not sure how or if I can post pictures with this comment. If someone knows how…..I’d appreciate the help.

  14. Hi Glenn,
    Just finished roofing the sauna “shed” building, and moving inside to the sauna part. Finally starting to get real!

    A question about how much Quikcrete Vinyl Cement I need. In these pandemic times of intense building supply demand, I can’t find a 40 lb bag of that product Quikcrete nearby (there is one about 60 miles away at a hardware store) . There are 10 lb pails of it available locally (or course, much more expensive)
    My sauna hot room floor is about about 47 square feet. I am planning on using your Durock/Quikcrete /sleeper/skim coat method of creating the hot room floor.
    I’m guessing I’ll be moving on to that phase of construction in a week or so, but trying to access my materials now. I’ve got the Durock/wafer screws and 2X for sleepers no problem.

    Can you give me a guesstimate on how much Quikcrete mix I”ll need for this if possible?

  15. Hi Maureen,

    I’ve done this project more than a dozen times, so my guesstimate for you should be close. For a 6×8 hot room, 48 sf., i’d be using about 3/4 of a 40# bag. Vinyl Cement Repair. It may be called something else in your neighborhood, but this is what you want.

    Please take note of how it is detailed in Sauna Build Start to FinnishSauna Build Ebook, which includes some critical instructions including:
    1. Sponge wet your cement board.
    2. Mix well, like an English milkshake. (I like the double bucket back and forth method, as the good stuff will want to settle to the bottom).
    3. Work into the corners, and along your drip edge, and trowel with the cement board as your guide.

    Hope this helps,

  16. Thanks for the quick reply, Glenn! I managed to get two pails of Quikrete Vinyl Cement repair, totalling 40 lbs. Next step is electrical and insulation, but after that’s completed, its on to the hot room floor. In good sauna building tradition, have just finished closing in the shed exterior today, and the fine weather has ended today. Looking forward to having first sauna around…..mid December….hopefully!

  17. Maureen:

    That’s so great! I can totally relate. As I think about it, I’ve undertaken most all of my many sauna builds during this same fall time of year. In the spirit of good sauna building tradition, it’s such a warm feeling to have the building completed, then the weather outside can become frightful, as we focus on the interior.

    I particularly like how after insulation and foil vapor barrier, our saunas can actually be warmed by a light bulb. Precursor of great things to come.

  18. Is there a concern when nailing your T&G cedar that the holes in the vapor barrier behind the boards will allow moisture into the walls?

  19. Brett,

    I know, right?

    Moisture is lazy. It’s like a teenage son getting ready for school. But given the right motivation, it’s out the door fast. What this means is that opening the door from a steamy hot room to a cold dry winter’s night, woosh, moisture movement like crazy.

    Yet tiny pin holes leading straight into wall joists..well, there’s really no way, and nowhere to go. Moisture will only permeate if there’s an easy path. And there’s no path. Moisture doesn’t much get behind our paneling. And the little that does can’t get through tiny nail piercing. If moisture could travel through the nail piercings, it can’t go anywhere as foil is sandwiched tightly to wall joists.

    So, that’s how I sleep at night. Teenage son dashing out the door, but not sneaking around.

    That said, there is the sauna design concept of insulation -> foil -> firing strips (air gap) -> t&g. This method gets away from foil nail piercings. There’s a lot of argument pro and con air gap, more questioning if foil is doing its job without an air gap than nail piercings. And all this is valid and comes at the minor expense of a tad smaller hot room, and how to deal with “cleats” or supports for our benches.

  20. Hi Glenn,

    This seems to be a rather successful method, but I am still wary of using it in the sauna that I’m building because I have a shower and spigot plumbed into my steam room. Is the amount of water this method can handle enough to run a shower onto?

    If I can use it, with some board running up the walls, do I tuck my foil vapor barrier over the top of the backer board to allow for smooth water flow, or do I install the backer over the barrier which runs to the floor.

    I have loved reading your humorous posts as I give life to my first sauna.


  21. Jonah:

    Glad saunatimes is working for you.

    Regarding considering your situation, I think it a good idea to think like water. And think like a contractor building a shower. In this case, contractors install a “pan” and “red guard” the floor. It’s a bigger hammer than the skim coat cement board method, and may be the right step up for your situation, where a shit ton of water is going to flow, with a shower in your hot room.

    Also, generally, foil wants to be behind everything, interior wise, but on top of your studs. Kind of like lettuce to your sandwich. This is the kind of thermal moisture break we’re looking for.

    Good luck on your project, Jonah! We’re with you in steam and spirit.

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