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Is there a better way to seal our sauna floor?

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

  1. Hey Glen! Hope your well man!

    I just poured a cement on top of a water proofing membrane on a subfloor part of a shed making into a sauna. First time doing that and didn’t cure it properly.

    Have some cement dusting now on the surface.
    Still planning on putting a waterproofing sealer on top, maybe that will help a bit

    But wondering if someday doing an acrylic skim coat over top with help with the issue

  2. If I were to apply a skim coat overtop of existing poor cement would I need to apply a bonding agent, or would wetting and applying skim coat be sufficient

  3. If i do put on the vinyl skim coat over poor cement floor, does it require the use of a bonding layer? or can it be applied after wetting the cement

  4. So I’m thinking of putting a sauna in my unfinished basement……Torn as to whether do the drain or not. If I do, I’d have to (presumably) build up the floor several inches, wherease putting it directly on the existing floor would save a lot of work. Interested in your thoughts. I do have your eBook by the way

  5. Thomas…

    I hear you on the corundum. A fellow thermal basement enthusiast is considering this gig. I think it could be a great work around! Lemme know if you advance in this direction:

    email exerpt:
    On Tue, Mar 21, 2023 at 1:50 PM Reed Alt wrote:
    Greetings Glenn, such a treat to talk to you about saunas today. thank you for your advice on sauna stoves and venting, i really appreciate it!!

    here is a link to a “Smart” water transfer pump which usually works in a marine setting. i am considering it as a no dig method for basement sauna. i could see it helpful foe those trying to keep their floor build as low profile as possible while adding a plumbing solution. I believe this company has several solutions Cheers!!

    and here is a video explaining how thr system works,vid:dP2HUh3fAtw

    Happy Saunaing!


  6. Curious about the vinyl component in the self leveling compound. My instinct is to avoid any vinyl in a sauna because of carcinogenic properties.would cement be more inert than sheet vinyl? Got a bid for building wood fired sauna in existing shed on blocks, with suggested flooring to be vinyl G-floor over existing plywood, brick hearth over that. Understanding that the floor is not the hottest place, and the hearth is, the need for waterproofing and fire safety, and not having a drain, it seems like tile, cement, vinyl, rubber (?) might be options? Can anyone comment on the health and safety concerns around vinyl in sauna? Any suggestions? Thanks!

  7. Hi Kathleen:

    I get you. I sleep better at night knowing that vinyl cement has a cedar duck board over it. So, that material doesn’t get hot. For me, it’s the right balancing act as it goes on like standard cement but has a bit of flexibility to it. So it seals really well.

  8. Hello,

    I’m building a 5×7 sauna in a corner of my 20×10 shed. My problem is that the current floor is untreated wood. Really perplexed as to what I should do for flooring of upcoming sauna. Should I lay down a vinyl mat, then frame on top of that? That seems very simple and easy? Caulk all around the framing of the floor. Or this durarock and skim coating? I’ve never built with durarock. Please help! What would you do in this scenario of an untreated wood floor currently.

  9. Hi John, in your situation i would do the ben square trevor trowel, sleeper, skim coat vinyl gig. I know how to do this and it works great.

    But if this is too much, or overkill, well, then i’d look to get a material like redguard and paint your untreated wood floor and call it good. I don’t like this choice as I am a big fan of a drain. But there is no right or wrong here. Hope this helps!

  10. Please type these words in the search bar above: ‘ben square” is a way to run sleepers (wood of different widths) and Trevor is a guy who troweled between the sleepers.. search bar above will help more with this.

  11. Hey Glenn- First off, your book has been a guiding light for me over the last three moths as I have been deep in my sauna build here in Washington state. So, thank you for that! I have completed the floor via the Ben Square/trowel/durock/skim coat method. Overall I’m really happy with it. The one hangup I’m experiencing is as the skimcoat cures, the portions overlying some of the concrete board screws are cracking and flaking off, exposing the screw heads (which are flush with or recessed into the concrete board, I made sure of that!). Have you experienced this problem at all? If so, any thoughts on how to get the the skimcoat to play nice?

  12. Hi Ryan,

    There are a few reasons why the vinyl cement skim coat may have not “played nice” around the screw heads. As you experienced, the slurry vinyl cement adheres great to the cement board. Kind of like peanut butter on the roof of your mouth. But yes, it doesn’t grab as well where the screws are. I’ve experienced this also. I’d wire brush where it’s not holding up, and the screws will be less shiny and then mix up a cupful of vinyl cement and pour it around, and use something like a credit card to help the wet vinyl cement smooth out over the first coat you laid down.

    Good on you Ryan! and Glad my ebook has helped you along.

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