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Community and Q&A

Gypsum floor

LEWHART | Posted in General Questions on

I purchased an old lake cottage (Wisconsin) that has been “added” onto over the years. I will be converting the attached garage to living space. Part of the home has a crawl space with wood joists, other parts on cement slab. Gutting out and redesigning entire home. Intend to have Gypsum floor poured to level all out. Mostly 3/4″ thick but garage area space will require about 4″. On humid days I have sweating on some of the concrete slab floors though not in garage. So I suspect improper or non existent vapor barriers. Thinking I will put down 3/4″ Rigid foam and a 6ml vapor barrier before having them do the Gypsum. Is that the right approach or better options? Will vapor barrier between the concrete and Gypsum likely solve the moisture problem?  In the garage area I could do 2″ rigid if that is better. I also am considering putting in electric concrete slab floor heat in a couple of rooms, not intended for room heating but just to warm up the floor area some. Seems like a good time to do that though not sure if benefits justify costs. (Can not afford to do actual hydronic heat). Thank you in advance for any info!!

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  1. Expert Member
    BILL WICHERS | | #1

    Some water heaters are rated to be used with small heating systems. If you use one of those, all you need is a small circulation pump and thermostat to control it. You can use PEX in the floor for the radiant heat system. You may find the costs to be comparable to an electric system if you’re careful. Something to think about.


  2. Expert Member
    AKOS TOTH | | #2

    I would price out the gypsum, when I looked at it, it was more expensive than concrete as it is mostly used for larger projects. I would also check if you can pour the gypsum over rigid insulation.

    You can probably get away with doing the rough fill in the low spots with concrete and a bit of self leveling afterwards where it would be too thin for regular mix. You can install then rigid and plywood over it.

    Electric heat mats are cheap enough that I would not hesitate to install it. For a couple of low load areas, the running cost is low enough that the extra cost of even simple hydronic is not worth it.

    1. LEWHART | | #3

      Thanks for the reply! I decided on gypsum so that I could add vapor barrier thinking it may eliminate my moisture problem as well as leveling out floor. I will be re-framing doorways so the additional height is not a problem within reason. That's why thinking of using only 3/4" rigid insulation and 3/4" gypsum. Hopefully someone can give their opinion of the effectiveness of this approach in regards to the moisture. Appreciate your feedback!

      1. Expert Member
        AKOS TOTH | | #4

        I'm not familiar enough to comment on gypsum flooring for basement, when I looked at it it was for above grade. I know gypsum doesn't stand up well to continuous water exposure, so as long as that is dealt with under the floor, it should work. Sweating of the concrete would go away once the VB+foam is installed, nothing to do with the gypsum.

        With foam, you might still need a layer of plywood under/over the gypsum, I would check with the manufacturer.

        Wisconsin is cold enough that more foam won't hurt, since you are already doing the work going up to 1.5"-2" is worth it.

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