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Magnesium oxide board over foam basement subfloor?

rossn1 | Posted in General Questions on

Is anyone using MgO board over EPS/XPS for basement subfloors, to minimize thickness of the flooring, and manage moisture?

Looking at products like Tyroc ( and Basement System’s Thermal Dry Floor Decking ( got me thinking about MgO over the 1″ EPS+1/2″plywood”+1/2″plywood appraoch. This would allow me to get the subfloor down to 1″ to 1-1/4″ in thickness to minimize impact to stairs, transitions, door heights, etc while allowing better moisture tolerance, as well.

To me, it seems like a pretty viable option and as I’ve read, Magnesium Oxide Board is a relatively green material that can work fine in areas that are not high humidity.

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  1. GBA Editor
    Martin Holladay | | #1

    No, I haven't heard of anyone trying that. If I were you, I wouldn't buy magnesium oxide wallboard and simply put it on the floor. Instead, I would use magnesium oxide subflooring. Here is a link to one manufacturer:

  2. rossn1 | | #2

    Thanks, Martin. Yes, definitely would look for a product that the manufacturer rates for subfloor. See any conceptual issues with this?

    Does anyone having experience working with MgO board have a sense as to if cupping would be an issue and/or if it may be able to just be laid (offset) over the foam or possibly glued down? As I understand, I'd need stainless hardware if bolting down to the ground.

  3. mdubois | | #3

    I am the owner of MgO Design Build, Inc. And I have installed Tyroc subfloor in about 50 basement remodels.
    Warning Tyroc subfloor is failing. The product will cup. The Tyroc company will not honor their warranty.
    If anyone would like to start a discussion about this Tyroc failures please post.
    MgO Board has many manufactures from China. Most of which are junk!
    I use exclusively ExtremeGreen MgO. Best MgO product that out pro forms all other MgO boards. ExtremeGreen has spent Millions with research and development and stands by the products.
    Thank you for reading and I look forward to hearing your comments.

    1. mwmwall | | #4

      I am an end consumer. I installed Tyroc in a basement bedroom several years ago because they stated it is "impervious" to water. I purchased it from Matrix Basement Systems in Arlington Heights Il.. I recently got some water in my basement and the stuff cupped badly at every seam. Matrix would not honor the warranty because they no longer carry Tyroc. They also told me once it dried it would flatten out and they had never seen this problem. Uh Huh. Tyroc would not warranty it either because they have bankrupted and reorganized. Emails requesting assistance received no answer. Did get hold of a sales guy who laid the blame on a supplier - Matrix Basement Systems! Might as well have put fiberboard down. Would love to know what they mixed with the MgO if they used MgO at all. Sawdust? Cardboard? The sales guy claims the product is fixed but they still won't help me. Might be able to help with shipping costs from Indiana.

    2. TomS123 | | #5

      I installed Tyroc in my basement in may 2016. I have the same failure. Cupping and the glue connecting the panels to the rubber failed. Tyroc refuses to honor the warranty and I bought after they came out of bankruptcy. If anyone is interested in a class action suit I would be willing to find a lawyer.

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