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Community and Q&A

Damaged earthen floor — repair or replace?

RVcP5sgoYe | Posted in Green Building Techniques on

Hello all-
I had an earthen floor installed in the cellar during a renovation/rehab of a multi-family townhouse. The major components of the earth floor (substrate, vapor barrier, tamped earth, etc.) were completed many months ago but the tamped earth was not sealed and finished.

The cellar has since been used as a staging site and work shop for much of the other work in the building, including some very wet work. The floor surface is now simply hard-packed dirt, at best–dusty, not entirely level and cracking. The floor in the boiler room is in particularly rough shape after major leaks during installation of the boiler and the sprinkler pipes and standpipe that are required by code.

We have invested in the earthen floor and would like to save it if it’s practical. My question is: What is the best way to finish a floor in this condition to ensure that we end up with a functional and durable (and hopefully rat-proof) cellar floor?

Our original contractor proposes to lay a thin layer of concrete over the tamped earth, as the “greenest” solution. Another contractor has suggested the floor won’t be durable unless the earth floor is dug out and prepared for a regular concrete pour. No one has suggested properly finishing and sealing the earthen floor as we originally intended, so I’m wondering if it’s still possible? Any thoughts on how to approach this would be appreciated!!

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  1. GBA Editor
    Martin Holladay | | #1

    I know that some homeowners are happy with above-grade earth floors, although the only one I have seen was in the home of a woman who decided she hated it, and was in the process of replacing it with a wood floor.

    In the Third World, families abandon earth floors as soon as the family makes enough money to afford concrete or tile.

    I have never heard of anyone installing a below-grade earth floor -- except for run-of-the-mill old crawlspaces and cellars that simply never had a floor in the first place. I can't imagine that such a floor is good for anything but a root cellar designed to store vegetables or wine.

    The contractor is right: it's time to pour a concrete slab. Especially if you have rats.

  2. RVcP5sgoYe | | #2

    Ugh-not exactly what I was hoping to hear but not totally unexpected.

    The contractor assured us that the earthen floor would be durable for normal cellar wear-and-tear and would be at least as rat-proof as the 2-3" "rat-slab" that is typically used in Manhattan to keep vermin from burrowing into cellars, courtyards and alleys. Maybe if it had been oil sealed?

    Nevertheless, if we forgo the earthen floor, as seems likely, will a thin layer of concrete over the existing hard earth do the trick--form a solid, durable, functional cellar floor? (This is the suggestion of the contractor who recommended the earthen floor.)

  3. GBA Editor
    Martin Holladay | | #3

    I think that if you are going to install a slab, you should go ahead and do it right. It should be 3 or 4 inches thick.

    Unless you live in a warm climate, you should be sure to install at least 2 inches of rigid foam insulation under the slab -- after all, it's hard to retrofit the insulation later -- with a layer of polyethylene between the foam and the concrete.

  4. RVcP5sgoYe | | #4

    Thanks for your advice, Martin. Do you recommend insulation for temperature control or moisture control or both?

    This is a 100+ year-old rowhouse in Manhattan where the ground temps are pretty moderate. The cellar is fully below grade, long and narrow, with the long ends sandwiched between the adjoining houses. (Only the 18' wide front and back ends of the house are exposed. The house is newly renovated to passive house standards. It doesn't meet the standards but the envelope is still very tight and we don't need much heat. Even on the coldest days this winter the cellar temp has been moderate, even though it's outside the insulation envelope. Given all this, I'm more worried about damp and mildew than temperature.

  5. GBA Editor
    Martin Holladay | | #5

    If the cellar is outside of the home's thermal envelope, then there is less reason to insulate the floor. However, an insulated slab will be warmer and less likely to be damp, since moisture won't condense on it. Whether the insulation is worth it depends on whether the cellar will ever be put to a different use.

  6. RVcP5sgoYe | | #6

    Very clear and helpful--thanks! It's unlikely we'll ever use the cellar for anything other than utilities and storage, so we'll take that into consideration.

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