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Community and Q&A

Air seal and insulation for 100-year-old fieldstone foundation

woobagoobaa | Posted in Energy Efficiency and Durability on


I’ve got a 100 yr old two story gambrel in Eastern MA w/ basement.  Field stone foundation in generally good shape, needs some re-point, 8 foot basement ceiling height over what I assume is a rat slab.  About 1′ of field stone is above grade all the way around the perimeter.

There is occasional minor water intrusion which I hope will be remedied with changes / fixes to the gutter system.  But basement is generally very humid in the summer.

I have read quite a bit of BSC etc. information and toured recently renovated similar houses looking at how the field stone was handled.

Why question.  I am often seeing these fieldstone foundations sprayed with closed cell foam.  Does this cause issues with water trapped in the field stone?  Frost heaving (frost line is 4′ in these parts)?  It also seems problematic when the fieldstone requires re-pointing?  Masking perimeter drainage issues?

Thanks for your advice.

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  1. Expert Member
    Akos | | #1

    cc SPF is the best way to deal with these older houses. It is very common in my area as well. Provided you deal with the water on the outside, there are no issues. If your walls are smooth you can also look at rigid foam, much cheaper than SPF.

    Mortar joints fails by having water move through it. The spf keeps moisture from migrating protecting the mortar, tuckpointing should pretty much last forever underneath.

  2. twoodson | | #2

    Piggybacking on this question as I have the same need. Is there any concern about hydrostatic pressure pushing the foam off of the stone? I don’t have water issues today.

    My belt and suspenders plan has bed the below, but I’d love to lower my cost as this isn’t a particularly usable space at 6 foot 10 ceilings.

    Repoint with type n on the interior.
    Attach dimple board to below grade portion.
    2 inches cc spf.

    1. GBA Editor
      Brian Pontolilo | | #3

      Hi Tom.

      As Akos said above, closed cell spray foam is commonly used successfully in this application, providing there are no existing water issues. If there are water issues, they must be fixed first, from the exterior.

      If you want extra insurance, you could install a dimple matt to alleviate hydrostatic pressure, but I can't see how that would help lower your cost, when you'll need to excavate the foundation to install the matt and the products themselves are expensive.

  3. woobagoobaa | | #4

    The permanence of the CC SPF directly over the rough fieldstone gives me great pause re: future access for repair, leak identification, etc.

    Tom may have been talking about dimple mat (Delta-Dry etc. ) on the inside of the foundation wall (between the fieldstone and CC SPF) to allow drainage to an interior perimeter drain.

    1. richmass62 | | #5

      I didn't use CC spray foam on the foundation wall, I ended up using it on the basement ceiling and kept the basement unconditioned. To address the wall we did a french drain to daylight (no pump needed at my location) and we applied Thoroughseal which is a masonry product to the inside. Also a lot of repointing of the wall on the interior and exterior. Not the whole thing but just the wet side of the house on the interior (efflourescence caused decay) and the exterior portions that were on the dry side but exposed to more wind and cold.

  4. nynick | | #6

    I have a relevant question. In my old house, we have both a fieldstone foundation in part of it and poured concrete in part of it as well. The concrete foundation is old and has "spalling", where chips and dust fall off. The basement overall is dry as a bone.

    I had planned on CC SPF the whole thing to condition the basement, but the CC SPF quote for the house is very expensive. Would it be advisable /ok to use solid Poly Iso or similar Foam Board insulation on the inside of the concrete foundation and then CC SPF on the fieldstone? I'm guessing this would save me a bunch of money.

    I was thinking the CC SPF would "secure" the concrete better to stop the spalling, but the price of that stuff is very high. What do you guys think?



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