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Do I need a sacrificial parge if I spray foam a rubble/brick foundation?

ranson | Posted in General Questions on

In one paper, Lstiburek, says that you should have an external sacrificial parge if you reduce internal drying of an old masonry foundation.

https://www.buildingscience.com/documents/insights/bsi-011-capillarity-small-sacrifices

In another paper, Lstiburek suggests that spray foaming field stone basements is essentially the best thing since sliced bread, but makes no mention of needing an exterior sacrificial parge.

https://www.buildingscience.com/documents/insights/bsi-041-rubble-foundations

I want to spray foam my foundation. I can’t do a sacrificial parge for appearance reasons. The building is 200 years old, and I don’t want to compromise its structure.  Am I inviting structural trouble if I spray foam and can’t parge the exterior? Is there any real data on the long term consequences?

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Replies

  1. Expert Member
    NICK KEENAN | | #1

    Brick is slightly porous, if it absorbs water and freezes it can crack. The stone typically used in foundations isn't porous and doesn't have this problem. Reading the Lstiburek article it sounds like just pointing the brick with a soft mortar affords protection, parging just provides more durable protection. He says the mortar has to be replaced "3 or 4 times a century" but that sounds like a lot unless you've got quite a bit of water. But the mortar has to be softer than the brick.

    Stone also tends to be harder than the hardest mortars so you don't have to worry about hardness with it.

  2. ranson | | #2

    I just found these papers, which are kind of great. I'm not sure if they'll directly address the issue, but they're really informative.

    https://www.nrel.gov/docs/fy12osti/54163.pdf
    https://www.nrel.gov/docs/fy12osti/54208.pdf

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