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Community and Q&A

Does an underground CMU stem wall need to be dampproofed?

Timothy Godshall | Posted in Energy Efficiency and Durability on

I am building a house in Harrisonburg, Virginia, with a suspended front porch concrete slab. One side of the slab rests on a 4″ ledge cast into the poured concrete house stem wall. The other side rests on an 8″ CMU wall that extends down about 10 feet to undisturbed soil. I am planning on back-filling soil most of the way on both sides of the CMU wall.

Do I need to do any damp- or water-proofing of the CMU wall for structural reasons? I read another thread on GBA talking about how water and salt will gradually eat away concrete. Will a subterranean CMU wall gradually disintegrate if not properly sealed? If so, what is the best way to handle this situation?

Here’s the blog post I read on efflorescence:

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  1. GBA Editor
    Martin Holladay | | #1

    I don't think there are any structural reasons for dampproofing. Nor is there any reason to worry about efflorescence. Typically, the above-grade portion of this foundation would be coated with stucco (cement-based plaster), at least on the exterior side, for aesthetic reasons.

  2. Timothy Godshall | | #2

    Thanks for the reassurance, Martin. We're planning to put brick on the outside for the aesthetic part.

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