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I have a couple of concrete holes in my basement I'd like to patch. One is a hole in the slab right in the corner that's about an inch deep, and about 1x4" in area:

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The other is about a foot from the wall, and about a foot long, 6" wide, and between 1/2" and 2" deep:

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The latter is an area of concrete that I had noticed was kind of "mushy" when I walked on it, and after poking at it with a pry bar, I found I could easy break it away in crumbly chunks, until I hit solid concrete around the perimeter. I don't know how this one happened, but maybe it's an old patch that was poorly done and broke down.

I'm wondering what the correct patch type is for these holes. The first hole actually actively seeped water slowly for a day or two during an unusually intense spring thaw, but otherwise neither actively seeps water, even during extended periods of heavy rain. They're just damp to the touch.

From my research, it seems like the two standard products would be either a vinyl concrete patch product, maybe with concrete bonding agent, or hydraulic cement. I'm leaning towards the hydraulic cement since it's designed to seal against water. However, every usage scenario description I've seen, including this previous question, seems to involve current active water ingress. If neither of these holes is actively leaking water, and are just slightly damp to the touch, is hydraulic cement the wrong product?

In case it's relevant, the foundation is about 90 years old poured concrete. I think the slab is much newer but I would still guess it's over 40 years old. Both are showing their age but not failed. I had them inspected recently by well-rated local foundation expert who didn't think they needed any major work at this time. Both holes have what I think are salt crystals from street salt. I live in the core of a city where there is very heavy street salting during the winter. I assume the ground water becomes salinated during the spring thaw, and leaves crystals behind as it evaporates.

Thanks.

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    With them being damp, and at least once seep water, I would go with the hydraulic. Imagine the small hole has micro fractures letting water in.
    – crip659
    Aug 22, 2022 at 23:32

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Hydrualic cement is perfectly fine to use for both, and can certainly be used (far more easily) without an active leak - just make sure the concrete is damp.

If you'd like to improve the odds for the patch, also make sure it's clean, (remove salt, for certain, also grease, also any soap residue from getting the grease, rinse well, multiple times) and ideally undercut the edges (so the bottom of the hole is slightly bigger than the top) rather than having the edges be thin bits that taper off to nothing - concrete patching is not drywall patching. Your hydraulic cement instructions probably even have a nice picture of properly undercut edges.

Yes, remove more material before patching so your patch might actually work - an edge with some thickness that is physically keyed in is much less likely to crumble than a very thin edge just laid on top.

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  • diy.stackexchange.com/a/37634/18078
    – Ecnerwal
    Aug 23, 2022 at 3:03
  • He might even consider renting an electric jackhammer to remove the material easier and get more depth.+
    – JACK
    Aug 23, 2022 at 12:54
  • Thanks for the advice. Any thoughts on whether Hydraulic cement results are improved at all by priming the repair area with concrete bonding agent? Or should it be used standalone?
    – SSilk
    Aug 23, 2022 at 17:01

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