I have a hole in my foundation that is letting a ton of water right into the crawlspace. I think it formed over several years from a gutter downspout that wasn't functioning properly (I plan on installing an underground downspout to fix the root of the problem).

The hole is about 2.5" wide, goes about 4" deep back into the wall, and is close to a foot tall (about 4" stick above the ground, and the rest down into the ground). Here are a few photos:

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How do I fix this? Can I just simply pour concrete to fill in the hole? If so, is there special kind of concrete I need to use? Any other considerations?

  • Appears to be a block (CMU, "Concrete Masonry Unit") foundation?
    – Ecnerwal
    Nov 8, 2021 at 15:07
  • @Ecnerwal - yes, I believe so! I took a photo of the inside here: snipboard.io/iJgjM0.jpg
    – jbyrd
    Nov 8, 2021 at 15:58
  • The cement looks very smooth at the back of that hole in second image. Almost like there was a cylindrical pipe in that hole at one time.
    – Willk
    Apr 8, 2022 at 0:11

3 Answers 3


Apparently the hole does not cause a strength problem . Concrete does not bond to old concrete, it mechanically interlocks ( with the right configurations). I would foam -in-place with urethane foam. It comes in a spray can and is often recommended for thermal insulation. It will expand to tightly fill any shape opening and sticks to everything, such as hands. It will resist water well and seal well.

  • Hmm...seems like a large area to use only urethane foam in; and plus I don't want the foam showing. What about something like a hydraulic cement, which expands as it hardens? (see washingtonpost.com/realestate/…)
    – jbyrd
    Nov 8, 2021 at 15:48
  • 1
    How well will the foam survive exposure to the elements? Wouldn't it need to be protected in some way? Especially since some of it would be in direct contact with the ground and would take physical abuse, too.
    – FreeMan
    Nov 8, 2021 at 16:12
  • 1
    A little soil could be put over the foam , UV turns it dark orange. but not a problem I had access to bulk foam liquid and made several lawn ornaments that lasted around about 10 years before mechanical damage destroyed them. It was sort of an accident ; I dug a two foot deep hole about 5 " in diameter . Mixed two liquids together and poured it into the hole . The foam came up out of the hole and made a big mushroom-like top. When hard , I pulled it out of the hole and had a 24" diameter by 30" tall mushroom . I did it to entertain kids and myself. Nov 8, 2021 at 23:09
  • Another concern with foam is that mice will chew right through it if that's a potential issue.
    – Mark
    Dec 8, 2021 at 20:42
  • "sticks to everything, such as hands." And clothes. Apr 8, 2022 at 4:48

Sounds like you get a fair amount of rain.

What year was your house built? A modern foundation would either have damp proofing or a dimple membrane applied to the outside of the foundation wall.

I'd dig the wall, wire brush the area, and parge at least the one defect area with mortar or dry pack. I'd then install some delta MS or other dimple board to waterproof and allow for hydrostatic pressure to drain to the perimeter drain (assume you have perimeter drain around your foundation).

  • It was built in the 1960's.
    – jbyrd
    Nov 8, 2021 at 21:58

For the wall thickness is around 4", I assume the wall is solid or fully grouted. The suggested repair procedure is as indicated below:

  1. Excavate and expose the entire hole.

  2. Thoroughly clean the surfaces of the exposed hole and remove any loose particles.

  3. Form the back of the hole. This is tricky if you do not have access to the crawlspace, or it is too low and too far for reach. In such a case, cutting a few strips of plywood, place tie wires through the predrilled holes, and then fasten the wires to the rod that is long enough to against the wall on the side of the concrete hole.

enter image description here

  1. Moist the concrete hole, apply a thin layer of cement mortar on the contact surface around the hole and fill the hole with low slump mortar or concrete. The mortar or concrete should be dry enough to be self-standing. A quick set type of cement (hydraulic cement) is recommended.

  2. Water cure for 7 days, or cover the surface with plastic sheeting immediately after finishing.

  3. After curing, fill the excavated hole with gravel and slope the ground surface away from the house.

  • The hole doesn't go all the way through - it goes into the wall 4" and then drops down - so the plywood backing wouldn't even be needed. But yes I was also thinking hydraulic cement, but hadn't thought of applying a thin layer of cement mortar first.
    – jbyrd
    Nov 9, 2021 at 14:41

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