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My basement floor has a hole cut where the water line enters the house. This hole is around 2ft square, and digging down a little I hit dirt and small roots. I'd like to seal this hole as I believe it provides an entry point for insects.

Basement Hole

In the picture above, you can see the water line coming in and leading to the meter. The tubing along the wall on the left is electric conduit, grounding the service panel. Note that the horizontal part of the water pipe is actually below the level of the nearby concrete floor, so a new floor in this area would have to be lower than the rest of the basement floor because I don't want to encase the pipe and valve in concrete.

What's the best way to fill in that hole? A few specific concerns:

  • Do I need to lay down a layer of gravel or something above the dirt?
  • Would the new concrete need to be tied into the existing floor somehow?
  • Is there a minimum clearance around the pipe that I should preserve?
  • Are there any structural concerns digging or pouring concrete here? The foundation is fieldstone parged with mortar.

The house was built in 1892 and I suspect this hole was cut when the water line was changed from lead to copper.

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3 Answers 3

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Let's not over complicate this little project. I have seen these open sump holes hundreds of times. I am absolutely sure there are no structural issues here, how long has the house stood without concrete in the hole? There was probably not a concrete floor when it was built and for many years after. If you want to simply keep stuff out and hide the dirt then let's do it simple. Dig out to about a total of 4 inches below your water pipe and valve. Mix up a small bag of Sacrete concrete mix and fill the hole to about 1 inch under the pipe. Float it smooth, you're done. There is no need to get carried away with a special base etc. The size and weight of the concrete patch is negligible as far as settling or shrinking is concerned. Get the stuff and be done with it in an hour!

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Below is based on what I would do in the UK.

Q. Do I need to lay down a layer of gravel or something above the dirt?

  • Excavate 13inches (325mm) below the finish level of the concrete patch you're putting in.

  • Compact 6inches (125mm) of sub-base (crushed rock) into the bottom of the excavation.

  • Spread a 1inch (25mm) thick layer of soft building sand on top of the sub-base. Compact and level.

  • Cut a piece of "Visqueen" Damp Proof Membrane (1200 gauge / 300mu) 6inches (150mm) bigger all around than the size of the hole.

  • Lay the Damp Proof Membrane on top of the building sand and turn up the edges (3inches / 75mm), against the sides of the existing concrete.

  • On top of the Damp Proof Membrane pour a 6inch (150mm) thick concrete slab. If I had a little bit of ¼inch or ⅜inch (6mm or 8mm) re-bar fabric (mesh) handy I would place it in the middle of the concrete. Though in your particular situation it really isn't needed.

Q. Would the new concrete need to be tied into the existing floor somehow?

No, see my above points. Plus, the slab isn't really a structural slab. Yes, it's a ground bearing slab, but in a domestic situation, therefore load really is too much of a concern, especially in your particular situation. Therefore there really is no need to tie-in the new concrete patch with the existing.

Q. Is there a minimum clearance around the pipe that I should preserve?

Apart from a practical point of view, I have nothing else to base the following on: I would leave a minimum clearance of 2inches (50mm), a little more if it proves practical.

Q. Are there any structural concerns digging or pouring concrete here? The foundation is fieldstone parged with mortar.

No, see my above points. Plus, you really aren't putting any load on the existing foundation in your particular case.

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Thank you for the thorough answer. At first glance, though, this seems like overkill. The rest of the basement floor has no membrane between earth and concrete, and apparently no gravel (at least in this section where the concrete layer has been cut away. I'd like to do it right but I don't know if it's worth the effort to have 2 or 3 sqft of perfectly installed concrete in a single non-structural spot in a basement. I'm no expert, though, so I'm curious what other people suggest. –  Shimon Rura Jul 29 '11 at 0:04
    
@Shimon Rura, if there definitely is no membrane under the existing slab (& rising moisture hasn't been a problem) then you could leave that out, along with the 1inch (25mm) thick building sand layer (which is only there to prevent the membrane from being punctured by the sub-base). I personally would still go with the sub-base material... –  Mike Perry Jul 29 '11 at 0:41
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Personaly, I would just make a wood cap over the hole so it can be removed and replaced at will. Paint it the same color as the concrete.

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