I removed a shower stall and there was a hole for the plumbing as expected but once I got a good look the entire area below the cement slab is open. I want to fill the whole as the bathroom is being converted into a mud room. I was assuming I would just have to get a bag or two of gravel and/or sand and fill the hole and then add 3-4" of concrete but since everything is open underneath I am not sure how to fill the hole now. Seems weird it is all open underneath. Any tips would be appreciated.

Hole where shower was. enter image description here

Picture underneath showing some more pipes. enter image description here

Another look at another direction. enter image description here

  • Not an expert on this, but it doesn't look like it's supposed to be open down there. It looks like the concrete was poured onto ground and the ground has since sunk or washed away from underneath it. What is supporting the slab now?
    – Egg
    Dec 30, 2018 at 15:02
  • It seems like it is a slab with iron support in it and it is resting on the edge of foundation. Not sure where it would have washed to and doesn't look wet at all like something consistently leaked. I am located in MN is that matters for any reason.
    – Chris
    Dec 30, 2018 at 16:06

1 Answer 1


Note the soil on top of the pipes. You should have this looked at by a good remodeling general contractor or structural engineer. Residential slabs do not generally span those distances even with rebar.

Filling with sand may be the answer but figuring out what’s going on should be the priority

  • Good call on dirt on top of pipes. Will get it looked at by a professional. Thanks
    – Chris
    Dec 30, 2018 at 18:01

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