I have in my barn (concrete floor) a pit, of about 36" x 60" x 10" deep which was originally used to install some machinery by the previous owner.

I have no use for it, and would rather have the floor space than a safety hazard. I don't know how deep the rest of the slab is, nor how much is left under this "pit". It is smooth sided and bottomed.

I'm not sure if I should fill it full with concrete or use filler?

Also, i am not sure if I need to prep the sides at all for adhesion or what kind of concrete to use.

  • As per this question and answer. diy.stackexchange.com/a/132860/18078 unless the slab around it is 10" thick and you have some use for 10" thick concrete right there, gravel/stone is cheaper than concrete.
    – Ecnerwal
    Jun 29, 2020 at 20:35

1 Answer 1


I'd fill it part way of compacted gravel leaving enough space for the thickness of concrete slab you want. The pour is going to be heavy enough that you really don't need to worry about adhesion.

  • 2
    Until John Wick wants his trunk back... :)
    – Solar Mike
    Jun 29, 2020 at 17:16
  • Maybe this should be edited into the question, but how thick of a slab should I need? This is a general purpose area, workshop/storage, maybe a sub-compact tractor on it.
    – Nick
    Jun 29, 2020 at 17:18
  • Generally 4" is enough for garage/driveway use but if your tractor is very heavy you could go to 6" but that's probably overkill.
    – jwh20
    Jun 29, 2020 at 17:20
  • 36x60" seems like it would be big enough for some rebar/wire-mesh, especially if any sort of machinery (like a tractor) might be driven over it.
    – FreeMan
    Jun 29, 2020 at 17:53
  • @FreeMan the rebar/mesh would be just in the new slab section for tensile strength yes?
    – Nick
    Jun 29, 2020 at 17:54

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