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Community and Q&A

Should I reuse a cracked concrete slab?

slugboy6000 | Posted in General Questions on

I’d like to rebuild a small, unheated, minimally insulated outbuilding in zone 5 that sits on a 3-1/2″-4″ concrete slab foundation (sheet poly underneath) that’s 15-20 years old.
The slab has cracked down its length and width.  The cracks are fine and I don’t detect any height differences.  I think that the stoney fill under the slab settled after construction.

Is it safe to reuse the slab, or should I be looking at other options?


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  1. Expert Member


    What holds up the existing building? Is the slab thickened at the perimeter?

  2. slugboy6000 | | #2

    It's just a plain ~4" slab (12' x 13') no extra thickness at the perimeter.

    I've got electrical and water connections,
    so building in situ would be a big bonus.

    I could pour a new slab over the old and add a thickened edge below grade and even a stem wall, but perhaps the cracking would translate up into the new slab?

  3. Expert Member


    My guess is that rather than inadequate compaction of the fill under the slab, it cracked because of the absence of footings. Depending on the size of the building, and how the loads of the new one fall, addressing that may be all that's necessary, and leaving the slab as is will be fine.

  4. slugboy6000 | | #4

    Food for thought, thanks Malcolm.

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