I have an old barn/garage that has mason block walls. The entire foundation is a concrete slab with footings for the exterior walls. For some reason, about 6 inches from the exterior walls, the concrete is cracked, and is sticking upwards.

Why is this happening and is it something I need to worry about?

I plan to frame a wall across this, however, the crack makes the flooring uneven, so how do I even out the floor?

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1 Answer 1


That crack looks too uniform (straight) to be a structural crack.

The concrete under the masonry wall is probably the top of the foundation wall. I suspect the slab was poured up against the foundation wall and the edges of the slab have spalled off.

If you notice there’s a control joint running perpendicular to the masonry wall too. This helps keep the slab from having random cracks.

Yes, the joints are a little rough. You can grind down the high spots and fill in the low spots with a concrete filler or sealant if you’re concerned about expansion. (Concrete continues shrinking as it ages, unless you live where the sun could heat the slab and make it expand.)

  • Thanks for the response! So it'd probably be safe to grind down the high spots and place a wall right over this crack? Jul 14, 2020 at 16:06
  • @GaryHoliday Yes, and it’s not structural so you don’t need to bolt it down...just use concrete nails.
    – Lee Sam
    Jul 15, 2020 at 0:48

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