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About 6 months ago a contractor poured a concrete slab to serve as a porch. The slab rests directly on the ground and measures 25' by 4' and is 4" thick.

The slab has remesh under it, no gravel, but the area was poorly prepared as evidenced by the edges of the pad where dirt was piled up and it sounds hollow under one corner when you stomp on it. Additionally, the contractor didn't saw any expansion joints.

A 4' hairline crack has appeared that bisects the pad roughly in the middle. Additionally this crack is right in the area of the entrance to the business.

I'm concerned that the crack will continue to grow as it freezes and thaws and that the pad will continue to degrade.

Should I be concerned about this crack?

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  • Sawed lines and most troweled lines are actually "control joints", not expansion joints. They're there because concrete slabs crack, always, and you can try to control where they crack or you can let nature decide. Either way, it happens, and it's not a major concern.
    – isherwood
    Commented Apr 11, 2016 at 14:24

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Yep, if there wasn't insulation &/or gravel under it, that would cause hollow sounding areas. But, he definitely screwed-up on not doing a control joint...every 10' is normal as well as required for exterior slabs.

However, your best course of action is to cut that crack open. Not actually all of the way through, but at least an inch deep. Control joints are meant to crack & making them in the first place usually ensures that any cracking will happen within them.

Since you only have 1 crack though, then you really don't have any other choice but to take that crack's lead. It would be reasonable to expect that there wouldn't be any other cracks in the future after that stress relief & stress relief focusing measure.

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  • I agree there should be expansion lines in a long skinny pad. Without proper footings cement will crack. I would use a flexible latex caulking for now to keep water out and let it settle. After next summer , late fall if the heat doesn't make it worse it may be ok. I would not cut the slab because if you cut the mesh it may really make the crack worse. Some times there are crack lines in the cement you can't see this is done by pushing the rock out with a thin blade in a line. Then finishing the surface so it not visible.
    – Ed Beal
    Commented Mar 12, 2016 at 10:06
  • Great points. Yeah, I'd do the cut an inch or so deep, in order to hopefully draw any other stresses to it. A straight clean line is much better looking than a craggily uncontrolled crack, even if caulked. There's only 2 types of concrete, that which has cracked & that which hasn't cracked yet.
    – Iggy
    Commented Mar 12, 2016 at 14:48

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