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basement cracksWe are in the process of buying a home and most of the homes we see have cracks on the floors in the unfinished part of the basements. We are worried about buying a home that is not structurally sound and one that will cost us thousands to fix down the road. We have also went under contract with one house and there was a foundation issue found on a wall. We backed out of the contract, but we paid the inspector $500. We don't want to keep paying $500 only to find out that the foundation is bad. It will take away from our down payment and every penny counts for us. I was told by the realtor that most basement cracks are not a problem but only the inspector can tell us for sure. Can anyone tell me by this one picture if this crack is an issue? I am planning on looking at the home again tomorrow and can take more pictures if needed. We really like this home but we're scared to make an offer. In case needed, we are in the Denver metro area. Thank you for any help you can offer. Michelle

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    I'm not a structural engineer - we have some on this site who are. However, based on this one pic and my experience it looks as if this is typical cracking that you get with a concrete basement floor. What you want to watch for are vertical heaves and severe wall cracking. The crack going off to the right looks like it gets more severe as it goes. More pics might help. I also live in Colorado and many areas have bentonite which is vertically expansive when it comes in contact with moisture. If you see that type of heaving around the foundation it pays to investigate further.
    – HoneyDo
    May 29, 2021 at 21:14
  • Also, is that moisture below the window where the wall and floor meet?
    – HoneyDo
    May 29, 2021 at 21:15
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    Cracks in floor, usually not big structural problem, could be place where moisture/water comes up. Cracks in walls usually can be more of a concern, especially if they continue onto the floor.
    – crip659
    May 30, 2021 at 0:03
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    I don’t see a reason to think this is structural, all concrete cracks it may be 1 year or 50 but it will happen! The slab is not structural, I would have more concerns about the dark marks on the wall under the window. I don’t see any high water marks but if the basement is dry I am sure I can find you a inspector that will say it is fine and another that says look there is a crack the sky is falling,,, oops wrong story the house will fall down but there is only evidence of a crack that has been filled in the past not properly but refer to my statement ALL concrete cracks. This is not unusual.
    – Ed Beal
    May 30, 2021 at 2:56
  • Almost any large concrete slab will crack in an irregular fashion as your picture shows, especially if it is not reinforced with rebar, steel mesh or both. One way to reduce the chance of that occurring is to separate the large slab into smaller sections with an expansion strip between the sections. Of course this has to be done when the slab is poured. Another technique that I think is used uses a v-shaped trowel to put a shallow groove into the surface of the concrete. This is usually done before the concrete cures completely. This causes the stress cracks to follow the grove cut.
    – SteveSh
    Jul 5, 2021 at 23:58

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I can't see the entire crack pattern but it does appear to be one of the "back-of-an-envelope"-patterns that strongly indicate a structural issue. This in itself does not have to be much of a problem, but it means there is a real risk that it will continue to grow. And if you try to repair it by injecting mortar or epoxy, it may very well reappear.

To estimate how much of a problem a crack is, the first thing to look at is the crack width. Some rough guidelines since I can't really tell the width from the photo:

  • 0.3 mm or so is no problem. This is the kind of crack that merits a comment like "all concrete cracks".

  • 0.5 mm is not a major problem, but repair is needed. Otherwise the concrete will eventually break apart and the rebars rust away. This is a process that takes years if not decades, so usually not exactly an urgent problem, but it will often be the cheapest solution to fix the crack sooner rather than later.

  • 1.0 mm is a problem. Not particularly dangerous for a typical basement floor, but definitely means it is coming apart.

I note that parts of the crack appear wet, indicating that water seeps through. This in itself doesn't have to be a big problem, as while it will eventually break down the concrete and the rebars, it will do so quite slowly. It does however indicate that the cracks go all the way through the slab, and therefore radon is likely entering the building as well. I don't know how much of a problem, radon is in your area, but globally it is one of the leading causes of lung cancer.

Along a part of the crack, there is something orange. If this is rust (and not just the result of sloppy cleaning), that means the rebars in the slab are in the process of rusting away, and the days of the slab are counted. Trying to repair the crack by injecting mortar or epoxy will likely be no help, and there is no realistic alternative to breaking it apart and casting a new slab. It doesn't have to be today or tomorrow, though.

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I live in Denver metro and I have some training as an engineer although I am not a practicing structural engineer. Personally, I am very sensitive to potential foundation problems in my own home so I will offer the following comments.

  • Basement floors are rarely structural and most often unreinforced. In Colorado, they will crack.

  • The crack in the floor here is caused by either soil expanding or contracting underneath the floor. That is very likely due to moisture fluctuations. It wasn’t cracked like that when it was poor.

  • Cracks in the walls are much more concerning than cracks in the floor.

  • it appears that one side of your crack is offset from the other— that is not good.

  • The precense of moisture related defects in the floor means there is a related increased likelihood of similar defects in the walls. No certainty however.

  • I would not close on this house without having a structural engineer examine the crack— it’s likely under 500 dollars to hire a PE. You want to hire an experienced, licensed PE, that has no affiliation with your real estate agent.

  • I occasionally find it useful to bound the worst case repair for a given defect. In the case of a floor crack, you could actually cut out the crack and repair concrete in the cavity. No guarantee it won’t crack. Repairs to walls are more challenging and expensive.

  • My opinion is that the greatest risk you face is that whatever caused the floor to crack has also compromised the footer underneath the basement walls.

  • If this house has a drain tile or sump pump, that is encouraging.

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