Concrete slab sinking

How to fix pic related? I don't want to have to replace the whole slab.
My best guess is to break up the sinking piece into large chunks, remove them, fill in underneath with sand+gravel, then replace the big chunks and cement them in place. Is this stupid? Is there any other way to deal with this?

  1. 3 weeks ago
    Anonymous

    Another angle. It's clear that the whole concrete slab is not well supposed, since there's a lot of space that I can see through those gaps.

    • 3 weeks ago
      Anonymous

      >Is this stupid? Is there any other way to deal with this?
      yes and yes

      >It's clear that the whole concrete slab is not well supposed
      i think you mean supported.
      remove the whole slab, repour it.
      actually, dont PrepHole this project, because from your op you seem a wee bit retarded

    • 3 weeks ago
      Anonymous

      It's not supported because it's being washed out from underneath. Probably from gutters. The slab is compromised, and whatever is compromising it, will laugh at your repair and get right back to work.

      Best case: remove slab, identify where run-off is coming from, run pipe to run rainwater/excess water past the slab, repour slab.

      What you'll do: patch slab poorly, hope it lasts more than a year.

      • 3 weeks ago
        Anonymous

        They probably dug for something there and didn't Compact the backfill at all, so it sunk 6 inches
        It's not gonna keep sinking

        The rest of the slab is up to grade, just lift the broken part
        Maybe Crack the chunk it half so it's easier to work with

    • 3 weeks ago
      Anonymous

      am i crazy or is there a weird grid on this photo? anyone know why that is?

      • 2 weeks ago
        Anonymous

        https://en.wikipedia.org/wiki/Chain-link_fencing

  2. 3 weeks ago
    Anonymous

    If water is draining into the crack (or coming up out of the crack, which is way worse) when it rains, then expect that the slab could be almost completely undermined.

    • 3 weeks ago
      Anonymous

      agree with this anon.
      you have a drainage problem and it has undermined the base. Break up and remove that corner, determine how best to divert the water flowing under it, and repour.
      Sorry there isn't an easy Dollar Store fix. Moisture needs to be eliminated or early or just avoided. It kills everything man tries to make

  3. 3 weeks ago
    Anonymous

    It could just be a trick of the light, but it looks like another crack or some other stress is forming about where Fido is in the original pic. At least, that's what I'm thinking those discolorations indicate.
    Although there's mudjacking and expanding foam options that could lift this, I'd say you should probably get it redone. Something tells me that sand is supposed to be under the slab. Removing it will give you an opportunity to see what's happening underneath and fix it if it turns out there's something wrong.

  4. 3 weeks ago
    Anonymous

    >How to fix pic related?
    Repour it.
    >I don't want to have to replace the whole slab.
    You don't really have a choice.
    Don't fuck up the base and maybe put some remesh in it this time.

  5. 3 weeks ago
    Anonymous

    you can inject expanding foam under it, it should lift it a little but it will stop it from sinking any more.

    • 3 weeks ago
      Anonymous

      No reputable waterproofing/foundation company would inject poly into this. If they do, they’re fucking you. You’re going to need to repour and fix the water issue.

      >t. Former foundation repair installer/tech/inspector

      • 3 weeks ago
        sqtddiot

        this
        buy once cry once

        Pour sand on top
        Level
        Put outdoor carpet on it
        Put rocks on carpet to keep it from lifting up

      • 2 weeks ago
        Anonymous

        I am the anon that posted this before reading this thread at all.

        Listen to this anon . I as never a concrete man but when I was my early 20's I worked for a company building swimming pools and after installing the in ground pool prepped the outside of the walls for the concrete people. There isnt much to it, as I already said you just need to pour gravel in your hole and grade it. Gravel allows water to flow through the cracks without undermining or sinking. Sometimes you can add piping if you want to make like a larger pvc sized hole under it but that is pretty rare and should only be used if you have a gutter drain you want to run under it or something. Just using gravel should be fine for your uses. You can use rebar too if you want reinforced concrete, we commonly did this. You just lay it on top of your gravel in a grid and use these little metal things like bread ties and swirling tool to tighten them. For something this small you dont need to reinforce it but it isnt much more expensive or labor intensive to do so so it is up to you.

        It isnt that much work, you can knock this whole thing out in a few hours on a saturday. I said jack hammer but if you have a big sledge it should work fine. You dont even need to wheel barrel it out if you want to bust it up enough to add to the gravel grading. You cant use huge chunks but if you bust it up pretty good you can just add it back to the new gravel and have less gravel you have to purchase.

        • 2 weeks ago
          Anonymous

          same anon here I just wanted to add here if this had been reinforced with rebar in the first place it would have collapsed like this

          • 2 weeks ago
            Anonymous

            *wouldnt have collapsed

  6. 3 weeks ago
    Anonymous

    Demo it and figure out why there is a void beneath it.

  7. 3 weeks ago
    Anonymous

    Pour sand on top
    Level
    Put outdoor carpet on it
    Put rocks on carpet to keep it from lifting up

  8. 3 weeks ago
    Anonymous

    That's not a crack, that's a sinkhole

  9. 3 weeks ago
    Anonymous

    Lift it up with a pickaxe or prybar
    Add gravel, set back down
    Problem fixed

    Why fuck around ?

    • 3 weeks ago
      Anonymous

      not OP here. Could he dig around the broken piece, pull it out as one piece, and fill/fix what it's sitting on? pretty much this

    • 3 weeks ago
      Anonymous

      OP here,

      My original (apparently poorly stated) plan was to do at this guy suggested, but I'm getting a lot of comments indicating that I'm apparently a big dope for wanting to fix this without a huge amount of concrete repouring.

      This is a pretty large overall area of slab, for two door entrances to the house. This particular crack existed when I bought the house, but it's descended another ~2 inches since then.
      I'm going to end up doing what

      Remove the broken part and assess the damage underneath. When you've done that come back to PrepHole and post detailed pictures for better suggestion

      suggests, so if the thread stays alive you can expect some new photos when I muster up a pry bar and some muscle.

      • 3 weeks ago
        Anonymous

        how much do you want to fix this? is a perfect slab your intent or is flat enough for you?
        just lift/investigate the broken area and fill it underneath with not dirt

        alternatively, just break up and remove the damaged section and repour whats needed

  10. 3 weeks ago
    Anonymous

    Remove the broken part and assess the damage underneath. When you've done that come back to PrepHole and post detailed pictures for better suggestion

  11. 3 weeks ago
    Anonymous

    the concrete floor in my living room is worse than that, no joke

  12. 3 weeks ago
    Anonymous

    I tell you what I'd do is make a deep saw cut along the red line (square to the house wall and break that chunk out. Then assess the soil conditions under what you break out as well as under the slab next to it. Then compact it and re-pour that section.

    • 3 weeks ago
      Anonymous

      I think this would be the best way to repair it, and it'd look clean too.

    • 3 weeks ago
      Anonymous

      Seconded. OP if you're not already familiar with concrete work, I'd strongly recommend finding a local reputable company (first generation legal mexican immigrants preferably) to prep the base and pour the slab. It really shouldn't cost too much for an area that size and would look pretty good after. You could even get them to put in a french drain or something while they're at it, should it help with whatever drainage issues you have going on.

    • 2 weeks ago
      Anonymous

      This is the best option
      Wet and compact wayyyy more gravel than you think since it's the low spot

  13. 3 weeks ago
    Anonymous

    Let me ask you this, are there any pvc sprinkler lines under that slab? I had a slab do this for no reason, decided to investigate sprinkler next to slab, turns out there was a pin hole in supply line that washed out the clay, was just sand/pebble mix that let my 4 inch porch slab sink 6 inches to one corner. I diamond wet saw cut it at the crack, Jack hammered out bad side, formed around, 3/4 agragate base, compacted, #30 silver sand, compacted, re-poured.

  14. 3 weeks ago
    Anonymous

    It looks like there's a lot of hollow space behind the slab. Hairline cracks are also forming on the left side. The problem is probably a lot bigger than you think. If you're pouring concrete, you should use chicken wire to reinforce.

    • 3 weeks ago
      Anonymous

      I did a quick repair once where I drove some bars into the higher slab and just filled the rest in with new concrete and wire mesh. For like $100 that's all the more I can be called to task.

  15. 3 weeks ago
    Anonymous

    be the lazy consumer. the crack exists. weight from the slab on the big broken piece is free to push on dirt below. it has not fallen and no evidence of a sink hole as its near the edge and exposed top soil is next to it.

    fill in crack with floor epoxy or casting epoxy (may be cheaper is you get a small amount online). let set. then pour over the top a thin layer of new concrete

    you spend less on everything and lets be honest its not worth the cost to redo the entire thing

    • 3 weeks ago
      Anonymous

      That kind of fix won't even last a month.

  16. 3 weeks ago
    Anonymous

    Just smash that bit of slab up, use it as hard core to pack out the ground underneath and just repour that small section

  17. 3 weeks ago
    Anonymous

    Keep adding concrete until it is level, let it sink again, top up.
    Simple as. Eventually it'll stop sinking... probably.

  18. 3 weeks ago
    Anonymous

    Your entire pad, including the step up, is subsiding. It's also started damaging the corner of your house if the cracks and gaps in the brick and mortar is any indication.

    The only proper solution is pulling up all of the concrete, removing the loose soil underneath, grading and compacting with proper fill, terrain cloth, gravel, and then pour concrete.
    Probably plan in some drainage, be it french drain or sloping the pad.

    • 3 weeks ago
      Anonymous

      t. Contractor scammer looking to ding a customer for 5 grand for nothing

      • 3 weeks ago
        Anonymous

        >retard looking to help someone destroy their house by improperly addressing a major drainage issue
        Notice how I didn't say anywhere to pay someone to do it and laid out all of the steps for them to research.
        gay.

      • 3 weeks ago
        Anonymous

        There's not really all that much in that advice that isn't already being recommended in the rest of the thread.
        There are plenty of possible culprits for this:
        The building sewer line could run under this area and not be backfilled properly, resulting in settling and cracks which then allowed water to come in and wash sand and whatnot out, compounding on itself.
        There could be a drain line (downspout, sump pump, etc.) which runs under here which broke or cracked and created a sinkhole with the concrete slab on top.
        The original installation could have just been for shit.
        I don't think it's going to be an issue where an underdrain/french drain would be needed or even particularly helpful, though. We're missing a good bit of detail of the site, of course, so it's not like I can say for sure, but if I were doing the grading design on it I would have pitched that slab to drain away from the building and into the yard which would also drain away from the building. I guess it's possible that runoff's coming down the sidewalk along the side of the house and then the patio acts as a plunge pool with water getting in between the joint between the patio and step. Otherwise I don't see how surface runoff would cause this problem given what should be a fairly limited area tributary to it.
        Bottom line is it's definitely a good idea to open up as much as possible to see what's going on underneath it and fix what's going on under there.

    • 3 weeks ago
      Anonymous

      Scam. OP, just use Great Stuff in a can, that's what youtube related videos taught me.

      • 2 weeks ago
        Anonymous

        So I can fix for a $6 can of foam?

        • 2 weeks ago
          Anonymous
  19. 3 weeks ago
    Anonymous

    Reinsert doggo into hole after jacking the slab. A blender works well to make doggo pourable.

  20. 2 weeks ago
    Anonymous

    Its a patio slab not a foundation. there's no way the cost is worth doing it the 'right' way.

  21. 2 weeks ago
    Anonymous

    Had a problem like that with a concrete patio slab at the in-laws house. Cracks, subsidence, etc.
    Builder had dug a trash pit for all the debris and trash, capped it with a layer of dirt, and poured the patio slab. Years later, the shit rots and compresses, water filtered in and turned it into a sump. A fuck ton of work to break up everything, clean out all the junk, backfill properly, and pour new slab.

  22. 2 weeks ago
    Anonymous

    Get a grinder with a concrete cutting disc and cut the section out, then sledge hammer the rest.

    Dig down a foot or so and Throw a few barrows of road base down, compact it , box it out and lay a new sectoon. Use bags of structural concrete, not quickset.

  23. 2 weeks ago
    Anonymous

    Rainwater has poured off that ledge and eroded the ground underneath that slab

  24. 2 weeks ago
    Anonymous

    You have to see what lies beneath. The biggest concern I would have is the proximity to the back corner of your house. You.might just have a void from run off or your foundation could be getting undermined.

  25. 2 weeks ago
    Anonymous

    This is why I hate concrete and concrete salesmen
    Every single time some bullshit like this happens and all the "professionals" give you a $6000 quote and try and scare you by saying noooo your house gonna fall down n shiiiieeet.
    Concrete always cracks and breaks and it always looks like shit and it doesn't matter how many thousands of dollars you spend on sealers and hardeners and snake oils, it won't ever look good without constant cleaning and spraying and fucking around.
    Honestly if this was my house I'd just fill the top in with more concrete and ignore the problem, this crap is never worth "fixing".

    • 2 weeks ago
      Anonymous

      If you demanded they pour 10 inch slabs with higher strength concrete, it wouldn't crack
      Concrete cracks because they are always pouring minimum thickness slabs

      Also they often just skip compacting, or prepping the base at all

      • 2 weeks ago
        Anonymous

        Eh. Maybe. But then it's more expensive than just building your house on stilts with smaller, deeper concrete posts in the ground.

        >Honestly if this was my house I'd just fill the top in with more concrete and ignore the problem, this crap is never worth "fixing".
        kys
        seriously, i mean it

        Lmao. Seething honkrete salesman detected. Honk honk.

        • 2 weeks ago
          Anonymous

          well, the OP pic is absolutely not normal. its highly likely that they did an absolute shit job of the prep work, and it's not sensible to suggest that just because its possible to do it wrong, that this represents an inherent problem with concrete as a building material.

    • 2 weeks ago
      Anonymous

      >Honestly if this was my house I'd just fill the top in with more concrete and ignore the problem, this crap is never worth "fixing".
      kys
      seriously, i mean it

  26. 2 weeks ago
    Anonymous

    1. jack hammer and remove the sunken part.
    2. use gravel to grade it evenly.
    3. re-cement

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