Structural Crack in Raised Slab

Discussion in 'Framing and Foundation' started by fooyay, Aug 25, 2016.

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  1. Aug 25, 2016 #1

    fooyay

    fooyay

    fooyay

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    Hi all,

    Adding to my assorted housing crises, today I was ripping up some carpet in order to prepare to install wood flooring for a nursery when I found this crack in the slab.

    It runs underneath the drywall and out of sight, and spans the entire width of the room. It begins from an exterior wall and runs under the opposite wall into a living space -- I can't tell how far it goes after that since there is hardwood flooring that I haven't ripped up (hopefully it doesn't come to that).

    There doesn't appear to be any shearing, although there is very sight (1-2mm vertical displacement).

    We have not noticed any other structural problems in the house, but then again we haven't really been looking. No cracks in drywall that we've found, and all the doors and windows open and close ok so far.

    The house is built on a raised slab atop some kind of fill, as are most houses in this neighborhood and area (eastern NC). It was built in 2003 and there were no records in closing that indicated any foundation issues.

    The house is single story (plus room over garage) and approximately 2000 sqft.

    Are the only real options:

    1.) Sell at a discount
    2.) Wait it out and hope it doesn't get worse
    3.) Major structural repair (helical piers, etc.)

    I'm guessing a crack like this can't just be patched effectively. Is it safe to assume that the flooring in the entire house will have to be removed to assess the severity of the problem?

    I am not sure what the perimeter drainage situation is around this house. I do know that the gutters are very poorly drained via downspouts that deposit only a foot or so from the foundation -- this is something I had been planning to fix regardless, before I knew about the foundation problem. I've also seen that the condensate line from the air conditioner deposits right next to the foundation -- it's not much water, but it's at a constant drip during the summer.

    Am I looking at over $10,000 possibly?

    Thank you for any help you can offer. I guess it's safe to say my wood flooring project will be on hold for some time to come :(

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  2. Aug 25, 2016 #2

    nealtw

    nealtw

    nealtw

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    Welcome to the site.:)
    Don't panic, concrete slabs crack, in driveways and deck slabs they put in expansion joints and trowel in control lines. The big surprise is when your basement slab doesn't crack.
    There are repairs you can do, even if it has sagged a little, it can be lifted again by pumping foam under it.
    That is not to say you don't do a detailed inspection of the foundation from the outside, not necessarily close to the crack in the floor.
     
  3. Aug 25, 2016 #3

    beachguy005

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    As nealtw pointed out it's pretty normal. In fact it's so normal that there is lots of material and information on tiling over cracks in slabs. I wouldn't start tearing up flooring looking for more. There are a lot of reasons for a slab to crack. Here's some info on it.
    If you're putting down a wood floor you want to check for level with a long straight edge or a laser level.

    http://www.cfawalls.org/foundations/cracking.htm
     
    Last edited: Aug 25, 2016
  4. Aug 25, 2016 #4

    fooyay

    fooyay

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    Thank you both for putting me a little more at ease.

    I know some cracks should be expected, so I'm sure there are some others, but my concern was that this crack was vertically displaced and not just split apart... also that it appears to continue to run into the rest of the house, which gives me the grotesque mental picture of my house splitting apart in two pieces like the Titanic.

    I've put a straight-edge all around that particular room, and there doesn't seem to be a single level spot anymore (either that or my straight edge isn't so straight :) ) And I've seen instruction on applying thinset or some kind of self-leveling compound to level it out for flooring, but I think I would need to get this crack closed up first, right?

    We will have a structural engineer come out and take a look. On the surface, does it look like mudjacking would solve the problem? My only issue with that is that if the settling is a result of poor fill under the slab, then I am worried this will be a repeating issue.

    Thanks again for your input, it's been very reassuring.

    I went outside today and took a picture of the exterior, and it looks like the crack carries up through the brick as well.

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  5. Aug 25, 2016 #5

    nealtw

    nealtw

    nealtw

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    The brick is not the foundation, the foundation will be concrete behind the brick.
    Level concrete floors are few and far between where I live.:hide:
    Pulling a tight string across the floor and lifting to 1" on both ends. You will be able to see high and low spots.
    You can check the fill below the floor by tapping the floor with a hammer, a void will return a hollow sound. It is a quick learning curve if there is a void.
    There are about four different types of slab floors. They all have names but the names change from area to area.
    In some areas they just do a thick concrete floor and build on that. It does not look like you have that.
    Our most common is a footing below frost depth and concrete walls up to the floor level, then it is back filled and the floor installed level with the foundation.
    The foundation is usually 8" thick so some is visible around the perimeter.
    One has the floor installed on top of the foundation
    And the last one is installed all in one footing foundation and floor as one piece of concrete.

    For peace of mind having an engineer look at, might be a good idea.
     
  6. Aug 27, 2016 #6

    GBR

    GBR

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    --Welcome to the forums!------

    First I thought is was a shrinkage crack until you showed the brick cracked also... appears to be a "settlement" crack, especially if the crack extends vertically as shown--- "The house is built on a raised slab atop some kind of fill,"---- could easily be the fill. Did you ask your neighbors if they have similar? https://www.nachi.org/visual-inspection-concrete.htm

    As the link brought out you could be in a stressed location; notice the green colored area of your state in the first US map? Appears the brick is your structural foundation the wood frame wall is bearing on.... a lot more serious that a simple slab crack.

    Gary
     
    Last edited: Aug 27, 2016
  7. Aug 27, 2016 #7

    fooyay

    fooyay

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    GBR, that's an awesome link; I've got it bookmarked for future reference. Tons of good gouge.

    I talked to an engineer who said our soil is mostly clay and these cracks should be expected. I also shot a level across the perimeter and noticed very negligible variation... maybe 1/4 to 1/2" over about 50-60 feet on the exterior brick veneer.

    Shot one inside the main structure as well and it only varies about 1/4 to 1/2" as well, and it's not really along that crack. I didn't measure the room with the crack because I already can tell there is some vertical displacement, but I'm guessing it's about the same as the rest of the house.

    You had me worried when you said that the brick is my actual foundation. I was able to get a hold of the plans for a twin model house built by the same builder. Looks like the brick is just veneer and not load-bearing except in the garage. At least that's my interpretation of it.

    Screen Shot 2016-08-27 at 10.55.02 AM.png
     
  8. Aug 27, 2016 #8

    GBR

    GBR

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    You are correct, I hope there are "weep" holes to let moisture out as I don't see any in the picture with green algae growing on the mortar joints between bricks. As per diagram drawing, the weep holes should be visible above grade and every 16" or ? on center spacing to help dry the wall as it is a water reservoir system susceptible to solar drive, possibly wetting the CMU; http://buildingscience.com/documents/reports/rr-0104-solar-driven-moisture-in-brick-veneer/view


    You could also paint the exterior bricks below grade to help waterproof the wall with a latex paint- vapor open to let moisture in lower bricks out but slow ingress capillarity there as it could saturate the brick, wet the concrete CMU and wick through the PT sill plate to rot the wood framing above, Fig.3; http://buildingscience.com/document...nsulationhttp://buildingscience.com/documents

    http://www.greenbuildingadvisor.com...code/information-sheets/crawlspace-insulation

    Make sure your flower beds near the house are sloped away to help drain the surface water to limit brick capillarity there: http://buildingscience.com/documents/digests/bsd-108-investigating-and-diagnosing-moisture-problems

    Appears I am repeating/rambling/mixing some links, sorry, need a nap...

    Gary
     
  9. Aug 28, 2016 #9

    fooyay

    fooyay

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    The engineer who came out also suggested possibly painting the veneer. We've been meaning to remove the flower beds entirely around the perimeter... we've had the house for a year, and I'm not sure how long the previous owner had those beds in place, but they definitely don't slope away.

    I looked around and did not see any weep holes in the brick above grade. I never thought about looking for them before, but shouldn't it be standard practice? Can you think of any reason why they wouldn't have been put in? The only kind I'm really aware of just look like a gap in the mortar every couple of bricks. Is there any kind of negligence involved if they weren't included?

    While looking around I noticed several other cracks in the brick veneer, but nothing that popped out at me except for one:

    On the opposite side of the house is another crack in the brick veneer. It's in roughly the right place to be connected to the original crack I found, assuming the original crack spans the width of the house. If that's the case, and it runs through both veneers and all the way through the 4" slab, is it potentially more troubling?

    I guess there's not much to be done if the structure so far is still sound/stable, according to the structural engineer, other than just keep an eye on it. I may get a second opinion or see if maybe I can get someone to come out and survey.

    [EDIT]

    I jumped the gun and missed part of the design layouts. I missed this little guy: "Slab Curtain Wall" and think this actually reflects what we have.

    Looks like you may have been right, and it would seem that the brick curtain wall is actually the load-bearing structure, and does not call for weep holes per the design spec.

    NOW should I be concerned if the crack runs through the entire house between both brick veneers? :)

    I'm going crazy with this.

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    Last edited: Aug 28, 2016
  10. Aug 28, 2016 #10

    GBR

    GBR

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    I'm guessing they made the weeps at the bottom, right on the brick ledge in the concrete. As you would be digging to that level to paint, add some membrane in front for drainage off the brick face, with an impervious membrane below the weeps. You don't want to block the weeps- if any are present. Might look up the Geotech soil records the builder supplied to county/city for permits to build on that soil, should tell you more. If the crack surfaces on both sides is same level (elevation), may not be a problem. 1/4 to 1/2" is SOP for a slab on grade with a production general for spec. houses. You do have rigid insulation on inside face of CMU, which is a good thing....

    " If that's the case, and it runs through both veneers and all the way through the 4" slab, is it potentially more troubling?"------- I'd get some better advice from a local that is there to see it in person, I'm only a retired carpenter...lol. As your average monthly low temp could freeze any water in the wall cracks splitting the brick work open, I'd have a mason repair them (and fix slab crack) before winter; https://www.google.com/#q=average+monthly+temps+for+NC

    With a 4" below slab frost line, not many worries there; http://www.ncdoi.com/OSFM/Manufactured_Building/Documents/Regulations/15-25.pdf

    Gary
    PS there are a lot of smart posters on here, one probably has more experience than I... wait for them.
     
  11. Aug 29, 2016 #11

    Mastercarpenty

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    I'll agree that you're probably OK, but while it's common, there is no excuse for a slab to crack. The problem is that residential builders and concrete workers don't know concrete as well as they think they do. My carpentry career started with industrial concrete formwork and along the way I learned about how concrete is properly done including rebar, wire mesh, different concrete formulations, water content, admixtures, it's handling, placement, and finishing. I've never seen residential work even come close to the testing and standards I dealt with.

    It is what it is, but I can safely say that almost no house slab in the US is done 100% correctly and most are a joke to those who really know their concrete.

    Your future with this is going to depend on two things: the qualities of the soil underneath it and you're keeping as much surface water away from it as you can. You can't fix the first so do all you can with the last. For the cracks themselves, there are liquid epoxies made which when used correctly can add a fair amount of strength against further shifting. After that differences can be feathered out with concrete grout or level patch. If nothing shifts within 5 years or so, you're probably OK. If it shifts like you see now you might want to consider patching and selling. If it's twice as bad or worse patch and sell PDQ because that's an indication of soil issues under the slab which can't be fixed without a total slab removal. Most folks get lucky so fix it and monitor it and don't worry until that's called for.

    Phil
     
  12. Aug 29, 2016 #12

    fooyay

    fooyay

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    Thanks Phil. They build these houses very quickly around here, so it's not surprising that either shortcuts were taken, or that the bare minimums were followed.

    I plan on adding drainage around the foundation. Unfortunately the house had been sitting here for 10 years prior to our purchase without any attention given to it -- gutters basically deposit AT the foundation line; planters installed very close and not sloped at all; etc. At this point like you said we can prevent anything further hopefully as far as that is concerned, but I think 10 years is a long time for it to be ignored.

    I wish the home inspector would have done a better job, but that's another story.

    Are helical piers or push piers (I think that's what they're called) a worthwhile investment if we intend to keep the place? Or are they fairly cost-prohibitive? The estimates I've seen range from $5k to $20k so it's not much to go off of until I actually get another person out here to look at it. I feel stupid having all these contractors out to assess the "damage" when there really is no damage yet, other than the crack itself and a little displacement.

    Is there a particular leveling compound you would recommend? The big box stores are mostly what's available around here, and I haven't read good things about the leveling compounds they carry... might be another thing to contract out, but I worry about that whole "bare minimum standard" again when it comes to that option.
     

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