From the Forum – Help! My basement slab is cracking..

by Prince Of Petworth December 7, 2015 at 2:10 pm 14 Comments


Help! My basement slab is cracking..

“Has anyone had to put in a new concrete slab for a basement and had any issues with cracking? I had a contractor pour our slab about 18 months ago and polish it, and now have nearly a dozen cracks. Some cracks are horizontal and some vertical, running across the entire basement space. It’s possible the ground was improperly prepared as there was flooding about four months before the slab was done.

I’ve waited this long so that the house/slab would settle. The contractor wants to fill the cracks with caulking/epoxy. But I’m not sure that’s going to be sufficient and need advice (will there be more cracks, will the current ones continue to deepen and how to remedy what has happened). So I’m looking for suggestions of people/companies to call who specialize in addressing this sort of thing. Thank you!”

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  • AnonV2

    “there was flooding about four months before the slab was done”

    Was the cause of the flooding fixed?!?! Because, yeah, if you are getting water in under the slab and causing erosion it is going to crack. Did you at least have a perimeter drain put in before the slab was re-poured? Even with that, unless you prevent water from getting under your foundation this problem is going to keep occurring.

    • wobber

      i’ll second that

  • BDale Res

    What did the contractor do to prepare the slab? how think is the slab? is there gravel underneath, if so, how much gravel? Did he use rebar or metal screening to reinforce the slab? If you had flooding in the past, what did you do to remediate the issue?

    I replaced my concrete slab about 3 years ago and haven’t had any issue and I WAS experiencing flooding on multiple occasions. I have not since…except for the DC Water issues. :-(

  • Philippe Lecheval

    Are you sure the cracks are excessive? Because I don’t think I’ve ever seen a concrete slab without at least *some* cracks. And epoxy is a normal remedy that should keep them from getting a lot worse.

  • Guillermo Brown

    All concrete cracks when the water in the mixture starts to evaporate. It’s not an issue unless it starts to exceed the tolerance for thickness, which can be easily looked up.
    Also, I’m guessing your basement slab is not a structural slab, meaning its only purpose is for you to have something to walk on. So your house isn’t going to fall down if there are minor shrinkage cracks everywhere

  • Also have a slab

    Some hairline cracks in a slab are inevitable, unless you specifically put breaks in it.

  • Dane

    All concrete will crack, just a matter of where. If your contractor didn’t put any control joints in there, then it’s going to crack where it wants to. If those cracks are so wide that you can get caulk in there, that’s another story altogether and probably means the substrate was improperly compacted. Still, if it was a retrofit, then it’s not structural. Lot’s of remedies for the aesthetics, tile, floating flooring, micro-topping, marmoleum etc..

  • BronxLivingInDC

    I’d report it to DCRA so an inspector can review it and give you some advice. Probably also good to ask another contractor to see if the original contractor did it correctly.

  • jshark202

    Thanks for the responses, everyone! Just to clarify, the flooding happened four months before the slab was poured, when the basement was being underpinned. The cause (a burst pipe coming in from the meter) was fixed and the foot or so of muddy water was drained . We had a french drain system installed, as well as radiant floor heating, so we can’t just tile over the concrete.

    The floor is structural and though I figured we might wind up with a hairline crack or two, I didn’t expect this many, this deep and so soon. It seems like at this point, I just want to have someone come in, take a look and give advice on what to do next. Any ideas on companies that do this sort of work?

    • anon

      Unless you create control joints, concrete will crack with temperature changes. Since concrete can’t handle tension, it will crack if it doesn’t have control joints. It’s basic physics.

      .What’s the distance between cracks?

    • thedcyears

      I agree with the other posters about assessing the source and addressing that first. I also have radiant floor heating in a slab, with tile on top. It’s fine, the heat comes through the tile, warm to walk on.

    • Dane

      Don’t get too worried by forum comment hyperbole. Assuming this is a typical rowhouse situation, it’s not structural- nothing about that slab is bearing any load. The footings bear the load and they function independently of the slab, even if they are embedded in it. So don’t worry about your house falling down. If you are actually seeing big sections of the slab sinking below the rest, well then, yes, you’ve got an issue, but again, not structural. 1/8 of an inch wide or less is fine and normal. The radiant tubing will actually lead to more likely cracking due to the rapid expansion and contraction because of the heat. Tile over the radiant is a perfectly fine option and won’t impact the performance on any measurable way-as is cork or any other floating floor appropriate for radiant heat. Once you get that slab stabilized at a certain temperature the materials touching it will also warm to that temperature. Color matched caulk would also be an option for the cracks. Google “normal concrete slab cracks”. It’ll make you feel better.

  • emp

    There’s an adage in construction that there are only 3 absolutes when it comes to concrete: it’s grey, it’s hard and it cracks. These are shrinkage cracks, they are to be expected and of no concern structurally. This is why concrete should not be used as a floor finish. There are methods to reduce the cracking (wet curing) or control it with control joints but those things must be done ASAP (within hours) after finishing the slab or they are ineffective. Engaging DCRA to review the installation is of no use, they require a 3rd party inspect geotechnical and structural work plus there’s nothing defective about shrinkage cracks in concrete. There’s no reason though that you couldn’t put down tile as others suggested, tile is an optimal floor covering over a heated slab. Make sure to use an uncoupling membrane such as Ditra by Schluter to prevent cracks transferring to the tile.

    To read about what should have been done to prevent cracking:

    • Anon Architect


      I wouldn’t worry at all about shrinkage cracking in a horizontal application unless a vapor barrier was not install below the slab on grade. I would find it difficult that a competent contractor would miss something like that, even if he missed tooling in control joints. Get the joints sealed. Given that it is a radiant floor, ensure that the chosen product will hold up through the heating and cool down of the slab.


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