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enter image description hereI am in the process of building a new home in North Carolina. This is slab based foundation house. The slab was poured in mid March when the temperatures were around 40-50 F. Now during the pre-drywall inspection I found that there were a number of cracks in the slab all over. In one area specific area of the slab there are few big cracks. There are also cracks in the garage and the front patio as well. Should I be concerned about these cracks? Is this a sign for any underlying big problem? Please help.enter image description here

  • What kind of steel reinforcement is in the slab--rebar or post tension cables? – Jim Stewart May 17 at 22:03
  • Thank you for your quick response. I added the picture. I am not sure the difference between rebar or post tension. – New Home Owner May 17 at 22:36
  • Article on post tension cesinspectionstexas.com/post-tensioned-foundation – Jim Stewart May 18 at 12:22
  • Is this construction subject to building inspection? if so, contact the building inspection authority and find out what they are approving. – Jim Stewart May 19 at 11:46
  • Yes the city inspection was done and it was approved. I will check what they were approving. – New Home Owner May 19 at 21:29
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Unfortunately that looks very unusual to me. I think you need a civil engineering consultant. It will cost something but saying "some guys on the internet said it looked bad " is worth nothing. And maybe the conclusions will be good.

  • Yes, I agree. Get an expert, like an architect, to review now. – Lee Sam May 18 at 22:19
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Yes, I think the cracks are structural and will be a problem in the future.

The crack is near a “control joint”, which is used to control expansion and contraction. The control joints are spaced appropriately and doing their job, unless the contractor did not stop the reinforcing steel through the control joint.

There is obviously a heavy load coming down on the foundation near these cracks (see the built-up column of 4 - 2x’s) and is probably contributing to the settlement (movement). If you look closely, the slab is poured with the exterior foundation system. The slab is not independent, so any movement in the foundation will affect the slab.

I’d keep a journal and place marks on the floor every 4’ along the cracks. Then I’d number the marks, measure the marks, and photograph the marks.

The cracks are small, because it’s new concrete. As the house ages a year or so and goes through a winter season and has furniture moved in, those cracks will enlarge.

I’d notify the contractor in writing that it’s unacceptable and you will be maintaining a journal.

  • The answers above indicate to me that you back out of the purchase on the grounds that the quality of the foundation is substandard and prone to failure. – Jim Stewart May 19 at 13:31
  • @JimStewart I doubt if you can “back out” on the possibility of future failure, but you can prepare for what will be future litigation. – Lee Sam May 19 at 15:29
  • Lee Sam, you surely know what recourse is available, but if the slab is supposed to have rebar in certain places and it has only mesh, how can the builder hold a customer to a purchase agreement? – Jim Stewart May 19 at 16:02
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    @JimStewart We don’t know the rebar was omitted. They may have installed it. It would be good to have a photo during the concrete pour. – Lee Sam May 19 at 16:40
  • Unfortunately I don’t have a picture while the concrete was poured. Could it be possible they do the mesh first and put the rebars at the time of pouring? – New Home Owner May 19 at 21:05
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I see a few problems in the construction photo you added: 1) wire mesh in slab, 2) wrong supports that are too far apart for wire mesh, 3) wire mesh laying on ground (vapor barrier), 4) lack of rebar in perimeter footing, 5) thickened edge of slab without proper amount of rebar, 6) no protection of vapor barrier. 7) reinforcing extends through control joints.

1) Wire mesh is not appropriate for slabs. There is a recommended ratio of reinforcing steel to quantity of concrete. You can obtain this with rebar, but not wire mesh. (That mesh is standard #4x#4/6x6 which is too small.)

2) Supports are too far apart and allow the mesh to sag and lay on the ground.

3) When mesh lays on the ground it is located in the wrong position in the slab. Reinforcing should be in the middle of the slab or in the upper half of the slab. When the concrete is poured thx contractor will have a person “hook” the mesh and try to pull it up into position. They can’t. It merely deforms the mesh and creates a small loop. You can’t move mesh through the concrete.

4) Some rebar appears in the footing adjacent to the other building. However, there is none in the other footings. The contractor may tell you that it just hasn’t been installed yet when the picture was taken. Not true. Rebar is installed prior to installing mesh. The mesh will just be in the way of installing rebar.

5) When a slab is thickened at the edge (perimeter), additional rebar is required. There is none.

6) If you have moisture problems on your slab in the future, it’s because there is no protection between the vapor barrier and the wire mesh. (Usually there is a 2” layer of sand placed on the vapor barrier to protect it from getting holes punctured in it.) When the concrete is placed, the workers will walk all over the area creating puncture holes from the wire mesh.

7) Wire mesh runs through control joints. This defeats the purpose of the control joints (does not allow proper expansion and contraction.)

Please let us know outcome.

  • Could this be fiber reinforced concrete? Could fiber reinforced concrete be used without rebar in a slab foundation? – Jim Stewart May 19 at 11:44
  • @JimStewart The slab could be fiber reinforced, (or no reinforcement) but it still must be installed with good building practices. We install slabs without mesh (or any reinforcement) but we recognize good practices by decreasing the spacing of control joints, protect the vapor barrier, etc. – Lee Sam May 19 at 15:09
  • I would disagree in my area wire mesh is recommended for slab less than 4” thick. After looking again I would agree that the spacing is two far for the blocking of the mesh but it can be pulled up but is difficult. – Ed Beal May 19 at 15:41
  • @Ed Beal, so would rebar be required in the thickened edges and in the internal beams of a slab foundation which is otherwise 4" thick? – Jim Stewart May 19 at 16:22
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    @EdBeal Everyone says the mesh can be pulled up, but it can’t. I’ve rejected many slabs that “had the mesh pulled up” but we found the mesh laying on the bottom. Mesh on the bottom of the slab is the worst place. When the slab begins to cure, it shrinks. The very top will shrink the most because it has the least resistance, while the very bottom will shrink the least because the mesh is there. (This is what creates cracks on the surface.) We use rebar (not mesh), install it in the middle of the slab, and we don’t EVER have cracks. The key is providing the proper amount of steel. – Lee Sam May 19 at 16:37
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First I will say there are 2 types of concrete, type one has cracks and type 2 will crack later.

Your cracks are kind of unusual because the built in crack lines are not far away, I am wondering about the quality of the pour was this an area that required some hand backfilling? I ask because of the discoloring an possible grind marks. With possibly a slight concern in this area I probably not be worried because the rebar or steel mesh will keep it from moving and all concrete slabs will crack over time.

  • Thank you for your quick response. The discoloring/grinding is due to the fact that the builder is attempting to fill those cracks. But my main concern is regarding the number of these cracks. On a floor of 1400sqft I see at least 10 such cracks and other 10 which are very small that appear as lines. Some of these crack are very long. – New Home Owner May 17 at 22:39
  • Fine cracks are totally normal with every slab. Big cracks can show a bad mix or an area that was not properly filled and that they shoveled from a different load to fill the low spot, if there is mesh or a grid of rebar it may not be as big of a deal, the temperatures you mentioned are awesome for a good cure , as long as the base under the slab was well packed with some rock and even it should be ok especially if the base was well watered prior to the pour, if the base was not compacted that could be a problem if not a level base that could also be a problem these are the biggies done wrong – Ed Beal May 18 at 1:15
  • I just saw the photos Of the prep did not see these before. If the mesh was pulled up , fork under vapor barrier was packed well this should not have happened, did they do compression tests or slump test? I have had drivers add two much water trying to get going faster but it caused failures, maybe that is your issue I wold get a pro and a lawyer at this point if there are no compression tests taken every yard. – Ed Beal May 18 at 1:23
  • thank you so much for the valuable feedback. Is that compression test for the land/soil? I will ask the builder. Can you suggest what the test would reveal? – New Home Owner May 18 at 1:30
  • In some areas tubes of concrete are required to be pulled and crushed with a hydraulic press and the crush point is recorded this is mostly on multi story and commercial buildings but I have lived in an area that it was required for residential. – Ed Beal May 19 at 15:34
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One additional suggestion would be to conduct a radon gas test to understand the levels at your specific property. DIY tests are not very expensive, and even professional tests by licensed testers are

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