I 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.
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.
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.
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.