Home FAQs Cracking & Joint Problems in Concrete My wife and I are building a new home. I have noticed hairline cracks. Will this cause problems?
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My wife and I are building a new home. I have noticed hairline cracks. Will this cause problems?

Q: My wife and I are building a new home. The construction company recently poured the slab for the foundation. However, my wife and I have noticed hairline cracks in various areas within the slab. Does this constitute poorly designed joint protection for the house? Also, will the hairline cracks forecast future problems with the house?

A:  If the cracks you have noticed are 'hairline' as you describe them, I doubt if you have anything to worry about.
For most slabs on grade (four inches thick), it is reasonable to expect concrete to crack in approximate squares, about 10 feet by 10 feet. If joints are to be sawn in the slab, they should be sawn on this spacing. If the joint spacing for sawn joints is greater than 10 feet by 10 feet, it is normal to see cracks appear outside of the sawn joints.
You did not mention whether or not the contractor installed any joints in the concrete slab, but it is important to understand that a joint is really just a pre-planned crack. Joints are used to get concrete to crack in a straight line, because this is less objectionable from an aesthetic point of view.
If there were no joints in your slab, the concrete simply made its own joints by cracking with the hairline cracks you observed. In most cases, these cracks will not get any wider, nor will they present any problems for the slab in the future.
If you notice the cracks getting wider, or if one part of the slab settles at the crack, this would be cause for concern. If this occurs, check first with your contractor, or call in a reputable consulting engineer to evaluate your project.