Question:

My concrete contractor failed to coat the finished slab foundation with a curing agent. The next day two hairline cracks appeared that ran from one side of the foundation to the other side. After two weeks, these cracks have not gotten any larger. Should I be concerned about foundation failure later, or are the two cracks simply cosmetic problems?

Answer:

I get the impression the cracks are in a slab upon ground. I also am thinking the slab is roughly rectangular in shape. The cracks are not just cosmetic, they probably go through the depth of the slab of concrete. The trouble I imagine is a rising dampness and water ingress into your structure through these cracks.

One thing before we continue, concrete cracks by nature, it is a matter of jointing it so the cracks are pre-engineered to occur in useful or expected places.

If I owned your concrete, I would have the contractor come back and answer your questions, I would ask him to hire a concrete expert and have the expert design a joint system for your concrete and then fill the joints with a high grade poly urea joint filler. This should get you the performance a reasonable man could expect.