My husband and I recently made an offer on a home and when inspected found a cracked concrete foundation slab. The crack runs from bathroom across hall to laundry closet. It is not quite large enough to fit a nickel into and is pretty even, not raised on either side of the crack but we are concerned. Could this be a "plumbing crack" and will the "epoxy injection" method of fix a good one. There is no visible moisture and the crack is about 6-7 feet long. This is southern california, and we keep hearing "it's no big deal."