I have recently removed all carpet from my home and I am preparing to install ceramic tile on my concrete slab. In removing my carpet I have found several hairline cracks, I have read this is normal but I am concerned with the location of these cracks. One crack is in the center of my house that extends from the front wall to the back wall. I then have a crack at all four corners of the slab, measuring from the point of the corner the crack is app. 3 to 4 foot away and extends from the side to the back wall or vis-versa front wall to the side wall. Imagine it as a triange and the corner of the slab is the top of the triangle and the crack is the bottom of the triangle. I have read that cracks are normal my house is 27 years old, but I am concerned about the location. Can anyone help and thanks in advance.