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.

A 27 year old house should not be settling anymore, I'd guess those cracks have been there for quite some time. Shouldn't be a problem for the tile, especially if they are just hairline cracks.

Thanks for your response and experience. I am certain that the cracks have been there for a long time. The carpet was installed when the house was built.

I've read that expansion cracks are not a worry as long as they as the floor is still flat. As if you put a level across the crack. If one side of the floor is higher than the other on either side of the crack, then you've got problems, as it indicates the slab or soil underneath is shifting.

There is a pad that should be used under the tile some if the slab cracks more or moves it will not hurt the tile. http://www.floorstransformed.com/membrane.html