We purchased our house new in late 2000. We have, in the last year, noticed hairline cracks in the tiles in 2 adjacent rooms. The cracks start at an exterior wall and follow the same path through one room and into the next. I have not noticed any structural damage (that I can tell) - no cracks in the walls and no cracks in the exterior portion of the slab at that location. I'm guessing that this is just settling because of the recent drought conditions and that we'll probably just have to pull the old tiles and redo the flooring. Is there anything in particular to look for on the slab (once we pull the old tiles) to indicate whether this is just a settling issue or a larger slab problem?

This sounds like settling to me, or it could be that the tile was incorrectly put down(wasnt level).

If any of us here had that perfect answer of Exactly why the concrete cracked I would be the most gifted crete person alive.

Concrete has its basic rules as to why it cracks and then after that it makes up its own again. I've been pouring concrete for over 30 years and its never been a perfect science.

If it took 8 years for the floor to get a hair line crack you are doing fairly good.

When you pull the bad tiles up tap on that spot to see if its sounds hollow. Take a hammer drill and drill a 1/2 hole through the slab and see if the drill bit is wet or moist dirt. This would help check to see if there is a water leak under the slab. Also it would help to gage if there is any post settling for what ever reasons. If its hollow or wet get back right away.

If the crack remains in the floor only then I would not be overly concerned.
There is a small trick to replacing that tile. Use silicone clear caulk to reset new. This would hold it enough to hold grout, but if the floor moves in that area the silicone will handle the movement and the crack won't telegraph through the tile. It may pop the grout but that's easy to fix

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Hi jazz man I'm sure you thought silicone is crazy for a repair. I've used that method In Puerto Rico when all floors walls ceilings are concrete and once in a while some tiles cracked. In PR instead of laying the tile directly on the concrete floor. They mix up and pour a bed 1 1/2 in hand mix crete and set tile in wet crete.

What that does is if the orginial concrete floors cracks, there's a better chance for the crack movement to be absorbed in the 1 1/2 conc sub straight.

The silicone to reset will do the same thing. To reset tile over crack you know it can very easily crack again. Better chance with silicone to absorb movement from underneath, and its still strong enough to stay still for grout to hold. Many P.R. houses are built on concrete columns. The floors are ALL concrete and set on piers. AND 99% of all homes are tiled. Very little cracks in tile because of that 1 1/2" sub straight.

Jazzman I laughed at your laugh. I would thought thee idea I had to re-set tile over a crack was insane 25 years ago until I tiled in Puerto Rico.

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Some interesting advice from both of you, for my background I have done housing design in auto cad, so I know the specs etc so forth but don't have much hands on(which I recognize is a huge difference) since I'm going to give positive rating to both of you, but the box doesn't have room for all of it I'm posting in addition.