i used to sell tile and we always made sure the customer knew what to expect with saltillo. basically, the tile cracks because it absorbs moisture. if you seal all sides (including edges) the tile should not crack -in theory. however because saltillo is a soft tile (not cooked at high temps & only cooked once) it will chip during normal wear - some people like it to look very worn like that. if the spots are not resealed before a freeze, the tile will absorb moisture and then possibly crack during a freeze. the only way to garuntee a tile won't crack is to buy a tile that has been at least double fired at extremly high temps. and the manufacturer will back that up. you will not find saltillo on any of those lists. that's why there are what is called fake saltillo. unfortunatly none of the fakes have the rich diversity each saltillo tile has. no two saltillo's are exactly alike. this i'm guessing is why you like it. also the freeze thing can happen when any tile is laid on a concrete slab as that also is a wick for moisture. so are the materials used for laying the tile. so, a membrane should be used to separate the slab from the rest above it and everything needs to be sealed after it is all cured including the grout.