Settling

• Cracking is often the result of the concrete slab settling. This occurs as the weight of the slab causes the ground beneath it to be compacted. If one section settles farther or faster than another, the result will often be a crack in the concrete.
  
  

Water

• Acting in much the same way as settling, too much water beneath the slab can cause it to be uneven. When the tension from the uneven distribution of weight becomes too severe, cracking and breakage will take place.
  
  

Improper Thickness

• If your contractor or installer improperly installed the slab or did not make it an appropriate thickness, cracking will be far more likely. A minimum of 4 inches is recommended, and the use or reinforcing wire or rebar is also a good idea.
  
  

Uneven Weight Distribution

• Depending of what you use the basement for, the furnishings may be able to cause cracking issues as well. If you install a hot tub, pool table or other extremely heavy item, the uneven weight distribution can cause basement floor cracking. This is made more likely if the slab is not of the proper thickness.
  
  

Freezing/Thawing

• When soil is frozen it expands and then contracts again as it thaws. As this is repeated over the years, the expanding and contracting soil will often shift the concrete slab slightly. This will eventually place pressure on the slab. When the pressure becomes too great, the concrete will crack and split. This process will be more rapid in areas with dramatic shifts in temperature.
  
  

Prevention

• By making certain the soil/earth beneath the slab is well compacted and by installing a French drain to divert ground water away from the slab, you can avoid many of the cracking issues listed here. These precautions, along with a slab of adequate thickness and reinforcing material, should allow you to have minimal cracking issues.