Curing

• Improper installation techniques may not allow stucco to cure sufficiently. The cement in stucco loses water when it hardens. If it hardens too quickly, the cement may lose too much water over a small period of time, leading to cracks. This often occurs if the stucco layer is too thin, if the temperature at the time of installation is too hot or if there is too much wind. These cracks usually have a spiderweb pattern.
  
  

Moisture

• Small cracks in stucco may let water from the outside penetrate into the stucco material, leading to larger cracks over time as the moisture spreads and loosens large areas of stucco. If you let these bigger cracks expand, they can eventually threaten the integrity of the entire structure. To correct this problem, you have to remove the damaged areas of the stucco and replace them with new stucco.
  
  

Materials

• The materials that make up the stucco structure may make it more prone to cracking. For example, the hidden boards that support the stucco may lose moisture over time and shrinks, putting stress on the stucco. In some cases, this may break the stucco. The stucco itself may contain too much cement, which may also shrink over time. The sand in the stucco may contain too much fine materials, clay or dirt, all of which may also contribute to shrinkage.
  
  

Structural Movement

• Cracks in stucco may develop because the entire structure moves, pulling stucco in different directions. For example, the soil or the foundation of the building may move because the structure was not built properly. Stucco in earthquake-prone areas, such as Southern California, may crack often because seismic activities move the building structure. Even the pressure from the wind may cause cracks if the stucco was not properly installed.