What causes plaster to crack?Updated 2 years ago

There are two main categories of cracks with plastering.  

1. Cracks from substrate movement:  

These are by far the most common type of crack.   Movement cracks tend to happen sometime after the plaster has been applied.   They are usually very fine and run in a straight line.   They are most common in areas of high stress in a building: corners of windows and doors,  point loads from ceiling rafters etc.    These types of cracks are a normal part of the settling process of a building and usually don't pose a risk for the functionality of the finish.   In some cases movement cracks can be repaired but if the building continues to move they may well return.  

2. Cracks from improper plaster application: 

These types of cracks will almost always appear as soon as the plaster is dry.  Most commonly, they are shrinkage cracks that occur from improper application (usually too thick).  They are typically shorter cracks that appear in a Y shape.     Depending on the situation, these cracks may cause problems for the functionality of the finish and should be evaluated for repair.