Why does stucco crack?
"Non Engineer" Answer: Because it's made from cement.
Explanation: Stucco (or plaster as it is also known) cracks for many different reasons but the main reason is because it's made from cement. Additional reasons or contributing causes to cracking can include improper construction, building features or application deficiencies.
Stucco is one of the most common exterior cladding systems utilized for residential structures whether for framed buildings or for concrete block buildings. Conventional stucco is a cementitious product composed primarily of Portland cement, sand and water. Since it is cementitious, as is any Portland cement based product, it has three inherent characteristics: it gets hard, it turns grey, and it cracks. Cementitious products, or those composed primarily of the ingredients described, shrink as they gain strength. As a result of this inherent shrinkage, cracks will often develop in the stucco making it necessary to control this cracking.
That's why the Florida Building Code describes the installation of exterior plaster and then references two ASTM standards which govern the application of "cement plaster" and associated components.
Commentary: Stucco also cracks because of construction deficiencies. Improper integration of wall fixtures, penetrations/openings, or improper implementation of flashings at these locations can lead to cracking and/or water intrusion. Uncontrolled water migration to the cladding system can result in corrosion of the metal lathe which is often utilized to secure the stucco to framed walls, as well as degradation of the framing components, particularly they plywood sheathing.
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