Most people understand what a crack is. However, in spas and bathtubs, both cracks and crazing can occur. There is a difference in these. Cracks are generally very detectable and occur as a single separation of the surface. They propagate in a straight or jagged line.

Cracks can occur due to mechanical impact, or due to excessive stress in the surface, which becomes higher than the material strength. Multiple causes of excessive stress exist. These are exaggerated when the surface gets hot due to sunlight, etc. There can be multiple cracks in a surface, and they go through the entire surface layer.