Delamination is the separation of layers in composite wood. There are a number of reasons this occurs, but they come down either the quality of the product itself, or exposure to elements.
The main problems that occur as a result of delamination have to do with the warping or bubbling up of the layers of wood. The most common cause of this degradation of a layered wood like plywood is exposed to the elements without proper protection.
Water and excessive heat are the main culprits in causing this separation. If a sheet of plywood is used as a in between rough wood and finished wood, the layers of the plywood, when delamination occurs, will result in the entire constructed piece being ruined.
Proper care should always be taken, in the purchase of quality materials when buying layered woods, and all layered wood should be sufficiently coated with primer and other protective coatings in order to prevent this deterioration.