The reasons for hull relamination are due to either osmotic problems or coved hulls that have issues with the outer laminate and core.
Osmotic problems are caused by excessive moisture absorption which can weaken the outer laminates to the point that they have no structural strength and are an unstable substrate on which to apply fresh laminate or epoxy coatings in these situations. In these situations it is necessary to remove the affected laminate back to a sound substrate and the amount of laminate removed determines how much new laminate will be required.
When a core and outer laminate have failed the repair procedure is often a lot more complex and expensive with the worst case scenario being replacement of the core and a new outer laminate dependent on the order of the boat will determine whether this is financially worthwhile. The cause of these problems are many but the most common is water absorption into the core often through badly fitted through hull fittings or poor adhesion between the outer laminate and the core.