Depends on how you do it Sailhog. And how large of an area you're dealing with. Some just drill holes to allow the core to dry out and then fill with
epoxy. To properly re-core, you need to remove the bottom skin and core, grind the upper layer, then put in new core and glass. And that doesn't even account for the stuff between you and the deck. There might be other ways, but that's the ways I know of.