[sailingdog]

If the core is wet but not rotten, then you can drill a series of holes over the wet area to allow it to drain and dry out. Then you can inject epoxy into the same holes and allow it to cure... which will solve your problem without having to cut away the laminate.

However, if the core is rotten... mushy and no longer able to serve its function, then you will have to cut away the skin and remove the rottten core, and replace it with a new piece.

You can do this from either the top or the bottom... doing it from the top is generally easier, but requires that you take more time to repair/replace the non-skid.

Doing it from the bottom would leave the deck's non-skid surface intact, but is a bit more difficult to do since you're fighting gravity. If you decide to do it from the underside, and have fairly good access to the area, you can do it in two stages... the first is removing the laminate and rotten core and laminating an new core to the upper laminate. Then the second stage would be to laminate a new inner skin. This makes it a bit easier than trying to do it all at once.

BTW, you should really remove and re-bed most of the deck hardware and pot all the holes with thickened epoxy if you do this repair, as that will help prevent having to do this type of repair a second time.