I use the outside skin I cut off as a pattern for the new core wood. I add new glass to existing inner skin (2) 1708 biax and let cure. Backfill putty the edges and let cure. Then glued (1) - 3/4" and (1) - 1/2" ply together with (1) - 1 1/2 oz mat. Use drywall screws to hold together then remove when cured. Wet out (1) - 1 1/2 oz mat on inner skin and clamp new core in. Let cure then remove clamps and putty/grind. Glassed outside with (4) - 1708 biax and a 1 1/2 oz mat to finish. Roll Duratec base primer and sand flat,gelcoat,wet sand,etc.
I don't see any benefit to grinding before you begin because you will have to grind again after gluing the core in anyway to remove drips and excess putty etc. I don't care for the grinding part but it's gotta get done!
