My Cal T-4 has wet and rotted plywood in the ceiling of the cabin. I cut an inspection hole through the thin fiberglass covering the bottom side of the ceiling and found the plywood comes out in shreds. I pulled enough away to expose the fiberglass of the top deck. Can the plywood be replaced from inside the cabin or does the top deck need to be removed? I'm pretty competent with home repairs but I'm new to boat repair. Any advice on the best way to proceed with this repair would be appreciated.
On other boats I've repaired it seemed better to leave the outer deck FG laminations intact, especially if nonskid or other molded-in features are involved. This way the job is inside, from the weather, and any final roughness is covered by the headliner:
- remove the inner FG lamination with a knife and/or a knee grinder (4.5" or 5") with 36 grit sanding disk and/or whatever from any wet/rotted core - keep going until you uncover an inch or so of good core all around the patch area
- remove damaged core material, finally using grinder to lightly scuff the underside of the outer deck FG (careful not to reduce its thickness much, or just add a layer of 6 or 10 oz cloth if thinnning did occur of if needed in any case (like just for peace of mind), and use the sander/grinder to add a 5:1 scarph all around the edges of the existing core material
- then use the grinder, to scarf (5:1) the edges of the new ply core material until it fits (lots of grind and fit, grind and fit here),
- core patch is 'clamped' in place with numerous 'bent-in-place clamp legs' from the floor or whatever structure is under the patch, legs maybe about 1/2" x 1.5" in cross-section (depending on wood type and length needed), custom cut to length to be a 'bend-in-fit' (to apply upward pressue on the patched in core matrerial - be sure to dry-fit all this until its perfect prior to actually applying epoxy goop, and use drop cloths/masking material under the patch and clamp legs to catch the goop that squeezes out)
- measue a scrap of the old laminate or otherwise determine the total thickness of glass needed for inner laminate
- then scarf (15:1) in the new interior FG laminations using epoxy.
Ask more questions if you like - I've done several of these.