Filthy Deck Hull Joint Help

pmbuck

.
Nov 7, 2020
16
C&C 39 Berkeley
We just recently bought a 1973 C&C 39 and are undertaking lots of fixes, as well as cleaning decades of grubbiness belowdecks. The deck hull joint is in fair condition and might have some minor leaks that we'll address in the near future.

More immediately, I'm eager for advice on how I might clean or care for the blackened raw edge of the fiberglass at the joint. For context, all of the below deck lockers, cabinets, seams, etc. were grubby and mildewy -- black and grimy in many places -- but they clean right up with vinegar or Simple Green and elbow grease. But along the vertical, unfinished edge of the joint it won't come clean.

In my fantasy world, there's
  • something like a gel-thickness cleanser that I can apply to soak in and kill the mildew and
  • something I can then paint onto it, seal or coat it with so that it no longer attracts grime with its unfinished edge.
am I dreaming?

I'd love your insight if you have dealt with unfinished fiberglass edges on an old boat before!

Many thanks.
 

DArcy

.
Feb 11, 2017
1,771
Islander Freeport 36 Ottawa
My old 1974 C&C 27 had what looked like butyl caulking oozing out of the hull to deck joint. It was still very pliable and seemed to be still sealing reasonably well but there was a leak along the low point on the starboard rail. I removed the screws and filled them with boatlife life caulk then reseated them which stopped the leak. I'm just about finished resealing the hull to deck joint on my Islander Freeport 36. That is a big job.
Whatever you use to clean it, make sure it doesn't erode the butyl caulking in the joint.
 

pmbuck

.
Nov 7, 2020
16
C&C 39 Berkeley
Here's a photo.

I'm already grateful for already gaining some insight here -- the fact that it's likely old butyl that's coated in mildew is super helpful. I can avoid acetone or spirits or anything oil-based that might remove the butyl.

Any ideas for a what sort of gel-like cleanser I might safely use? Something I can coat on it and let soak in and then wipe or scrub off, perhaps?
 

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