Light coming through fiberglass repair - SailNet Community
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post #1 of 4 Old 07-30-2012 Thread Starter
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Light coming through fiberglass repair

I patched a hole from an old knotmeter in my exterior cockpit bulkhead with fiberglass CSM and cloth and West Marine Polyester "Boater's Resin," with WM Finish Gelcoat on the outside.

The problem is that the finished repair is translucent. The sunlight outside can be seen inside, and if a bright light is on inside, you can see the outline of the repair outside.

The color of my repair is golden yellow, and translucent, whereas the old fiberglass was fairly opaque and brown-purple.

Why did this happen? Is this going to be a problem, such as by allowing UV infiltration which could weaken the fiberglass? Do I need a thicker layer of gelcoat? (I drilled out a section for a new instrument, and it looks like my gelcoat is actually thicker than the original gelcoat.)
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post #2 of 4 Old 07-30-2012
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Re: Light coming through fiberglass repair

My boat's the same way and the hull's an inch thick.
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post #3 of 4 Old 07-30-2012
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Re: Light coming through fiberglass repair

aaron, you forgot to buy marine grade photon-inhibitor additive, which would slow down the photons coming through your new work.

No, seriously...FRP is normally translucent. There are additives, fillers, dyes, added to make up the color. If the exterior gelcoat you applied is the same "white" as the bulkhead when viewed with reflected light, then that's fine. Just add some opaque layer on the inside, i.e. a couple of coats of black or gray primer or other paint should stop the light from showing through. Ideally you'd go back and add an opaque additive/filler to the FRP, but painting over it will be just fine. By all means, match the color of the existing stuff as a top coat if you will be looking at it.
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post #4 of 4 Old 07-30-2012
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Re: Light coming through fiberglass repair

A lot of it depends on the resin color. The resin we use is purple when cured so it doesn't allow as much light through.

Baggett and Sons Marine Restoration
The Landing at Colony Wharf
Bellingham, WA.

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