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Old 20-12-2009, 07:36   #1
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Thru-Hulls in Cored Hulls

I need to install additional mushroom head thruhulls in a cored area of the hull. Above the waterline, but still need to do it right.

I know I need to remove the core material between the skins and replace with thickened epoxy, but how far deep do I need to dig it out ? This will be a 1 1/2 inch thruhull, so I'm guessing the hole will be 2 inches or so. I thought I'd seen mention of this on the WEST Epoxy site, but I don't see it now.

A guess would be that I should go out to maybe half the flange of the thruhull, but I'd appreciate hearing what others would say.
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Old 20-12-2009, 08:53   #2
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Good morning ggray, you are on the right track,what i do is take an allen wrench and grind a cutting edge on the short leg,chuck it up in an electric drill and cut away about 1/2" or so of core, paint it out with straight epoxy(no filler) and let it soak in a while,then fill with a thickend mix with cabosil and milled glass fibers to a no slump consistency.
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Old 20-12-2009, 09:22   #3
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Section 7 - for fasteners but can be easily applied to thru-hulls: http://www.westsystem.com/ss/assets/...aintenance.pdf
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Old 20-12-2009, 19:51   #4
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Thanks Steve and Lodesman
That 1/2 inch core removal is what i was looking for.
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Old 20-12-2009, 20:48   #5
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I've just gone a little larger on the hole size and lay in some glass cloth w/epoxy. That way there's no chance of the water sneaking past a cracked seam.

Anything below the water line is very important to seal off in cored hulls. One pin hole can ruin a whole summer on the hard drying out a core.
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Old 21-12-2009, 05:16   #6
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I recommend removing core & backfilling /w epoxy to a diameter beyond the bearing edge of and fastener or thru-hull.
In doing so, you provide structural strength to the laminate, to resist crushing forces.
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Old 21-12-2009, 21:26   #7
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Gord, I may just do that. Once I get the fitting and start digging out the core, I'll evaluate. But it will be at least 1/2 inch.
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Old 22-12-2009, 09:07   #8
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Delmarrey is right about any pinhole letting water through,this is why it is very important to preseal the core after routing out the hole before you backfill.This gives you 3 lines of defence against water getting to the core,the 1st is the caulk,the 2nd is the bondline of the backfill to the inner and outer skins and the last is the core sealed with neat,unfilled epoxy.I also like to add milled glass or PE fibers to the backfill mix and i also prefer to use epoxies which are less brittle than,say ,west epoxy,although i think their new toughened epoxy may be great for this use but i havnt used it yet.
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