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Old 17-03-2010, 05:45   #1
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Best Materials for a Thru-Hull Patch?

Can anyone recommend a good combination of fiberglass materials for two thru-hull patches that I will be doing on my 1978 Pearson 26? I have found some good information on the repair but a lot of it is conflicting.

Ideally these would be things I could pick up at a West Marine or similar store and not have to order b/c I'm hoping to do the repair this weekend.
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Old 17-03-2010, 08:25   #2
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are you completly filling in the hole? If so, I suppose you'll use a "hole saw" and cut a suitable sized plug to dip in resin and insert before trying to cover with glass matt and resin finish coats right?
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Old 17-03-2010, 09:56   #3
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Basically… First bevel the edges of the hole from the outside as much as possible to increase the surface area of the hole. I like to use a rasp (a wood bastard file). Clean the interior surrounding fiberglass, sand it to remove any paint and rough up and expose clean fiberglass.

Paint the inside with unthickened epoxy, and when it begins to kick, lay on a bandage of biaxial cloth that overlaps the hole, and paint the fiberglass cloth with enough epoxy to saturate it.

Wait for the epoxy on the inside patch to begin to cure, still tacky to your finger, and lay on a biaxial round patch the size of the hole on the outside and paint with epoxy. Cut circular patches each ¼” or so larger than the last to build up layers of fiberglass that overlap onto the beveled outside edge you created earlier. Add layers to bring the thickness close to that of your hull—however thick that is—and finish, again when the epoxy is still tacky, by thickening some epoxy and fairing the patch.

When it is completely cured, wash the area with clear water and a 3-M scrubee to remove the anime blush from the epoxy. Sand the exterior with 80 grit sandpaper to knock off the high spots and make the low spots, if any more visible. Use more thickened epoxy to fill the low spots until you have a smooth finish.
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Old 17-03-2010, 10:23   #4
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I would use a biax like this: Fiberglass Biaxial Cloth

and West System epoxy. I don't know what your local West Marine store stocks.
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Old 17-03-2010, 11:05   #5
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I am 90% there with David with minor changes.

If the hull is thick enough I would bevel the inside and the outside of the hole. I would shoot for 7-10X the thickness. That is if the hull is 1/2" thick shoot for a 4-5 inch bevel all around the hole. for small thru hulls (2 inch diameter or so) I would reduce the bevel some.

With a double bevel the plug overlaps original material on both inside and outside. The 1/4" increasing patches is the right ticket. I would work the inside and then work the outside. I would also prepare an area an inch or two beyond the bevel and the top layer of fiberglass overlaps the whole thing thicker than original hull thickness and then gets ground/sanded off. I don't prefer to have the plug "thinner" than the hole and filled with raw epoxy as epoxy is non-structural and I prefer fiberglass at least as thick as the original hull. On the inside you do not have to grind/sand back to original surface - Clean it up smooth and leave it a little thicker unless you really don't want the repair to show and are going to also finish it on the inside.

When you grind/sand the plug back to flush pay attention to what happens - If "weave" breaks loose and stands up free, you didn't penetrate the resin into the fibers well enough. If there are minor imperfections after you grind/sand back I would fill with a microballoon and sand /prep for paint.

West System is easy to use and I have found it reliable. I had to "rebuild" my pulpit area after hit and run collisions while my boat was moored. For smooth surfaces mat weave is fine. I had compound curves and found chopped mat the right ticket for me.

Fiberglassing is chemistry. Mix the parts per spec. Too much activator and the mix will get superhot and pot life will suffer. Mix a small batch exactly per instructions and practice on something - get used to pot life and how much time you have to work it. A larger batch in a deep tub will activate faster as well - its got to do with the chemical reaction.

Oh final two thoughts - when you are ready to lay in teh fioberglass make sure everything is superclean with thinner. No oils or debris. Get a box of surgical gloves and wear them. I am a slob and can't keep my fingers out of stuff. Once you contaminate your gloves strip them and put a new pair. As the epoxy starts to activate things get very sticky...
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Old 18-03-2010, 15:38   #6
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Here are a couple of good videos using West Systems to repair a hole in the hull.



Hope this helps you
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Old 18-03-2010, 16:19   #7
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Davids got it down pat. The only thing I do different is to alternate woven roving with CSM as I build up the layers, otherwise the process is the same.

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Old 20-03-2010, 17:01   #8
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Thanks a lot, everyone. I did the grinding and prep work today and I will finish the patches tomorrow. All your responses where very helpful, especially those videos! Thanks again.
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Old 22-03-2010, 10:43   #9
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I removed 3 thru holes in my hull. Basically used a sanding attachment on an angle grinder, and made the whole thing about 8" diameter on inside and outside beveled down to the hole size. Then I used 4 layers on inside and 4 on outside of increasing diameter patches of glass cloth soaked in epoxy (Used west system). I tried to get the air bubbles out too but there may be a few.

In any case, all 3 holes held with no leaks after a few months in the water. I am much more confident now and I dont mind doing fiberglass repair! I have since fixed holes above the waterline the same way.
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