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Old 21 March 2007, 09:21   #51
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We cut a hole deckside and were surprised that it's over an inch thick. Looking into the hole directly above the crack there is no apparent damage on the inside. It's not wet or broken on the inside. Does this mean we can get away with grinding out the crack on the outside on the bottom of the hull to affect repairs. Maybe my brother can explain a bit better.
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Old 21 March 2007, 10:07   #52
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Quote:
Originally Posted by Rogan View Post
We cut a hole deckside and were surprised that it's over an inch thick. Looking into the hole directly above the crack there is no apparent damage on the inside. It's not wet or broken on the inside. Does this mean we can get away with grinding out the crack on the outside on the bottom of the hull to affect repairs. Maybe my brother can explain a bit better.
In a word, yes. Glass repair isn't really rocket science. Grind back to good solid laminate, then fill with cloth, mat, chopped strand or whatever is appropriate for the size of the repair. Recore if necessary, though I don't think most RIBs are cored construction. Lay up as many layers of wet out glass as necessary to bring the glass close to the orginal level. Add layers immediately, while the resin is wet, you want them to cure together for the best bond.

I prefer West System epoxy for this sort of stuff, vs. polyester resin, unless it's an extremely large repair, i.e. several square feet. Epoxy has much better bonding characteristics for holding onto existing laminates than polyester, though it's more $$. Polyester is more cost effective when building a complete structure from scratch. Then grind and/or sand smooth, fair as necessary (again, West System, with 410 Microlight filler, easily sand-able) and paint or gel coat for cosmetics, if you care to.

It's even possible to do a "blind patch" of a hole without access to the inside, but that's another lesson...
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Old 21 March 2007, 12:30   #53
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That sounds like good news, I really didn't want to have to cut a larger hole in the deck. I have ample supply of west system epoxy resin and two types of filler one for filling and one for bonding. Im thinking of using the one for bonding after I layer fiberglass mat and fiberglass chopped strand since it will be stronger and I should still be able to sand it and then do a final clear coat of epoxy resin in peperation for sanding and the first layers of primer coat. I am going to use Interlux international Perfection primer and topside to finish off the hull and deck.

What do you think of mixing international perfection colors to obtain the desired color of rescue orange. I was going to mix yellow and red and record the ratio for the entire boat, Do you think there might be a problem with the fact that it is a 2 part paint. Thanks
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Old 21 March 2007, 20:01   #54
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On your layup you want to use thinner layers and more of them than the original layup and start with the smallest and work to the largest pice of CSM or mat. In your case i would use CSM(chopped strand mat). you need to grind even tapers around the repair(follow the lines in the old glass. i would also use west system epoxy. you can brush on gel coat its an easy colour to match you want to use a mil guage and have about 18-24 mm of coverage. good luck
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Old 22 March 2007, 08:29   #55
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Thanks OceanEco and dctucker for the info. I am going to flip the boat and do the repairs as soon as the weather clears. We will post pics.

How important is a mil gauge and can anyone recommend a good one?
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Old 22 March 2007, 09:30   #56
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Here's a decent primer on glass repair, albeit, working from the inside
http://www.boatus.com/boattech/casey/17.htm

Working from the outside, all the same principles apply, except that you're doing gelcoat (or paint) last, instead of first, and unless you're repairing a hole, you don't need the backing plate. To do a blind patch of a hole from the outside, you would insert some sort of backing plate from the outside (cardboard is actually OK) and either bond it to the interior of the hull, mechanically fasten it, or hold it from the middle with something you'll remove after the repair sets up, then just fill & fair the holes.

In either case, the wide grind area is important (feathering), as is building up layers of glass. It's the glass that provides the structure, the resin is just there for the bond, you actually want as little resin as possible.

All this is assuming you have a rather large repair, where structural integrity may be compromised by the damage. If you've ground out more than say, 1 1/2 to 2", I'd be putting some glass in there. For smaller cracks, just fill with gel paste or West and an appropriate filler. Microlight would be my recommendation in this case. Spend the $3-$4 to buy West's guide to understanding the characteristics of their different materials. A Dremel is good for grinding out small cracks which will likely just need filler. If you've broken out the angle grinder, you're probably talking about adding glass...

All my boats (power & sail) are so old that I'm not terribly concerned with cosmetics, so I'm not your best advisor on color matching! I'd be willing to bet that you could mix the 2 part paints to get the right color match though. A quick call or email to International will give you a definitive answer. As long as it's the same type of paint, it's seems perfectly logical to me, to do so to get the right match.

Color matching is more of an art than a science. I have an old school chum who is a 3rd generation body shop painter. He's amazing, can nail a color match like nothing, while it may take me 4-5 tests to get it right. Keep in mind that most paints and gelcoats will "dry down" a couple of shades darker. It is best to test small amounts on some cardboard or something before you commit large expensive batches of material to the actual repair.

And personally, I wouldn't bother with a mil guage, but I'm more of a seat of the pants kind of guy. If you're an analytical engineer type, you may want one. Three to 5 light coats of gelcoat is about right IME. With paint, just follow the mfg's recommendation.

In either case, if you're going to sand to blend your repair with the eixisting surface, make put on an extra coat or two. If your final cosmetic is to paint or gelcoat the entire hull, just make it as fair as possible for a nice finish, and again, follow the mfg's directions.

Looking forward to seeing pics!
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Old 22 March 2007, 12:41   #57
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mil guage ensures you get get the right thickness of gelcoat they are about $2 up here. you can just paint on the gelcoat thick and skip the mil guage. It sounds like you are going to use an 2 part epoxy paint so you may not need it unless you use gelcoat for your repair first.

another good idea is when you are cutting you mat/cloth you can make a template with some clear poly and a jiffy marker. you trace the rings on the taper that you have ground then you use this template to cut your layers of mat/cloth. cut the largest piece of cloth first then cut away the poly to you next size then cut your mat again so on and so on. this just ensures that all you pieces of mat/cloth will fit. thinnner layers and more of them are better than thicker layer for repairs like this.

From your picture it looks like the large repair doesn't go right thru the hull so you want to grind about a 20-1 taper and make sure you don't gring right thru the hull.
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Old 22 March 2007, 14:18   #58
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Quote:
Originally Posted by OceanEco View Post
another good idea is when you are cutting you mat/cloth you can make a template with some clear poly and a jiffy marker. you trace the rings on the taper that you have ground then you use this template to cut your layers of mat/cloth. cut the largest piece of cloth first then cut away the poly to you next size then cut your mat again so on and so on. this just ensures that all you pieces of mat/cloth will fit. thinnner layers and more of them are better than thicker layer for repairs like this.
That's a pretty cool idea, I like it!
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Old 22 March 2007, 17:40   #59
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Thanks for all the info! We'll have the boat flipped and the crack ground out on sat. I'll post some more pics then
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Old 22 March 2007, 17:50   #60
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I decided to go with a 2-part primer by interlux and then do a one-part topcoat of international Brightside (red and yellow). Cheaper and easier. I also almost forgot to be sure to wipe down the fiberglass with a wax and mold release stripper before sanding. Thanks for all the advice guys it is much appreciated I am going to taper the repair as advised and use layers of mat cloth with a final layer of cloth i think. The idea of using some clear poly as a template is perfect. Thanks
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