Gel-Coat Cracks in oc1 canoes

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What to do and what not to do when repairing your outrigger canoe.

In the last article I talked about the construction of the canoes, the materials used, epoxy, carbon fiber, core-mat (a foam core), and gel-coat. The gel-coat is the color, and being a polyester resin product, is brittle. As I said last time, if there is any flexing of the canoe, the epoxy, carbon fiber laminate can handle it, but the gel-coat might crack, especially if it is thick like most of the older boats are. Some manufacturers have gotten wise to this and are applying their gel-coat as thin as possible and still make an even color. Although this makes repairs a little more difficult, it is much better and eliminates most gel-coat cracking.

The bonding of the epoxy laminate to the gel-coat is another critical thing. Manufacturers have learned and improved on this process, and for the most part the bonding is excellent on the newer boats. I have seen many older boats, however, where, once there is a gel-coat crack, you can literally chip off the gel-coat with your fingernail. The learning curve of the manufacturers has all but eliminated this problem, and if you have a new boat that does this, something is wrong.

An interesting and important fact about the relationship of epoxies and polyester resins is that epoxy will adhere to cured polyester, but polyester will NOT bond to epoxy. Because of this repairs should not be made with polyester resin. I have repaired many of these "polyester repairs", and although it may seem to work, in the long run if there is any stress to the area, the bond will let go, causing further problems. Make sure whoever repairs your epoxy canoes, uses epoxy. Now, you can understand the repair dilemma� I never use gel-coat, a polyester resin, for repairs. Instead, after making the structural repair, and fairing it, I spray with and an epoxy primer, and then spray a quality linear polyurethane paint. The color is matched with computer color matching. If it is gel-coat crack only (common in older boats with thick gel-coat), I sand the crack out, making sure the surrounding gel-coat has a good bond, fill with thickened epoxy, fair, prime and paint. That being said, for the home repair job of a gel-coat only crack, using the stock color gel-coat would be easier, filling the sanded out area. The gel-coat can then be sanded smooth, finer and finer (to 1500 grit) and then polished out. I really don't recommend this except the smallest of hairline cracks on the older, thick gel-coat boats. In larger cracks the bonding problem of gel-coat to cured epoxy becomes an issue.

If the area around a crack is soft, or after you gently sand the gel-coat off, you can see a stress line in the carbon fiber, then some reinforcement repairs are needed. One other note while we are on the subject. The Hurricane, a very popular canoe by Maui Fiberglass, does not use gel-coat. Hurricanes are painted with a linear polyurethane paint, which I think is an excellent idea, but from a manufacturer's viewpoint, adds many new production problems, including cost and time.

In the next article, I would like to address the steering systems on OC1s, and especially from the safety standpoint, checking your cables. Aloha for now.

--Steven

Posted by SteveGates on Sat, 12/14/2002 - 6:22pm

37 comments

May I ask you two questions?

1. If epoxy resin is waterproof and if the gel coat on your canoe has many hairline cracks then do you need to repair the cracks or are they waterproof? I have an old wave blade w/ many hairline gel coat cracks and I put tape on them because I did't know if they are waterproof and I didn't want water to get in the hull or under the rest of the gel coat around the crack and cause more gel coat to crack off. I'd rather do nothing to them if they are only cosmetic.

2. I had my wave blade completely painted w/ an epoxy primer and Awlgrip marine paint. Now there are tiny bubbles forming on the hull. I asked the guy who painted it "what is going on?" and he said he wasn't sure. Do you have any ideas? When I take my boat to work it is in the sun for two hours in the middle of the day. Maybe is the heat doing this? What can I do to prevent further damage?

Thanks so much for any assistance. Mahalos


#1 Thu, 01/16/2003 - 3:29pm


I would keep the tape on the cracks, because I know if there is not enough epoxy in the carbon fiber cloth, water can soak into the foam core mat. As for the paint, I don't know. What color is your boat? or what color is exposed to the sun? white is a lot lot cooler than other colors. heat can cause damage after a while.

I am sure Steve can expand on this..


#2 Fri, 01/17/2003 - 5:48pm


My boat is white top and yellow bottom w/ a yellow ama. What's strange is that my ama isn't getting the tiny bubbles and it is in the sun just as much. The only difference is that it wasn't painted w/ the epoxy primer and the main hull was.


#3 Fri, 01/17/2003 - 8:14pm


First of all gel coat is a polyester resin, and therefore is capable of absorbing moisture. Yes, keep tape (the clear packing tape works good) over the cracks as moisture soaking in can result in further gel coat cracking, or even chipping away from the laminate. The latter is due to poor original bonding between the gel coat and and the epoxy laminate, common in some older boats, and I have had many older Wave Blades in my shop with this problem. Also, in some of the older boats, a looser weave carbon and not enough epoxy allows water to absorb into the foam core, trapping moisture indefinitely, causing further gel coat problems. I suspect this may be the case with your boat....moisture somewhere, in hairline cracks, in the core, and this moisture is causing the bubbling in the primer and paint as well. An epoxy primer, Awlgrip marine finish is an excellent finish, but if there is moisture underneath it there will be problems. So, aside from repairing gel coat cracks with epoxy, keep them dry and taped. If there is any soft spot near cracks, or creasing, then the laminate has been damaged and repairs should be made......Steve


#4 Sat, 01/18/2003 - 8:58pm


Anonymous

Hello,
I was wondering where you got your Linear Polyurethane paint. I am painting a carbon fiber
bike and have heard a Linear Polyurethane paint
would be best to sheild the epoxy from UV damage.
Can I get this paint from a boat store? Was it hard
to apply?

Thanks for your help.
-Sam-


#5 Fri, 03/21/2003 - 11:57am
edit


Steven,

your article very interesting. I have just got a plug for an OC1 released from Australian Customs. I need to get my building process down as I aim to build them for a living! I have been making vac-bagged Rescue boards for the junior surf lifesavers in part, importantly, to get a viable process down and, as they favoured a gelcoat finish and I had various problems getting vacuums down on totally polyester laminates, I "invented" the idea of going epoxy vac-bagged laminate inside the gelcoat. Acutally, to give myself some texture, I laminated 1 layer of 4oz against the gelcoat.

I have to say, my results have been questionable. Even with the epoxy laminate held under pressure against the polyester laminate by the vacuum process, poor bonding has led me to bin some thousands of dollars worth of boards. You get a creaky loose bit of laminate that shows as a slight wobble in the gelcoat. Firm pressure with the thumb tells you you've got another damn reject.

Prior to this I was doing the boards all-epoxy laid into a mold with Duratec clear or sanding primer as a 'gelcoat'. The bond here was not problematic.

I was astonished to catch your article as it dealt with a problem that will have me out of business if I don't sort it.

I'm not new to the business having built circumnavigating catamarans, carbon wingmasts and assorted industrial stuff. But this polyester/epoxy interface is driving me near to extinction. Your comments more than eagerly awaited.

Thanks
Rob
(For your info, Strabroke Island is off the Queensland coast of Australia, not far from Brisbane)


#6 Mon, 05/12/2003 - 9:17pm


Aloha Rob,

Yes, some manufacturers still have a bonding problem, but some have it solved. I can't say I know the exact technique, but they are using Duratec (surfacing primer?) as a bonding agent. Also one manufacturer I know is sprayng the gel coat thin, so cracking is less likely, but print through of the weave becomes an issue. Having repaired many of his canoes, I know his bonding techniques are working. Perhaps I can find out more about his Duratec use.

Thanks too for the info about Strabroke Island I am curious about all islands. Also, what circumnavigating catamarans did you build. I own a trimaran, and have built several composite power catamarans.

Steve


#7 Wed, 05/14/2003 - 11:10am


Hi Steve,

wow, this site really works! Believe it or not I sprayed my first hybrid Duratec/polyester gel into a mold just before getting yor reply, which is none theless appreciated. For your further info, I got from the Gougeon bros the fact that Ferro make a tie coat. The disadvantage of a tie-coat being extra work extra clean-up extra weight.

The last cat I built was designed by Nic Bailey (who has a website, try searching the name or Feral catamarans...I've lost his card around the office) It was 40', carbon wingmast. The hull vac-bagged epoxy/Airex foam sandwich laminated with unidirectional glass +/- 45 degrees and a layer of 6oz. I structured the wingmast which is still standing and flogging accross the Atlantic regularly between charter seasons in Trinidad. Search under Orinoco Flo and you should find them and an article or two on the boat from Multihull International (UK based.)

I had a lot of very willing info from great people and it's the first project I have ever undertaken which led me to realise, really realise, that people need people.

I'll try and support your website. I think the concept is just great.

Kind regards,
Rob


#8 Fri, 05/23/2003 - 1:08pm


Anonymous

From Australia
THIS IS A GREAT SEGMENT. WILL SEND THE SITE ADDRESS TO OUR MAINTAINCE OFFICER. iN AN ATTEMPT TO REPAIR SEVERE OZMOSUS (SPELLING?) THE CANOE WAS SANDED BACK AND PAINTED. WHAT A DISASTER. iT NOW IS A FLOATING SPONGE. I HAVE A STRIP OF BLISTERS ON THE FORDECK. HELP
THANKS
DEB


#9 Tue, 05/27/2003 - 2:48am
edit


Fantastic Info, do you have any advice on repairing the Carbon Fiber under my get coat.

I noticed on my OC1 I have some freyed fibers. Thankfully it only seams to be appox 1" on the bow of the canoe.

Could someone point me to some resource on carbon repair.

I have done a fair bit of glass repair, are the principles the same?

Thanks,

Cam


#10 Tue, 06/10/2003 - 12:53pm


Hi this is a but late, but for the sake of others and documentation... It sounds like it's just the bow, I would touch it up with thickend epoxy and then sand it smooth. But if it's obvioiusly weak, I would recoomend reinforcing it with carbon fiber or fiber glass. Be sure to use epoxy.
And it's similar to using fiber glass, but a bit more flexible.


#11 Wed, 11/12/2003 - 11:01am


An interesting and important fact about the relationship of epoxies and polyester resins is that epoxy will adhere to cured polyester, but polyester will NOT bond to epoxy.

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#21 Fri, 10/29/2010 - 1:52pm


My boat is white top and yellow bottom w/ a yellow ama. What's strange is that my ama isn't getting the tiny bubbles and it is in the sun just as much. The only difference is that it wasn't painted w/ the epoxy primer and the main hull was.
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#22 Fri, 11/19/2010 - 4:18pm


I was astonished to catch your article as it dealt with a problem that will have me out of business if I don't sort it.
I'm not new to the business having built circumnavigating catamarans, carbon wingmasts and assorted industrial stuff. But this polyester/epoxy interface is driving me near to extinction. Your comments more than eagerly awaited.
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#24 Tue, 12/14/2010 - 10:14pm


Now I can differentiate the about the relationship of epoxies and polyester resins is that epoxy will adhere to cured polyester, but polyester will NOT bond to epoxy.. Thank you for posting.
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