Repair

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irso4b
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Repair

Post by irso4b »

Hi,

I'm looking some advice on gelcoat repair. As the images (will hopefully) show there are 3 separate areas. 2 spiderweb cracks, including one with a chip coming off. 1 series of very fine cracks from the bow going along the hull. Also a few gouges not shown.

As far as I can see the process is clean and mark out the area, sand-apply gelcoat-sand/polish. Is it generally the whole area that gets sanded down or widen each individual crack? Is there any easy way to match the hull shape when the gel is drying, I had read of people using acetate sheets.

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Any help is appreciated.

[Images fixed by moderator: they weren't showing because the links were to the page the image was on, not the actual .jpg]
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leighv
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Re: Repair

Post by leighv »

I'd start by actually using a Dremel on the cracks. This ensures the cracks are properly dealt with, and provides a channel into which to put the flowcoat. This makes it easier to eventually sand everything back to its original shape, as opposed to sanding the entire area down and then trying to reapply flowcoat to everything. Acetate can help smooth the result but you still need to sand it with wet and dry sandpaper.

By the way, use flowcoat, not gelcoat. If you use gelcoat you will have to use acetate sheets, otherwise it will not dry.

Jeremy Vore has an excellent series of videos that I learned from:

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MikeB
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Re: Repair

Post by MikeB »

What happened? What condition is the substrate in? Yes, you're going to need to open up each crack, if you feel you have to. I've had excellent results using packing tape to give a smooth finish btw.
irso4b
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Re: Repair

Post by irso4b »

leighv wrote:
Tue Apr 09, 2024 11:50 am
I'd start by actually using a Dremel on the cracks. This ensures the cracks are properly dealt with, and provides a channel into which to put the flowcoat. This makes it easier to eventually sand everything back to its original shape, as opposed to sanding the entire area down and then trying to reapply flowcoat to everything. Acetate can help smooth the result but you still need to sand it with wet and dry sandpaper.

By the way, use flowcoat, not gelcoat. If you use gelcoat you will have to use acetate sheets, otherwise it will not dry.

Jeremy Vore has an excellent series of videos that I learned from:

Thanks very much I'll have a look at the vid.
irso4b
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Re: Repair

Post by irso4b »

MikeB wrote:
Tue Apr 09, 2024 1:48 pm
What happened? What condition is the substrate in? Yes, you're going to need to open up each crack, if you feel you have to. I've had excellent results using packing tape to give a smooth finish btw.
Hi Mike,

The two spiderweb cracks are from bangs of the rocks. The cracks at the front, I'm not sure what caused them. As far as I can tell it's only the gelcoat and the undelying glass/mat hasn't been affected. Okay cool.

Cheers.
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MikeB
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Re: Repair

Post by MikeB »

Sounds like the hull is ok then, which is good. If you really, really, want to repair then maybe have a read of this earlier discussion and follow the links once you've read the advice therein. Opinions differ on this, but my view is that gel is essentially decorative and sacrificial. Even on a kayak hull. Now, a yacht, constantly immersed, that's a different matter.

I spent hours dealing with the star cracks on the rear deck of a Nordkapp I had - they were renowned for it. The first time I put any weight behind the cockpit, getting out, it cracked again. I also had a second-hand Aleut that arrived in less - than - wonderful condition, having had a hard life, with a mass of star cracking all over hte hull. The price was right, so it never bothered me and there was never a problem while I had it.
irso4b
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Re: Repair

Post by irso4b »

MikeB wrote:
Tue Apr 09, 2024 3:47 pm
Sounds like the hull is ok then, which is good. If you really, really, want to repair then maybe have a read of this earlier discussion and follow the links once you've read the advice therein. Opinions differ on this, but my view is that gel is essentially decorative and sacrificial. Even on a kayak hull. Now, a yacht, constantly immersed, that's a different matter.

I spent hours dealing with the star cracks on the rear deck of a Nordkapp I had - they were renowned for it. The first time I put any weight behind the cockpit, getting out, it cracked again. I also had a second-hand Aleut that arrived in less - than - wonderful condition, having had a hard life, with a mass of star cracking all over hte hull. The price was right, so it never bothered me and there was never a problem while I had it.
Mike,

I've had a read through it, very informative. Hopefully I'll get a start on it tomorrow. Thanks very much.
charleston14
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Re: Repair

Post by charleston14 »

When you dremmel out the cracks be sure to get down deep enough that you get to the bottom of the crack and all the way along to its very end (this is often as deep as the underlying glass fibres) if you dont dremmel out deep enough then the repaired area can get “print through” of the old crack. It’s tempting to do as little grinding as possible but all my better repairs have been when I’ve been a bit more bold with the grinder.

After all the careful sanding (of progressively finer grades), then compounding , if you then use use a marine boat wax you’ll get the glossy shine back.
irso4b
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Re: Repair

Post by irso4b »

charleston14 wrote:
Wed Apr 10, 2024 8:21 am
When you dremmel out the cracks be sure to get down deep enough that you get to the bottom of the crack and all the way along to its very end (this is often as deep as the underlying glass fibres) if you dont dremmel out deep enough then the repaired area can get “print through” of the old crack. It’s tempting to do as little grinding as possible but all my better repairs have been when I’ve been a bit more bold with the grinder.

After all the careful sanding (of progressively finer grades), then compounding , if you then use use a marine boat wax you’ll get the glossy shine back.
Thanks for the help.
Chris Bolton
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Re: Repair

Post by Chris Bolton »

be sure to get down deep enough
That's true, but also take care not to go into the glass fibres as they are what gives it the strength. Maybe your boat has kevlar fibres, cutting those is worse because apart from losing strength, they go fluffy and won't sand smooth. I would use the dremel with a disc held fairly flat, maybe 20º between the disc and the boat, so that you make a shallow scoop and you can see if the crack is going deeper - rather than cutting a V along the track. I hope that description is clear, if not I'll do a sketch.
irso4b
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Re: Repair

Post by irso4b »

Chris Bolton wrote:
Fri Apr 12, 2024 9:24 pm
be sure to get down deep enough
That's true, but also take care not to go into the glass fibres as they are what gives it the strength. Maybe your boat has kevlar fibres, cutting those is worse because apart from losing strength, they go fluffy and won't sand smooth. I would use the dremel with a disc held fairly flat, maybe 20º between the disc and the boat, so that you make a shallow scoop and you can see if the crack is going deeper - rather than cutting a V along the track. I hope that description is clear, if not I'll do a sketch.
Chris very helpful, the description makes sense. Thanks.
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Re: Repair

Post by Sean_soup »

Chris Bolton wrote:
Fri Apr 12, 2024 9:24 pm
I would use the dremel with a disc held fairly flat, maybe 20º between the disc and the boat, so that you make a shallow scoop and you can see if the crack is going deeper - rather than cutting a V along the track.
I use a bullet shaped grinding stone rather than a disc myself, but it's the same idea - cutting a rounded 'U' shaped valley rather than a 'V'.
irso4b
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Re: Repair

Post by irso4b »

Sean_soup wrote:
Sat Apr 13, 2024 2:11 am
Chris Bolton wrote:
Fri Apr 12, 2024 9:24 pm
I would use the dremel with a disc held fairly flat, maybe 20º between the disc and the boat, so that you make a shallow scoop and you can see if the crack is going deeper - rather than cutting a V along the track.
I use a bullet shaped grinding stone rather than a disc myself, but it's the same idea - cutting a rounded 'U' shaped valley rather than a 'V'.
I'll have a go with both and see how they turn out. Thanks.
Chris Bolton
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Re: Repair

Post by Chris Bolton »

It's a good point. A bullet grinding stone may produce a better job, I wore mine out very quickly and didn't have any more, but I had lots of discs and they're relatively cheap. Your experience may be different, so as you say, try both.
irso4b
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Re: Repair

Post by irso4b »

Hi,

A few problems arrived. Mainly I have had small pinprick holes in the coat, presumably from air bubbles. Any top tips to help sort this out?

I used the bullet and pointed tips for the Dremel and they both worked well. I used the bullet tip more but it just depended on crack.
Sean_soup
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Re: Repair

Post by Sean_soup »

I've had a bit of bother with that, and yes it's little air bubbles that cause it - can be quite frustrating.

When I can be bothered to sort them out, I go back to the grinder and open each one out to about the size of a dimple in a golf ball, clean up with some acetone and start again. Once I've mixed up some more topcoat, I put a very small blob on a flat surface (lately I've been using a ceramic tile) and spread it extremely thinly with a flexible filling knife with a nice straight edge on it, then scrape it up again in very small quantities and dab a tiny blob into each dimple with a corner of the knife.

I've seen it suggested that you should do similar using a Stanley knife blade and I can see how that might perhaps get better results, but I think if I do that it's only a matter of time before I slice a finger open. (Always going to smart a bit whilst sloshing acetone about.)

Anyway, the idea is that you spread the topcoat so thinly that any air bubbles will burst, and then gather it back up without stirring any more air in. I try to do that with my repairs in the first place, but it's only really effective for a very small quantity at a time. (Just about feasible while dealing with star cracks I guess, but not really anything bigger.)
irso4b
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Re: Repair

Post by irso4b »

Sean_soup wrote:
Thu Apr 18, 2024 10:54 pm
I've had a bit of bother with that, and yes it's little air bubbles that cause it - can be quite frustrating.

When I can be bothered to sort them out, I go back to the grinder and open each one out to about the size of a dimple in a golf ball, clean up with some acetone and start again. Once I've mixed up some more topcoat, I put a very small blob on a flat surface (lately I've been using a ceramic tile) and spread it extremely thinly with a flexible filling knife with a nice straight edge on it, then scrape it up again in very small quantities and dab a tiny blob into each dimple with a corner of the knife.

I've seen it suggested that you should do similar using a Stanley knife blade and I can see how that might perhaps get better results, but I think if I do that it's only a matter of time before I slice a finger open. (Always going to smart a bit whilst sloshing acetone about.)

Anyway, the idea is that you spread the topcoat so thinly that any air bubbles will burst, and then gather it back up without stirring any more air in. I try to do that with my repairs in the first place, but it's only really effective for a very small quantity at a time. (Just about feasible while dealing with star cracks I guess, but not really anything bigger.)
Thanks very much, really helpful.
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