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Old 26-04-2024, 13:22   #1
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Question What do to with my damaged gelcoat hull

After removing the old paint layers down to the gelcoat on my 7m fiberglass boat, we discovered a lot of damages, scattered across the full length of the submerged part of the hull.



There were no bubbles or blisters and no smell, however on 4-5 small spots, a very sticky substance is leaking out now (where the fiberglass is exposed).















The plan now was to sand down the spots with broken gelcoat a bit further, wash the boat regularly, and to fill them up with epoxy after the boat has dried (located on the Canary Islands).


The fiberglass itself is too thin to peel the hull, as this was a mass produced boat from the early 2000s (only around 8mm of wall thickness).


My main concern now is that the boat will not dry properly for the repair with the Gelcoat on within a few weeks - I think the hull has had some time to soak.


We took some measurements with a Tramex but as the inside of the false bilge was still a bit moist the results might be off. It was all around 25 on the submerged hull side.


Is this a stupid project or does she still have potential?


I have had two surveyors come, talked to several mechanics here but most of them say it would be possible to dry it here for a few weeks, use epoxy and the boat should have no issues over the next few years.



On the other side I am reading everywhere that the hull needs to be almost completely dry, otherwise I would just get more bubbles from sealing the moisture and chemicals in.
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Old 26-04-2024, 14:42   #2
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Re: What do to with my damaged gelcoat hull

Hi, C,
The proper way to do this type of repair is to soda/sandblast the bottom completely and allow it to dry out. Then, basically, you're doing a complete bottom job: re-epoxy with filler as needed and a barrier coat(2 coats). If this were going to be my boat long term, that's the only way to do it. I don't think I'd do less on the boat if I were doing anything other than day sailing in a protected bay. The bottom is junk as it is portrayed in the pix.
Good luck, Rognvald
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Old 26-04-2024, 14:49   #3
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Re: What do to with my damaged gelcoat hull

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Hi, C,
The proper way to do this type of repair is to soda/sandblast the bottom completely and allow it to dry out. Then, basically, you're doing a complete bottom job: re-epoxy with filler as needed and a barrier coat(2 coats). If this were going to be my boat long term, that's the only way to do it. I don't think I'd do less on the boat if I were doing anything other than day sailing in a protected bay. The bottom is junk as it is portrayed in the pix.
Good luck, Rognvald

You mean removing the gelcoat? As I said, the hull itself is too thin for that and it would probably lose too much material in the process.
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Old 26-04-2024, 14:58   #4
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Re: What do to with my damaged gelcoat hull

Hi, C,
If you sand/soda blast the bottom, only the damaged sections would, theoretically, come off the hull. Anywhere where the adhesion of gelcoat is intact should be fine. However, if you're handy, you could fill in all the voids after dry and apply a layer or two of 1708 biaxial cloth over your repair and you'd basically have a new boat. It's only 7 meters and could be glassed(1 layer) a day. Do you have a pix of the boat?
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Old 26-04-2024, 15:49   #5
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Re: What do to with my damaged gelcoat hull

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Hi, C,
If you sand/soda blast the bottom, only the damaged sections would, theoretically, come off the hull. Anywhere where the adhesion of gelcoat is intact should be fine. However, if you're handy, you could fill in all the voids after dry and apply a layer or two of 1708 biaxial cloth over your repair and you'd basically have a new boat. It's only 7 meters and could be glassed(1 layer) a day. Do you have a pix of the boat?
Rognvald

This was before:





I don't like the idea of glassing over the gelcoat, our idea was to just fill sand down all the loose gelcoat and fill the holes up with epoxyfiller. Henkel Profiller can be applied up to ~5mm.

Then 4 barrier coats + 2 coats Antifouling. In theory this would be perfect, but as I said I am not sure if the hull ever dries out enough to put epoxy on.
All I read for hull drying is to strip the gelcoat, and even use vacuums and infrared heaters.
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Old 26-04-2024, 16:05   #6
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Re: What do to with my damaged gelcoat hull

Hi, C,
If you soda/sand blast the bottom, you'd have no adhesion problems after the hull is completely dried. You don't need to remove all the gelcoat if it is sandblasted since once it is dried, you will fill in all the voids with epoxy filler and then epoxy coat the bottom. I think 4 barrier coats is overkill. I'd be happy with 2-3 good coats and then apply bottom paint. Remember: THE HULL MUST BE COMPLETELY DRIED before any repairs or they will not adhere long term and you've wasted a lot of time. During dry time, you should spray the bottom with fresh water as much as possible to release any residual chemicals and leech out unwanted elements in the hull. It looks like a nice boat . . why not do it right??
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Old 26-04-2024, 16:38   #7
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Re: What do to with my damaged gelcoat hull

So sanding it down would not prepare the gelcoat surface properly?

I think coating the whole thing in epoxy can be a pain in the ass for future repairs on the hull, I would definitely only apply the epoxy onto the affected areas.



The drying is the issue here. Not sure if it dries out completely with the gelcoat on, we took measurements but I doubt it will be ready for epoxy within a few weeks. But maybe I am wrong and the low thickness of the hull makes it dry out very quickly.
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Old 27-04-2024, 05:38   #8
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Re: What do to with my damaged gelcoat hull

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So sanding it down would not prepare the gelcoat surface properly?

I think coating the whole thing in epoxy can be a pain in the ass for future repairs on the hull, I would definitely only apply the epoxy onto the affected areas.



The drying is the issue here. Not sure if it dries out completely with the gelcoat on, we took measurements but I doubt it will be ready for epoxy within a few weeks. But maybe I am wrong and the low thickness of the hull makes it dry out very quickly.
Hi, C,
If you have serious delamination/layup problems with your hull, the only way to fix it properly is to remove the gelcoat and allow the bottom to dry completely with the method I described above. If you are certain it is only a few spots, then, yes, a spot repair can be made but if you're wrong and it's the whole hull, then you've only put a Bandaid on a wound. You might want to employ a certified fiberglass specialist to sound your bottom and ask his advice but remember, if the whole bottom is compromised you're wasting your time doing spot repairs.
Finally: 1.) two weeks is insufficient dry time--3-4 months minimum depending on humidity conditions where you live and 2.) an epoxy bottom is as easy to repair as one with gelcoat. Remember, the epoxy serves the same purpose/function as the original gelcoat. I have areas I've fixed on my boat that are over 25 years old and in perfect condition. However, they were done properly with no shortcuts. Best, Rognvald
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Old 28-04-2024, 05:02   #9
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Re: What do to with my damaged gelcoat hull

One last remark, C,
The pix you showed indicates that when the hull was laid up at the factory, the fiberglass was not wetted out completely which caused these voids. If you're lucky, it's just in those spots. However, if it's the entire hull a major repair is needed. Good luck!
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Old 28-04-2024, 07:49   #10
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Re: What do to with my damaged gelcoat hull

Have a surveyor tap the hull looking for serious (structural) delamination. This is a 25 year old boat. If it was going to fail due to layup or resin issues, it probably would have happened by now. Most of those spots just look like poor layup - probably looked that way when new. Don’t know what the black goop is but if it’s only a few spots I wouldn’t assume it’s a big problem.

Is there a core? If it’s solid fiberglass it will dry quickly. Aim a few heat lamps at the spots after grinding. If you are worried about adhesion - use Splashzone or similar underwater structural epoxy to fill larger voids.
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Old 28-04-2024, 14:42   #11
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Re: What do to with my damaged gelcoat hull

Thanks guys, this is giving me some confidence.



I posted a video, those are definitely the worst spots where the gelcoat separates from the fiberglass. But there are also smaller damages scattered across the entire hull where the glass is exposed.






It is uncored fiberglass, thickness mostly around 8-10 mm. The boat is drying in a marina in the south of Tenerife, Canary Islands.
It is around 25-28 degrees celsius there (daytime), night time a bit more mild but far from cold.


The surveyor was there a few days ago, he said it looks bad but there is no delamination.
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Old 29-04-2024, 06:39   #12
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Re: What do to with my damaged gelcoat hull

Excellent video, C!
It's a complete failure of the gelcoat/substrata most likely caused by insufficiently cured/improperly wetted fiberglass which has caused the open sores of significant depth throughout the bottom. If it were my boat, the only proper fix is to sandblast the entire bottom, dry, and epoxy coat after repairing the large voids with filler to insure a uniform bottom. Anything less than this approach is a band aid on a wound. Don't be duped by a boatyard that might just want you to pay for a quick fix that will not solve the problem. Good luck! Rognvald

P.S. delamination is a completely different issue and its absence does not mean that the bottom is fine. Also, I'd be more confident with the assessment of a fiberglass specialist without a connection/link to the boatyard and, although this may not be your case, surveyors have also been known to work with boatyards without your knowledge. When we were in Illinois, there were two rogues who were notorious for this practice and cost boaters untold inadequate/unnecessary repairs. R
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Old 30-04-2024, 15:57   #13
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Re: What do to with my damaged gelcoat hull

I have also received info from a friend that has a sailboat, they asked the head of the marina there and got the same answer - gelcoat off, dry, and new layers on.



As the boat is pretty old and the fiberglass very thin, I will probably only fix it with epoxy for now, when the hull is totally dry.
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Old 02-05-2024, 09:53   #14
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Re: What do to with my damaged gelcoat hull

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I have also received info from a friend that has a sailboat, they asked the head of the marina there and got the same answer - gelcoat off, dry, and new layers on.



As the boat is pretty old and the fiberglass very thin, I will probably only fix it with epoxy for now, when the hull is totally dry.
Hi, C,
The voids need to be filled and the bottom fair before epoxy application.
Good luck,
Rognvald
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Old 03-05-2024, 10:46   #15
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Re: What do to with my damaged gelcoat hull

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As the boat is pretty old and the fiberglass very thin, I will probably only fix it with epoxy for now, when the hull is totally dry.
That's what I would do. Looks like mostly gelcoat failure. Can't see any real deep blisters. Let it sit for as long as you can. Wash it with fresh water everyday. In the Canaries, a hull that thick should dry fairly quickly, 2 or 3 weeks would probably do it. Then epoxy fill the damaged areas, sand and apply a few coats of good quality barrier coat before bottom painting.
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