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Old 21-03-2017, 12:56   #1
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Repair of Gel Coat Micro-Cracks

We have a few isolated micro-cracks on our gelcoat scattered around our boat and seeking a solution to fill these up. Ive tried gelcoat epoxy paint only to find that they re-open (not to mention the mismatch in color). These do not penetrate much deeper than a millimeter or two but I tend to think that they should be repaired or filled as they can just fill with water, dirt, etc which cant be good in the long run.

Any wise ideas out there?
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Old 21-03-2017, 14:27   #2
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Re: Repair of Gel Coat Micro-Cracks

I'm only a monohullist, but what I think is happening is that flexing is causing the cracking in your gelcoat, and some kind of reinforcement underneath is what will cure the flexing.

You can buy liquid gelcoat with a tinting kit to match the color (had to do this one time and got an artist friend to help with the tinting, but there are instructions on line for this).

Meantime, maybe another of the Lagoon people who had the same problem will come along and tell you how it went for them with fixing it.

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Old 21-03-2017, 14:42   #3
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Re: Repair of Gel Coat Micro-Cracks

Use a dremel to V out the crack before filling. Otherwise u r just covering for the most part.
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Old 21-03-2017, 14:46   #4
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Re: Repair of Gel Coat Micro-Cracks

Cracks can be caused by more than just routine stress. A sudden impact or flexing of the area can cause it, poor original application can case it, weathering and water penetration can cause it. If the cracks are due to routine stress, they are going to generally radiate out from a high load point, like a winch, or they will run along an obvious flex/stress area, like where it turns a corner, for example from a combing to a flat perpendicular area. If they are not in obvious stress areas, they probably have a different cause.

Your gelcoat is only 25-30 mils thick, so if the crack is more than that, it's down into the glass laminate (1 millimeter would be approximately 40 mils). Fairly often, and arguably most of the time, the cracks in the gelcoat go down into the glass.

This is important because if you don't fix the crack in the glass underneath, the cracks in the gelcoat will just reappear after any sort of repair.

Grind out the crack with a dremel tool. Wipe it with a solvent like alcohol to clean it out as you go to monitor if you've reached the bottom of the crack. If it indeed is only in the gelcoat, then you can patch with gelcoat. If it goes deeper, you're going to want to grind it out to good glass, repair the glass, fair, then patch with gelcoat.

Color matching with gelcoat can be difficult, and this is the real craftsmanship part and what you pay for if you go to a professional who specializes in gelcoat repair. One method for getting a good match is to mix a batch, dab it on the existing gelcoat, and lay some plastic kitchen wrap down on it and press the air out and observe the mixed gelcoat against the old (this makes the reflectivity uniform on both, allowing more accurate matching). Mix and adjust as necessary, repeat, etc.

Lagoon may very well sell patch kits with premixed gelcoat in the color they use, or be able to give you advice on the best product to use for color matching. It may still be off a bit, but it will be fairly close.
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Old 21-03-2017, 15:39   #5
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Re: Repair of Gel Coat Micro-Cracks

Capt. Tolleys maybe? https://www.westmarine.com/buy/capta...t-2-oz--243990

https://vimeo.com/57859621
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Old 22-03-2017, 02:16   #6
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Re: Repair of Gel Coat Micro-Cracks

More than likely, it doesn't go into the underlying fiberglass and is not structural (hard to be certain without photos but since you call them "micro" that's my assumption)

Grinding out with a dremel and refilling is your best bet but otherwise they are just look bad but do no harm.
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Old 22-03-2017, 08:41   #7
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Re: Repair of Gel Coat Micro-Cracks

Great YouTube channel for this is Boatworks Today. He goes over the process in detail including matching colors.
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Old 22-03-2017, 09:17   #8
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Re: Repair of Gel Coat Micro-Cracks

This sounds sad. The substrate is flexing. Glass fibre resin keeps curing with time. As such it turns brittle and is unable to take stress without cracking. The cracks then act as sheers with further stress and the subsequent movement cuts the fibres. And your boat falls apart. There is nothing you can do about it. Take all that is salvageable out of the boat and put it into a wooden boat. At least you can replace rotten wood.

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Old 22-03-2017, 09:34   #9
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Re: Repair of Gel Coat Micro-Cracks

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Old 22-03-2017, 09:35   #10
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Re: Repair of Gel Coat Micro-Cracks

First things first:

- get the dremel out and using a metal routing bit, plunge straight down into the crack until you reach the actual fiberglass. Now you can measure the thickness of the gelcoat. Everybody says it is very thin, but I have found spots where it is 3/16" thick which is a recipe for cracks because it is much harder than fiberglass.

- if it is thicker than 0.5mm or 1/32" then I recommend you remove most of the cracks by sanding. That's right, sand the gelcoat down, which takes the cracks away with it. Then, what's left if it, route it out with the dremel, fill with epoxy, sand flush and paint with gelcoat using one of those "discardable" sprayers.

For filling the cracks, I developed this mixing recipe that I like. It is regular West system epoxy with slow hardener, thickened with colloidal silica (or Cabosil) until it is syrup consistency, then I add a drop of West System white pigment for epoxy, to make it much whiter so that a very thin coat of paint or gelcoat will cover it. I apply this using a syringe. If it is not horizontal, then you need to add more colloidal silica and you may not be able to use the syringe.

- if the gelcoat is thin enough or when you do the above but the cracks come back then you need to reinforce the fiberglass laminate. Often a single layer of woven cloth applied with epoxy on the backside will do the trick. Always use rounded corners.
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Old 22-03-2017, 11:01   #11
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Re: Repair of Gel Coat Micro-Cracks

I have had this problem. If you don't want to go to the work of grinding, filling sanding and polishing, you can use a latex crack sealer from West Marine. I use a insulin syringe from the drug store. You can seal the crack and keep moisture out quickly . Not the perfect cure but it is fast and economical.
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Old 22-03-2017, 14:23   #12
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Re: Repair of Gel Coat Micro-Cracks

I had some cracks from the PO banging the bow into a dock. I used an old church key and other misc hand tools to clean out the cracks and get down to solid material. gradually added layers of Gel Coat Repair (not necessarily this brand) wet sanding between coats.
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Old 24-03-2017, 14:48   #13
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Re: Repair of Gel Coat Micro-Cracks

Well, thats a host of ideas and support.Thanks.

These are micro-cracks and don't penetrate into the substrate/underlying fiberglass. Cats flex as we know and nearly all of these I can contribute to the flexing and as gelcoat is harder/more brittle than fiberglass, then these appear. Grinding out (dremmel tool) and resurfacing is a solution but Im not quite ready to go there yet as I envisage going down this path, refilling it, re-gelcoating it and then the microcrack reappears again as the flexing continues.

I'd ideally like to source a compliant polymer to act as a fill solution. I'll look into this latex crack sealer from Westmarine.

Thanks
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Old 26-03-2017, 11:33   #14
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Re: Repair of Gel Coat Micro-Cracks

Quote:
Originally Posted by sailrfred View Post
Great YouTube channel for this is Boatworks Today. He goes over the process in detail including matching colors.
Agreed, I was about to mention it. A very thorough set of videos.
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Old 26-03-2017, 16:43   #15
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Re: Repair of Gel Coat Micro-Cracks

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Originally Posted by valhalla360 View Post
More than likely, it doesn't go into the underlying fiberglass and is not structural (hard to be certain without photos but since you call them "micro" that's my assumption)

Grinding out with a dremel and refilling is your best bet but otherwise they are just look bad but do no harm.
My entire deck has these cracks. My understanding is it is a manufacturering fault of the gel coat being too thick. It would be high hundreds or even thousands of lineal feet, so any direct repair of the cracks is clearly not economical. As the core is dry, and I don't care about cosmetics, I ignore it. If I wanted​ it to look good, only painting would be feasible.

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