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Old 13-10-2018, 02:14   #1
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What is your favourite way of plugging small holes in fibreglass?

Hi all,

One of the problems with older boats is the number of little holes in the boat from bits of equipment that have been removed. I reckon I must have around 20 or more. I'm talking holes in the roof and sides of the deck and quite a few on the topsides of the hull.

The hull is about 30mm thick, solid fibreglass, the deckhouse is also solid fibreglass, around 6 - 8 mm thick.

The holes are all just standard bolt diameter, so around 4 - 6 mm.

I'm thinking of mixing up a batch of epoxy with microballoons as a thickener, but does anyone have any other preferred method? Appearance is not a big issue, I am yet to paint the boat so I can attend to the finish later, I'd just like to stop the drips.

Matt
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Old 13-10-2018, 02:32   #2
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Re: What is your favourite way of plugging small holes in fibreglass?

I overdrill the holes just a bit to make sure that any sealants are gone and to get a fresh GRP surface.

My preferred filler is epoxy with a structural filler rather than microballoons/fairing filler. If the hole is large or deep I'll use a dowel to take up most of the volume. Depending on inside access I'll tape the inside to make a 'bottom' [edit - the worst feeling in the world is go back inside later and find hardened lumps of epoxy filler tenaciously glued to your finished interior surfaces under the hole you filled [/edit]. Also depending on size/depth I sometimes use a syringe and large bore needle (you can get them at kitchen stores for injecting under the skin of turkeys/chickens for cheap) to tremie (fill from the bottom up while withdrawing the needle) in the fill (this results in less chance of air pockets).

Last step is UV protection (for epoxy fills). Either way I usually leave the fill a bit low (1-2mm) or drill out the top bit with a Forstner bit (flat bottom). Then fill with gel coat (if that is how the boat is finished) or fairing goop if painting.
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Old 13-10-2018, 02:54   #3
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Re: What is your favourite way of plugging small holes in fibreglass?

Just repair it using poleysyer resin , cheap and easy .
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Old 13-10-2018, 06:13   #4
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Re: What is your favourite way of plugging small holes in fibreglass?

If I could get to the hole on the inside of the skin I'd lay a patch (glass/epoxy) over the hole, then fill the hole from the outside using polyester/talc filler (or epoxy/talc) then sand and paint.

Clive
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Old 13-10-2018, 06:29   #5
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Re: What is your favourite way of plugging small holes in fibreglass?

Quote:
Originally Posted by GILow View Post
Hi all,

One of the problems with older boats is the number of little holes in the boat from bits of equipment that have been removed. I reckon I must have around 20 or more. I'm talking holes in the roof and sides of the deck and quite a few on the topsides of the hull.

The hull is about 30mm thick, solid fibreglass, the deckhouse is also solid fibreglass, around 6 - 8 mm thick.

The holes are all just standard bolt diameter, so around 4 - 6 mm.

I'm thinking of mixing up a batch of epoxy with microballoons as a thickener, but does anyone have any other preferred method? Appearance is not a big issue, I am yet to paint the boat so I can attend to the finish later, I'd just like to stop the drips.

Matt
I like MarineTex. For a solid, uncored substrate, no glass is needed over the hole. Go inside and use gray tape to cover the hole, fill it MarineTex. Available white or gray.
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Old 13-10-2018, 07:05   #6
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Re: What is your favourite way of plugging small holes in fibreglass?

While dsanduril gave great instructions for what is likely a terrific fix, albeit time consuming, we just saw this product at the Annapolis show: http://www.max1.us/product.php?produ...cat=252&page=1

The demonstration was amazing. You would fill the hole with the filler material which is like sand, put a drop of glue on top to seep down in, then touch it with the accelerator. Immediately done. Can’t speak for longevity, but would likely hold for long enough, I think.
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Old 13-10-2018, 08:18   #7
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Re: What is your favourite way of plugging small holes in fibreglass?

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...I'm thinking of mixing up a batch of epoxy with microballoons as a thickener...
Microballoons have no strength and should be used only for fairing tiny imperfections in the surface before priming/painting. Use high strength filler.
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Old 13-10-2018, 10:47   #8
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Re: What is your favourite way of plugging small holes in fibreglass?

If the holes are strictly cosmetic, IE no wet core, delamination, structural bits attached, I fill them with gelcoat. You can buy kits that have tubes of color to mix and match the original. Takes a little trial and error but you can get very close to the old color. My first try I came out with about a 4' match.
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Old 13-10-2018, 12:46   #9
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Re: What is your favourite way of plugging small holes in fibreglass?

Drill out old hole, clean with acetone or isopropyl.
Fill with West Six10 epoxy
If interior, finish with primer
If exterior, prime and paint or use gel coat repair.

As previously mentioned,
You can buy hobby glue syringes on Amazon.
and through holes should be taped securely on the other side
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Old 13-10-2018, 12:55   #10
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Re: What is your favourite way of plugging small holes in fibreglass?

It is the kind of thing we would use Marine Tex for, as well, but I do not think it is available in Oz. Might be able to use epoxy putty, but UV degrades epoxy, so you'd need to paint over. If you clean out the holes well, and can figure out how to get it in the holes without a huge mess, the polyester resin, catalysed, should work, and be compatible.

Ann
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Old 13-10-2018, 13:55   #11
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Re: What is your favourite way of plugging small holes in fibreglass?

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I like MarineTex. For a solid, uncored substrate, no glass is needed over the hole. Go inside and use gray tape to cover the hole, fill it MarineTex. Available white or gray.
Yup, Marine Tex. Quick, easy and strong.
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Old 13-10-2018, 14:21   #12
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Re: What is your favourite way of plugging small holes in fibreglass?

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Yup, Marine Tex. Quick, easy and strong.
I love MarineTex. It is certainly quick, easy and strong. I only filled my old screw holes with Gelcoat because they were small and very visible. You can hardly tell where they were from inches away.
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Old 13-10-2018, 16:09   #13
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Re: What is your favourite way of plugging small holes in fibreglass?

Plumber's epoxy putty. Purchased at Home Depot. It takes paint just fine, and before it sets it is moldable to match contours where needed. It sands just like wood. I have several nicks and divots on my deck that I filled 8 years ago that show no sign of wear. It bonds well to both wood and FRP. Just press it in with your fingers.


It will set under water, if you ever need to plug a hole below the water line in an emergency. I always have a tube of it on board.
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Old 13-10-2018, 16:18   #14
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Re: What is your favourite way of plugging small holes in fibreglass?

Exactly what dsanduril said however I would leave out the wooden dowels if the holes are less than 8mm (5/16)

If the deck or hull is cored though don't do the work on a day that is heating up as expanding air in the balsa core etc tends to blow the epoxy filler out of the holes.

Andrew
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Old 13-10-2018, 16:48   #15
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Re: What is your favourite way of plugging small holes in fibreglass?

Regardless of the filler used,I suggest chamfering the hole also.
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